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Corrosion studies under dynamic conditions Dey, Walter Ross 1959

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CORROSION STUDIES  UNDER DYNAMIC CONDITIONS  by  WALTER  ROSS  DEY  B.A.Sc. U n i v e r s i t y of B r i t i s h Columbia 1957  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n the Department of CHEMICAL ENGINEERING We accept t h i s t h e s i s as conforming t o t h e standard required from candidates f o r t h e degree o f MASTER OF APPLIED SCIENCE  Members of the Department o f Chemical Engineering  THE UNIVERSITY OF BRITISH COLUMBIA MAY, 1959  ABSTRACT Laboratory tests on s t e e l pipe corrosion subjected to varying velocities of aerated Vancouver c i t y water have been made.  The water  was circulated through seven v e r t i c a l sections each containing from eight to ten specimens of standard  A inch s t e e l pipe.  The water was  removed at a constant rate so that the volume of water i n the apparatus was renewed from one to two times daily.  Exposure times varied from  5 to 25 days with temperatures of 90°F and 130°F.  The amount of  corrosion was evaluated by determining the weight loss.  The solution  potential of some designated corroding specimens was measured against a s i l v e r - s i l v e r chloride reference electrode throughout the time of exposure.  No changes i n the pH from that of the i n l e t water occurred  and the iron ion content fluctuated corresponding to the fluctuation i n i n l e t water. At 130°F the amount of corrosion, for 10 day t e s t s , was greatest at 1.5 fps velocity, but for tests of greater duration, was greatest at .75 fps v e l o c i t y .  This reversion did not take place at  90°F where the amount of corrosion was greatest at 1.5 fps for a U tests.  At both temperatures the lowest amount of corrosion occurred  at the highest v e l o c i t y l e v e l irrespective of the test duration within the l i m i t s investigated.  Amounts of corrosion were i n a l l  cases higher at 130°F as expected from previous work where maximum temperature effects occurred at about 1S0°F. The corrosion product consisted mainly of a black f i n e crystalline matter (assumed to be magnetite) at the surface of the specimen, with a porous reddish precipitate (assumed to be f e r r i c  hydroxide) over the magnetite.  The t o t a l amount of magnetite  increased with increasing temperature for similar conditions of flow and time of exposure. The corrosion mechanism i s considered i n the l i g h t of available oxygen supply, potential change, the effect of v e l o c i t y , cathodic depolarization and variables involved i n the mass transfer of the oxygen.  The correlation for the l a t t e r with v e l o c i t y i s  compared with results from an oxygen-pick up investigation of corrosion.  The results of t h i s investigation are q u a l i t a t i v e l y  consistent with previous knowledge of oxygen as a passivator i n such systems.  In presenting  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of  the r e q u i r e m e n t s f o r an advanced degree a t the  University  o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make it  freely  a v a i l a b l e f o r r e f e r e n c e and  agree t h a t p e r m i s s i o n f o r e x t e n s i v e f o r s c h o l a r l y purposes may  study.  I further  copying, of t h i s  be g r a n t e d by t h e Head o f  Department o r by h i s r e p r e s e n t a t i v e s .  g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n  The U n i v e r s i t y of B r i t i s h Columbia, Vancouver 3, Canada. Date  AftlrfK  fo  19 S?  my  I t i s understood  t h a t c o p y i n g or p u b l i c a t i o n o f t h i s t h e s i s f o r  Department of  thesis  financial  permission.  ACKNOWLEDGMENTS I wish t o acknowledge the continuous encouragement and advice provided by Dr. L. W. Shemilt under whose guidance t h i s i n v e s t i g a t i o n was made p o s s i b l e . I a l s o wish t o acknowledge the f i n a n c i a l assistance provided by Standard O i l Company o f B r i t i s h Columbia and the N a t i o n a l Research C o u n c i l o f Canada. Furthermore, I am a l s o indebted t o the f o l l o w i n g concerns who so generously helped t o make t h i s i n v e s t i g a t i o n achievable by * donations o f s e r v i c e s , equipment and m a t e r i a l s . B r i t i s h Columbia Research C o u n c i l Carlon Pipe D i v i s i o n , Beardmore and Co» L t d , Huntington Rubber M i l l s Imperial O i l L t d . I n d u s t r i a l Coatings L t d . Paterson B o i l e r Works Ltd. Western Canadian Pipe M i l l s L t d . Western I n s u l a t i o n Co. L t d .  