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A study of the stress corrosion cracking of mild steel in alkaline and alkaline sulphide solutions Singbeil, Douglas Lloyd 1981

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A STUDY OF THE STRESS CORROSION CRACKING OF MILD STEEL IN ALKALINE AND ALKALINE SULPHIDE SOLUTIONS  by  DOUGLAS LLOYD SINGBEIL B.Sc,  The U n i v e r s i t y o f B r i t i s h Columbia, 1977  A THESIS SUBMITTED IN PARTIAL  FULFILMENT OF  THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE  in THE FACULTY OF GRADUATE STUDIES The Department o f M e t a l l u r g i c a l  Engineering  We accept t h i s t h e s i s as conforming t o the r e q u i r e d s t a n d a r d  THE UNIVERSITY OF BRITISH COLUMBIA July,  ©  1981  Douglas L l o y d S i n g b e i l ,  1981  In  presenting  this thesis  requirements British  it  freely available  for  that  f u l f i l m e n t of the  f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y  of  agree  in partial  Columbia,  I agree  f o r reference  permission  scholarly  that  the Library  shall  and study.  I  f o rextensive  for  that  copying  f i n a n c i a l gain  or publication  shall  Department o f  of this  Y  28  >  1  9  8  1  It is thesis  n o t b e a l l o w e d w i t h o u t my  M e t a l l u r g i c a l Engineering  The U n i v e r s i t y o f B r i t i s h 2075 Wesbrook P l a c e V a n c o u v e r , Canada V6T 1W5  J u l  thesis  p u r p o s e s may be g r a n t e d by t h e h e a d o f my  permission.  Date  further  copying of t h i s  d e p a r t m e n t o r by h i s o r h e r r e p r e s e n t a t i v e s . understood  make  Columbia  written  ABSTRACT  The C-1018  mild  composed mol/kg tial  stress  of  latter  steel  of  NaOH  was  12.5  NaOH,  mol/kg  It  was  Na,,S,  was  found  to  transition  in  NaOH  0.42  mol/kg  mol/kg  used and  to  I)  double  study  stress  velocity for E  mechanics  the  solutions.  and  and  corr  mol/kg  SCC by  of a  solutions,  NaOH  each  in  2.5  The  poten-  2.5  in  the  strain  higher  solution  V  and  steel  slow  slightly  II  beam  effects  stress  -1.00  V  of  potential stress  intensity  of  technique,  cantilever  Both  behavior  region  three  At ST  rate  than  (-1.00 mol/kg  the  v"  s c e  NaOH  +  2  electrochemical  three  -0.88  an  Na S).  A fracture precracked  and  to  be  in  in  of  respectively.  assessed  active-passive 3.35  (SCC)  3.35  susceptibility  solutions  technique.  cracking  investigated  mol/kg  + 0.42  maximum two  corrosion  found.  ~ 24  kJ/mol in  specimens,  crack  intensity  12.5  were  then  temperature  velocity  in  dependent  (region  Apparent  fatigue  was  intensity,  independent  was  see  on  utilizing  II)  activation  NaOH.  3  (region  crack  determined at  mol/kg  all  energies  both  Crack  velocities  -9 of  the  order  of  10  m/s  12.5  mol/kg 3  NaOH  and  at  3.35  mol/kg  NaOH  and  2.5  were -1.00  measured V  mol/kg  11  see  and  NaOH  +  at  E  „ in corr -0.88 V in see n  0.42  a  mol/kg  Na S, 2  respectively.  The c r a c k  v e l o c i t i e s measured  at -1.00  V  s c g  -8  i n 12.5  mol/kg  fractography mol/kg  NaOH were o f t h e o r d e r o f  of the cracks  NaOH a t E  fractography in a l l  c o r r  was  three  tion  transgranular  A mixed  observed  as was  at the a c t i v e - p a s s i v e  o f t h e two t e c h n i q u e s the r o l e of  stress  as  mol/kg  It  thought  NaOH c o u l d b e s t  mechanism  The most l i k e l y  t o be one i n v o l v i n g dissolution.  t h e p u l p and p a p e r  i i i  by a by  eliminated  transition  mechanism  was  mixed a c t i v a t i o n - d i f f u s i o n  Applications  industry  at E „ „ corr  assisted  at the a c t i v e - p a s s i v e  dis-  mechanisms  be a c c o u n t e d f o r perhaps  and  passiva-  Anodic  H y d r o g e n e m b r i t t l e m e n t was  the s o l u t i o n s .  controlled  i n t e n s i t y and  was d e c i d e d t h a t t h e r e s u l t s  dissolution.  a possible  in a l l  transition  were compared  experiments.  hydrogen e m b r i t t l e m e n t mechanism, anodic  12.5  h y d r o g e n e m b r i t t l e m e n t and a d s o r p t i o n  were c o n s i d e r e d . i n 12.5  in  The  intergranular-transgranular  r a t e i n f r a c t u r e mechanics  solution,  m/s.  solutions.  The r e s u l t s discussed,  -  was  10  were  of the r e s u l t s  considered.  to  TABLE OF CONTENTS  Abstract  ii  T a b l e o f Contents  ,  '  iv  L i s t of Tables  viii  L i s t of Figures  x  L i s t o f Symbols  and,Abbreviations  xvi  Acknowledgement  xviii  Chapter 1  INTRODUCTION 1.1  Stress  1  Corrosion Cracking  ..  1  1.2 SCC Techniques •1.3 SCC o f M i l d S t e e l 1.4 O r i g i n s  2  3  in Alkaline Solutions  o f the Present Work  12 1  8  2  2  2  2  2.2 M a t e r i a l s  2  3  2.2.1  Steels  2  3  2.2.2  Solutions  2  7  2.3 Equipment and Apparatus  2  7  2.4 Experimental Procedures  3  2  3  2  3  4  3  9  EXPERIMENTAL 2.1  •  Scope o f the P r e s e n t Work  2.4.1  SSRT Experiments  2.4.2  F r a c t u r e Mechanics  2.4.3  Anodic P o l a r i z a t i o n Curves and L i n e a r  Experiments  OQ  P o l a r i z a t i o n Experiments 2.4.4  S u l p h i d e and C h l o r i d e A n a l y s i s i v  4  1  Chapter  3  Page  RESULTS . . . . 3.1  3.2  3.3  42  Anodic P o l a r i z a t i o n Curves and L i n e a r P o l a r i z a t i o n Results  4  2  SSRT R e s u l t s  4  7  3.2.1  3.35 mol/kg NaOH  4  7  3.2.2  2.5 mol/kg NaOH + 0.42 mol/kg Na S  50  2  F r a c t u r e Mechanics R e s u l t s  5  3  3.3.1  General  5  3  3.3.2  12.5 mol/kg NaOH  5  7  5  7  5  7  6  0  6  0  6  3  6  3  6  3  Fractography  6  6  3.4.1  General  6  6  3.4.2  12.5 mol/kg NaOH  7  2  The E f f e c t o f S t r e s s  Intensity  The E f f e c t o f Temperature and  ...  Potential 3.3.3  3.3.4  3.35 mol/kg NaOH  The E f f e c t o f S t r e s s  The E f f e c t o f P o t e n t i a l  ...  2.5 mol/kg NaOH + 0.42 mol/kg Na S 2 3.4  Intensity  The E f f e c t o f S t r e s s  Intensity  The E f f e c t o f S t r e s s  The E f f e c t o f Temperature and Potential  v  Intensity  ...  ...  72  75  Chapter  3  Page  RESULTS  (continued)  3.4.3  3.4.4  3.35 mol/kg NaOH  The E f f e c t o f S t r e s s  The E f f e c t o f P o t e n t i a l  ...  80 80  2  The E f f e c t o f S t r e s s  78  Intensity  ...  80  DISCUSSION  83  4.1  83  4.2  General 4.1.1  SSRT  83  4.1.2  F r a c t u r e Mechanics Technique  85  4.1.3  Kinetics  87  4.1.4  Fractography  89  Mechanisms  9  4 . 2 . 1 . The Role o f S t r e s s  Intensity  Passivation  4.3 5  Intensity  2.5 mol/kg NaOH + 0.42 mol/kg Na S  4  78  4  and 95  4.2.2  Anodic D i s s o l u t i o n  4.2.3  Hydrogen E m b r i t t l e m e n t  1°  4.2.4  A d s o r p t i o n o f Damaging Anions  112  4.2.5  Assessment o f Mechanisms  Industrial  Implications  9  ^  8  7  2  116  CONCLUSION  121  5.1  Conclusions  121  5.2  Suggestions  f o r Future Work  vi  123  BIBLIOGRAPHY  APPENDIX A  APPENDIX B ..  LIST OF TABLES  Table  Page  I  Y i e l d Strengths  II  C o r r e l a t i o n Between S o l u t i o n , P o t e n t i a l , F a t i g u e Level  and Chemical Composition o f S t e e l s  and S t e e l  24  Batch i n F r a c t u r e Mechanics  Experiments  35  III  Results  46  IV  Comparison o f Crack V e l o c i t y and S t e e l Batch  V  E f f e c t of Stress  o f L i n e a r P o l a r i z a t i o n Experiments  Intensity  12.5 mol/kg NaOH a t E VI  c  Q  r  r  56  on Crack Growth i n and 92° C  58  E f f e c t o f Temperature and P o t e n t i a l on Crack Growth  i n 12.5 mol/kg NaOH a t Kj = 31-43 MPa^T VII  E f f e c t of S t r e s s  Intensity  61  on Crack Growth  in  3.35 mol/kg NaOH a t - 1 . 0 0 Vand 92° C see  64  3  VIII  E f f e c t of Stress  Intensity  on Crack Growth i n  2.5 mol/kg NaOH + 0.42 mol/kg Na S a t -0.88 2  V  s c e  and 92° C IX  Value's,  6  of  from i X  i  P r e d i c t e d a t the T e s t  a Values  Potential  corr C a l c u l a t e d O v e r p o t e n t i a l s Based on Estimated Values o f i  „ on Bare Metal corr  vi i i  7  101  1  0  8  Page  Table  XI  C a l c u l a t e d pH and E + ^ H  H  f o r a l l Solutions  at  100° C  BI  Activity Coefficients  1  (Y  O H  - ) and A c t i v i t i e s  (a  Q H  1  -)  f o r OH" and C a l c u l a t e d pH f o r a l l Three S o l u t i o n s  i x  1  135  LIST  OF  FIGURES  Pa__e  Figure  1.  Stress-strain  curve f o r specimens t e s t e d i n SCC  s u s c e p t i b l e and i n e r t environments using where A  and A are the areas o sec r e s p e c t i v e curves  2  Schematic o f a t y p i c a l regions  I,  II  SSRT,  under the 6  l o g v - K- c u r v e ,  showing  and III  9  3  Schematic o f the K r a f t c y c l e  20  4  DCB specimen geometry  21  5  SSRT t e s t c e l l  29  6  F r a c t u r e mechanics t e s t c e l l  7  Anodic p o l a r i z a t i o n curves o f m i l d s t e e l  geometry  geometry  mol/kg NaOH and 2.5 mol/kg NaOH + 0.42  31 in  3.35  mol/kg  Na S at 92° C  43  2  8  Anodic p o l a r i z a t i o n curves o f m i l d s t e e l  in  12.5  mol/kg NaOH a t s e l e c t e d temperatures,  9.  E f f e c t of potential mol/kg  upon r e d u c t i o n i n area f o r  45  3.35  NaOH superimposed upon the anodic p o l a r i z a -  t i o n curve o b t a i n e d i n the same s o l u t i o n  10  Appearance o f f i n a l  48  f r a c t u r e r e g i o n a f t e r SSRT t e s t  i n 3.35 mol/kg NaOH a)  E = - 1.00 V  b)  E = - 0.62 V  see  49  see  x  Page  Figure  11  E f f e c t of p o t e n t i a l  upon r e d u c t i o n i n area f o r  2.5  mol/kg NaOH + 0.42 mol/kg Na,,S superimposed upon the anodic p o l a r i z a t i o n curve o b t a i n e d i n the same solution  12  51  Appearance o f f i n a l i n 2.5 mol/kg  13  NaOH + 0 . 4 2 mol/kg  a)  E = -0.90 V  b)  E = -0.50 V  Macroscopic  f r a c t u r e r e g i o n a f t e r SSRT t e s t Na S 2  see  52  see  view o f s t r e s s  c o r r o s i o n crack  o f DCB specimen t e s t e d i n 12.5 mol/kg E  14  corr  a  d  K  I  =  2  3  E f f e c t of stress mol/kg  15  n  '  "  8  2  5  A  M P a v  ^"  NaOH a t 92° C, *  •  i n t e n s i t y on c r a c k v e l o c i t y i n  NaOH a t 92° C and E  c  Q  r  A r r h e n i u s p l o t o f the r e g i o n 12.5 mol/kg  surface  NaOH a t E  c  Q  r  r  5  12.5 59  r  II  crack v e l o c i t i e s  and - 1.00  V  s c e  in  ,  Kj = 31 - 43 MPa^m  16  E f f e c t of stress mol/kg  17  62  i n t e n s i t y on c r a c k v e l o c i t y i n  NaOH a t 92° C and - 1.00  Effect of stress  4  V  3.35 65  s c e  i n t e n s i t y on c r a c k v e l o c i t y i n  2.5  mol/kg NaOH + 0.42 mol/kg Na S a t 92° C and 2  -  0.88  V „  68  Q  see  xi  gure  18  Comparison o f the c o r r o s i o n product on the  stress  c o r r o s i o n c r a c k s u r f a c e i n d i f f e r e n t environments. a)  12.5 mol/kg NaOH, E  •. K- = 31.0-33.7 MPa/m  b)  12.5 mol/kg NaOH, - 1 . 0 0 V  s c e  ,  K.=  31.3-43.1 HPaJm  c)  3.35 mol/kg NaOH, - 1 . 0 0 V  s c e  ,  K-=  20.7-24.3  d)  2.5 mol/kg NaOH + 0.42 mol/kg N a S , - 0 . 8 8 2  V  MPa.vfiT. s c e  ,  K- = 2 5 . 9 - 2 6 . 7 MPavfiT  19  20  B r i t t l e o v e r l o a d f a i l u r e near the c r a c k t i p . a)  b e f o r e c l e a n i n g with i n h i b i t e d a c i d  b)  a f t e r c l e a n i n g with i n h i b i t e d a c i d  Comparison o f f r a c t o g r a p h y between specimens machined from d i f f e r e n t batches o f s t e e l -1.00 V  see  at  and 92° C.  a)  Batch A, 12.5 mol/kg NaOH, K-=  b)  Batch B, 12.5 mol/kg NaOH, K.:= 31.8-37.4 MPa/m  c)  Batch A, 3.35 mol/kg NaOH, K.=  3 0 . 3 - 3 2 . 7 MPa/m  d)  Batch B, 3.35 mol/kg NaOH, K-=  29.7-33.3 MPa/m . .  xi i  3 1 . 0 - 3 3 . 8 MPa/m , .  Figure  21  V a r i a t i o n o f f r a c t o g r a p h y with s t r e s s 12.5 mol/kg NaOH a t 92° C and  22  a)  Kj = 17.9 - 18.1 MPavffi"  b)  Kj = 23.8 - 25.4 MPavmT  c)  Kj = 30.1 - 32.7 MPavfiT  d)  K = 35.0 - 37.8 MPavfiT  E  c o r r  intensity  .  T  V a r i a t i o n o f f r a c t o g r a p h y w i t h temperature i n 12.5 mol/kg NaOH a t  E  c o r r  -  a)  55° C, Kj = 34.5 - 37.7 MPavffi"  b)  70° C, Kj = 34.0 - 35.0 MPaVfiT  c)  105° C, Kj = 35.4 - 41.9 MPavfif  d) 115° C, Kj = 35.2 - 41.1 MPavffi"  23  V a r i a t i o n o f f r a c t o g r a p h y with temperature i n 12.5 mol/kg NaOH a t - 1.00  V  s c e  .  a)  70° C, Kj = 31.3 - 34.8 MPavfif  b)  92° C, Kj = 31.8 - 37.4 MPa*€  c ) 105° C, K  T  = 31.3 - 43.1 MPavfii"  xi i i  Page  Figure  24  V a r i a t i o n o f f r a c t o g r a p h y with s t r e s s 3.35 mol/kg NaOH a t 92° C and - 1.00  25  a)  Kj = 15.5 - 16.1 MPa^m"  b)  Kj = 20.7 - 24.3 MPavm"  c)  Kj = 29.7 - 33.3 MPav'm  d)  Kj = 35.7 - 43.0 MPavfiT  intensity V  s c e  in  -  79  V a r i a t i o n of fractography with stress  intensity  in  2.5 mol/kg NaOH + 0.42 mol/kg Na S a t 92° C and 2  - 0.88 V . see  26  a)  Kj = 15.5 - 15.6 MPaVm  b)  Kj = 21.2 - 22.2 MPav'm  c)  Kj = 31.4 - 32.5 MPavfiT  d)  Kj = 36.0 - 38.9 MPav€  81  Comparison o f uncorroded f a t i g u e p r e - c r a c k s u r f a c e s o f Batch A and Batch B s t e e l  27  a)  Batch A  b)  Batch B  92  Anodic p o l a r i z a t i o n curve o f bare metal s u r f a c e under a c t i v a t i o n c o n t r o l and mixed a c t i v a t i o n - d i f f u s i o n control  .  xi v  103  Page  Figure  28  E f f e c t o f s u l p h u r a d d i t i o n upon E  c  Q  r  r  in  2.5  mol/kg NaOH + 0.42 mol/kg Na,,S superimposed on the anodic p o l a r i z a t i o n curve f o r the  sulphur  free solution  Al  Stress corrosion crack surface of machined from a 32 mm x 32 mm b a r . 3.35 mol/kg NaOH a t - 1 . 0 0 V 3  K  T  = 48-53 MPav'm  xv  see  specimen Tested in  and 92° C.  LIST OF SYMBOLS AND ABBREVIATIONS  Symbols  crack a  OH"  length  chemical a c t i v i t y o f OH~  B  thickness  o f f r a c t u r e mechanics  b_  anodic T a f e l  slope  cathodic Tafel bulk 'OHP  specimen  slope  concentration  c o n c e n t r a t i o n at the o u t e r Helmholtz 3  d density of iron  (7.86 x 10  plane  3 kg/m )  D diffusion  E E  coefficient  potential corr  E "rev F  free corrosion  thermodynamically Faraday  H i.  'IC V  ISCC  reversible  (9.85 x 1 0  DCB specimen beam anodic current  corr  potential  4  potential  A.s)  height  density  corrosion current  density  diffusion  density  current  exchange c u r r e n t  density  stress  f a c t o r f o r mode I  intensity  critical  stress intensity  factor  t h r e s h o l d SCC s t r e s s i n t e n s i t y  xvi  opening  factor  Symbol s d i s s o c i a t i o n constant f o r water load Q  apparent a c t i v a t i o n energy  R  gas constant (8.314 kJ/mol.deg)  R"  r  1  P  y  T  r e c i p r o c a l p o l a r i z a t i o n resistance crack t i p p l a s t i c zone radius absolute temperature crack v e l o c i t y  v  v o l t s with respect to the saturated calomel  V see  reference electrode  w  equivalent weight of iron  W  DCB specimen length  Y  0H"  d i f f u s i o n l a y e r thickness  6  A n  D n  T n a  a c t i v i t y c o e f f i c i e n t of OH  ys  a c t i v a t i o n overpotential d i f f u s i o n overpotential t o t a l overpotential y i e l d stress  Abbreviations DCB  double c a n t i l e v e r beam  LEFM  l i n e a r e l a s t i c f r a c t u r e mechanics  OHP  outer Helmholtz plane  SEM  scanning electron microscope  SCC  s t r e s s corrosion cracking  see  saturated calomel xvi i  reference electrode  ACKNOWLEDGEMENT  Special for  his  guidance  Crowe  and  L.  gave,  and  for  the  thanks  work  and  sharing  done  for  Musil  and  many  to  thank  all  the  both  assistance Research  I standing  Council  the was  am g r a t e f u l  supervisor, throughout  by  credit  office R.  in  most  with  McLeod,  in  enjoyable  from  and  an  others  I  my  deserve  people  s u p p o r t i n g me when here  me  to  counsel  Frederick  P.  stay  go  the the  National  emotional  H.  help  I  and  and  they  Klassen, would  department  for  making  my  Financial Engineering  appreciated.  Gillis  for  she  the  help,  provided.  D.  appreciate  department.  Science  xvi i i  the I  Tromans,  project.  E.  worthwhile.  support  D.  Tump,  it,  gratefully  to  for  Metallurgy  needed and  the  me.  H.  Dr.  under-  like for  It  would  anticipate  failures  places,  the  do  not  so  as  so loom  of  understanding  seem,  this  industrial  large.  * D i s c u s s i o n of T r a n s o f ASM,  not  therefore,  type  occurring  implications  Failures  are  rare  that in  we  may  unsuspected  of  this  phenomenon  and  will  become  spreads...."*  p a p e r by H o d g e , 28, 25, (1940).  xi x  J.C.  and  Miller,  J.L.,  more  Chapter  1  INTRODUCTION  1 .1  Stress  Corrosion  Stress  corrosion  penetration  and  action  of  a  tensile  a  in  excess  rate  singly.  chemical it  is  stress  all SCC  is  of  serious  the  cost  1940,  of  vital  failure,  of  repairs  when  austenitic  the  by  and  that  piece  of  SCC  can  be  written  stainless  factor  failures  dangerous  loss  and  of  of  in  frontispiece  become related  a major  of  this  concern  corrosion  of  thesis, both  research.  1  the  study  industrial  a  catasfrom  the  production  paper the  on  of  and  the  comment  2 the  the  expensive.  a  included  in  Aside  of  prohibitively  steels  acting  because  warning  personnel  discussion  at  constitutes  untimely  attendant  the  conjoint  equipment.  to  as  environment  first  the  injury  the  the  related  the  often  defined  either  particularly  is  be  corrosive  show  detectable problem  can under  corrosion  possibility  Since SCC  surveys^  a  the  a  produced  of  of  (SCC)  a metal and  failure  vicinity and  that  of  readily  corrosion  trophic the  of  33%  of  stress  industry.  not  cracking  cracking  Industrial  approximately  Cracking  SCC  has  academic  on  2 Traditionally,  SCC  was  associated  metal-environment  combinations,  steels  chloride  exposed  solutions is  now  and  to mild  steel  recognized  that  such  SCC  may  as  innocuous  as  few  in  in  3  stainless  ammoniacal However,  a wide  including water,  specific  austenitic  solutions.  occur  distilled  a  brass  alkaline  metal-environment-combinations, ments  as  solutions,  in  with  variety  exposure  and  that  to  no  it  of environ-  single,  4 unifying  theory  A large addition clude  to  the  can  number  the  chemical the  the  electrochemical  the  reactions  residual  or  cation  is  rosion  crack  applied  that  the  may  used  of  variables  these  indicated rosive  for  to  the  of  and  the  SCC  These  metallurgical  history  the  ion(s)  metal  in  in  of  competing  surface the at  greatly  characterize  SCC.  interact  combination  of  metal.  the  from  and  tip the  metal  the  bulk  a  the  surface, anodic  effects  stress  and of  complicor-  conditions  Furthermore,  synergistically, tensile  of  solution,  A further of  in-  solution,  kinetics  on  in  environment.  the  metal  SCC.  process  on  environment  environment.  of  films  stresses  may  the  damaging  of  passive  differ  commonly  affect  and  of  potential  on  occurrences  and.specific  nature  cathodic  all  variables  concentration  nature  temperature,  for  composition  metal,  and  of  metal  the  presence  account  stress  some as and  or  all  already cor-  1. 2  SCC In  affect  Techniques accordance w i t h the m u l t i p l i c i t y of v a r i a b l e s  SCC, many d i f f e r e n t t e c h n i q u e s  study  SCC phenomena.  These  ments where t h e l i f e t i m e rosive  environments  is  are measured  measured,  some t e c h n i q u e s  Since  as  from t r a d i t i o n a l e x p e r i -  f i l m growth  the b e h a v i o r  This  of the m e t a l .  time of the s t r e s s  It  ficant  f r a c t i o n of the t o t a l  crease  the propagation  to  towards  cracks test  occurred.  the specimen  or p r e c r a c k i n t o the  corrosion aggres-  ( w h i c h can be a  on  corrosion  include  signi-  i t can  Some common methods  the s o l u t i o n  to  the i n i t i a t i o n  time).and/or  in-  cracks used  increasing  concentration, con-  p o t e n t i a l , and i n t r o d u c i n g a n o t c h specimen.  Two r e l a t i v e l y new t e c h n i q u e s  7  dependent  SCC w i t h r e s p e c t  can d e c r e a s e  i n c r e a s e t h e s e v e r i t y o f SCC t e s t s  trolling  Parkins.  the r e l a t i v e  r a t e of the s t r e s s  the t e m p e r a t u r e , changing  stress  and  of  c a n have two m a j o r e f f e c t s  corrosion  i n i t i a t i o n has  most  by i n c r e a s i n g  of the t e s t environment situations.  