NOMENCLATURE md  milligrams per square decimeter  ACE  S i l v e r - S i l v e r Chloride  fps  feet per second  rpm  r e v o l u t i o n s per minute  mg  milligram  in  inch  ft  feet  sq f t  square f e e t  cu f t  cubic f e e t  °F  degrees Fahrenheit  lbs  pounds  sec  second  sq cm  square centimeter  Electrode  TABLE OF CONTENTS Page Acknowledgment s Abstract Nomenclature Introduction  1  L i t e r a t u r e Review 1. 2. 3.  Theory and Mechanism Velocity Types of Apparatus Used  4 8 1°  Apparatus 1. P r e l i m i n a r y Testing 2. Main Testing 3. Flow Apparatus a. Head Tank b. Pump c. D i s t r i b u t o r Heads d. Control Valves e. Test Sections 4. Measuring Apparatus a. Thermometer b. Potentiometers and Electrode c. Rotameters d, A u x i l a r y Flow System Measurments e. Balance and Weights f . Microscope g. Spectrophotometer  14 17 19 20 20 21 21 22 22 22 23 23 23 23  Materials  Procedure  1. Water 2. Test Pipe 3. Chemicals f o r Analysis  24 24 24  1. P r e l i m i n a r y Test 2. Main Test a. Iron Analysis b. Oxygen A n a l y s i s c. I n s t a l l a t i o n of the Test Sections d. P o t e n t i a l Check on Electrode  28 28 29 29 34  Results  1. Preliminary Run 2. Main Test Run  Discussion of Results 1. Preliminary Run 2. Main Test Run a. Water b. Corrosion Products c. Time 3. Velocity a. Actual Effects b. Theoretical Effects 4. Temperature 5. Potentials 6. S t a t i s t i c a l Design  35 35 59 60-a 61 65 69 74 82 82 88  Conclusions  91  Recommendations  92  Literature Cited  93  Appendix I  98 Original Data Tables XXIV to XLI  Appendix I I Miscellaneous Data and Schematic Representation of Apparatus Figures 24 to 26 Appendix I I I Calendar of Test Runs Figure 27 Sample Calculations  119-a 120  LIST OF TABLES I  Greater Vancouver Water D i s t r i c t Physical and Chemical Analysis of Water Supply, Average for 1958  26  II  Chemical Analysis and Physical Properties of Type B Pipe  27  III  Results of Weight Loss Tests Velocity 4.5 fps Temperature 45°F  37  IV  Potentials at end of Preliminary Test  38  V  Results of Weight Loss Tests Velocity 4.5 and 3.0 fps Temperature 90°F  38  Results of weight Loss Tests V e l o c i t y .75 f p s Temperature 90°f  39  VII  Results of Weight Loss Tests V e l o c i t y .75 and 1.5 f p s Temperature 90°F  40  VIII  Results of Weight Loss Tests V e l o c i t y .75 and 1.5 f p s Temperature 90°F  41  IX  Results of Weight Loss Tests V e l o c i t y 3 . 0 and 4.5 f p s Temperature 90°F  42  X  R e s u l t s of Weight Loss Tests V e l o c i t y 1.5 f p s Temperature 90°F  43  XI  Results of Weight Loss Tests V e l o c i t y 3 . 0 and 1.5 f p s Temperature 130°F  44  XII  Results of Weight Loss Tests V e l o c i t y 4.5 and 3 . 0 f p s Temperature 130°F  45  XIII  Results of Weight Loss Tests V e l o c i t y .75 and 1.5 f p s Temperature 130 F  46  XIV  Results of Weight Loss Tests V e l o c i t y .75 and 4.5 f p s Temperature 130 F  47  XV  V a r i a t i o n of Water during Tests  48  XVI  P o t e n t i a l s a t end of Main Test  49  XVII  Comparison of P o t e n t i a l s of P r e l i m i n a r y Run w i t h S t a t i c Conditions  60  XVIII  Comparison of Results of Previous Study to the Present Study  71  XIX  Comparison of P o t e n t i a l s of Main Test w i t h s t a t i c Conditions and the Amounts of Corrosion of Main Test  85  XX  Comparison of Corrosion Rates  87  XXI  A 2  89  XXII  Weight Loss Tests V e l o c i t y 4.5 f p s Temperature 45°F  98  XXIII  P o t e n t i a l TLne Data f o r Specimens 1, 2, 3 . V e l o c i t y 4.5 f p s Temperature 45°F  98  VI  i  3  F a c t o r i a l Design  XXIV-  Weight Loss Tests V e l o c i t y 4.5 and 3.0 f p s Temperature 90°F  99  XXV  Weight Loss Tests V e l o c i t y .75 f p s Temperature 90°F  100  XXVI  Weight Loss Tests V e l o c i t y 1.5 and .75 f p s Temperature 90°F  101  XXVII  Weight Loss Tests V e l o c i t y .75 and 1.5 f p s Temperature 90°F  102  XXVIII  Weight Loss Tests V e l o c i t y 3.0 and 4.5 f p s Temperature 90°F  103  XXIX  Weight Loss Tests V e l o c i t y 1.5 f p s Temperature 90°F  104  XXX  Weight Loss Tests V e l o c i t y 1.5 and 4.5 f p s Temperature 130 F  105  XXXI  Weight Loss Tests V e l o c i t y 3.0 and .75 f p s Temperature 130 F  106  XXXII  Weight Loss Tests V e l o c i t y 1.5 and 3.0 f p s Temperature 130°F  107  XXXIII  Weight Loss Tests V e l o c i t y .75 and 4.5 f p s Temperature 130°F  108  XXXIV  P o t e n t i a l Time Data f o r Specimens 20, 24, 26, 162, 167. V e l o c i t y .75 f p s Temperature 90°F  109  XXXV  P o t e n t i a l Time Data f o r Specimens 173, 179. V e l o c i t y 1.5 f p s Temperature 90 F  110  XXXVI  P o t e n t i a l Time Data f o r Specimens 1, 5, 134, 190. V e l o c i t y 3.0 f p s Temperature 90°F  111  XXXVII  P o t e n t i a l Time Data f o r Specimens 13, 17, 195, 196. V e l o c i t y 4.5 f p s Temperature 90°F  112  XXXVIII  P o t e n t i a l Time Data f o r Specimens 67, 70. V e l o c i t y .75 f p s Temperature 130°F  113  XXXIX  P o t e n t i a l Time Data f o r Specimens 105, 109. V e l o c i t y 1.5 f p s Temperature 130°F  114  XL  P o t e n t i a l Time Data f o r Specimens 121,  126,  115  140.  V e l o c i t y 3.0 f p s Temperature 130°F XLI  P o t e n t i a l Time Data f o r Specimens 113,  157,  116  159.  V e l o c i t y 4.5 f p s Temperature 130 F  LIST OF FIGURES  1  E f f e c t of Increasing Oxygen D i f f u s i o n and Increasing F i l m Resistance on Corrosion Rate  9  2  P r e l i m i n a r y Apparatus  15  3  Cathode Follower  16  4  Laboratory Equipment f o r Corrosion Studies  18  5  D e t a i l of Test Section Assembly  31  6  D e t a i l of Wire Lead Connections  33  7 a, b, c, d, e, f .  'Specimens Showing Corrosion Products formed a t Various V e l o c i t i e s  62 63  8  Amount of Corrosion a t 90°F  66  9  Amount of Corrosion a t 130°F  67  10  Potential,Time Curves V e l o c i t y 4.5 f p s Temperature 45°F  50  11  P o t e n t i a l Time Curves V e l o c i t y .75 f p s Temperature 90 F  51  12  P o t e n t i a l Time Curves V e l o c i t y 1.5 f p s Temperature 90°F  52  13  P o t e n t i a l Time Curves V e l o c i t y 3.0 f p s Temperature 90°F  53  14  P o t e n t i a l Time Curves V e l o c i t y 4.5 f p s Temperature 90°F  54  64  15  P o t e n t i a l Time Curves V e l o c i t y .75 f p s Temperature 130°F  55  16  P o t e n t i a l Time Curves V e l o c i t y 1.5 f p s Temperature 130 F  56  17  P o t e n t i a l Time Curves V e l o c i t y 3.0 f p s Temperature 130°F  57  18  P o t e n t i a l Time Curves • ' V e l o c i t y 4.5 f p s Temperature 130 F  58  19  E f f e c t of Water V e l o c i t y on Amount of Corrosion  73  20  L o c a l i z i n g of Corrosion Attack caused by changing V e l o c i t y on Type A Pipe  74  21  E f f e c t of the P o s i t i o n of the L o c a l Anodic P o l a r i z a t i o n Curve on the Influence of V e l o c i t y on Amount of Corrosion  77  22  Comparison of Speeler and Kendall Results w i t h a Mass Transfer C o r r e l a t i o n  78  23  E f f e c t of Temperature on Amount of Corrosion  83  24  C a l i b r a t i o n of Spectrophotometer  117  25  V a r i a t i o n i n Oxygen Concentration w i t h Temperature  118  26  Schematic Representation of Test Apparatus  119  1  INTRODUCTION  In nature, the forces which cause corrosion are as constant i n t h e i r action as the sea.  The losses incurred by private  individuals and i n d u s t r i a l concerns amount to more than s i x b i l l i o n dollars annually.  Corrosion dissipates our resources and the  products of our labour, interrupts production and precipitates accidents.  I t i s therefore an engineering problem of considerable  importance. Different metals are affected to different degrees and corrosive attack takes many forms.  Attack may be by general  tarnishing or rusting with occasional perforations i n especially affected areas (70).  Corrosion may develop preferentially near the  junction of two different metals (69). localized attack by p i t t i n g (69).  The metal may suffer highly  The strength of a metal'may be  destroyed by cracking induced by corrosion (60).  Corrosion may  also be confined to crevices under gaskets or washers, or i n sockets (79).  I t may have the effect of removing one of the constituents  of an alloy so as to leave a weak residue (45). The study of corrosion considers reactions between a metal and i t s environment.  