cor-  current  Reviews 6  SCC can be a r e l a t i v e l y s l o w , t i m e  accomplished  once  5  have been w r i t t e n by P o u r b a i x  testing  industrial  placed in  k i n e t i c s and  a f u n c t i o n of time.  by l a b o r a t o r y s t a n d a r d s ,  siveness  samples  to t r i b o e l 1 i p s o m e t r i c  phenomenon is  have been used t o  of s t r e s s e d  e x p e r i m e n t s , where p a s s i v e density  range  which  of p a r t i c u l a r  interest  4  to  this  the of  study  fracture  are  slow  mechanics  accelerating  requiring  the  that  the a  they  compare  they  contribute  approach.  stress  change  well  strain  rate  technique  Both  have  corrosion  be  made  in  the  process  the  test  with  traditional  methods.  unique  information  to  the  (SSRT)  and  advantage  without  environment In  and  addition,  understanding  of  SCC.  The  SSRT  was  first  extensively  used  by  Parkins  and  o his  coworkers,  method of  of  and  has  since  assessing  the  SCC  environments.  SSRT.  The  lasts  first  longer  is  than  longest  constant  is  a  that  There  slow  strain  The  fashion,  indicating  ductile SCC  is  dependent  tip  of  a  with at the  crack stress  precracked  constant  creep  in  the  upon  per  the  the  is  local  tensile  se.  This  beam  plastic  caused zone  ahead  of  for  the  The  second  tests. with  or  the rate  would were  in by  a  positive a  brittle  normal  premise  that  produced  rather  the  the  days  specimens.^  cracking  to  60+  ends  on  number  rarely  demonstrated  cracks  a  test  SCC,  strain  useful  in  prematurely  stress, was  intensity,  which  always  based  a  rate  to  occurrence of SSRT  be  metals  strain  either  cantilever  stress  conditions  the The  by  test  to  advantages  strain  compared  fails  of  major  constant  rate  specimen  overload.  tensile  or  two  slow  hours,  load  result.  a  found  behavior  are  that  48  been  than by He  upon  the  showed  established tip  the  Parkins,  propagate  crack  at  was  that  only  if  before  5 exhausted.  A typical jecting slow,  a  slow  standard,  constant  posing rence  it of  specimen, meters  which  specimen.  rate  affect  This  is  compares  constant  for  specimen  tested  a  ments. in  area,  tion men  Some  of  time SCC,  to by  surface,is  Studies  inert  used  and of  sub-  specimen  occurs,  to  the  behavior  of  schematically  by  the  % elongation. secondary  Figure  1,  curves  %  environ-  reduction  Visual  cracks  para-  test  susceptible include  ex-  by  the  very  occur-  of  stress-strain SCC  a  while  Since  ductility  and  of  characterized  parameters  observation also  best  temperature  failure,  have  is  relative  in  commonly  failure  mechanical  illustrated  which  test  environment.  the  the  consists  tensile  susceptibility assess  test  until  appropriate  will  SCC  rate  waisted,  strain  t o - an SCC  strain  confirma-  on  the  speci-  recommended.^  shown  that  there  is  both  an  upper  and 12  lower The  limit  upper  advance while which can  be  on  limit  with  the  the  occurs  respect  lower  !  ruptured  chemical  SCC  by  will  produce  of  insufficient  the  amount  of  strain  thought over  strain.  with and  which  result  is  the  rate a  itself,  varies  potential,  as  to  limit  e s t a b l i shes ;  producing  strain  the  to  the  be  metal,  temperature,  '  crack  occurring,  due to a p r o t e c t i v e f i l m  crack  The  SCC.  13  tip  optimum  faster strain  environment, and  must  be  than rate  ;  it for  electro-  0  S C C  STRAIN ( 6 ) Figure 1  S t r e s s - s t r a i n c u r v e f o r specimens t e s t e d i n SCC and i n e r t environments u s i n g SSRT, where A  and A „ o  areas under the r e s p e c t i v e  curves.  susceptible s c c  are the  7 experimentally  The  SSRT  the  severity  SCC  under  a more has  a  tests  in  proven  cracking  test  thought to  of of  in to  be  form  been e s t i m a t e d  The the  to  explain  1  0  '^  in  stress  quickly  It  has  traditional  to  SCC,  assessing of  where  reason,  in  the  same  environments  more  corrosion strain  quantify  crack  failure  was  difrate  encountered environ-  have  data,  also  1 5  SCC  mechanics  brittle  pre-  strain  velocities  to  be  and  Quantitative  tests.  approach  fracture  slow  aggressive  tests.  rate  to  SCC  this  the  found  methods,  For  in  to  combinations or  both  metals  been  4  mechanics  elastic  and  than  laboratory  f^om s l o w  linear  for  studied.  susceptibility  immune  than  used  fracture  of  SCC  be  rather  of  system  conditions.  conducted  normally  and  each  metal-environment  initiate.  may  the  useful  SCC  industrially ments  has  variety  produced  ficult  for  of  severe  viously  determined  is  an  (LEFM) of  extension  approach  high  used  strength  l fi materials. to  study  istics  of  The  use  SCC  makes  a  single,  it  of  a  possible  planar  intensity  at  the  tip  of  corrosion  crack,  the  stress  K-,  the  characterized  by  opening.  magnitude  applied  The stress  and  fracture  crack  the  to  crack  follow as  crack.  a  Kj  a  at  At  growth of  typical the  intensity  increases  length.  the  technique  function  For  intensity  stress of  mechanics  character-  the  stress  stress  tip  can  be  factor  for  mode  with  increasing  sufficiently  high  I  8  values, which  i t reaches  spontaneous,  In most velocity crack  as  log  is  measured  v vs.  II,  III  of changes to K j . c r a c k growth The u p p e r  and t h e l o w e r l i m i t  not d e t e c t a b l e .  is  In  s u c h as  decades,  not observed  In  stress  data  intensity  region  v -  I,  at  dependent.  F i n a l l y , at high which  is  usually  Kj  once a g a i n  when Kj -•• K j ^ threshold propagation  difficult  to  some a r b i t r a r y  time or the  velocity is  than the r a t e of d i s s o l u t i o n  is  stress  ^ISCC'  given  In  values,  i n t e n s i t y below which  period.of  below which the c r a c k  are  a p l a t e a u value which  p r a c t i c e , Kj^^.^ i s  a f t e r a set  the  Three d i s t i n c t r e l a t i o n -  r e a c h e d when Kj =  the s t r e s s  crack  Since  of the curve occurs  e x p e r i m e n t a l l y and i s  designation,  slower  limit  Kj.  i n t e n s i t y below which s u b - c r i t i c a l c r a c k  quantify  is  occurs,  occurs.  of a t y p i c a l log  the c r a c k v e l o c i t y i s  the v e l o c i t y reaches  dependent.  is  several  2.  at  e x p e r i m e n t s , the  a f u n c t i o n of  The shape  Figure  intensity  fracture  between l o g v and Kj a r e a p p a r e n t .  independent  stress  as  spans  Kj.  shown i n  low Kj v a l u e s ,  region  fast  stress  SCC f r a c t u r e m e c h a n i c s  ,vi is  Kj c u r v e  region  unstable  v e l o c i t y commonly  plotted  ships  K j ^ , the c r i t i c a l  equal  SCC  stress to  o f t h e m e t a l by  or general  corrosion.  The e x i s t e n c e o f a Kj i n d e p e n d e n t  region  in a log  v - Kj  9  i I  Figure 2  Schematic o f a t y p i c a l I , I I and I I I .  l o g v - Kj c u r v e , showing r e g i o n s  p l o t makes stress ful  i t possible  to separate  independent mechanisms.  stress  This  is  dependent  particularly  i n d e t e r m i n i n g the e f f e c t s of t e m p e r a t u r e ,  and s o l u t i o n  composition  21 velocity. these for  use-  viscosity,  corrosion  crack  22 '  The n a t u r e o f t h e d e p e n d e n c e  variables  SCC  on t h e s t r e s s  from  o f SCC  on  can l e a d t o t h e e l u c i d a t i o n o f a mechanism  i n the m e t a l - e n v i r o n m e n t c o m b i n a t i o n  under  study.  G e n e r a l l y , the complex i n t e r a c t i o n which o c c u r s  between  stress  I and  i n t e n s i t y and t h e e n v i r o n m e n t  of the l o g  v - K-  in regions  c u r v e make i t d i f f i c u l t  to t r e a t  III  the  data m e c h a n i s t i c a l l y . Another is  that  This  Several rate  initiation is  stage  advance  include direct optical  its  and t h e m e r i t s requirements  observation,  electrical  ultrasonic monitoring  method has  and a c o u s t i c  o f one t e c h n i q u e o v e r  The c h o i c e o f  studies. the  test.^  crack  resistance  own p a r t i c u l a r a d v a n t a g e s  of s p e c i f i c  propaga-  may be e m p l o y e d t o measure  i n a f r a c t u r e mechanics  d i s p l a c e m e n t measurements, ments,  in k i n e t i c  approach  separation  from t h a t of c r a c k  e s p e c i a l l y useful  d i f f e r e n t methods  of crack  These  of the f r a c t u r e mechanics  i t a l l o w s , at l e a s t t h e o r e t i c a l l y , the  of the crack tion.  advantage  opening measure-  emission. and  another  Each  disadvantages depend on  experiments.  specimen  geometry  is  important  in  the  11  f r a c t u r e mechanics geometry,  Kj i s Kj  Where  P is  and Y (a) loading  is  by e q u a t i o n  = |- Y  (a)  Perhaps  the specimen length,  has  the  dimension  been shown t h a t f o r  be c o n s i d e r e d  useful  1  thickness  a , and  t h e most c r i t i c a l  It  Kj may o n l y  1:  of the crack  thickness.  crack  ....  load, B is  a function  geometry.  ratio,  For a s p e c i f i c  given  the a p p l i e d  the specimen P/B  experiments.  is  constant  i f a certain  1o  thickness stress  is  state  zone  forms  zone  is  exceeded. exists  ahead o f  strongly  specimen  Eventually, strain plane  a plane  at the crack  t i p and a l a r g e  plastic  the t i p .  is  stress  the crack  only  plane is  along  as  of the  strain  surface.  r e a c h e d where the crack  conditions,  the  plastic  plane  front  a t t h e e x t r e m e edges o f  constant  of  and  the  the s i z e  and i n d e p e n d e n t  can s u p p l y  o n l y when p l a n e s t r a i n front.  thickness;  the s i z e  is  plastic  of  position  front.  LEFM t e c h n i q u e s  crack  of the  from the f r e e  thickness  predominate  exists  Under  The s i z e  increased,  a limiting  t h e p l a s t i c zone along  t h i n specimens,  with distance  conditions  specimen.  very  a f f e c t e d by s p e c i m e n  thickness  zone d e c r e a s e s  In  v a l i d engineering  can be a p p r o x i m a t e d  Therefore,  a minimum s p e c i m e n  across  data the  thickness,  1 2 related  to is  ~. y '.*o a  S  K.  and  the  required.  criterion  usually  Srawley  and  1 3  yield  strength  Equation  adopted,  ASTM  of  2 shows  which  is  the  the  that  material,  thickness of  Brown  and  E399-78a.  .2  The  consideration  fracture been  plane  mechanics  found,that  cracks  will stress  to  plane  under  plastic  the  strain  experiments some  propagate  Fracture applied  of  plane  stress  important  conditions,  very  slowly,  because  stress  if  at  in  all,  in  of  The  first  hot,  Mild  of  techniques SCC  Steel  in  reported  alkaline  has  through  have  behavior  of  been a  successfully  number  of  21 22 i n c l u d e aluminum a l l o y s , titanium, high 23 24 25 steels, brasses, and s t a i n l e s s steels.  SCC  it  corrosion  These  1 .3  SCC  zones.^  mechanics study  is  vs.  Alkaline  failures  environments  were  materials. strength  Solutions  by  the  in  SCC  riveted  of  mild  steel  boilers  on  26 steam  locomotives  occurred with  in  the  a whitish,  surface  of  ment  riveted  of  the  near  the  vicinity  of  "caustic" stress  turn the  by  the  century.  rivets  precipitate  corrosion  boilers  of  and  welded  ones  were  deposited  cracks.  Failures associated on  Although helped  to  the replace-  eliminate  failure, problem  caustic in  many  industrial appeared  occurrences  industries  the  by  the  the  (NACE),  alumina  of  mild  industries.  during  Engineers  cracking  of  At  SCC  1950's.  National 27  and  process  steels  least  in  two  was  a  Association other  industry.  surveys  alkaline  One  the  continued  28  be  a  of  environments  survey of  of  several  Corrosion  detailed A  to  experience  laboratory  study  in  of  29 caustic  cracking  Despite  a  growing  cracking, occur.  was  it  Some  also  published  awareness  remains recent  a  and  problem  examples  at  this  time.  understanding and  failures  include  of  caustic  continue  failures  in  to  pipes  of  30 an u n d e r g r o u n d h o t w a t e r h e a t i n g s y s t e m i n D e n m a r k , a c a t h o d i c a l l y p r o t e c t e d n a t u r a l gas p i p e l i n e i n t h e U n i t e d States,  31  digestor  a  clarifier  failure  Although steel  in  the  alkaline  tradictory, of  an  in  of  solutions due  34  '  35  Canadian- pulpmi11 pulpmill.  early  were  to  variables,  Parkins,  a  Alabama  results  primarily  experimental  emerge.  in  rake  poor  a  Reinoehl  on  and  picture  and  the  SCC  confusing  control  clear  and  a  33  work  often  32  Berry,  and  mild  con-  understanding  has 26  of  begun  and  to  Carter  and  36 Hyatt Recent  have work  perature  all  reviewed  shows  strongly  solutions.  SCC  that  the  both  influence  has  been  subject  solution the  SCC  reported  in  in  recent  years.  composition of  mild  steel  solutions  and  tem-  in  varying  alkaline in  concentration  from  4%  to  75%  NaOH, ' 8  2  7  '  2  with  9  the  most  SCC  has  26 severe  cracking  reported vated  outside  this  temperatures  required  to  cause 27  centration. plays  occurring  37 '  a major  (> SCC  at  ~ 33%  NaOH.  No  range.  Most  failures  occur  70° C ) ,  with  the  decreasing  with  minimum  at  been  ele-  temperature  increased  NaOH  con-  38 '  The  role  in  content  determining  Maximum  susceptibility  between  0 and  0.02%,  carbon  to  SCC  SCC  occurs  of  the  steel  also  susceptibility. at  a  carbon  content  decreases with increased carbon 34 38 c o n c e n t r a t i o n in the s t e e l . ' A carbon content of g r e a t e r than 0.20% appears to p r o v i d e a measure of p r o 36 t e c t i o n from SCC. L i t t l e i s known a b o u t t h e e f f e c t s o f other  components  steel  in  alkaline  It  has  alkaline  SCC  does  strength  .of 8  produced  '  been  rate  material  tests  at  and  behavior  of  mild  36  laboratory,  the  initiate  methods  to  initiate using  have  stresses that  27 '  of  SCC  in  traditional  been  used  below  a minimum  stress  failures,  has  predominantly 8  have  '  SCC  in  industrial  traditional  solutions,  35  the  difficult  Examination  by  a  on  proved  strain  not  the  steel  the  to  show  yield  strain  rate  is  39  required.  follows  often  Slow  the  solutions.  solutions  methods.^ that  in  and  shown  corrosion  SSRT  that  experiments,  SCC  intergranular  cracks  of  path  mild in  and  steel  alkaline  37 '  although  observed.  '  cases  of  transgranular  cracking  15 Several potentials in  studies  near  alkaline  the  have  linked  the  active-passive  solutions,  as  occurrence  transition  defined  by  anodic  of  of  SCC  mild  to  steel  polarization  8 3 7 40 curves. in  '  '  surface  surface film  Thus,  coverage  (active  (passive  SCC  of  the  state)  to  state).  the  freely  93°  C may  rest  at  depending  upon  the  can  be  metal  from  complete  Reinoehl  corroding  NaOH  (F-  active  a  with  freely  coverage  and  potential  either  correlated  Berry  c o r r  or  )  of  in  change  corroding  by  a  protective  have  shown  that  mild  steel  at  passive  concentration  the  potentials,  solution  and  the  26 previous  electrochemical  The affect  ability  the  appears and/or  SCC  to  of  solution  behavior  depend  anodic  addition  of  history  of  polarization amounts NaOH  shifting  steel  3  E  c  o  r  of  r  the  which  causes  amounts the  of  the  passive  substances  SCC  to  same  region have  active-passive  occur.  into p c  been  shown  transition  to and  the  impurities  alkaline  effect  solutions  on  mild  to  E  c  o  r  r  steel.  agents  such  The  as  has  the  effect  of  SCC  susceptible  region,  o A.  '  '  confers  or  the  oxidizing  The  substances, and  of  solutions  o  specimen.  in  their  curve  0 , NaN0 , a n d PbO t o 2  steel  upon  of  the  additions  mild  primarily  small  of  addition  of  however,  shifts  E  protection  from  SCC.  shift thus  the  potential  change  the  c  o  larger r  r  into Other  of  the  potential  2fi37 41 region such  as  of  SCC  susceptibility.  quebracho  and  valonea  ' tannins,  Only which  a  few act  substances, as  SCC  16  inhibitors, steel  appear  to  affect  in  alkaline  solutions  chemical  behavior  of  The has  led  these  have  correlation  to  several  films.  ficult  to  as  an  SCC  8  '  with  passive 42  initial  adsorbed  further  oxidation  of  becomes  either  passive  transition.  layer  passive  the  FeOOH  of  the in  iron FegO^.  At  still  electro-  film  This  general  occurs  2  At  and  the  of  are  dif-  experiments in  the  higher  at  potentials,  the  potentials,  43 44 '  active  passive  occurs  higher  behavior  properties  Fe(0H) occurs  or  mild  the  voltammetry  formation of  of  changing  films  cyclic  film  behavior  38  investigations  Although  that  SCC  without  metal.  of  characterize,  shown  region  the  the  film  active-  the  FeOOH  3Q  or the  Fe^O^ o x i d i z e s films  formed  to at  form SCC  y-fe^O^.  It  susceptible  has  been  potentials  solutions a r e m o r e b r i t t l e t h a n t h e y~^ 2°3 h i g h e r p o t e n t i a l s a n d , t h e r e f o r e , a r e more e  under  the  application  39 studies tible  46 '  a  tensile  '  have  with  shown  produces  the  that large  dissolution  surface  before  repassivation  rupture  of  passive  in  the  lated  the  anodic to  the  l  in l  m  alkaline formed at to r u p t u r e  s  likely 45  stress.  that  Other  47  potentials  associated  of  f  shown  current  film  can  rupture  current of  iron  stability  the  At  other  or  behavior of  SCC  from  little  This  at  suscep-  transients,  occur.  causes  density.  thermodynamic  film  a  no  exposed potentials  increase  has  soluble  been iron  re-  species, current  HFeO^,  within  transients  sivation  of  Most explain  the  of  the  p r o d u c eid d  are  exposed  the  caustic  potential  cracking  of  electrochemical  dissolution  while  of  the  films. of  sides  This  is  the  and  also  the  active-passive  however,  as  the  to  which mild of  crack  consistent  HFeO^ w i t h i n with  the  range  are  of  these repas-  based  at  the  in  SCC  crack  by  Opinion  has  stress  tip,  passive stability  which and  to  upon  thermodynamic  between  which  proposed  protected  potentials  by  rate  been  metal  the  transition. method  steel  the  with of  the  have  remain  correlation  the  aain d  where  46,47  metal  mechanisms  39  region  SCC  the  been  occurs,  region  of  divided,  corrosion  crack  46 propagation via  occurs.  Hoar  strain-assisted  being  to  create  mechanism.  Scully  '  49  models  the  slip  subsequent  of  felt  with  and  of  the  Staehle  whereby  steps  dissolution  at  the  that role  at  50  film the  exposed  crack  SCC of  occurs  strain  and t o p r e 35 of the exposed m e t a l . Parkins also assisted, continuous dissolution  48  surface  slip-dissolution emergence  Jones  dissolution,  fresh  vent r e p a s s i v a t i o n supported a s t r a i n  and  have  tip  both  rupture  tip  of  metal  the  is  is  supported caused  crack  by  and  controlled  the  by  51 repassivation that up  kinetics.  Vermilyea  and  film  rupture  occurs^when  a  the  passive  film  crack  in  occurs  until  at  repassivation  the of  Diegle  critical  the  tip.  surface  proposed  strain  has  built  Dissolution is  complete,  at  18  which  point  argued drop of  the  that  in  cycle  anodic  pH o f  hydrogen  crack  tip  at  enters  the  steel  ment  of  metal  and  ahead  Perdius  the  solution  thermodynamically  then  the  itself.  dissolution  the  is  repeats  crack until  subsequently  of  the  tip the  possible.  crack  al*  causes  a  evolution  This  causes  tip.  52  et  hydrogen  embrittle-  Mazille  and  38 Uhlig  supported  adsorb  onto  strained  the  a mechanism  metal  metal  at  bonds  whereby  the  enough  crack to  damaging  tip  allow  and  anions  weaken  mechanical  the  failure  to  occur. Other aspects based and of  of  on  the  SCC  anodic  Flewitt a  authors  54  change  of  attempted  mild  steel  dissolution  and  in  have  Melville  potential  to  in  alkaline  theories.  55  have  down  the  model  Thus,  all  specific solutions, Bignold,  examined  cracklength  the on  53  Doig  effects SCC,  and  56 Mogensen  et.  repassivation potentials. intergranular have  been  al.  have  kinetics None or  of  investigated of  the  developed  to  1.4  Origins  of  Several  industries  a  for  dissolution at  various  mechanisms  specify  crack  account  of  formation  proposed  transgranular  modes  on  oxide  the  path  the  and  and  an  explanations  o c c u r r e n c e of  both  propagation.  regular  the  basis.  Present  One  Work  deal of  with  these  highly is  the  alkaline pulp  and  solutions paper  19  industry. white  In  the  liquor,  primarily  M'-NagS,  is  leaving  cellulose  liquor vessels When ing as  used  come  pulp. then  and  as  store  the  NaOH  level  and  to  fresh  white  turned  the  to  schematic  is  other  with  a  and  large  black series  Na^S  chips  spent  and large  687-750  the  it  is  tanks  and  further  Kraft  use.  process  to  re-  The  pressure, until  Figure  and  is  original  solution.  stored  the  called,  their  atmospheric  chips, from  designed  to  the  now  kPa.  contain-  wood  l i q u o r , as  operations  0.6  pressure  liquor,  from  -  white  separated  from  as  chips,  is  9 2 ° C and  the  in  C and  concentrations  for  wood  species,  of  settling  of  the  residue  impurities at  in  other  150-170°  known  M NaOH + 0 . 2  The  each  complete,  digestors  diagram  at  solution  lignin  pulp.  soluble  or  to  the  or  sulphur  liquor,  in  2-3  digestors,  remove  clarified  containing  contact  spent,  subjected  a  fibres  oxidized  The  process,  dissolve  digestion  lignin well  to  into  called  the  Kraft  3  is  reis  emphasizes  a its  57 cyclic  nature.  contains Na^CO^  a  number  and  Kraft  liquor  liquor  process;  clarifiers  cracking  of  of  mild  NaOH  and  impurities,  NaCl , w h i c h  White the  Besides  cannot  contacts in and  steel  the  mild  such  steel  tanks.  a major  as  removed  digestors,  storage is  be  Na^S,  at  and  white  Na2$20.-, by  the  in  in  also  Na^SO^,  process.  three  points  the  Although  problem  liquor  in  white caustic  the  pulp  and  20  WATER mud thickener  /  mud wasner white liquor storage  CHIPS  LIME STONE  1  lime kiln  white liquor clarifier  \ digestor  /  WATER \  causticizer  \  pulp washer  PULP  /  weak black liquor storage green liquor clarifier  /  evaporator  \  dissolving tank  strong black liquor storage  dregs washer  molten chemical weak liquor storage  MAKEUP CHEMICALS  Figure 3  Schematic o f t h e K r a f t  cycle.  paper  industry,"""  solutions interest ions  on  work  was  and  to  the the  the  rectify were  in  very  temperature industry,  caustic  undertaken this  little  to  storage  and  has  been  concentration  on  range  the  cracking  of  mild  with  the  anticipation  of  The  environments  chosen  for  liquor  clarifiers  encountered  in  of  of  on  that  effect  done  or  situation.  similar  research  steel.  white  sulphide The  present  beginning  to study  tanks.  41 Preliminary  work  pendently  by  dition  sulphide  of  process, tion by  to  Wensley  NaOH  potential  Tromans  to  the  work,  shift  in  SCC  vestigate posed  to  compared hoped i)  insight  steel  and  a  ii)  the  data  SCC  steel  white  by  problems liquor.  were  use  to  of  liquor  this  to  in  It  mild  did  the  SCC  in  Kraft  NaOH  caustic  transi-  postulated was  most  The  goals  of  whether  mild  containing  ad-  steel  occur,  and  this  to  steel  inex-  NaOH a n d  solution.  investigation of  the  was  discover  plain  inde-  active-passive  which  potentials  mechanism of  the  that  accordingly.  severity  of  found  ~100mV.  at  strength  confirmed  showed  5 8  level  raised  shift  white  results  into  the  therefore,  similar  the  at  steel  would  relative  avoiding to  SCC  and  Charlton,  potential  simulated  to  that  mild  susceptible  the a  ions,  the  susceptible present  and  Tromans,,  solutions  of  that  by  would  cracking  the  pulp  and  paper  associated  with  the  exposure  Na^S It  was  provide of  mild  industry of  in  mild  Chapter  2  EXPERIMENTAL  2.1  Scope  of  During solution  the  the  Present  course  compositions  of  and  A SSRT  was  adopted  to  on  SCC  of  steel  the  mol/kg  NaOH  technique gate  the  strain  order  which  strain to  mild  other  rate  in  test  used  steel  to  8  1139  the  known  results a  The  establish be  the  stress  the  two  solutions.  Na S.  annealed  investiNaOH  of  for  the  used  before  corrosion To  22  study  stress crack  the  best  in  use  slow was  of  the  the in  strain initiated  intensity velocity  of  subsequent  the  of  slow  conditions  obtained  mechanics  the  the  history.  from  This  2  purpose  used  3.35  metallurgical  effects  on  of  to  The m a t e r i a l  was  potential  concentrated  to  fracture the  mol/kg  '  to  employed.  of  composed  '  experiments.  a  were  successfully  more  SCC  different  effect  0.42  in  was  three  methods the  NaOH +  experiments  investigated  work,  solutions  workers.  establish  on  in  been  experiments  experiments,  potential steel  of  two  mol/kg  already  mechanics  Based rate  2.5  this  investigate  susceptibility  fracture slow  by  rate  maximum  and  had SCC  solutions  mild  Work  of  and mild  author's  knowledge, made  of  no  the  solution.  previous  SCC  of  For  were  solution  order  in  mild  this  experiments  fracture steel  reason,  in  any  in  a  compare  fracture  12.5  the  studies  had  been  of  NaOH  concentration  parallel  conducted to  mechanics  mol/kg  results  mechanics  (33%)  of  the  NaOH fracture 8 26 37 38  mechanics Since of  previous  mild  the  technique  high  work^  steel  was  material yield  those  had  used  in  these  strength,  that  plane  proved  to  tailed  fractography  other  to  SCC  was  at  high  conducted  stress the  '  '  cracking  tested  met  '  laboratory,  worked  were  on  the  was  cold  conditions  caustic  in  experiments  only  techniques.  that  obtain  as-received,  strain  undergo  of  indicated  difficult  ensure  all  with  in  the  condition if  the  material  intensities. crack  to  De-  surfaces  of  specimens.  2.2.  Materials 2.2.1  Steel The  AISI One  C-1018 batch  while  the  mild  was  The  of  mm x  stress yield that  of  given  steel.  25.4  each  at  were  of  at  this  9.5  were  The  20° C f o r  with  chemical  not  the  of  mm d i a m e t e r received  batches  92° C d i d  work  batches  received  mm. the  in  Three as  batches  bars  stress  used  received  other  stock. 25.4  steel  is  a  nominally  steel cold cold  square  in  were drawn  drawn  used. rod, bar  Table  and  yield  I.  The  significantly  stock.  an  cross-section  composition  given  change  bar  as  was  from  Table  Yield  I  Strength  rod  9.5  Chemical  Yield Strength' (MPa)  S i ze (mm)  Batch  and  dia  Composition  of  Steels  E  1 e m e n Si  t**  C  Mn  P  S  Ni  Cr  297  0.17  0.65  0.012  0.01  ND  ND  ND.:  ND  •0.01  Mo  Cu  bar  A  25.4  x  25.4  631  0.16  0.72  0.005/  0.02;  0.23  0.05  0.15  ND  0.37  bar  B  25.4  x  25,4  656  0.20  0.58  0.014  0.02  0.25  0.04  0.16  0.04  0.12  *  rod  **  weight  ND  not  at  92° C,  bars  at  20° C  percentage  detected  ro  Slow from of  the  strain  9.5  rate  mm d i a m e t e r  5 mm d i a m e t e r  254  mm l o n g  tensile 320  in  10  a  lowed  grit vol  by  vacuum  had  in  at  920°  capsules  Double specimens  threaded  cantilever machined  geometry  shown  mm,  specimen  length  and  specimen  thickness  initial  machined  and  beams  application  of  crack  were  then  plane ethanol  desiccator  load  and  until  in  in  gage  receive  were  rinsing  and  specimens air  was for  cleaned  water  sealed  were  cooled  the  polished  and  with  dried  section  grips  chloroethane  was  machined  specimen  sections  minutes,  beam  (DCB)  from  the  square  4.  Beam  Figure  from  crack  were  gage  The  Each  were  folunder  subsequently  and  stored  the  (B)  dried.  to  The  polished  25.4  the  threaded (P).  loading  was  from  to The  fracture bar  according  height line  (H)  (W)  was  was  6 6 . 7 mm  The  loading  line  was  25.4  grips  for  the  faces  length  perpendicular  grit,  specimens  washed were  in  to 11.6  mm.  receive  600  mechanics  of  to  the mm  the  water,  stored  in  a  used.  1g Brown bration  for  and the  Srawley DCB  in  used.  the  the  45  reduced  to  After  capsule.  until  were  The  specimen  C for  a  ends  degreased  each  specimens  length.  solution.  Vycor  test  with  '25.4mm  paper,  % HC1  a  rod  machine.  ethanol,  annealed their  and  and  testing  with  tensile  have  geometry  is  shown  that  given  by  the  Kj  equation  cali3.  Figure 4  DCB  specimen  geometry.  27 Kj = P ,  ( 3.45  a  The c a l i b r a t i o n i s a/W  < 0.6  valid for this  each t e s t .  solutions  Reagent  by Amachem,  grade  and r e a g e n t  (Na S,9H 0) 2  used a t a l l (g  solvent)  by a d d i n g  the d i s t i l l e d  water.  were p r e p a r e d  by f i r s t  i t with N  grade  specimen  hydroxide  hydrated  for  solutions basis.  sodium  boiling  distilled  2  f o l l o w e d by t h e N a S - 9 H 0 c r y s t a l s . 2  2  amount  o f NaOH t o solutions  w a t e r and  atmosphere  and  The n o m i n a l  solution  NaOH,  NaOH + 0.42  mol/kg  Na S.  of the s i m u l a t e d w h i t e  liquor  and t h e c o r r e s p o n d i n g  s o l u t i o n was  2.3  3.35  Equipment Slow  mol/kg  and  strain  2  mol/kg  were  mol/kg  mol/kg  The t o t a l  then  temperature.  were 12.5  2.5  water  solutions  t o room  3.35  Bell,  were p r e p a r e d on a  the d i s t i l l e d  a N  supplied  Coleman and  The NaOH  while cooling  to  sulphide  The s i m u l a t e d w h i t e l i q u o r  NaOH p e l l e t s were added u n d e r  compositions  prior  pellets  Singly  the r e q u i s i t e  gas,  2  prepared  by M a t h e s o n ,  and a l l  were p r e p a r e d  purging  sodium  the s o l u t i o n s .  times  solute/kg  were f r e s h l y  supplied  2  were u s e d t o p r e p a r e  molal  type of  Solutions All  was  H  i f W/H > 5.  2.2.2  crystals  + 2.415  NaOH and Na  +  molality NaOH  Na . +  Apparatus  rate tests  were c a r r i e d o u t on a f l o o r  28  mounted  Instron  tensile  testing  machine  capable  of  achiev-  -4 ing  a minimum  schematic 5.  The  carbon  cross-head  diagram  cell  was  polymers  condenser,  and  materials.  400)  was  sides  externally  and  A  into  the  wrapped  the  heating  tape  YSI  model  room  was  or  cell.  of  71A  a  was  ~ 1 mm f r o m of  Princeton  Applied  Research  specimens  SF-l-U  constructed treated grip  was  to  were  fatigue of  high  provide  provided  the  test  purge  toughness.  or  to  The  was 173  by  to  op-  an tape.  connecting  An  and  ensure  to  a  external  maintained via  the  Luggin of  the  capillary specimen.  maintained  by  potentiostat.  by  Fatigue  A universal  tests  model  at  by  cell  precracked  steel  the  transformer  section  model  floororeflux  of  heating  the  machine. tool  PTFE  (YSI  heated  (see),  specimen  Figure  spectrograph!'c  maintained  gage  in  positioned  power  A  line,  probe  controller.  (PAR)  testiing  2  resistance  fatigue  later  N  capillary.  strength  in  FEP  was  electrode  the  control  model  cell  shown  of  two  were  Variac  Luggin  is  mm/s.  constructed  and  connected  Potential  DCB  all  C was  reference  filled  positioned  The  1°  a  10  thermistor  temperature  temperature, KC1  +  through  calomel  saturated  with  cell,  electrical  control  at  coated  x  used  entirely  fitted  the  8.47  cell  capillary,  FEP  Temperature  saturated  was  of  counterelectrodes  of  71  test  constructed  inserted  graphite  posite  the  Luggin  same  grade  of  speed  a  grips  were joint even  Sonntag were  heat in  one  loading  a  29  LUGGIN CAPILLARY SPECIMEN N  2  PURGE  P T F E CAP  FEP  -H  BEAKER SOLUTION  COUNTER  ELECTRODE  J  ^COUNTER PTFE  Figure 5  SSRT  test  cell  ELECTRODE  SEAL  geometry.  30 across  the  crack  Fracture  plane.  mechanics  constructed  entirely  in  strain  the  shown  slow in  coated  Figure  The  cell  and  temperature  as  for  by  a  the  an  an  fatigue  of  the  Luggin  control  controlled model a  541  was  the  ml  beaker-type  over  PAR  cell.  were  long  and  in time  apply  anodic 173  A gel  The or a  the  cell  a  just  same  Monsanto constant  manner  was  the  monitored  load  ~ 1 mm  the stable  68TS10  to  the  potenwas ECO  mounted  testing  curves  equipped  or  was  edge  length  potential  tensile  to  leading  ran  assembly  plane  capillary,  the  The and  grade  crack  situated  maintain  polarization  potentiostat,  mantle  connected  thread  68FR0.5 cell  and  below  to  cell.  heating  Luggin  is  Teflon the  the  in  was  periods.  models  Hounsfield  model  KC1  order  of  spectrographic  mounted  A cotton  potentiostats.  to  Two  cell,  employed  of  in  a  one  Temperature  temperature,  surface  Wenking  used  maintained  specimen.  precrack.  Independent by  room  capillary  by  horizontal  which  600  rate  the  bottom  in  the  by  the  thermometer.  of  at  provided  on  agar/saturated  specimen  the  was  out  to  bar  was  strain  SCE  of  tial  A schematic  a  control  sides  with  the  tests.  counterelectrodes  external  from  by  carried  similar  Stirring  heated  coated  opposite  filled  rate  were  Teflon,  stirring  slow  Teflon  graphite on  was  of  6.  magnetic  tests  in  machine,  specimen.  were with  generated a  PAR  model  LUGGIN  PTFE  REFLUX  CAPILLARY'  3  CAP P  —  f  '  f  -  f  '  S  y  <  *  > ~ — '  >  7  7  .r FEP  —  P  SPECIMEN  BEAKER SOLUTION  N  2  PURGE o  ure 6  F r a c t u r e mechanics t e s t c e l l  geometry.  376  logarithmic  meter  probe  programmer  current  and and  connected a  Houston  corder.  Fractography  scanning  electron  imaging  mode  and  from  the  were  measured  converter  Luggin  to  a  was  KeV  a  model  examined  on  (SEM)  and  175  an  2000  secondary  ion  RTS  membrane ence  system  equipped  specific  ion  Experimental 2.4-1  electrode  Orion  and  contamination  822  Ag  automatic 2-  /S  double  solid  junction  refer-  SSRT  Procedures Experiments  A tensile capsule 60  before s  at  30  test,  V  a  trioxide,  rinsing  with  diameter  was  All  areas  for  the  of  gage  current  solution cell  were  cell  was  test  each  chromic  duce  an  electron  electrode.  2 .4  for  with  re-  concentration  + titration  X-Y  Autoscan  Chloride  model  electro-  universal  ETEC  using  sulphide  Radiometer  178  model  excitation.  capillary,  with  PAR  model  Omnigraphic  microscope 20  and  in  135  water,  the  ml  flushed  with  and  N  9  a  and  and  to  7 ml  with  minimize  attached  gas  before  the  changes  to  microscope. except  tape in  adding  to  re-  the  specimen the  After  gage  solution,  The  and  g  water.  Teflon  its  polished  travelling the  test.  from  2.5  1  drying,  optical  wrapped  during  assembled  acid  exposed  were  requirements  composition  an  removed  containing  ethanol,  with  was  electrochemically  acetic  specimen  section,  then  and  solution  then  measured  specimen  and  Instron.  ~ 500 m l s  of  test The test  solution  to the c e l l  l o a d was  a p p l i e d to the specimen  was  brought  potential time.  under  to the t e s t  a N  sce  a  s  w h i l e the c e l l  tensile  solution The  specimen  was m o n i t o r e d , but n o t c o n t r o l l e d , d u r i n g  When t h e t e s t  w  A small  t e m p e r a t u r e o f 9 2 ° C.  t e m p e r a t u r e was  e q u i l i b r i u m of the apparatus V  atmosphere.  2  a  PPl  polarization  1  e  d  t  thermal  a c h i e v e d , a p o t e n t i a l of  the specimen.  0  r e a c h e d , and  this  s c a n a t 1 mV/s  was  A f t e r 120 s . ,  an  initiated until  -1.25  anodic  the  desired —6  test was  p o t e n t i a l was  A strain  then a p p l i e d to the specimen  Typically, Temperature out  this  was  18-20  to provide  sulphide  2  gas  until  3.3  failure  x 10  was  bubbled  /s  occurred.  hours a f t e r the s t a r t  a stirring  of the  continuously  test.  throughthrough  a c t i o n and p r e v e n t  oxidation  ions.  At the c o n c l u s i o n test  r a t e of  and p o t e n t i a l were m a i n t a i n e d c o n s t a n t  t h e t e s t , and N  the c e l l of  reached.  specimen  o f a t e s t , t h e two h a l v e s  were removed  with water, rinsed cross-sectional  from the c e l l ,  were e x a m i n e d w i t h t h e SEM f o r on t h e s u r f a c e  near  o f a few s p e c i m e n and t h e f a c e s  polished  polished  faces  solution  to reveal  signs  of secondary The gage  were s e c t i o n e d  t o a 1 ym diamond  were ' e t c h e d ferrite  The r e d u c t i o n  in  and t h e f a i l e d ends  the f r a c t u r e t i p .  halves  the  c a r e f u l l y washed  i n e t h a n o l , and d r i e d .  a r e a was m e a s u r e d ,  of  with a 2 vol  cracking sections  longitudinally, finish. % HNO^ i n  and p e a r l i t e g r a i n  The ethanol  boundaries,  34  r and  the  crack  paths  of  secondary  cracks  were  examined  by  SEM. 2.4.2  Fracture  Mechanics  Throughout were  used  to  specimens Kj  machined  level  from  the  of  bar  cracked  fatigue  12  +  B and at  a  fatigue  from  B,  bar  mol/kg cracked  at  extended fatigue crack  two  intensity. precrack in  All  the  of  a  mol/kg  extended  2-4  remainder those  of  mol/kg  NaOH a t  A fatigue  K-  level  of  dropped  to  further  ~ 1 mm.  intensity  7 +  was  correlation intensity  2.5  -1.00  12  +  was  11  between  cases,  machined  ,  NaOH were  before  the  +0.42 fatigue  initiated  and the  fatigue  cases,  the  steel  solution  e  MPa/m  most  than  c  a  initial  mol/kg  5 MPa/m a n d In  above  the  s  at  fatigue  the  V  the  machined  specimens  crack  lower  and  specimens  In  in  of  cracked  mm f r o m  tested  All  NaOH w e r e  the  procedures  the  test  maximum  stress  batch,  fatigue  composition  is  shown  II.  Prior  the  12.5  a  stress  Table  wrapped  The  was  The  fatigue  7 +_ 5 M P a / m .  levels.  stress  A were  of  was  different  specimens.  level  ~ 2 mm a t load  the  3.35  and  extended  fatigue  MPa*^.  including  Na^S  bar  three  in  crack  crack.  precrack  from  11  work,  tested  K-  machined  the  Experiments  in  crack  to  assembly  Teflon tip  was  tape left  in  the  so  that  exposed  cell, only to  the  the a  specimens  small  area  solution.  were around  As  for  Table  II  Correlation Stress  Between  Environment,  Steel  mol/kg  NaOH,  "  3.35  2.5  mol/kg  mol/kg  E  • -  NaOH,  NaOH  and  Fatigue  Intensity.  Envi ronment  12.5  Batch  1  c  Q  '  r  0  Batch  r  0  -1.00  + 0.42  V  sce  V  s  c  e  mol/kg  Na S, 2  -0.88  V  see  Fatigue  Stress Intensity (MPa/m)  A  12 +  11  B  12 + 7 +  11 5  B  7 + 5  B  12 + 11 7 + 5  co cn  36 the  slow  total  strain  current  position test  cell  550  to  assembled  First, to  mis  the  be  of  The  controlled,  was  reached of  ditions  the  was  reside  in  the  V  which  served  c  specimens  with  N  otherwise  region.  return  on  the  E  the  these  o  r  to  the  but  potential  corroding a  found  s  r  for  active  brought  temperature  the  cases,  specimen  the  and  test  w c  if  monitored,  freely E  and  Otherwise  cell  noted),  under  In  gas,  was  When  com-  tensometer  2  the  the  specimen  ions.  potential  tested  impressed  to  the  into  time.  solution  in  Occasionally,  passive  was  e  this  measured.  -1.25  $  specimen  minimize  The  sulphide  poured  to  in  control.  flushed  were  (92° C unless  done  mounted  was  during  was  changes  contained  solution  temperature.  most  and  and  cell  added  not  of  this  potentiostatic  were  solution  tests,  requirements  during  frame.  ~  rate  a a  con-  to  potential few  of  minutes,  region.  After  corr allowing moved  E.  from  c o r r  to  the  eel 1.  control  were  then  anodic  or was  an  reached.  potential  A  intensity  to  specimen.  the  During capillary of  was the  at  r  automatically,  at  tests  -1.25 scan  1 mV/s  load, at  the  Specimens  polarized  stress  E  stabilize,  tested V  was  tip  without  occasionally  the  a  the  give  crack,  reinserted The  test  the  was  manually potential  desired  then  the  the  current  re-  minutes,  either  control, into  was  potentiostatic  few  desired  to  potential  measured.  under  initiated,  until  of  capillary  for  see  precalculated  the  specimen  Luggin  applied  Luggin  cell  passed  and by  the  37 potentiostat  to  periodically  for  control.  The  monitored  daily  was to  those  applied  prevent  48  occasion,  solution  in  specimens  course  solutions of  to  check  2  cell  to  plain  NaOH  solutions  check  for  few  days  of  As during  distilled  to  make  the  was  course  of  all  for  aliquot  of  chloride  or  200  test  an  crack  near  was  They had  the  the  crack  range  pH  a  number  of  to  capillaries.  A  the  cell  the  every  crack  the  test  2  it  paper.  mm.  the was  when At  was  liquid  measure  tensometer. was  3-4  solution  When  N ,  continued  terminated  with  to  growth  were  extended  removed  tip  the sulphide  of  were  replaced  liquid  re-  losses.  concentration.  from  narrow  and  the  to  experiments  hrs.  were  ions  periodically  to  monitor  experiment,  in  removed  Hydrion  the  solution  sulphide  liquid  400  specimen  sufficiently and  test, -  that  of  the  a  added  evaporation  the  from  using  were  gas  2  sulphide  correct  Luggin  N  were  concentration.  added  the  the  to  lowered  failure  from  for  the  aliquots  monitored  impossible  estimated  cooled  was  water  test.  concentration  proved  conclusion  frozen  up  were  it  uninterrupted it  chloride  contamination  a  sulphide  maintain  The  mis  the  crystals  2  of  and  recorded  temperature  containing  sulphide,  was  potentiostatic  the  concentration.  few  under  throughout  Na S-9H 0  test  potential  solution  hrs  the  specimen  and  oxidation  every  the  load  bubbled.through  moved On  control  N,,.  the  An  final  specimen  had  overloaded  to  The  pH  of  the  measured  as  it  melted,  Both  halves  of  the  specimen dried.  were The  then  initial  the  specimen  and  the  to  limit  extension measured  of  of  for  of  stress  stress  each  Specimens  required  further  for  The  The  using  corrosion  fractured posed  of  the  film  specimen 4 mis  35%  half  of  SEM, was into  the with  the  inhibited  specimen  sectioning extension side  them of  dried,  examined  cracks  the  were  travelling  it  in  until  at  the  corrosion  ferrite  and  pearlite  grain  etching  the  polished  face  etched  to  a  surfaces  a  of  and  were  were  water, the  of  halves  polishing finish.  revealed  examined  cleaned  by  farthest  % HNO^ in with  :  cleaner  paths  specimen  1 ym d i a m o n d  2 vol  of  com-  50:mls  with  crack  point  crack  boundaries with  washed  few  +  ultrasonic  The  longitudinally  piece  an  the  HC!  fractography  a  sectioned  3 mis  place.  solution  the  SEM.  in  immersing  then  the  first  film  was  in  stress  was  cleaning  examined  the  The  and  with  of  solution.  by  2 b u t y n e - 1 , 4 - d i o l '+  The  secondary  the  accurately  a desiccator  corrosion  an  mins.  surface  from  visible  optical  surface  removed  for  crack  were  an  in  then  suspending  ethanol ,  with  crack  and  in  crack  of  growth,  growth  farthest  and  line  crack  crack  the  stored  water,  rinsed  to  ethanol  loading  fatigue  corrosion  distilled 20-30  of  the  with  analysis.  fractography  examined,  limit  corrosion  were  rinsed  from  growth  specimen  microscope.  water,  length  visible  fatigue  the  in  crack  the  increment  visible  washed  the The  by  ethanol the  SEM.  A few  specimens  before  being  water,  and  The  face  diamond  were  next and  2  as  the  finish  was  open  sectioned  of  path  N ,  broken  were  then  etched  examined by  piece as  Anodic  all  three  PAR  potentiostat from  600  grit,  before cell  (Figure  holder  and  The cell  and  admitted  the  to  reveal  the  crack.  polished  to  a  described. The  the  crack  1 ym The  specimen  specimen surface  halves  in  was  crack  liquid examined  square 10  bar  The  with  was  run  mm a n d  and  curves  Linear  mild  steel  equipment. to  dimensions  tapped  to  accept  faces  rinsed  to  in  accept  a  were  using  were  of standard  and  fracture  the  the  polished  ethanol  A Teflon  in  Specimens  stock  scan.  modified  of  potentiodynamically  exposed  water,  polarization 6)  Curves  Experiments  associated  holder.  washed  each  were  and  10 mm x  specimen  the  polarization  solutions  PAR  with  SEM.  Polarization  Anodic  10 mm x  well  overloading  Polarization  ~  rinsed  already  of  tensometer  N,,,  was  the  the  before.  2.4.3  machined  liquid  with  fractography  described  from  longitudinally  separated  the  in  sectioned and  removed  PAR  to  dried mechanics  specimen  specimen.  nitrogen brought to  the  to  purged  test  temperature  cell.  The  solution before  specimen  was  was the  added  to  specimen  polarized  at  the was  -  1.25  V  see  for  was  initiated.  the  cell,  and  magnetic  N,, the  stirrer  mol/kg  NaOH  run  different  at  specimen tests.  from  and  surface  of  to  No  remove  allowed  to  return  the  cell made  same  2.5 and  was  specimens  were  .  in  both  the  at  each  potential  polarized  cathodic was  and  at  anodic  measured.  were  solution.  The  SSRT  made  salt  tensile 0.42  previously was  used,  taken to  as  the  correct  from  concentra-  bridge.  were  conducted  above  for  curves.  the  between  NaOH +  was  V  s  c  e  After  the  The  for  E  using deter-  specimens  ~ 15  surface.  corr the  scans  arising  -1.40  from  E  12.5  experiments  polarization  films  the  mol/kg  described  at  coated  procedure  experiments  through  In  the  section  the  mV/s  repolished  on  differences  to  cell.  and  rate  in  a  the  attempt  polarized any  in  gage  apparatus  anodic  by  polarization  cell  the  polarization and  of  NaOH a n d  gradients  cathodically  order  of  potential  the  Teflon  strain  area.  thermal  specimens  mination  area  1  stirred  were  slow  small  mol/kg  at  bubbled  the  tests  scan  continuously  temperatures  the  exposed  anodic  successive  corrosion  for  an  bottom  The  2  the  then  the  removed  Linear  in  on  Na S.  specimen  were  solution  3.35  the  the  was  in  described  tion  before  gas  Comparative  mol/kg  for  s  solution,  was  specimens  and  120  mins  They had  were  stabilized,  corr 3 mV  and  6 mV,  directions,  and  respectively, the  current  2.4.4  Sulphide  and  Chloride  Sulphide  analysis  Analysis  was  carried  out  according  to  59 a  procedure  by a  similar  Raudsepp, titrant  drawn  mediately aliquot  the  of  this water  pared  samples  AgNOg  to  the  The  5 mis  were  100  mis  was  then  of  exception 3  to  were  of  pipetted  then  titrated  endpoint  for  similar  the to  from  into  0.100 in  ~ 2 mis  the  ~ 40  given  mis 3-4  N AgN0 .  No  presence  and  N NaOH.  of  with  and  0.100  titrator.  ions of  diluted  this  This then  determina-  ions.  to  solution  HNO^.  ion  sulphide  pre-  Aliquots  dilute  chloride  of  chloride  above.  of  with-  im-  The  deionized water.  with  of  were  mis  automatic  aliquot of  ~ 40  solution  as  A 10 ml  triplicate  the  test  pH  the  10  determination that  3  in  by  A 10 ml  to  of  into  used  used  solution  was  containing  was 5 mis  solution  acidified  made  test  and  3  volumetrically.  pipetted  with  AgN0  Aliquots  2  containing  volumetrically.  titrated  that  Papp  mis  withdrawn  was  by  100  were  was  developed  Hg(N0 ) .  sulphide  solution  tions  the  procedure  solution  that  sulphide  diluted  deionized  in  with  6 0  instead  from  to  N  Chapter  3  RESULTS  3.1  Anodic  Polarization  Curves  and  Linear  Polarization  Results The  anodic  polarization  curves  determined  for  41 work  are  similar  to  those  shows  representative  steel  in  0.42  the  mol/kg  features,  3.35 Na,,S  with  presented  anodic  mol/kg  polarization  NaOH a n d  solutions.  E  just  elsewhere.  Both lower  2.5  curves  than  -  defined  active  behavior. are  i)  the  The  the  steel  in  peak  followed  higher  simulated  by  anodic  the  V  rapid  taining to  s  the  c  e  in  the  increase  white  sulphide in  liquor,  current  mild  similar and  potentials  oxidation  of  sulphide  polarization  42  to  both  i i ) the V in see  a  well  the  the  than  of  two  curves  attained  the  solution,  higher  curves  passive  by  active  s h i f t in the onset t h e NaOH s o l u t i o n to  in  higher  to  density  at  density  at  anodic  between  containing  solution  The  transition  current  r  0.89  a  differences  peak and i n t h e p a s s i v e r e g i o n , o f p a s s i v e b e h a v i o r f r o m - 1.03 -  the  7  see  important  much  of  V  corr  Figure  NaOH +  have  1.1  58 '  curves  mol/kg  this  -  and  sulphide 0.75  oxidation  mild  iii)  steel  V_  conc e  >  states.  in  due  43  Figure 7  Anodic p o l a r i z a t i o n curves of m i l d s t e e l i n 3.35 mol/kg NaOH and 2.5 mol/kg NaOH + 0.42 mol/kg Na S at 92° C. 2  44 12.5  mol/kg  Figure  NaOH a t  8.  These  transition. the  anodic  the  passive  curves  Raising current  concentration  12.5  mol/kg  NaOH  density  significant  The in  each  by  a  and  least  o  r  r  >  by R"  squares  -  where  b  a  b  respectively. ~ 0.06  b  as  a 3  :~  the  c  are  0.72  r  -  linear  of The  of  the  anodic No  steel.  experiments  was the  corrosion  the  anodic  of  vs.  calculated line,  polarization  the  in  to  peak  density  line  slope  7)  the  batches  each  and  decrease.  between  current  peak  (Figure  polarization  as  increase  Increasing  to  corr  in  resistance,  current  density,  69  +  a  b  ;lb 1  the  (for  V/decade  \ i .  c  a' c'  Doig^and  V/decade  r  E  reciprocal  4:  Q  C caused  different  to  c  to  active  NaOH  noted  slope  related  the E  shown  active-passive  92°  and  plotted  be  A  both  at  method.  2.303 / b  and  as  8)  are  served  mol/kg  were  the  ;  at  3.35  is  an  decrease  the  best  equation  1  of  were  the  exhibit  increase  of  solution  F  c  from  curves  (Ai/AE) , _,. corr R~ , and can i  to  (Figure  results  potential  and  differences  polarization  temperatures  temperature  density,  to  J  also  the  region,  NaOH  current  different  b  c  /  anodic x Flewitt  r  ....4  r  ' and  cathodic  have  hydrogen at  o  .92° C  given  Tafel the  reduction) in  8 M NaOH  constants,  value  and  that  of  b  c  of  solutions.  5 4  '  6 8  45  to"  IO"  2  I  1  CURRENT DENSITY ( i ) ,  Figure 8  Anodic  io  10  2  A/m*  p o l a r i z a t i o n curves of mild s t e e l  NaOH a t s e l e c t e d  temperatures.  10*  i n 12.5  mol/kg  Table  III  Results  of  12.5 Bar  ^corr  Rp  i  1  ^sce^  (n"V ) 2  (A/m ) 2  corr  v  '  '  Linear  mol/kg A  Polarization  NaOH  Bar  B  3.35 Bar  Experiments  mol/kg  A  Bar  NaOH B  2.5  mol/kg Bar  NaOH  A  +  0.42  mol/kg Bar  ;B  -1.24  -1 . 2 4  -1.15  -1.15  -1.16  -1.16  140 + 40  150 +20  55 + 25  68 + 10  36 + 25  52 + 17  2.0 + 0.6  2.1 + 0.3  0.52 + 0.37  0.74 + 0.23  0.78 + 0.35  0.97 + 0.14  Na S 2  47 Using  these  "I'corr  for  in  each  Table  surface  values  the  solution  III. of  for  the  Tafel  and  batch  A tarnish  film  specimens  at  E  r  film  formed  thicker  than  The the  the  that  of  w  a  of  J  mol/kg There  no  of  i  R  in  p  was  about  in  in  all  in  double  for no  that  mol/kg  NaOH  form  was  and  - 1  p  on  the The  blacker  and  solutions. III  represent  for  each  batches  of  of  i  corr  the  in  the  of Within  difference  of  other  observed  NaOH a n d  batch  experiment.  significant  two  difference mol/kg  R  tabulated  to  Table  each  value  3.35  ,  r  the  The  corr  are  NaOH  experiments used  E  solutions.  liquor  plain  corr  between  significant  corr  „ corr  experiments,  solutions.  steel  observed  white  i  three  of  was  the  and  - 1  or  the  NaOH was  values  of  observed  the  was  formed  solution of  s  corr any  simulated  two  Fresh  accuracy  in  the  values  average  steel.  in  in  constants,  steel 12.5  two  solutions,  between  the  simulated  white  1i q u o r .  3.2  SSRT  Results  2.3.1.  3.35  Figure rate  experiments  upon  the  anodic  solution.  The  potential. at  -  1.00  The V  s  c  e  ,  9 shows  conducted  the in  minimum  are  3.35  the  slow  NaOH  curve  of  the  steel  plotted  as  % reduction  % reduction  corresponds  of  mol/kg  polarization results  results  to  the  in  area,  potential  superimposed in  which at  strain  the in  same  area  occurs  which  the  vs,  Figure 9  E f f e c t of potential NaOK s u p e r i m p o s e d obtained  upon r e d u c t i o n i n a r e a f o r 3.35  upon t h e a n o d i c p o l a r i z a t i o n  i n t h e same s o l u t i o n .  curve  mol/kg  49  Figure  10  Appearance o f f i n a l  fracture region  test  NaOH.  i n 3 . 3 5 mol/kg  after  SSRT  mild  steel  was  coincides passive  most  with  the  within  At  a  A decrease from of the  the  mean  numerous  firmed  SCC  SCC.  the  strain  50 mV  % reduction  level  was  always  where  the  the  cause  of  tested  to  in  this  photographs at  SCC  of  a  by  the  also  presence  surface This  failure. the  to  specimen  the  occurred.  of  SCC  active  potential.  area  penetrating  premature  failure  from  accompanied  failure  potential  employed,  from  the  cracks  This  steel  rate  in  near  as  to  of  r e g i o n of +  representative  specimens  the  secondary  specimen  shows  transition  behavior.  occurred  susceptible  of con-  Figure  appearance  susceptible  10  of  (-  1.00  V  ) j U C  and  nonsusceptible  Examination  of  ferrite cracks  was  ferrite  the  and  )  potentials  which  etched  had  intergranular,  through  both  respectively.  been  showed  ferrite-pearlite  observed  2.5  mol/kg  The  results  simulated  obtained The  S Q Q  sectioned  that  between  grains.  pearlite  secondary ferrite-  Transgranular grains  and  grains.  3.2.2  in  primarily  \'  halves  polished  grains.and were  0.62  specimen  longitudinally, cracking  (-  in  minimum  the  white plain  NaOH + of  the  liquor NaOH  % reduction  in  0.42  mol/kg  slow  were  similar  solution, area  strain  as  occurred  Na S 2  rate to  shown at  -  experiments  those by  Figure  0.88  11.  V_„„, a  Figure 11  E f f e c t of p o t e n t i a l upon r e d u c t i o n i n area f o r mol/kg NaOH + 0.42  2.5  mol/kg Na S superimposed upon the 2  anodic p o l a r i z a t i o n curve obtained i n the same s o l u t i o n .  a)  E = - 0.90 V  see  potential  just  transition  potential.  % reduction face  slightly  in  cracks,  specimens..  area  while  (-  no  were  shows  V  )  the  which  exhibited  cracks  12  0.90  than  Specimens  also  Figure  susceptible  higher  showed  numerous visible  specimens  and  active-passive a  reduced  secondary  on  the  tested  nonsusceptible  other  at (-  sur-  SCC 0.50  V  see potentials, to  be  granular  3.3  entirely  cracks  Fracture 3.3.1  than  stress shown  the  of  edge  the  of  shallow the  crack 13. of  The of  the  fewer  NaOH  were  found trans-  solution.  the  A.  a more  The  never  of  from  and  to  pronounced the  most  the  specimen  appeared  crack obvious  regions,  The  commonly  found  be  to  described  of  straighter  is  are  leading  for  on  Gener-  for  longer  shorter  discussed  macroscopic  a  crack  specimen.  curvature front  13  as  propagate  extent to  distinguish  Figure  tested.  in  precrack,  overload in  open  to  fatigue  cracks  specimens,  front  shape  was  split  easy  observed  specimens  crack  the  had  brittle  corrosion  ally,  crack  and  Features  varied  Appendix  specimens  the  stress  The  DCB  between  curvature  in  was  Results  boundaries  front  cracks.  mol/kg  quite  "W".  and  3.35  usually  most  surface  cracks  the  with  was  Figure  typical  in  the  it  corrosion in  cracking  General  nitrogen,  visually  Secondary  intergranular,  Mechanics  After liquid  see  respectively.  almost  )  further  features  of  54  fatigue SCC overload  Figure 13  Macroscopic view of stress corrosion crack surface of DCB specimen tested in 12.5 mol/kg NaOH at 92° C, E „ ^ and K = 23.8 - 25.4 MPav'm. corr I rtv  T  the  crack  surface  lel  to  the  direction  across  the  entire  faces,  as  pH o f  specimens,  all  solutions,  three  of  in  the  after  solution  lary  was  as  usually  crack  as  a  stress  frozen  the  The  between  at of  room  running They  paral-  occurred  corrosion  crack  the  tip  of  the  ion  leakage  0.002  crack test,  sur-  the  14  bulk  pH  of  concentration  in  from  M .and  of  was  temperature  chloride  result  ridges  13.  termination was  of  propagation.  and  liquid  the  series  Figure  solutions.  test  the  fatigue  observed  The  three  were  0.2  the  in  Luggin  M at  the  all  the  capil-  end  of  test.  Too relation In  3.35  few  between mol/kg  3  velocities tested  at  the  faster.  An  NaOH  same  being  NaOH  at  The  -  by  crack  growth  that,  under  a  -  specimen  V  s c e  are  crack  measuring  V  >  occurred  a  two  batches  ,  the  ratio  see  machined  with  from  was ratio  the  in  velocity, the  obtain  the  The  shown  load  to  intensity  fastest.  1.00  constant  of  1.00  stress  the  which  conducted  results at  results  average  determined  were  the  between  A specimen mol/kg  tests  bar  Table  v,  during  conditions,  steel.  of  crack  each  bar  and  with  the  was  3 in  12.5  B specimen  bar  being  T  specimen  stress  test. K  of.  1.2,  each  of  the  cor-  IV.  for  increment  good  was  corrosion  This  increased  meant during  a  Table  IV  Comparison at  9.2° C ,  of -  Crack  1.00  V „  Solution  12.5  3.35.  mol/kg  mol/kg  NaOH  NaOH  Velocity and  K  T  Between = 30  -  Different 37  Velocity  Batch  A  x  IO"  7.1  x  10"  9  Steel  (m/s) Batch  8  of  MPa/m.  Crack  2.5  Batches  6.9 x  5.7  x  B  IO"  8  10"  9  cn cn  57 the  test  each  and  consequently,  12.5  mol/kg  of  Kj  is  plotted  for  NaOH  The  Effect  . The crack  growth,  average  in  maximum  tests  was  -  length  velocity Table  crack  6.1  minimum  17.9  the  crack  tabulated  the  range  specimen.  3.3.2  The  a  x  V.  of  the  A  of  test  and  mol/kg  Log  v  plotted  is  measured  at  a  K-  stress  of  was  Intensity  stress  12.5  measured  MPa/m.  Stress  for  m/s  9  velocity  18.1  increment  velocity  10"  of  the  corrosion resultant  NaOH  at  E  vs.  Kj  in  a c  o  r  Figure  during  this  series  38.3  44.8  MPa/m  0,25  -  x  10  -9  m/s  independent,  region  was  between  e  r  r  at II  14.  of and  a  K-  of  crack  -9 velocity 28  of  MPa/m and 40  observed for  SCC  crack a  ~ 2.5  below was  region  III  10  25  found above  crack  -  1.00  V  on see  A different Arrhenius  A region  MPa/m,  above 40  the batch  rate  a 18  I  crack  velocity  threshold MPa/m.  MPa/m may  The  a  Kj  can  stress  indicate  The  Effect  The  dependence  temperature ,  but  observed  be  intensity  increase the  of  in  onset  of  velocity.  velocity  m/s  MPa/m.  not  velocity  x  was  results of  law. o f  of  steel the  of  Temperature of  the  investigated which was  are  used  following  at  at  region E  o  form  was  r  r  in  Potential II  a c  tabulated each  and  n  d  crack a  t  Table  potential. assumed:  VI. An  58  Table  V  Effect in  12.5  of  Stress  mol/kg  Intensity  NaOH  Crack Growth (mm)  at  £  n  n  on r  r  Crack and  Test Length (hrs)  92°  Velocity C.  Crack Velocity (m/s) x 10 J  MPa ^m 17.9  -  18.1  0.4  476  0.3  23.0  -  23.9  1.7  479  1.0  23.8  -  25.4  2.7  479  1 .6  2.5.6  -  27.6  3.1  409  2.2  30.1  -  32.7  3.1  413  2.1  31.0  -  33.7  3.9  386  2.8  35.0  -  37.8  3.4  385  2.5  38.3  -  44.8  7.0  313  6il  59  -7  10  i—:—rr  i  r  CO  E  != o o  -8  10  10 -9  _j  UJ  <  -10;  10  12.5 m o ! / k g  or o  92° C,  10  20  STRESS  14  E, 'CORR  -II  10  Figure  NaOH  Effect of stress  30  INTENSITY  40 (K,),  i n t e n s i t y on c r a c k v e l o c i t y  mol/kg3 NaOH a t 92° C and E c o r r .  ' M P a - v /m n  i n 12.5  50  60 v  where Q  is  the  v  is  the  the  experiments It E  is  average  activation  absolute  than  A;  are  at  -  least  levels  crack  in  was  15  more  -  of  1.00  V  of  23  to  steel,  was  about  there  velocity J  at  -  3.3.3  1.00  3.35  tests  in  Table  VII  All held  tests  the  3.35  and were  constant  a  an  it  -  both  log  and  T  series  is  of  v  vs.  1/T.  to  the  data  at  It  E  yielded at  E  at  region  difficult  potentials the  and  magnitude  that  the  at  the  II  to  two  an r  assumed  within  of  The  results  1.00  was  between  Effect  of  data  kj/mol  was  The  NaOH log  performed at  constant,  c o m p a r e the the  same  batches  faster  of  crack  „ . corr  NaOH  mol/kg  plot  order  than  mol/kg  9  .  see  differences  V _ see  the  +  crack v e l o c i t i e s o b t a i n e d at d i f f e r e n t , due  of  as  a  constant  scatter  remained  Although  temperature?  is  q  gas  results  analysis  velocities  employed.  the  Figure  energy  at  R is  V  see  squares  1 kJ/mol  K-  V  velocity,  The  there  1.00  and  measured  energy,  that  activation  + —  crack  plotted  apparent 24  R T  temperature.  apparent  _ corr  e"Q/  o  v  at V  c /  of  Stress  of  solution vs.  Kj  9 2 ° C and  , , Q  the  the  Intensity  fracture  are  is  tabulated  shown  the  mechanics  in  Figure  potential  potential  at  in  which  was the  16.  Table  Batch  VI  Effect  B  Temperature  P o t e n t i al  T  < sce>  (°C)  V  A  of  ^corr-  -  1 .00  and  Potential  I (MPa/m) K  on  Grack Growth (mm)  Crack  Test Length (hrs)  Velocity  in  Crack Velocity ( m / s ) x 10  12.5 mol/kg  1/  T  x  NaOH.  10  Q  (°K  _ 1  55  34.5  -  37.7  4.8  499  2.2  3.05  70  34.0  -  35.0  3.4  477  2.0  2.92  92  35.0  -  37.8  3.4  385  2.5  2.74  105  35.4  -  41.9  7.7  260  8.2  2.65  115  35.2  -  41 .1  10.5  479  6.1  2.58  70  31.3  -  34.8  6.5  45  40  2.92  92  31.8  -  37.4  6.8  28  69  2.74  105  31 .3  -  43.1  14.3  46  87  2.65  )  3  62  Figure 15  Arrhenius p l o t of the region I T crack v e l o c i t i e s i n 12.5 mol/kg NaOH at E  c o p r  and - 1.00 V  s c e  ,  K. = 31 - 43 MPa^m.  SSRT The at  showed  mild  maximum a  Kj  of  measured  steel  crack 36  was  -  be  velocity  43  1.9  to  MPa/m  x  10  - 9  most  susceptible  measured  and m/s  the at  was  1.2  slowest  a  Kj  of  to  x  10  crack  15.5  SCC. - 8  m/s  velocity  -  — MPa/m.  16.1  - 9 A region  II  crack  observed  between  determined crack  in  velocity a  Kj  this  velocity  of  s  c  g  ,  the  potential  simulated  white  found,  contrast  was  not  tion. -  in  The  compared at  -  37.7 batch  1.00  to V  MPa/m. of  s  to  at  stress  0.88-V  of  the  region  e  and  All  =  35  10  33.6  observed  of  V  II  was  in  e  crack 35.3  specimens  Kj  KJCJQQ  w  although  below  also  ~  a  s  n  t  o  region  20  tested  crack rate  the  I  MPa/m.  test,  velocity  92°  1.9  x  t  7.2  of  between  machined  -  SCC  30.3  from  the  0.88 in  the  was  where  strength at  MPa/m was  levels  to  at  velocity  same  velocity  were  be  Potential  strain  crack  similar  can  susceptibility  slow  -  m/s  MPa/m.  A measurable  corrosion  Kj  c  be  maximum  0.88  and  x  experiments,  Effect  the  -  7.2  specimen  liquor.  observed  of  The  ~  .rarid~  can  A V  20  series  behavior  of  SCC  solu-  C, IO  m/s,  - 9  x  10  MPa/m  m/s and  same  steel .  3.3.4  2.5  mol/kg  experiments  in  the  NaOH +  0.42  The  Effect  The  results  simulated  mol/kg  of  white  Stress  of  the  liquor  Na S 2  Intensity  fracture are  mechanics  tabulated  in  64  Table  VII  Effect in  K  of  3.35  mol/kg  Crack  I  Stress  Growth  (mm)  MPa/m  Intensity  NaOH  at  Test  92°  on  C and  Length  (hrs)  Crack -  Velocity 1.00  Crack  V  Velocity  (m/s)  x  10.3  -  11 . 2  4.3  381  3.1  15.5  -  16. 1  2.9  423  1.9  20.7  -  24. 3  6.7  428  4.5  25.1  -  28. 0  5.5  221  6.9  29.7  -  33. 3  5.3  258  5.7  35.7  -  43. 0  8.3  196  12  10  9  65  0  £  t o  10  -7  -8  10 -9  o  -J  UJ  > o < rr o  10  -10  3.35 mol/kg 92°  i0"  n  L  C , -1.00 V SCE  1  10 STRESS  Figure 16  NoOH  20  30  INTENSITY  40 (K  ),  50 M P o ^  E f f e c t of s t r e s s i n t e n s i t y on crack v e l o c i t y . i n 3.35 mol/kg NaOH at 92° C and - 1 . 0 0  V  ..  Table  VIII.  fewer  specimens  other  solutions,  crack  velocity  in  Log v i s were  solution  potentials. observed to  is  that  crack  delineate in Figure  intensities  was l o w e r  in the corresponding  velocity  behavior  b u t n o t enough  data  between  A region  in the  corrosion  active-passive  t h e boundary 17.  17. Although  than  the stress  than  at the respective I  solution  stress  liquor  below ~21 MPa/m,  II  v s . Kj i n F i g u r e  in this  clear  white  Region  clearly  region  tested  at comparable  the simulated  NaOH  it  plotted  II  transition c a n be was o b t a i n e d  region  crack  I and  velocity  of  - 9 4  x 10  m/s was o b s e r v e d ,  comparable -  0.88 V  2.2  s  c  velocity g  x 10 "  measured 31.4  -  1  The s l o w e s t  crack  over  VIII;  always  from  test  v e l o c i t y was  m/s a t a K j o f  is  concentration included  0.31 M t o 0*46 M.  decreased  over  NaOH a t  and t h e f a s t e s t  sulphide  o f each  than t h e  in  The s u l p h i d e  the length  of a  test.  Fractography 3.4.1  General Unless  stress the  1 5 . 6 MPa/m, -9  The average  varied  faster  crack  was 5 . 0 x 10  the length  it  concentration 3.4  velocity  is  i n 3.35 mol/kg  measured  m/s a t 1 5 . 5 -  0  3 2 . 5 MPa/m.  measured Table  .  observed  which  corrosion  leading  minimize  edge  otherwise  crack  surfaces  of the crack  the influence  noted, were  a l l fractographs taken  as c l o s e  a s was p o s s i b l e ,  of general  corrosion  of  to  in order  on t h e  to  Table  VIII  Effect  of  +  mol/kg  0.42  Crack MPa/m  Stress  Na S  Growth  (mm)  Intensity 9  at  on  Crack  9 2 ° C and  Test  Length  (hrs)  -  Velocity  0.88  Crack (m/s)  in  2.5  mol/kg  NaOH  V  Velocity x  10  9  T s " ] a v.g 2  (ti)  15.5  -  15.6  0.2  235  0.2  0.46  21.2  -  22.2  2.0  236  2.3  0.31  25.9  -  26.7  1 .1  214  1 .4  0.40  31.4  -  32.5  3.0  165  5.0  0.37  36.0  -  38.9  3.5  212  4.6  0.44  68  10  -7  8  10'  >CJ  I0~  9  O _l LU >  <  10  -10  NaOH +  Na S 2  cr  92°  CJ  10  V  SCE  -II  10 STRESS  F i g u r e 17  C , -0.88  20  30  INTENSITY  40 (K,),  E f f e c t o f s t r e s s i n t e n s i t y on c r a c k v e l o c i t y  50 MPaVm  i n 2.5 mol/kg  NaOH + 0.42 mol/kg Na„S a t 92° C and - 0.88 V 2 see  69 appearance  of  of  each  at  randomly  change the  specimen  in  crack  the  from  scattered  points  across  the  crack  observed  for  any  All  crack  crack of  surfaces corrosion  test  ness  and  appearance,  specimen rosion  solutions.  potential  product and  the  crack. on  tested  product  E  obscured  at  the  much  the  No  specimen  top  taken  front.  oriented  n  d  coverage  of  and  length  18  was  corrosion  outside  than  observed  of in  when  layer on of  on  to  across  with the  edge  the  bottom  of  the  stress  the  in  on  on  12.5  the  in  thick-  the  surface  leading  of  The  mol/kg  edge  crack layer  NaOH  surface,  solution,  surfaces  generally  of  corrosion  it  fractography.  exposed  cor-  machined  corrosion  crack  each  the  was  cracks.  the  conditions.  a  composition,  the  the  the  obscure  crack  on  coverage  thick  product  at  of  the  transition  varying  Usually,  surface  by  removed  solution  test.  various  covered  were  of  thinnest  features  not  was  especially  sho»ws  were  they  the  the  and  quite  the  did  specimens that  This  under  active-passive  thinner  specimens  product  crack,  leading  corrosion a  all  precrack,  Figure  the  of  thickest  corrosion  specimens  corr  from  depending  and  was  fatigue  stress  product of  are  fractographs  page.  the  of  fractographs  propagation  from  the  was  several  fractographs  chosen  of  layer  crack  Representative  were  front.  The black  topography.  fractography  direction of  the  much  at while was  The of  of  the  thinner  70  a)  12.5 mol/kg NaOH,  b)  Kj = 31.0 - 33.7 MPa>mT  c)  3.35 mol/kg NaOH, -1.00 V Kj = 20.7 - 24.3 MPav£  12.5 mol/kg NaOH, -1.00 V Kj • 31.3 - 43.1 MPav'm  see  d)  2.5 mol/kg NaOH + 0.42 mol/kg Na S,-0.88 2  V  s c e  ,  Kj = 25.9 - 26.7 MPa>4n Figure 18  see  Comparison of the c o r r o s i o n product on the s t r e s s crack surface in d i f f e r e n t environments.  corrosion  a)  b)  Figure 19  before cleaning with i n h i b i t e d a c i d  a f t e r cleaning with i n h i b i t e d a c i d  B r i t t l e overload f a i l u r e near the crack t i p .  72 A detailed was  conducted  This  after  :• s o l u t i o n  ing  brittle  the  solution,  graphs 3.35  of  produced  shown  the  two  20.  The  with  features  running  B.  the  These  Occasionally, static  primarily leading was  as  in  -  the  the  parallel  to  V  by  steel s  from  at in  representative  crack  surface  at  E  by  examin-  exposure  to  NaOH  12.5  mol/kg  92° C are batches  long of  shown of  and  in  steel  ribbon-like  crack  less  is flat  propagation  frequently under  in  In  all of  following  in  batch  potentio-  intergranular  termination  the  solution.  in  versa.  the  acid  after  specimens  vice  specimen  fracto-  primarily  or  crack  of  each  confirmed  and  both the  as  of  Representative  and  e  of  path  to  cases, the  the  test  sections.  NaOH  The  Effect  The  crack  general  direction  shows  c  of  obliterated.  the  19.  occurred  mol/kg  etched  were  before  of  described  12.5  features  inhibited  direction  crack  badly  the  Figure  1.00  changed  and  3.4.2  were  in  features  of  shown  in  surfaces  transgranular,  edge  surface  artifacts,  exception  the  control  the  fractography  similar,  batch  no  batches  NaOH a t  of  cleaning  fracture  mol/kg  Figure  examination  of  surfaces  dissolution Large  of  Intensity  of  all  and  secondary  crack  fractographs and  Stress  most  selected  the  stress  stress  fine  cracks  propagation. of  specimens  ran  Figure  21  corrosion  intensities.  A.  a) Batch A, 12.5 mol/kg NaOH, K  T  = 31.0 - 33.8 MPav'm  c) Batch A, 3.35 mol/kg NaOH, K  r  = 30.3 - 32.7 MPa/m  Figure 20  b) Batch B, 12.5 mol/kg NaOH, K  T  = 31.8 - 37.4 MPa^m  d) Batch B, 3.35 mol/kg NaOH K- = 29.7 - 33.3  MPa^  Comparison of fractography between specimens machined from d i f f e r e n t batches of s t e e l at - 1.00 V  „ and 92° C.  a)  Kj = 17.9 - 18.1 MPa/m  b)  Kj = 23.8 - 25.4 MPa/m  1  c)  Kj = 30.1 - 32.7 MPa/m  F i g u r e 21  d)  Kj = 35.0 - 3 7 . 8 MPa/m  V a r i a t i o n o f fractography with s t r e s s mol/kg NaOH a t 9 2 ° C and E  corr  intensity  i n 12.5  75 The  fractography  the  specimen  covered  by  and  not  was  other ran  in  dimples  specimens  .at  18  characteristic  penetrated  by  as  Occasional  were  sometimes  associated  The  path  crack  transgranular.  fracture failure  and,  was at  The in  the  in  cases,  The  the  and  different  the  crack  and: p i t t e d . secondary crack much  The  cracks  less  was  graphy  crack at  of  the  tongue  into  was  of  the  features  cracking  observed  brittle  to  corrosion  stress  found  of  corrosion  overload  a  of  Temperature  large  specimens  as  shown  to  be  observed  in  tested  Figure  severely  The  specimen  corrosion The was  on  surface  and  the  at  FAt  apc o r r  55°  C,  deep  direction  70° C  of  showed than  sharply  transgranular. discussed  in  22.  surface  were  Potential  :corroded  the at  crack  features  been  in  tested  the  primarily  already  run  and  variation  to  9 2 ° C has  the  specimens.  stress  were  path  as  secondary  transgranular,  general  coalescence  all  c r a c k p a t h was  specimens.  the  a  was  surface  temperatures,  propagation.  other and  crack  surface  the  specimens  Effect  There of  with  all  partly  cracks  in  for  front.  pearance  propagation  intruding  crack  microvoid  was  f1 a t * r i b b o n - 1 i k e  progression  many  noticed  crack  except  surface  secondary  long,  of  similar,  Its of  many  direction  uneven  was  MPa/m.  the  observed.  was  all  tested  specimens.  These  be  of  defined  The  (Figure  the  fracto-  21).  76  F i g u r e 22  V a r i a t i o n o f f r a c t o g r a p h y with t e m p e r a t u r e i n 12.5 mol/kg NaOH a t  E  r  corr  .  77  78 At  1 0 5 ° C,  The  the  crack  path  directional secondary surface  was  short, face  at  -  V  and  the  23  was  of  the  specimens. and  thegrain  generally  corroded.  topography  strongly Long  specimen.  The  markedly  dif-  1 1 5 ° C was  intergranular,  illustrates  70° C, g  .  The  fractography  secondary  cracks  boundaries.  smooth  the  and  The  the  fractography  92° C and. 105° C in  The  crack  ribbon-like crack  tensive  crack  free  path  path  of  was  observed  quite  features  propagation. or  deep  in  corrosion  3.4.3  3.35  solutions  rough  could  all  be  at  E  12.5  were sur-  sharp  c  o  r  edges  The  broken.  seen  running  as  in  NaOH  to  at  was  the  trans-  topography Occasional  cracking  specimens  specimens  specimens  contrast -  r  of  mol/kg  three in  and  Secondary  these  of flat,  in  the  direction  was  not  as  those  ex-  tested  at  potential.  mol/kg  NaOH  other  at  badly  propagation.  length  tested  followed  grains  specimens  the  of  the  the  crack  intergranular-transgranular,  granular  of  specimen  of  and  was  off.  tested  the  down  entirely  Figure  1.00  ran  that  the  rounded  mixed  direction  shallow  of  specimen  the  the  almost  the  transgranular  cracks  from  of  was  in  of  ferent  surface  NaOH  The  Effect  of  Stress  Intensity  All  specimens  tested  in  exhibited  both  transgranular  3.35  and  mol/kg  intergranular  79  A)  K J = 1 5 . 5 - 16.1 MPa/m  b)  Kj = 20.7 - 24.3 MPa/m  C)  Kj = 29.7 - 33.3 MPa/m  d)  Kj -  F i g u r e 24  V a r i a t i o n o f fractography with s t r e s s NaOH a t  92° C and - 1.00 V  see  35.7 - 4 3 . 0 MPa/m  i n t e n s i t y i n 3.35  mol/kg  features. did  not  of  No  appear  exposed  graphy  pitting  edges  with  be  pagation.  These  associated  with  ridges.  of  and  at  pitted  graphy. N^  and  was  a  The split  specimen opened  the  of  sides  corrosion. and -  the  1.00  Few  see  .  .3.4.4  at N,,.  did  in  crack  was  E  C  Q  r  This  not  mol/kg  the  was  crack for  r  g  c  be  cracks appear  were  0.42  be  crack  pro-  were  the  specimen  )  was  badly  e  the  frozen  be not  etched  fracto-  in  and  liquid the  Consequently, before  cause  of  the  observed, as  rough  be  face the  being observed  however, as  those  determined,  mol/kg  Na S 2  The  Effect  of  Stress  Intensity  The  effect  of  stress  intensity  white  liquor  is  simulated  often  ridges.  sectioned  the  could  NaOH +  of  Long,  of  hours  to  can  obscured  path.  ~ 24  may  path ^  V  which  it  24.  Potential  immediately  Instead, the  of  (-0.88  not  Figure  macroscopic  off  fracto-  cracking  surface  corrosion  crack  fractography  The  secondary  The  2.5  Effect  reveal  features V  The  rounding of  direction  the  potential  specimen  liquid  of  corrosion  cracking  transgranular  resided  in  in  lines  general  to  shown  the  a  variation  to  apart.  polished  is  for  parallel  passive by  general  except  transgranular  tested  and  The  intensity  lengths  running  observed  extensive,  and  stress  ribbon-like observed  to  was  shown  on in  at  81  c)  K, = 31.4 -  F i g u r e 25  32.5 M P a » €  d)  K  V a r i a t i o n of fractography with stress  T  - 36.0 - 38.9 MPav^n  i n t e n s i t y i n 2.5  NaOH + 0.42 mol/kg Na,,S a t 92° C and - 0.88 V  mol/kg  82 Figure  25.  broken,  and  surfaces. running path i ng.  was  The  topography  deep  secondary  Again,  long  longitudinally a mixture  of  of  all  cracks  specimens were  transgranular along  the  observed  ribbons  fracture  intergranular  and  was  rough on  were  surface.  and  all observed The  transgranular  crack  crack-  Chapter  4  DISCUSSION  4.1  General 4.1.1  SSRT In  method  of  caustic  cracking  fracture  and  severe  A  a  transition was -  also  0.88  strain  SCC  V  in  mild  each  in  see  rate  by  the  the  of  less  than  1.00  the  by  this  -  relating  it  c  e  with  -  to  SCC  though  This  SSRT.  83  a  3.35  steel  the  a  of  NaOH was  not  the  most  SSRT  observed in  produced  of  the  active-passive  a  is  strain  at  slow  mechanics a  measur-  growth,  discrepancy  effect  to  demon-  mol/kg  fracture  crack  to  sulphide  solutions  was  valuable  (compared  solution  conditions  the  mild  limitation  corrosion  be  alkaline  Na^S  NaOH  3  stress $  work.  mol/kg  same  V  A  to  uneqivocally  both  mol/kg  even  of  and  to  in  associated  3.35  increment at  served steel  experiment, under  proved  experiments  solution.  able  best  short  NaOH + 0 . 4 2  revealed  experiment  of  potential  SSRT  alkaline  tests)  of  the  susceptibility  plain  series  mol/kg at  the  in  mechanics  that  2.5  work,  assessing  solutions.  strate  this  albeit  jexplained rate  in  Parkins the  range  strain This two  of  rate  is  test  because  rate  corrosion ductile  too  crack  time  in  before  to  initiate  used,  the  initiate  and  ductile  overload  occurs.  fast  compared  to  rate  a  specimen  is  and  ductile  the  the  the  strain  employed  is  decreased.  slow  governed  the  stress  fail  by  cracks a  by  If  of  have  slower  cracks  have  specimen  rate  by  a  will  If  corrosion into  in  rate  corrosion  propagate.  propagate The  to  that  tearing.  specimen  stress or  occurs  strain  stress  that  SCC  relation  the  demonstrated  the  of  SCC  to  was  as  failure  high  have which  propagation,  overload  is  '  over  processes;  is  rate  '  increases the  opportunity  strain  others  conditions  competing  strain  an  and  used  before  in  Humphries  this  and  work  Parkins  8 in  NaOH  solutions.  as  at  0.88  -  V  s  c  Under in  e  3.35  borderline mol/kg  conditions  NaOH,  the  s t r a i n r a t e m i g h t have r e s u l t e d i n the at - 0.88 V in the slow s t r a i n r a t e see discrepancy  A the  further  SSRT  of  whether  "propagation  the  implication  provides  initiation blish  between  SCC or  occur  two  of  an  excellent  in  an  SCC,  a  slower  of  o c c u r r e n c e o f SCC t e s t and e l i m i n a t e d  n  the  use  for  techniques.  this  result  measure  environment,  not  the  conditions  in  the  presence  of  it  is  that  while  the  ease  of  does  not  esta-  required  for  crack  of  an  existing  crack. 78  This who  is  important  showed  corrosion  in  light  of  the  that  the  environment  crack  can  be  very  at  work the  different  by tip from  Brown of the  a  et  al. ,  stress bulk  environment. required SCC.  Thus,  to  understand  A technique  kinetics  of  an  4.1.2  better  SSRT.  19  the  '  of  '  steel  the  which  in  to  of  made  region  the  data  though  in  that  an  also  provide  the  environment the  data on  propagation  required.  Technique of  of  quantitative  experiments data  times  in  and  the of  composition  an  excellent  be  data  is  obtained  this  work  much  from  the  to  aluminum  and with  DCB  given the  SCC  principal  of  limitation  obtain  the  amount  of  data  boundaries  of  region  the  behavior,  batches a  of  heat the  to  of  of  steel.  steel of  between the  I  Al-  the  in  this  about  two  different  same  nominal 21  treatment. present  tests,  correlate  .accurately  scatter  velocity  of  and  batches  determine  same  results  the  the  specimens  the  on  assessing  of  observed  crack  The  of  length  different  measured  variables  different  Speidel  method  mechanics  the  velocity  to  fracture  was  define  from  the  the  solutions.  impossible  between  Hyatt  reason,  difficult  crack  was  consistent  is  this  adequately II  work,  batches  crack  mechanics  alkaline  obtained  it  scatter  it  to  and  of  investigate  environmental  technique  required  can  than  For  proved  influence  mild  effects  Mechanics  fracture  cannot  2122  '  technique  alone  interpretation  established  17  the  which  Fracture  from  SSRT  existing  The obtained  the  work.  This  is  The  results  conducted light the a  of  low  the  halted the  the  SCC  plastic  crack,  r , y  may  w  that  intensity. at  estimated  from  viewed  in  applied  the  to  growth  of  or  completely  at  of  a  the is  16  the  be  inhibited,  intensity  developed  be  be  experiments  intensity  out  formed  stress  stress  zone  might  zone  should  stress  pointed  crack  fatigue  mechanics  intensities  has  plastic  test  fracture  fatigue  Brown  the  maximum the  stress  corrosion  by  the  maximum  specimen.  stress  to  at  of  tip too  The  tip  large  maximum  of  the  equation  crack  6.  if  compared size  of  fatigue 3  6  This  formula  strain  applies  plastic  Substituting strength  tip  due  to  As average  for  zone  the  the  plane  stress  plastic  approximately value  and  a  of Kj  maximum two  sizes  crack  values  determine  the  fatigue  all  are  steel,  during  mum p l a s t i c  a  average  the  respectively, developed  zones  an  of  to  of  643 MPa of  12  0.06  for  the and  stress  cycles  mm o r  third  MPa/m  fatigue  fatigue  one  zone.  large.  yield 24  MPa/m,  intensities  used*  0.22mm  as  Plane  gives at  the  maxicrack  precracking.  velocities  over effect  a  period that  measured of  this  time, size  of  in it  this is  work  were  difficult  plastic  zone  to  would  87 have  had  cally, crack  were  in  stress  the  12.5  the  should  liquor  error  from  the  be  of  a  size  crack  or  the  of  15.5  MPa/m  test  subject  in-  intensity,  tested the  zone  stress  stress  in  corrosion  plastic  significant.  specimens  Realisti-  stress  the  the  fatigue  considered  few  quantitative  temperature  solutions.  activation  at  of  the  been of  velocity.  On  this  at  18  basis,  MPa/m  simulated  to  significant  Kinetics  effect  alkaline  and  length  maximum  have  crack  source.  Only of  the  NaOH  this  4.1.3  fatigue  not  could  the  than  velocities  mol/kg  white  either  than  crack  corrosion  greater  of  higher  effect  if  much  ahead  tensity  only  the  however,  formed  the  on  energy  on  the  Bohnenkamp  of  75  kJ/mol  studies SCC  of  measured for  have  mild  an  Armco  been  steel  made in  apparent  iron  in  33%  Mazille  and  37 NaOH  at  Uhlig and  a  kJ/mol,  0.24%  Cr-Mo was  88  active  reported  73  Newman  the  passive  apparent  steel  that in  kJ/mol. These  activation  activation  respectively,  C martensitic found  transition.  the  steel  for  under  apparent  8 M NaOH a t  the  energies  a  0.09%  of  44  C mild  similar  activation  kJ/mol  steel  and 38  conditions. energy  active-passive  of  a  3%  transition  v<  6 1  results energies  are of  somewhat 23-24  higher  kJ/mol  than  the  determined  in  region this  II work.  B a s e d on s i m i l a r  results  obtained  f o r t i t a n i u m by  Beck  21 and.aluminum  by H y a t t and S p e i d e l ,  the a c t i v a t i o n energy region  I crack  and M a z i l l e This  1.00  found  V  in t h i s  velocities  likely  for  specimens  The r e s u l t s  region  spent  II  in region  I  SCC.  crack  NaOH a t failure  followed region  of such  This  II  calculations by  indicates  f r a c t i o n of the time to f a i l u r e of  was  of  Bohnenkamp  to f a i l u r e r e p o r t e d  and M a z i l l e and U h l i g .  The a c t i v a t i o n e n e r g y activation  by  the time to  assuming the c r a c k s  a r e much l o w e r t h a n t h e t i m e s  substantial  mol/kg  i t to e s t i m a t e  throughout.  Bohnenkamp  found  the region  12.5  that  representative  represent  by t a k i n g  work  ••, and u s i n g  of t h e i r specimens,  The v a l u e s  also  can be s u b s t a n t i a t e d  velocity -  he d e t e r m i n e d was  velocities.  and U h l i g  Newman d e c i d e d  that a  their  I.  for  controlled reactions  charge  transfer,  can v a r y  or  from 21-105  67 kJ/mol, usually found  w h i l e t h a t f o r aqueous d i f f u s i o n 17-18  region  kJ/mol. II  this  controlled  Both  Beck  a c t i v a t i o n energies  t i t a n i u m and aluminum that  6 3  v a l u e was  alloys  6 2  of  ions  and H y a t t and of  ~ 21  respectively.  kJ/mol They  i n d i c a t i v e o f aqueous mass  is Speidel for  concluded  transport  processes.  T h e r e was more s c a t t e r  i n the data o b t a i n e d  in  12.5  mol/kg  NaOH  at  E  probable  explanation  the  of  lack  rosion of  current  steel  assumed one  control  were that  batch  the  had  the  literature  Scully of  has  mild  included  film  free  at  scatter  c o r r  two  '  V  is  potential, E-  the  -1.00  see  and  been  it  thus  Although  have  The  that  potentials,  would  .  most  reflects  the  cor-  different it  has  batches  been  similar  if  only  employed.  is to  in  very  which  that  fractography  with  the  the  lack  showing  the  is  due  to  surface.^  of  this  Perdius  the  et  work.  of  SCC  thick  Bohnenkamp ^  4  3  cracking  transgranular and  published  fractography  intergranular  and  potential  results  of  solutions  obscures  transition  corrosion  little  compare  alkaline  micrographs  active-passive the  at  suggested  steel  corrosion  the  at  Fractography There  in  of  this  results  been  4.1.4  for  density used  than  corr  at  cracking al.  the  at  published  52 a  few  fractographs  Berry  observed  work,  with  individual ment  with  of  in  predominantly  instances grains. the  SCC  of  granular  These  fractography  NaOH.  transition  cracking  was  NaOH.  Reinoehl  intergranular  cracks  transgranular results  in  cracking  are  observed  intergranular-transgranular active-passive  35%  in  cracking each  observed  at  general  this  work.  observed  solution  and  E  12.5  ">  n  c  o  r  r  in  their  across  in  was  and  agreeMixed at  the  transmol/kg  In active  general ,  or  intergranular  pre-existing  strain-generated  paths.  of  of  the  mechanism  usually  considered  boundaries  are  due  to  either  elements film  is  the  to more  centre  kamp  the  has  to  a  a  result  of  52  The  of  In  the  surface  granular  if  face,  the  or  boundaries emergent  alkaline  emergence  or  the  the  slipstep/  is  to thin  the  of  occur.  occur  sii  psteps.  grain of rich  location  '  passive is  where  kinetics  transgranularly  height  slow,  along  the  film  the  passive  the  may  such  If  to  than  in  Bohnendissolve  considered  They  sufficient  compared  passive  will  or  grains  to  occur  dislocations  66  expose the  grain  dissolved  the  areas 37  slipsteps  the  or  former,  of  '  of  the  usually  49  are  The  boundary  are  repassivation,  can  repassivation  can  grain.  only  because  solutions.  paths  thickness  rate  are  dissolution surface  the  of  a  carbon  35 on  or  at  paths  surrounding  precipitates  support  that  the  to  regardless  boundaries.  to  to  cracking  pre-existing  respect  disrupted  related  applies  grain  boundaries,  grain.  the  This  along  is  transgranular  '  with  grain  in  49 '  Strain-generated as  45  be  demonstrated  preferentially  and  segregation  easily  of  paths  cracking.  active the  cracking  of  then  the  sur-  that  the  grain  action  on the  crack  planes  inter-  on  bare  film  be  of  of  metal the  an for  grain  slipsteps, propagation the  emerging  91 The depends the  fractography  upon  long  other  flat,  consistent  or  strain-generated fatigue batch  inclusion  lustrated  of  in  numerous  the  in  trenches  precrack  features  with  the  their  of  removal  solution. in and  Figure  26  run  often  observed  those  visible  ligaments  their  at to in  between  the  almost on  that  these  different form  the  Figure groups  formation  directionality.  of  13. of  The  in  to  occupied  sides  large  bridging  stringers  these  can  macroscopic  ribbon-  observed been  due  on to  solutions,  the  stringers  same  level  trenches  SCC  also  or  acid  ridges, by  fatigue  the  the  Adjacent  and  surfaces,  by  at  i l -  longer  inhibited  levels.  The  is  the  not  have  sometimes  of  crack  of  alkaline the  many  appearance  on  that  may  the  trenches  side-by-side,  A.  were  This  cleaning  the  of  corrosion  stringers  by  of  from  This  stringers  stress  uncor-  machined  both  20-25  pre-existing  of  are  of  Figures  either  direction  identical  inclusions  in  presence  batch  also  presence  direction).  surfaces.  of  the  the  in  the  the  during  Several  sometimes  explain  the  by  observed  stringers  B than  observed  corrosion  dissolution to  is  exception  stress  The  occupied  surfaces  like  the  batch  in  rolling  26.  the  specimens  revealed  the  crack  Examination  of  oriented  Figure  work,  along  paths.  surfaces  in  this  dissolution  B steel  (i.e.  corrosion  features  crack  stringers  propagation  more  with  crack  A and  stress In  ribbonlike  not  both  a  factors.  is  roded  of  were  such of  help  ridges,  the to and  as  a)  b)  F i g u r e 26  Batch A  Batch B  Comparison o f u n c o r r o d e d f a t i g u e of B a t c h A and Batch B s t e e l .  pre-crack  surfaces  93 The in  12.5  transition  mol/kg  cracking One of  at  NaOH t o  -  1.00  explanation a  change  F_corr' formed, crack  on  Thus,  c e  the  can  be  the  transition  metal  broken the  granular,  strain-generated  increased  to  -  explained  1.00  V  of  the  to  and  adherent.  disrupt  the  dissolution film  was  account  more  formation  of  a  two  occurred  as  a  film.  thin  c  o  r  r  or  At poorly  slipsteps  potential  film  ways.  result  at  predominantly  the  passive  the the  broken.  for  the  mixed  at  the  active-passive  observed  of  was  As  emerging  along  easily  E  became  the  trans-  was more  r  The  occurred  at  one  emerging  path.  , the  in  passive  followed  see stable  the  surface  by  crack  cracking  intergranular-transgranular  properties  easily  tip.  transgranular  mixed  that  the  film  and  V^  is  in  the  from  slipsteps  film grain  This  were  across  the  boundaries,  explanation  less  grains  and  where  the  can  intergranular-transgranular transition  in  the  able  also crack  other  path two  solutions.  An path is  from  that  E  alternative  a  to  for  transgranular  to  change  mechanism  -  1.00  corr  in  the  V  .  mixed  the  change  for  One w h i c h  which  A mechanism  the  favours  of  cracking  favoured  strain  such  as  generated  cracking  pre-existing  crack  occurred  hydrogen J  transgranular  in  intergranular-transgranular  see  brittlement, account  explanation  paths  em-  3  paths,  observed could  from  then  at  could E  c  o  r  r  account  -  94 for at The E  the the  active-passive  is  transition  observed  anomalous  other  4.2  and  at  in  all  115° C in  cannot  be  cracking  three 12.5  solutions.  mol/kg  explained  in  r  observed  NaOH  at  relation  to  specimens.  M e c h a n i sms Any  fully  1)  intergranular-transgranular  fractography  corr  the  mixed  proposed  the  In  following  the  crack and  mechanism  stress  be  able  to  : e x p l a i n.. s u c c e s s -  observations:  fracture velocity  must  mechanics showed  experiments,  regions  independence.  of  This  the  stress  measured  dependence  applied  to  all  three  solutions. 2)  As  defined  NaOH  3)  and  by  2.5  the  SSRT,  mol/kg  was  limited  the  active-passive  Although -1.00  V  SCC  see  velocity  to  was  in  was  a  NaOH +  narrow  in  the  0.42  3.35  mol/kg  mol/kg Na S 2  range  of  potentials  transition  in  each  both  E  observed  12.5 an  SCC  at  mol/kg  order  of  NaOH,  the  magnitude  c  Q  solutions about  solution. r  and  r  measured higher  at  crack the  latter. 4)  The of  stress  magnitude  than -  corrosion  in  1.00  the V  see  faster 3.35  crack in  mol/kg  the  velocity 12.5  NaOH  is  mol/kg  solution  about NaOH at  an  order  solution  92° C  and  5)  The  stress  corrosion  NaOH + 0 . 4 2 the  3.35  mol/kg  mol/kg  The  stress  NaOH was  Na,,S  NaOH  active-passive 6)  crack  solution  solution  transition  corrosion  slower  at  velocity  crack  -  0.88  is  at  in  in  than  SCC  the  12.5  mol/kg  dependent,  with  an  of  in  in  3.35  than  at  -  ~ 23 k J / m o l  at  E  NaOH  solution  apparent c  o  r  is  mol/kg  1.00  V„ . see  temperature  activation  and  r  ~ 24  in  solution.  see 7)  mol/kg  respective  velocity V  2.5  slower  the  each  the  energy  kJ/mol  at  -  1.00  V see 8)  There  was  no  solution  pH  apparent from  the  change bulk  in  value  the in  crack any  of  tip the  solutions. 9)  10)  The  fractography  mol/kg  NaOH a t  -  V  1.00  The  c  g  ,  it  c  mol/kg  0.42  r  of  NaOH  mol/kg  Q  was  fractography  3.35 +  s  E  of  the r  specimens  was  transgranul ar,  mixed  in  12.5  while  at  intergranular-transgranular  specimens  solution  Na^S  tested  and  solution  tested the  was  in  2.5  mixed  both  mol/kg  the NaOH  intergranular-  t r a n s g r a n u l a r .at the a c t i v e - p a s s i v e t r a n s i t i o n i n each s o l u t i o n . 4.2.1  The  Role  Stress to  provide  on  which  u •  u  o.u  a  the  bare  of  or  strain  metal  . • cracking  Stress  Intensity  in  surface,  process  can  SCC free  is  and  usually  from  occur.  Passivation postulated  passive  35 , 4 8 , 5 0 ,51 ' ' '  films,  96 Crack  advance  is  often  considered  to  occur  via  a  continuous 48  cycle In  of  film  fracture  both  stress  example, 3%Cr-Mo his  rupture,  mechanics  experiments  dependent  and  Newman steel  results  repetitive In  in  film  this  appropriate  was  assumed  was  that  mild  Within  controlling  sufficient  bare  metal  not  the  bare  of  both  Kj. c u r v e . in  intensity  surface of  a  a  that  in  region  II  region,  was  Thus,  solution  not  of it  stress  dissolution the  crack  conditions  consideration  in  and  the  mechanism.  stress  growth  steel  a  tip.  a  of  involving  for  was  of  kinetics  this  step  repair  and  in For  concluded  investigated  curve.  '  regions.  ;temperature,  environmental  of  -  rate  of  51  tip.  the  formation  v  crack  '  studied  a mechanism  by  determining log  Kj  He  6 1  established  determination  of  the  -  be  SCC  crack  rupture  rate  v  I  the  film  the  log  C.  with  were  repair.  independent region  effects  potential  SCC' c a n  100°  the  film  at  was  amount  at  and  available  rate  If  the  the  at  consistent  that  and  always  8 M NaOH  rupture  and  stress  studied  work,  the  activated  has  were  composition  dissolution  50  exposed  passive the  the  film onset  As  alkaline  at  the  at  film, will and  the  crack  controls  any  one  time  then  the  stability  be  a  critical  extent  of  electrochemical  solutions  tip  is  by  II  potential  increased  disrupting, and  factor  region  from  the  in  in of the  a  active-passive  transition,  the  passive  film  becomes  more  43 44 45 adherent, At  some  unable tip  and  the  point, to  trolled  for  will  towards bility  has  such  that  metal  is  0.88  V  creased film  at  bare  a  crack region  of of  I,  for  shifting  of  at  -1.00  V  stability  of  mild  the 3  t  a s  c  e  same  why  in  greater  from the  than  rate the  results  caustic  v  -  crack  of  the  Kj  curve  the  sta-  will bare  to  propagate.  measured than  the  be  at  those The  in-  surface  active-passive of  solutions  the  con-  film  sufficient  slower  crack  from  temperature.  repassivation  explains  much  NaOH was the  log  velocity  be  alkaline  surface  corrosion  crack  potential  steel  the  '  crack  intensity  Eventually,  before  stress  mol/kg  and  increased also  a  the  the  the  potential  • *  will  at  and  steel • in  intensities.  why  3.35  the  '  intensity  surface  stress  mild  rate  increases.  propagation  increasing  stress  in  potentials  tion.  of  effect  explains  see  with  SCC  amount  approaches  transition that  the  exposed  measured  stress  repassivation  This -  II  transition  higher and  to  repassivation  region  maximum  Thus,  active-passive solutions  the  fall  value.  of  given  maintain  required  velocity  a  rate  46  the does  SSRT not  active-passive  showed occur  transi-  98 4.2.2  Anodic  Dissolution  Anodic has in  long many  been  to  the  film  considered  systems.  sequence  of  In  charge  dissolution  at  25°  dissolution  C is  Fe  higher  film  is  formed  formation  follows:  [FeOH]  a d  presented  by  mechanism  will  the  If occurs,  +  be  OH"  OH" ^  of  FeOOH  in  a  leading  passive  + e"  7b  7c  2  + H 0  2  +  HgO •+  factors  be  Robins the  7d  2  composition  To  over  proposed  reactions of  SCC  of and  100° C ,  following  Fe^^,  or  7e  the  passive  F^O^  consistent at  e"  with 7 1  may data  the  above  discussion.  vice  be  versa,  The  does  not  analysis.  continuous then  and  of  tip  7a  HFe0  kinetic  FeOOH.  d  FeOOH  the  crack  + e"  Fe(0H)  + OH"  used  g d  [FeOH]^  +  2  upon  Biernat  consideration affect  2  =  the  44  [FeOH]  temperatures,  of  the  and  a d  instead  solutions,  of  iron,  at  propagation  chemical  [FeOH]  dependent  of  and  ;Fe(0H)  At  method  alkaline  OH"  Fe(0H)  material  transfer  as  +  the  of  the  dissolution  crack  velocity,  of v,  material may  be  at  the  related  crack to  the  tip  99 anodic  current  density  at  v  the  =  i  a  crack  tip,  i  a  ,  via  equation  w  ....  8  8  Fd _3  where  w is  divalent  the  equivalent  species),  F  is  weight  the  of  iron  Faraday  (27.9  (9.65  x  3  d  is  the  clear,  density  however,  able  to  predict  test  potential,  iron  what  to  (7.86  potential  and  the  equilibrium  the  total  voltage  actually  the  sum  is 70  n  T  n  A  . +  D  n  kg/m i  ).  +  fusion the  n  is  the  activation  overpotential  and  not to  be  between  potential  several  is  of  n . T  the  the  M/M  This  different  The  values  solutions,  of  such  drop is u s u a l l y , D 55 and n .  com-  iR  9  n  is  the  drop  dif-  iR  is  the  potential  value  of  i  will  depend  upon  through  In  highly  conductive  the  re-  D  n as  overpotential,  ,  n  and  the  ones  considered  iR.  employed to  be  in  this  work,  small  in  relation  under  activation  the to  iR n  H  If equation  n +  over-  and  A  n  A.s)  D  solution.  lative  kg,  order  difference  A where  4  It  in  overvoltage,  of  10  10  3  for  The  is  4.  10  v.  E  ponents:  x  substitute  electrode,  r e v  >  of  x  the 10  metal is A  is  dissolving  obeyed: b  control  67  a fA log  ]  ••"  10  35  100 where  i  is  the  reaction,  and  portional  to  at  an  i  anodic  anodic  b a  exchange  current  is the T a f e l a > the r a t i o of  o v e r p o t e n t i al  o v e r p o t e n t i al  n  A  c  slope. the  n-j , a  n  density  D  for  Since  crack  to  that  v  anodic  is  pro-  velocity produced  expressed  e  2  the  in  produced at  terms  an A n-j ,  of  A and  n  as .shown  2  log  This  v  the  values  technique  i  an  ,  \ \  a  assumes  tion  a  equation  / -= l o g / i  0  equation  If  in  are  estimate  - < A ; n  <  i  i  is  the.  A  11  T  the  same  obtained  corr  substituted  ..of  - n  9  r  that  of  11:  into  current  by  at  both  the  equation  densities  potentials.  linear  polariza-  11...  place  in  required  of  for  l  activation The  results  densities  Clearly,  are  in  shown  required  velocities  the  control  to  all in  three Table  support  in  each  solution  more  than  enough  crack  velocities  tions^',!! 12.5 The  crack  and  at  -  for  by  the  mol/kg  velocities 1.00  V  s  above  c  g  in  IX, the  current  and  observed 3.35  analysis.  along  at the at  mol/kg  may  is the  the  region  from  obtained. current II  to  NaOH  in  white 12.5  cannot  transi-  liquor.  mol/kg be  8).  support  active-passive  c o r r  crack  equation  available  simulated E-  be  with  measured  (calculated  measured NaOH  solutions  NaOH  accounted  Table  J  X  -\l a 1 u e s and  i  a  of  i  Required  Predicted  From  i  to  E ( sce) V  12.5 mol/kg NaOH  A  3.35 mol/kg NaOH  2.5 mol/kg NaOH + 0.42 mol/kg  Na "s 2  the  Measured  Crack  Velocities  corr  Batch  Solution  Support  i  V  '  .' (m/s)  a  required (A/irr)  2.4 x 1 0 "  9  8  i  predicted  ?  (A/m ) 2  .65  2.0 + 0.6  680  4300 + 1300  A  -1.00  2.5 x 1 0 "  .B  -1.00  6.8 x 10  A  -1.00  7.1  x 10"  9  190  95  B  -1.Q0  7.2 x 1 0 "  9  200  120  B  , -0.88  4 x 10  8  -9 y  1800  110  4500 i  600  + 42 +20  5700 + 1800  102 Two Table  IX  exist.  measured film  possible  by  difference in  Table  metal  The  the  covered  interpretations first  linear  surface  is  great  IX.  surface  and  exists.  E  as  soon  as  the  specimen  at a  E  is  corr  1.40  V  maintained ,  higher  The  at  the  for  dissolution  more  in  12.5  at  An  polarization  activation  and  i  o  bare for  „„„ corr that  of  a  and  film  film  on  was  a  densities  than  r  the  the  observed  return  stress the  a  specimens  allowed-to  of  of  discrepancies  polarization  was  tip  i  is  the  A tarnish linear  of  metal,  than  the  to  corrosion  metal  predicted  clarity,  crack  are  shown  to  tip  is  surface would  be  was  pure  as  line)  are  the  not  same  be  under  of  drawn  predicted  simulated can  it  and  controlled  axes  and  schematically  (dashed  be  the  instead  curve  the  and  transition  illustrated  control  required  NaOH  activation-diffusion For  of  technique  free  control  This  rev  is  the  control.  E  film  value  presence  the  active-passive  activation-diffusion  line).  If  mol/kg  liquor  mixed  .  between  i  a  the  difference  of  under  the  results  result.  values  anodic  the  of  potential  current  3  reasonable  if  see  of  the  account  at  the  crack  to  for  on  -  that  Evidence  form  from  not  enough  to  corr  that  polarization  corr surface  E  is  of  for  accounted mixed  activation in  Figure  would as  to  both  27.  appear  modified  mechanism  drawn  white  by  (solid  scale  and  E, a n d 1  E . c 0  103  F i g u r e 27  Anodic p o l a r i z a t i o n c u r v e o f bare metal s u r f a c e a c t i v a t i o n c o n t r o l and mixed  under  activation-diffusion  control.  104  In  the  and  present  -  1.00  anodic  V  for  would  density be  much  activation  In  E^  would  from  n  under lower  in  R is  the  diffusion  equation  D  absolute changed fusing the  the  12:  gas  the  at  concentration  (inside  the  diffusion  1 og  OH"  rate  controlling  more  likely  calculated equilibrium the  crack,  determine. current  constant  to by  z  the of  to  is  (see  but  a  Both  density  predicted  c,  b  due  is  OHP  Q  r  r  The  by  equation  that  to  n  is  7a  u  n  1  of  T  is  plane in  (OHP) the  possible  -  for  c^  the  OHP  to  be  7e),  the  latter  is  may  HFeO,,  in  the  crack  is  covering more  related by  the  to  the  be in  sides  difficult  of  to  anodic  equation  is  solution  from  HFeO"  i^,  dif-  either  for  diffusion,  of  bulk  c^  are  ex-  and  of  film  2  the  equivalents  concentration  HFeO"  is  OHP  be  \  D  J/mol.deg),  the  it  for c  may  n°,  b  species  or  passive  and  n  Helmholz  A value  value  cOHP „ c  number  equations  assuming the  Cg^p  Although  occur.  with  the  outer  the  /  (8.314  diffusing  crack).  of  c  NaOH.  overvoltage,  \  reaction,  species  E  7 0  2.303RT  temperature, in  mol/kg  to  activation-diffusion  that  zF  where  12.5  mixed than  correspond  control.  principal,  calculated  and  » respectively,  current  control 12  work,  13: ^ 7  105  P  1  i^.  =  (C  V  OHP -  6  where the  D is  the  diffusion  functions  diffusion layer  of  ••••  13  coefficient  thickness.  temperature,  of  the  ion  6  are  complex  D and  solution  composition, 63  viscosity it  was  not  present the  and  possible  work.  test  that  Thus,  second  the  of  i  E  in  12.5  anodic crack in  could  corr  and  CQ be  film  only  of  solutions  can  at  a  ion  at  the  the  '  and  for  therefore by  n^  in  surface  the  this  results  a  73  '  for  method.  Table  of  effect  velocities to  72  the on  process  the  crack  tip.  explained  by  dissolution  at  other  r  IX  linear  observed  active-passive  be  controlled  and  the  solution  values  slight  due  still  ,  the  crack  material  obtained  the  determined  of  had  the  H P  on  NaOH w e r e  3  activation-diffusion (Figure  of  not  a  that  mol/kg  velocities the  of  of  meaningful  interpretation  dissolution  all  derive  specimens  value  number  values  presence  polarization  corr  to  conditions  The is  transference  and 6 i s  than  The transition  a  mixed  mechanism  27).  Evidence  for  this  interpretation  comes  from  the  work  46 of  Hoar  ments NaOH  to at  and  Jones.  show  that  120° C rose  They the  used  current  less  than  straining density  5 times  on upon  electrode  experi-  0.1%  10 M  C  in  straining  at  106 potentials the  lower  passive  than  film  protective,  it  -  1.1  formed  can  V  at  reduce  c  .  e  This  active i  shows  that  potentials  from  the  is  value  while  poorly  obtained  on  cl bare  metal.  observed crack  An  by  rate  increase  Hoar in  and  3.35  in  Jones  mol/kg  i  of corr i s enough  NaOH  at  the  magnitude 3  to  account  -1.00  V  3  12.5  mol/kg  NaOH a t  E  c  Q  r  The  values  active-passive estimated  by  of  n  transition  n  bare  metal  additional HFeO^ on  is  the  that  mined the  E  E  rev  92°  the  value of  the  at  The  C was  each  the the is  (FeOOH) by  calculated  at  the  from:  7 1  at  can  increased  The the  with  the  and  2)  the  in  by  the  be  five  times  following  value  E  value  from:  of  passive r  e  c  of  b  c^  for  film  for  v  of  concentration  "1-314 - 0.072 l o g  solution  solutions  1.)  equilibrium  dictated  experiments  value.  made:  equilibrium  =  not  J  9 2 ° C was c a l c u l a t e d FeOOH + e " ^ HFeO~  Fe00H/HFe0:  for  measured  crack  is  all  i' „ corr  were  in  reaction  above.  crack  the  assumptions  sides  Fe/HFeO^  over  for  in  3  on  but  D and  assuming  ,  the  .  r  A  see  for  the  deter-  HFeO^  in  7 1  14a  [HFeO"],  active-passive  ....  14b  transition  and  107 HFeO"  + H 0  +  2  2 e " =^  Fe +  15a  30H  15b  see  The  pH  of  each  solution  exchange  current  reaction  from  the  equation  10.  An  92°  C was c^,  n  calculated  D  F_  r e v  »  and  of the  important a mixed  i  68  taken  from  Appendix  , was  then  calculated  value  Tafel  Table for  Q  each  9 and  and  apparent  the  activation  of the  10  of  is  the  energy  of  i  0.072  corr  The for  )  Values are  using  n  and  tabulated.  processes  and  the  assumption  mechanism  justified. activation  This  is  energy  kJ/mol  at  values A  of  also  controlled  each  V/decade  diffusion  24  B.  calculated  overpotential  transition  results  (5  corr  solution.  activation-diffusion  with  i  slope  activation total  of  X shows  equations  the  active-passive  sistent An  anodic  both to  i  assumed  from  Clearly, are  density,  assumed.  of  was  is  at con-  analysis.  high  for  a  63 diffusion range  of  controlled activation  controlled 4.2.3  and  Hydrogen  a mechanism  acidic  energies  reactions.^  While sidered  reaction,  expected  on  the  for  low  end  charge  of  the  transfer  7  Embritt1ement  hydrogen for  solutions,  and  it  the has  embrittlement SCC not  of  many  has  metals  received  much  been in  conneutral  support  as  Table X  Calculated Overpotentials  test  Solution  Based  C  on E s t i m a t e d V a l u e s  (mol/dm )  sce>  on B a r e A  0  n  (A/m )  3  (V  i  ^rev  b  of i  2  Metal. D n.  (V)  (V)  12.5  mol/kg  NaOH  -1 .00  4.4  x  10"  5  -1  .35  3.0  x  10"I  0. 27  0.08  3.35  mol/kg  NaOH  -1 .00  4.4  x  10"  5  -1.28  7.6  X  10"  0. 25  0.03  -0.88  9.4  x  10"  7  -1 .32  2.2  0 . 27  0.17  2.5 0.42  mol/kg mol/kg  2  NaOH + Na S 2  X  10"  3  109 an  explanation  Reinoehl  and  ment  be  may  for  the  Berry  caustic  have  suggested  responsible  transgranular  cracking  for  cracking  the  that  of  mild  hydrogen  occasional  observed  in  steel.  mild  embrittle-  instances  steel  of  exposed  to  uptake  of  26 alkaline  solutions.  hydrogen  in  of not  a  the  3%Cr-Mo feel  Dahl  mechanically  steel  that  exposed  there  was  hydrogen  embrittlement  observed  an  crack  tip  potential assumed  increase  of  a  steel  near  that  the  the via  duction  to  H  +  subsequently material  at  The the so  crack that  tip  the  for  Biernat  and  reversible reduction  of  to  in 33%  7a  -  metal  in  7e, in  to  at  but  the  to  matrix  al.  near  a  also the  9 0 ° C and 52  a  They  crack  allow  fell  the  crack,  and  did  postulate  et  metal  the  re-  which  embrittled  the  tip. the  present  does of  not  work'  hydrogen  in  occur.  have for  given  shown  that  hydrogen by  show  change  to  is  C,  transition.  embrittlement  +  specimens  225°  NaOH  solution  hydrogen  the  the  the  H  of  Perdius  at  potential  an  zones  NaOH a t  possible  Robins  of  the  solution  evolution  hydrogen  exposed  atomic  thermodynamical1y  20%  hydrogen  equations  results  to  mechanism.  in  crack  observed  stressed  active-passive  entered the  al.  s u f f i c i e n t evidence 74  pH o f  sufficiently, of  et  that  from  the  bulk  At  the  of 92°  pH  bulk must  the  of  value, be  solution  C and  1  atm.,  thermodynamical1y  evolution  equation  the  crack  pH  the  16:  7 1  via  the  no E  Table the  H /H +  XI  all  three of  of  every  hydrogen  Ej^+^  NaOH  ment  cannot  be If  to  it the  fractography  mol/kg  NaOH  hydrogen  is  E +' u  The  in  the  s  c  and  / u  in  was  pH  crack  of  Appendix  noble the  tip  ...  16  each  of  e  experiments  eliminating  at  V  determination  shown  transition  at  E  ruled the  C  Q  SCC  would  r  energy  ,  the  of  B.  carried  to  the  those  the The out  at  appropriate  possibility  of  crack  however,  as at  E  _ corr  of  specimens  of  lower  23  kJ/mol  than  embrittlement  of  the  i-  of  due  V  s  c  o  r  on  E  C  Q  c  -  e  r  and to  r  33-38  embrittle-  under  in  those  rate the  in  change  a mixed  at  the E  C  Q  r  in  inter-  apparent in  r  observed  neutral  em-  3  While  kJ/mol  :  hydrogen  crack  determined  steels  SCC  to  »  r  in  hydrogen  rapid  at  1.00  possible  J  of  transgranular -  and  was  the  value  at  is  a mechanism  explain  measured  from  is  r  in  out  granular-transgranular activation  of  9 2 ° C.  evolution  mol/kg  relation  0.072 p H ,  value  at  ., t h u s  12.5  brittlement,  -  6  grounds.  Hydrogen  conditions.  4  specimen  evolution  thermodynamic  8  solutions  active-passive  value  1  the  solutions  potential the  ° -  tabulates  three  pH o f  "  = 2  12.5  for  the  aqueous  75 conditions, rejected. by  the  rate  hydrogen The of  rate the  of  embrittlement hydrogen  still  evolution  electrochemical  cannot  will  reactions  at  be  be controlled  the  crack  Table  XI  Calculated  pH a n d  E  u + / U  at  Solution  92°  C.  pH  E  H /H +  ( V 2  sce  12.5 mol/kg NaOH  13.5  -  1.18  3.35 mol/kg NaOH  12.8  -  1.13  12.6  -  1.11  2.5 mol/kg NaOH + 0.42 mol/kg Na S 2  )  11 2 tip. the  Thus  the  crack  electrochemical  measured  of  Adsorption  mild  adsorption  steel of  be  controlled  which  is  by  the  reflected  rate  in  of  the  energy.  Mazille SCC  will  reactions,  activation  4.2.4  rate  of  and  in  Damaging  Uhlig  alkaline  damaging  Anions  have  contended  solutions  anions  onto  is  the  that  due  metal  the  to  the  surface  at  38 the  crack  bonds  in  already  tip. the  requires  the  are  alkaline  quantify, invoke shown  in  solutions.  by  it  is  damaging  ion  4.2.5.  hydrogen  of  and  it  Fe  by  for  under  of  three  embrittlement  and  failure  for  the  to  not  the  dissolution  surface  SCC  of  mild  steel  are  difficult  to  appear  necessary  to  bonds  when  Fe  to  removed  be  test  involving  it  can from  conditions. the  be the For  adsorption  further.  Mechanisms mechanisms anodic  and  adsorption  of  the  the  Since  metal  the  of  anodic  solvation,  effects  does  intrametal1ic  rupture.  7a-7e onto  considered  Assessment the  0H~  rupturing  possible  not  mechanical  important  a mechanism  was  Of  of  the  facilitate  These  dissolution  reasons,  and  weaken  equations  obviously  however,  that  by  removal  a mechanical  lattice these  bonds  adsorption  subsequent  ad-ions  lattice  proposed  processes in  iron  stressed  mechanism  the  These  discussed,  dissolution  only appear  of  a  11 3  relevant mild  to  this  steel ,  anions  does  not  capable  possible passive  solely  Hydrogen  mechanism  rejected  On  the  as  other  a  mechanism  based  fitted  to  the  it  did  not  an  anodic  of  passive  from  the  NaOH, film  value  reason,  it  SCC all of  a  one  SCC  was  though  E  an  observations  at  the  but  in  must  reduced  be the  12.5  metal.  Hoar  and  a  activenot  mol/kg  NaOH.  control  three  that i  as  could  c  o  solutions,  at  the r  was  answer.  operative  measured  of  dissolution  all  accepted  depth.  dissolution  eliminated  satisfactory was  in  the  corr  in  anodic  anodic  was  of  damaging  nor  anodic  data  of  pursued  activation-diffusion  mechanism  bare  not  occurred  at  cracking  involving  solutions,  completely  it  for  three  caustic  adsorption  all  which  velocity  dissolution  mol/kg  from  mixed  crack  of  the  greatly  even  on  on  embrittlement  cause  provide  12.5  based  case  explaining  of  hand,  the  embrittlement  for  transition  be  a  this  hydrogen  of  work.  differ  For  Neither  this  In  a mechanism  dissolution.  was  work.  E  If l  c  o  r  n  r  presence  significantly  r  Jones  have  shown  4 6 that  this  assumption  is  dissolution  mechanism  control  be  the  can  used  active-passive The  most  to  probably  based  on  explain  transition  consistent  incorrect.  mixed the in  anodic  activation-diffusion  results  all  An  three  interpretation  of  obtained  at  solutions. the  data  is  to  114 apply  a  12.5  hydrogen  mol/kg  NaOH  dissolution all  three to  12.5  mol/kg  a  90°  portion  in  for  energy  C  7 6  and  observed  -  1.00  V  fortuitous, evolution, rate  at  of of  E  c  while  Q  the  r  the  observed with  or  24  kJ/mol  is  higher  at  aqueous  charge  E  the  may  the  The  consistent  the  *  measured 12.5  indicate crack  a dissolution  model.  r  in contri-  in  r  hydrogen dissolution  pH  9.  .  pH 6, This  7 9  activation NaOH.  expected but  The  for  within  reactions.  activation  energies  mol/kg  that rate,  the is  NaOH may rate  of  have  evolution  transition  is  by  at  fractography  hydrogen  63  '  been  hydrogen  controlled occurring  a  the  controlled  intergranular-transgranular active-passive  controlled  also  mol/kg  than  reactions  a  Q  apparent  12.5  transgranular with  at  diffusion,  transfer  in  corr  in  r  p r o p r i d h a t e . at  the in  electrochemical  mixed  with  C  from  solution  V-  by  r  p r e v i o u s l y . . . . been  sodium 3  E  anodic  has  1.00  thus  crack.  is  HC0  to  -  and it  region  1 M  -  3  Q  may  at  mechanism  at  between  see  velocity  in  consistent  for  and  the r  C0  controlled  agreement  tip  of  a  c  transition  processes  transition in  E  active-passive  crack  active  steel  in is  value  mechanism  at  the  determined  measured  The  the  at  activation-diffusion  the  A change  mild  mechanism  Dissolution  of  NaOH.  interpretation  range  at  active-passive  observed and  a mixed  mechanism  embrittlement the  and  solutions.  bute  at  embrittlement  the  the observed  mechanism,  fractography consistent  67  115 The mol/kg a  similar  NaOH  mixed  crack  solution  velocities  and  the  observed  simulated  activation-diffusion  in  white  controlled  the  3.35  liquor  support  mechanism.  The  2role  of  S  ions  in  the  appears  primarily  to  be  and  formation  of  a  the  caustic to  cracking  delay  the  protective  of  onset  film,  mild  of  as  steel  passivity  postulated  by  41 Tromans.  This  potentials  than  results  in  the  observed  in  plain  small  difference  in  white  liquor  3.35  either  the  of  and  change  i  c  o  r  r  occurrence NaOH  observed  mol/kg  in  OH"  an  observed  can  SCC  at  solutions.  between  NaOH  of  be  concentration,  the  The  simulated  attributed or  higher  to  the  to  presence  ions. The  also  lack  of  consistent  results.  The  with  the  mobility  pH  above  of  OH  change  down  the  interpretation is  greater  of  than  crack  is  the  that  of  72 other  ions,  and  compared  to  makes  unlikely  been  it  HFeO"  measurably  Although cally  lower  significant of  the  for  combined in  the  that  the  in  measured  Batch  OH"  large  in  the  excess crack  concentration  the  than  not  Likewise,  of  OH  (Table  would  X),  have  crack.  values  A steel  d i f f e r e n c e was  measurements.  the  solution  the  depleted  with  of  i  for  observed no  firm  c  o  r  r  Batch  were  systemati  B steel,  within  the  conclusions  a  error could  be two or  reached  about  batches crack  of  the  steel.  velocity  attributed  to  differences Any  between  in.crack  differences the  compositional  two  velocity  observed  batches  differences  of  in  of  in  steel  the  i  the c  o  r  can  r  be  steels, 35  and  their  effect  formation may  also  4.3  and  had  Industrial major  crack  initiation  lies  with  composition  and  thus,  so  mild  of  this  bility F-corr  to  under  oxidant is  in  segregation.  inclusions  on  the  the  in  crack  The  the  steels  rates.  c  white  r  r  outside the  liquor  of the  to  conditions the  present  in  of  about  shown  active-  of in  this Figure  between  maximum  and  corrosion  the  potential as  pulp  stress  varies  steel  measured white  may  ion,  S  under limits liquor,  vary,  process  the  the  6.  mills,  7  susceptibility  SCC.  the  simulated  in  in  for  of  range  change  potential  o  work  composition,  structure  E  this  association  the  polysulphide  usually  of  potential  and  present  the  a  the  the  mill  are is  of  was  SCC  the  solution  steel  work  oxidants  which  with  will  Although  effect  in  transition,  The  the  an  of  implication  industry  transition  boundary  Implications  paper  passive  grain  distribution  have  The  of  on  X  white  conditions  of  suscepti-'  the  value  particularly  stream.  2-  the  (where liquor  One  such  x>l), in  if  58  small  of  7  117  quantities  as  a  result  of  white  liquor  during  or  larger  quantities  in  the  addition  according  of  to  inadvertent  preparation by  elemental  equation  2xS ' + (x-l)0  sulphur  2  2  tion in  is  equilibrium  established  solution,  as  white  or  17a, by  liquor  in  17a  S " X  17b  2  controls 2S. ,  the  ,. S  x  equation  the  S  2-  2-  concentra-  A  and  $2^3  2-  ions  18.  4S " + 6 ( x - l ) 0 H ' ^ 2 ( x + l ) S " + ( x - l ) S 0 2  .......  2  which  between  shown  oxidation,  the  the  equation  2S ~ + 4 ( x - l ) 0 H "  2  an  to  air  via  of  17b.  (x-l)S + S "  In p r a c t i c e ,  oxidation  storage,  deliberate  + 2(x-l)H 0 -  2  or  air  2  2  2 3  " + 3(x-l)H 0 2  . . . . 18  2The the  effect  corrosion  where  E  after  the  c  sulphur, for  the  o  r  is  in  the  of  mild  was  free  active  centration  of  of  free not  S  x  to  v  This  8  in  the  given on  the  determined,  passive  is  liquor  shown  amount  in  to  Figure  white of  is  raise 28,  liquor,  60  s  elemental  anodic  p o l a r i z a t i o n curve 2Although the S ion conA  Figure  potential regions,  present.  white  simulated  solution.  corrosion or  S  steel  superimposed  sulphur  the  adding  potential.^  addition  centration that  r  of  of  28  clearly  mild  steel  depending  Consequently,  E  on c  o  r  shows may  the r  °f  lie conthe  118  0.5  Figure 28  E f f e c t of sulphur a d d i t i o n upon E  in 2.5 mol/kg  NaOH + 0.42 mol/kg Na^S superimposed on the anodic p o l a r i z a t i o n curve f o r the sulphur f r e e s o l u t i o n .  steel  structure  maximum tion  may  fall  susceptibility  changes  so  that  potentials,  then  tion  critical  may  be  Another and  paper  velocity simulated not to  use  white  they  cold  do  also  the  crack stress  In  clearly  show  quite in  the  Kraft  is  subjected  of  these  in  results  a  large may  in  work  the  use  mol/kg  to  the  pulp  crack  of  and  this  which  is  purposes, of  stress  to  of  mild  to  likely  this  particular,  the  also  occurs  encountered  when  intensity.  work  steel  those  the  An  metal  awareness  catastrophic  33 failure  of  The hydrogen liquor  a  continuous  possibility  that  embrittlement,  cannot  be  digestor  SCC,  may  eliminated.  in  by  occur  Alabama.  anodic at  Judging  E  c  o  by  r  dissolution r  in  the  are  unlikely  SCC  is  the  work  and  of  prevented  pc  industrially,  results  similar  transi-  NaOH  magnitude  which  stress  have  of  construction  cracking  in  SCC.  results  the  at  the  of  industry,  for  by  between  3.35  the  for  conditions and  of  2-  taken  encountered  caustic  process, to  this  the  material  terms,  range  ion c o n c e n t r a X a c t i v e to passive  from  time  While to  S  occurrence  intensities  that  the  correlation  guidelines  general  readily  of  intensity  velocity  potential  r  of  the  If  varies  the  liquor.  worked  occur.  is  applicable  provide  corrosion  corr length  to  the  SCC.  application  stress  directly  to  E  the  industry and  within  white results  or  obtained  in  the  12.5  mol/kg  crack  velocities  should  lower  than  measured  those  be  NaOH at  at  solution,  least the  an  the  order  of  active-passive  expected magnitude transition.  Chapter  5  CONCLUSION  5.1  Conclusions The  C-1018 NaOH  results  steel  solution  solution  i)  of  a  are  the  12.5  and  support  comparisons batch  in  of  a  mol/kg  2.5  the  present  NaOH  mol/kg  following  between  work  on  SCC  solution,  NaOH  +  0.42  a  AISI 3.35  mol/kg  conclusions.  specimens  of  All  machined  from  Na S  ;  ?  direct the  same  steel.  The to  potential SCC  in  3.35  0.42  mol/kg  near  the  of  mol/kg  Na S 2  at  Maximum  -  V  maximum  NaOH  and  susceptibility 2.5  mol/kg  92° C occurred  active-passive  tion. 1.00  regime  transition  susceptibility  was  in  The  2.5  in  each  observed  soluat V  see  2  steel  in  +  potentials  i n 3 . 3 5 m o l / k g NaOH a n d - 0 . 8 8 see m o l / k g NaOH + 0 . 4 2 m o l / k g Na S.  dependent ing  NaOH  at  a  ii)  mol/kg  exhibited and  each  of  both  stress the  intensity  three  121  stress  intensity independent  solutions.  crack-  122 iii)  The  region  NaOH  iv)  at  92°  C,  2.5  x  10"  8  (~  2.4  x  10"  9  The  region  and  92° 6.9  NaOH  x  region  the  most  in  3.35  2.5  m/s),  8  10"  II  energy  in  12.5  than  in  crack  (  V  -1.00  mol/kg  V  S 0 6  NaOH  3.35  mol/kg  at  9 2 ° C and  velocity  „ see  NaOH  -  for  SCC  V  )  0.88  at  in  each  was  faster  see (~  0.42  7.2  x  10"  mol/kg  m/s)  9  than  in  Na S 2  m/s).  9  rate  law,  of  24  +  velocity  in  12.5  velocity  1  The  crack  for  a  different  batch  an  Arrhenius  rate  energy  see  m/s).  9  NaOH +  Arrhenius  V  Q r r  at  and  An  tion  (  (-1.00  10"  mol/kg  1.00  E ,  potential  3.3  to  at  12.5  -  susceptible  (~  crack  at  velocity  faster  x  mol/kg  tion  in  m/s).  mol/kg  x  than  crack  10"  The  faster  m/s)  II  7.2  (~  velocity  was  C was  solution  vi)  crack  (-  (~  v)  II  of  23  in  +  with  apparent  k J / m o l , was mol/kg 12.5 of law  9  an  obeyed  NaOH a t  mol/kg  steel and  kJ/mol  was  -  by  also  apparent  the  1.00  NaOH a t  was  an  activa-  E  V c  o  r  $  c  r  fitted activa-  obtained.  e  1 23 vii)  Cracking 12.5  followed  mol/kg 3  A mixed  viii)  No  at  mol/kg  mol/kg  transgranular  at  E  corr  , with  path  one  -  1.00  NaOH,  V  and  NaOH + 0 . 4 2  detectable  occurred  in  see  r  at  in  in  the  liquid  results  are  best  path  mol/kg  was  NaOH  and  3  -  mol/kg  change  12.5  in  exception.  transgranular-intergranular  followed 3.35  NaOH  a  0.88  V  g  c  in  e  2.5  Na S. 2  pH  from  the  trapped  at  explained  by  bulk  the  value  crack  tip.  ix)  The a  mechanism  ment  and  anodic  and  involving  mixed  embrittle-  activation-diffusion  controlled  a mechanism  diffusion  at  eliminated  in  each  „ corr  at  solution  of  on  Future  Work  1)  Investigate  the  effects  of  particular  with  each  .respect  at  heat tc  the  solution.  embrittlement  thermodynamic  for  NaOH  activation-  active-passive  Suggestions  mol/kg  dissolution  in  5.2  in  12.5  3  mixed  hydrogen  the  in  anodic  transition  possibility  be  E  involving  controlled  active-passive The  hydrogen  dissolution  both  postulating  can  transition grounds.  treatment the  on  SCC,  microstructure  124 of  ii)  the  heat  Investigate mol/kg Na^S  affected  zones  the  SCC  of  NaOH a n d  2.5  mol/kg  under  simulating  pressure the  mild  and  of  welds.  steel  in  NaOH + 0 . 4 2  temperature  environment  the  inside  3.35  mol/kg  conditions  a  Kraft  process  digestor.  iii)  Extend a  the  range  of  transition determine hydrogen and  the  occurs.  fracture  mechanics  potentials in  each  whether  up  solution the  at  the in  mechanism  embrittlement, potential  to  study  or  which  include  active-passive order of  anodic the  to  to  SCC  better is  dissolution,  transition  1 25 BIBLIOGRAPHY  Speidel,M. 0 . a n d F o u r t , P. M. , S t r e s s Corrosion C r a c k i n g and H y d r o g e n E m b r i t t l e m e n t o f I r o n Based A l T o y s , e d . R.W. S t a e h l e , J . H o c h m a n , R. D. McCright and J . E. S l a t e r , N A C E , H o u s t o n , ( 1 9 7 7 ) , p p . 5 7 - 6 0 . S t a e h l e , R. W. , F u n d a m e n t a l A s p e c t s o f S t r e s s C o r r o s i o n C r a c k i n g , e d . R. W. S t a e h l e , A . J . F o r t y , a n d D. v a n R o o y e n , N A C E , H o u s t o n , ( 1 9 6 9 ) , p p . 3-14. H e r t z b e r g , R. W . , D e f o r m a t i o n a n d F r a c t u r e of Engineering M a t e r i a l s , J . Wiley & Sons, (1976). Parkins,  R.  N.,  Ambrose, (1972).  J.  R.  Brit.Corr. and  Kruger,  J . , 7,  15,  Mechanics New Y o r k ,  (1972).  J . , Corrosion,  28,  30,  P o u r b a i x , M., in A l l o y s , ed. pp. 442-448.  Theory of Stress Corrosion Cracking J . C. S c u l l y , NATO, B r u s s e l s , (1971),  P a r k i n s , R.N., in A l l o y s , ed. pp. 449-468.  Theory of Stress Corrosion Cracking J . C . S c u l l y , NATO, B r u s s e l s , (1971),  Humphries, M.J. 7, 7 4 7 , (1967).  and  Parkins,  Stress Corrosion Cracking: T e c h n i q u e , STP 665 , e d . G. P a y e r , ASTM, P h i l a d e l p h i a , P a r k i n s , R. N . , S t r e s s S t r a i n Rate T e c h n i q u e , a n d J . H. P a y e r , A S T M ,  R.N.,  Corrosion  The Slow S t r a i n M. U g i a n s k y a n d (1979).  Science,  Rate J . H.  C o r r o s i o n C r a c k i n g : The Slow STP 6 6 5 , e d . G. M. Ugiansky P h i l a d e l p h i a , (1979), pp. 5-25.  P a y e r , J . H . , B e r r y , W. E. and B o y d , W. K., Stress C o r r o s i o n C r a c k i n g : The Slow S t r a i n Rate T e c h n i q u e , STP 6 6 5 , e d . G. M. U g i a n s k y a n d J . H. P a y e r , A S T M , P h i l a d e l p h i a , (1979), pp. 61-77. P o w e l l , D. T . 151, (1968).  and  Scully,  J.  C ,  Corros i on,  24,  126 13  D i e g l e , R.B. a n d B o y d , W. C r a c k i n g : The Slow S t r a i n e d . G. M. U g i a n s k y a n d J . P h i l a d e l p h i a , (1979), pp.  1.4  Mom, A . J . , D e n c h e r , R. T . , v . d . W e k k e n , C. J . a n d S h u l t z e , W. A . , S t r e s s C o r r o s i o n C r a c k i n g : The S l o w S t r a i n R a t e T e c h n i q u e , STP 6 6 5 , e d . G. M. Ugiansky a n d J . H. P a y e r , A S T M , Philadelphia, ( 1 9 7 9 ) , pp. 305-319.  15  S c u l l y , J . C , S t r e s s C o r r o s i o n C r a c k i n g : The Slow S t r a i n R a t e T e c h n i q u e , STP 6 6 5 , e d . G. M. Ugiansky a n d J . H. P a y e r , A S T M , P h i l a d e l p h i a , (1979), pp. 2 3 7 - 2 5 3 .  16  Brown,  17  W e i , R. P . , Fundamental Aspects of C r a c k i n g , e d . R. W. S t a e h l e , A . J . R o o y e n , NACE, H o u s t o n , ( 1 9 6 9 ) , pp.  18  K n o t t , J . F. , Fundamentals of F r a c t u r e J . W i l e y a n d S o n s , New Y o r k , (1973).  19.  B r o w n , B. Toughness (1966).  20  ASTM  21  H y a t t , M. V. a n d S p e i d e l , M. 0 . , Advances in C o r r o s i o n S c i e n c e and T e c h n o l o g y , V o l . 2, e d . M. G . F o n t a n a a n d R. W. S t a e h l e , P l e n u m Press, New Y o r k , (1 9 7 2 ) , p p . 1 1 5 - 3 3 5 .  22  B l a c k b u r n , M. J . , F e e n y , J . A . , a n d B e c k , T . R. , A d v a n c e s i n C o r r o s i o n S c i e n c e and T e c h n o l o g y , Vol.3, e d . M. G. F o n t a n a a n d R. W. S t a e h l e , P l e n u m Press, New Y o r k , (1 9 7 3 ) , p p . 6 2 - 2 9 2 .  23  M c K i n t y r e , P., Stress Corrosion Cracking and Hydrogen E m b r i t t l e m e n t of Iron Based A l l o y s , ed. R. W. S t a e h l e , J . H o c k m a n n , R. D. M c C r i g h t and J . E. S l a t e r , N A C E , H o u s t o n , ( 1 9 7 7 ) p p . 7 8 8 - 7 9 7 .  B. F. ,  Met.  K. , Stress Corrosion R a t e T e c h n i q u e , STP 6 6 5 , H. P a y e r , A S T M , 21-46.  R e v . , j _ 3 , 1 71 ,  (1 9 6 8 ) . Stress Corrosion F o r t y a n d D. van 104-111. Mechanics,  F. a n d S r a w l e y , J . E . , P l a n e S t r a i n Crack T e s t i n g , STP 4 1 0 , A S T M , Philadelphia,  E399-78a,  ASTM,  Philadelphia,  1978.  127  24  L e e , L . P . and T r o m a n s , D., Environment Sensitive F r a c t u r e o f E n g i n e e r i n g M a t e r i a l s , e d . Z. A . F o u r o u l i s , A I M E , New Y o r k , ( 1 9 7 9 ) , p p . 2 3 2 - 2 4 9 .  25  R u s s e l l , A. and T r o m a n s , 1229, (1979).  26  Reinoehl , J . 151, (1972).  27  S c h m i d t , H. W. , G a g n e r , P. J . , H e i n e m a n n , G. , P o g a c a r , C . F. a n d W y c h e , E. H. , C o r r o s i o n , 7_, 295, (1951).  28  Champion,  29  B e r k , A. A. and W a l d e c k , 235, (1950).  30  P o u l s o n , B., C o r r . J . , 9,  H e n n i k s o n , L. 91 , ( 1 9 7 4 ) .  31  Townsend,  H.  E.,  32  Charlton,  R.S.,  33  MacMillan (1980).  Bloedel  34,  P a r k i n s , R.N., Fundamental Aspects of S t r e s s C o r r o s i o n C r a c k i n g , e d . R.'W. S t a e h l e , A. J . F o r t y , a n d D. v a n R o o y e n , N A C E , H o u s t o n , ( 1 9 6 9 ) , p p . 3 6 1 373.  35  P a r k i n s , R. N . , S t r e s s C o r r o s i o n C r a c k i n g and Hydrogen E m b r i t t l e m e n t o f Iron Based A l l o y s , e d . R. W. S t a e h l e , J . H o c h m a n n , R. D. M c C r i g h t a n d J . S l a t e r , NACE, H o u s t o n , ( 1 9 7 7 ) , p p . 6 0 1 - 6 2 4 .  F.  E.  D.,  and B e r r y ,  A.,  Chem.  Mat. Mat.  and  W.  E. ,  Trans.  W.  F. ,  Chem.  and A r u p ,  Perf. , Pine  A,  Corrosion,  I n d . , 967 ,  Prot.,  Inc.,  Met.  V\_, 3 3 , 1_7 , 27 , Hills,  1 OA,  28,  (1957). Engng.  H.,  5_7,  Brit.  (1 9 7 2 ) . (1 9 7 8 ) . Alabama,  36  C a r t e r , C. S. a n d H y a t t , M. V . , Stress Corrosion C r a c k i n g and Hydrogen E m b r i t t l e m e n t o f I r o n Based A l 1 o y s , e d . R. W. S t a e h l e , J . H o c h m a n n , R. D. M c C r i g h t a n d J . E . S l a t e r , N A C E , H o u s t o n , ( 1 977 ), pp. 524-600.  37  B o h n e n k a m p , K. , F u n d a m e n t a l A s p e c t s o f S t r e s s C o r r o s i o n C r a c k i n g , e d . R. W. S t a e h l e , A . J . F o r t y , a n d D. v a n R o o y e n , N A C E , H o u s t o n , (1969), pp. 374-383.  E.  128  38  M a z i l l e , H. a n d 427, (1972).  39  H u m p h r i e s , M. J . a n d - P a r k i n s , R. N . , Fundamental A s p e c t s o f S t r e s s C o r r o s i o n C r a c k i n g , e d . R. W. S t a e h l e , A . J . F o r t y a n d D. v a n R o o y e n , N A C E , H o u s t o n , ( 1 9 6 9 ) , pp. 384-395.  40  Grafen,  41  Tromans, (1980).  42  B r u s i c , V. O x i d e s a n d O x i d e F i l m s , J . W. D i g g l e , M a r c e l D e k k e r , I n c . , ( 1 9 7 2 ) , pp. 2-91.  43  M a c D o n a l d , D. D. a n d R o b e r t s , A c t a , 2_3, 781 , (1978).  44  S c h r e b l e r G u z m a n , R. S . , V i l c h e , J . R. a n d A r v i a , A . J . , E l e c t r o c h e m i c a A c t a , 2 4 , 3 9 5 , (1 9 7 9 ) .  45  D i e g l e , R..B. 411, (1976).  46  H o a r , T . P. a n d 725, (1973).  47  D i e g l e , R. S o c . , 1_2^,  B. a n d V e r m i l y e a , 1 8 0 , (1 9 7 5 ) .  48  Scully,  J.  C ,  Metal  49  Scully,  J.  C ,  Corrosion  50  S t a e h l e , R. W. , S t r e s s C o r r o s i o n C r a c k i n g and Hydrogen E m b r i t t l e m e n t of Iron Based A l l o y s , e d . R. W. S t a e h l e , J . H o c h m a n n , R. D. McCright, and J . E. S l a t e r , N A C E , H o u s t o n , ( 1 9 7 7 ) , p p . 1 8 0 207.  51  V e r m i l y e a , D. 26, (1976).  52  P e r d i u s , F. , B r a b e r s , M. a n d Van H a u t e , A . , Mechanisms of Environment S e n s i t i v e Cracking of E n g i n e e r i n g M a t e r i a l s , e d . P. R. S w a n n , F. P. Ford, a n d A . R. C. W e s t w o o d , T h e M e t a l s S o c i e t y , London, ( 1 9 7 7 ) , pp. 53-65.  H. ,  Uhlig,  Corrosion  D. ,  J.  H.  H.,  Science,  Electrochem.  and  Vermilyea,  Jones,  A.  and  Corrosion,  R.  W. ,  Science,  7_,  Soc. ,  B.,  D.  (1967).  127 ,  Electrochemica  Corrosion,  Corrosion  D.  A.,  1_7 ,  R.  1 253,  V o l . I, ed. New Y o r k ,  A.,  Science,  Diegle,  1 77 ,  28,  J.  290, 20 ,  B.,  32,  Science,  13,  Electrochem.  (1 9 7 8 ) . 997 ,  (1 9 8 0 ) .  Corrosi on,  32,  129 53..  Bignold,  G.  54  D o i g , P. 9A, 357,  and F l e w i t t , (1978).  55  Melville,  56  M a g e n s e n , M. , M a a h n , E. , a n d B e c h - N i e l s o n , B r i t . C o r r . J . , ]_]_, 181 , (1 9 7 6 ) .  57  P u l p a n d P a p e r M a n u f a c t u r e , V o l . 1, R. G . M a c d o n a l d , M c G r a w - H i l l , 1 9 6 9 .  2nd  58  Wensley, 36, 385,  Corrosion,  59  Papp, 1  4  7  j  (  P.  J. ,  H. ,  Corrosion,  Brit.  D. A . a n d (1980).  J . , Cellulose -j-;  P.  28,  E.  307 ,  J . , Met.  Corr.  Charlton,  J . , 1_4,  R.  Chemistry  S.,  and  (1972). Trans.  1 5,  A. ,  (1 9 7 9 ) . G.,  ed.,  ed.  Technology,  5_,  1 9 7 1  60  R a u d s e p p , R., M.Ap.Sc. T h e s i s , B r i t i s h Columbia, (1981).  University  of  61  Newman, J . F. , M e c h a n i s m s o f E n v i r o n m e n t Sensitive C r a c k i n g o f M a t e r i a l s , e d . P. R. S w a n n , F. P. Ford, a n d A . R. C . W e s t w o o d , T h e M e t a l s S o c i e t y , L o n d o n , ( 1 9 7 7 ) , pp. 1 9 - 3 1 .  62  B e c k , T . R., The T h e o r y o f S t r e s s Corrosion C r a c k i n g i n A l l o y s , e d . J . C. S c u l l y , N A T O , B r u s s e l s , (1971) , pp. 6 4 - 8 5 .  63  G l a s s t o n e , S., La i d l e r , K. J . , a n d E y r i n g , The T h e o r y o f R a t e P r o c e s s e s , M c G r a w - H i l l , York, (1941).  64  Scully, J. C , S t r e s s C o r r o s i o n C r a c k i n g and Hydrogen E m b r i t t l e m e n t of Iron Based Alloys, e d . R. W. S t a e h l e , J . H o c h m a n n , R . - D . McCright a n d J . E. S l a t e r , N A C E , H o u s t o n , 1 9 7 7 , p p . 4 9 6 - 5 0 8 .  65  L e e s , D. J . , Mechanisms o f Environment Sensitive Cracking of M a t e r i a l s , ed. P. R. S w a n n , F. P. F o r d , a n d A . R. C . W e s t w o o d , T h e M e t a l s Society, London, ( 1 9 7 7 ) , pp. 557-573.  66  S t a e h l e , R. W . , S t r e s s C o r r o s i o n C r a c k i n g a n d Hydrogen E m b r i t t l e m e n t of Iron Based A l l o y s , e d . R. W. S t a e h l e , J . H o c h m a n n , R. D. M c C r i g h t a n d J . E. S l a t e r , N A C E , H o u s t o n , 1 9 7 7 , p p . 1 8 0 - 2 0 7 .  H., New  1 30 67  W e s t , J . M. , E l e c t r o d e p o s i t i o n a n d Corrosion P r o c e s s e s , D. v a n N o s t r a n d , L o n d o n , (1965).  68  Doig, 369,  69  S t e r n , M. a n d G e a r y , 104, 56, (1957).  70  B o c k r i s , J . O'M. and R e d d y , A . K . N . , Modern E T e c t r o c h e m i s t r y , V o l . 2, P l e n u m , New Y o r k , (1 9 7 0 ) .  71  B i e r n a t , R. J . a n d R o b i n s , A c t a , 1 7., 1261 , (1 9 7 2 ) .  72  M o o r e , W. J . , P h y s i c a l P r e n t i c e - H a l l , London,  73  Vetter, K.J., Electrochemical P r e s s , New Y o r k , (1967).  74  D a h l , L . , D a h l g r e n , T . , and L a g m y r , N . , High Temperature High P r e s s u r e E l e c t r o c h e m i s t r y in Aqueous S o l u t i o n s , e d . R. W. S t a e h l e , D. de G. J o n e s a n d J . E. S l a t e r , N A C E , H o u s t o n , (1976), pp. 533-545.  75  K e r n s , G. E . , W a n g , M. T . a n d S t a e h l e , R. W. , S t r e s s C o r r o s i o n C r a c k i n g and H y d r o g e n Embrittlement o f Iron Based A l l o y s , e d . R. W. S t a e h l e , J . H o c h m a n n , R. D. M c C r i g h t a n d J . E. S l a t e r , NACE, H o u s t o n , (1977), pp. 700-735.  76  J o n e s , de G. D . , Newman, J . F . a n d H a r r i s o n , R. P., P r o c e e d i n g s of the 5th I n t e r n a t i o n a l Congress on M e t a l l i c C o r r o s i o n , e d . N. S a t o , N A C E , Houston, ( 1 9 7 4 ) , pp. 434-438.  77  Mueller,  78  B r o w n , B. F . , F u j i i , C. T . , D a h l b e r g , E. J. Electrochem. S o c , 1 16 , 21 8 , (1 9 6 9 ) .  79  Parkins,  P. a n d (1977).  W.  R.  Flewitt,  A.,  P.E.J.,  A.L.,  TAPPI ,  N. , w r i t t e n  J.  R.  Corr.  17,  Electrochem.  G. ,  4th  Ed.,  Kinetics,  1 29 ,  Soc. ,  Electrochemica  Chemistry, (1972).  40,  Sci. ,  Academic  (1 9 5 7 ) .  discussion  of  Ref.  P.,  52.  131  APPENDIX  The  Effect  of  Residual  Shape  The lead and  tendency  several lag  this  on  the  or  forming  milling  rolled  25.4  mm x  from  the  surface  the  to  C-1018  25.4 bar  of  other  strength  at  Three  bars  of  these  in  3.35  Figure  Al  shows  surface  crackfront crack  has  of  was  reported  2 0 ° C was  tested  crack  bar  595  NaOH  mm x to  the  one  of  31.8 a  obviously  mm  were  to  the  whether  bars  by  then  the  I,  infrom  equally  cross-section  The  to  Table  specimens,  cross-section,  square  similar  of  machined chemical  composition  and  the  yield  MPa.  at  these  specimen  as  in  described.  in  the  to  environmental  left  machined -  1.00  a macrophotograph  of  of  investigated  specially  mol/kg  to  specimens  previously the  due  was  bar  cracks  speculation  was  31.8  DCB  edges  stresses  steel  mm.  as  a  the  corrosion  the  caused  This  on  Crackfront  stress  shape  of  Stresses  from  residual  sides  composition  the  the  process.  the  cold  of  of  characteristic  fluences,  of  millimeters  the  A  s  c  the  and  e  lagged  some  were  92°  stress  specimens.  still  propagated  of  V  specimens  C.  corrosion  Although at  the  distance  on  the  edges, the  the  132  Rgure  Al  Stress corrosion  crack surface  from a 32 mm x 32 mm b a r . NaOH a t - 1 . 0 0 V  o f specimen machined  T e s t e d i n 3.35  „ and 92° C.  K  T  = 48-53  mol/kg MPa/m.  133  surface  of  machined which  the  from  the  the  used  on  stress  in  the  stress  propagating of  specimen.  this  25.4  mm x  corrosion  the  free  corrosion work  to  cracks  stresses  The  that  still  state  lagged  at  the  considerations  portant  also.  or  mm b a r s  Thus,  residual  bar  contrast  surfaces.  effect  fact  in  showed  can  process.  25.4  propagate  shown  is  cracks  specimens of  be  This  to  be  the free  in  the  along  at  least  left  in  no the  bar  environmental  for of  inability  rolled  surface  c r a c k f r o n t . of surfaces  13),  evidence  partly  the  specimens  (Figure  cold the  to  due by  effects  of  the  to  the  the  the  indicates  material  forming  special that  are  stress  im-  134 APPENDIX  Calculation  The from of  data  water  were The  pH  of  each  supplied and  the  activity  0.35  at  ture  towards  of  by  from  water  2 5 ° C.  It  the  was  ideal  activity  coefficients  range  pH  are  of  shown  taken  as  *Conway, (1 9 5 2 ) .  in the  for  an  Table  at  Conway.*  9 2 ° C was The  value  of  0H~,  increase  of  water  Al.  pH  of  The of  each  Electrochemical  The  0H~  0H~  92° C  temperatures.  solutions with  between  of  the  and  the  0.35  solution  is  tempera-  values  activity,  each  constant  at  lower  NaOH  1.0.  the  of  at  concentrated to  estimated  dissociation  obtained  assumed  of  92° C  coefficients  data in  at  activity  midpoint  B.E.,  pH  solution  activity  extrapolated  of  B  and  1.0  was  range."  Data,  Elsevier,  Amsterdam,  Table  BI  Activity  Coefficients  Calculated  pH f o r  all  (Y -) and QH  Three  Activities  (ag^-)  for  0H~ and  Solutions.  Y  a  12.5 mol/kg NaOH  1.0  12.5  13. 3 - 13.7  3.35 mol/kg NaOH  0.7  2.4  12. 5 - 13.0  0.6  1.5  12. 3 - 12.8  Solution  OH"  2.5 mol/kg NaOH + 0.42 mol/kg  Na S 2  pH 0H~  OJ  on  


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