Corrosion i n iron and steel i s of particular  importance i n that about 90 per cent of a l l construction i n the process industries i s accomplished with the use of these two metals. The action of the atmosphere and water on iron accounts i n  2  l a r g e part f o r the reputation i r o n has as a poorly r e s i s t a n t metal. I t i s t r u e that these are the most commonly encountered c o n d i t i o n s , yet i t i s equally t r u e that i r o n i s unusually v e r s a t i l e i n r e s i s t a n c e when the range of corrosion substances i s viewed as a whole.  In c e r t a i n a c i d s o l u t i o n s , i n a l k a l i n e s o l u t i o n s , against  various gases and molten metals, i r o n i s o f t e n the best a v a i l a b l e metal even when i t s advantage i n cost comparison i s disregarded  (44).  McKay and Worthington (44) s t a t e that i r o n corrodes i n aqueous s o l u t i o n s , l i k e other metals,, by change from the metal t o the metal i o n .  In the n e u t r a l range of pH of aqueous s o l u t i o n s i n  the presence of a i r , i r o n has poor r e s i s t a n c e , the f i l m t h a t develops being poorly p r o t e c t i v e at best.  However, the p r o t e c t i o n derived  from the f i l m depends g r e a t l y on the conditions i n which i r o n i s placed.  I t i s therefore very important t o explore conditions  such as: (a)  types of water  (b)  temperature  (c)  flow conditions  (d)  aeration  (e)  potentials  Since Vancouver tap water i s used e x t e n s i v e l y f o r i n d u s t r i a l purposes, and no q u a n t i t a t i v e data are known, i t would be of considerable value t o study the e f f e c t s of some of the above conditions on the amount of corrosion of m i l d s t e e l i n t h i s medium. In t h i s study a s e r i e s of temperatures has been taken, w i t h v e l o c i t y as the main v a r i a b l e , maintaining water conditions such as  3  pH, oxygen concentration and iron concentration almost constant. Electrode potential measurements oh such corroding specimens are also important. This study i s therefore the continuation of the s t a t i c tests previously carried out at the University of B r i t i s h Columbia (8, 23, 36, 37) with the determination of the amount of corrosion again being given by weight loss measurements. This type of work also allows f o r a s t a t i s t i c a l design of experiments such as Davies (22) i l l u s t r a t e s , f o r l a t e r more detailed investigation.  LITERATURE REVIEW Theory and Mechanism As i m p l i e d above, the term " c o r r o s i o n " i s understood t o mean the slow d e s t r u c t i o n of materials by chemical or electrochemical agencies.  Corrosion occurs because i n many environments most metals  are i n h e r e n t l y unstable and tend-to r e v e r t t o some more s t a b l e combination.  The m e t a l l i c ores, as found i n nature, are f a m i l i a r  examples of these combinations.  Probably the most common form of  corrosion i s the d e s t r u c t i o n of the metal through o x i d a t i o n , w i t h an oxide being formed, u s u a l l y hydrated to a greater or l e s s degree. This form of corrosion i s the type that i r o n i s mostly subjected t o . I t i s now regarded as an e s t a b l i s h e d f a c t t h a t i n nearly a l l cases of corrosion i n the present of water, the d r i v i n g force of the corrosion r e a c t i o n between i r o n and i t s environment i s electrochemical i n nature.  The magnitude of t h i s electrochemical p o t e n t i a l , which  v a r i e s w i t h environment of the i r o n , determines the tendency of the r e a c t i o n t o proceed, whereas the r a t e of corrosion i s determined p r i m a r i l y by the r e s i s t a n c e t o the continued progress of the r e a c t i o n set up by c e r t a i n of the c o r r o s i o n by-products (44). According to Cushman (21) when a s t r i p of i r o n i s placed i n contact w i t h water, a d e f i n i t e tendency f o r the ions of i r o n to go i n t o s o l u t i o n i s established.  However, as the s o l u t i o n must remain  n e u t r a l i t can only do so i f an equivalent number of p o s i t i v e ions are somehow displaced.  These p o s i t i v e ions i n water are hydrogen,  which immediately gather on the i r o n surface as a t h i n i n v i s i b l e f i l m .  5 The reaction taking place can be described as follows: Fe  +  2H  Metal  Fe^  +  Ions  +  Ion  (l)  2H  Atoms  An e l e c t r i c current i s thus produced which i s carried from one point on the metal surface to the solution again by the escaping iron ions, and from the solution back to the metal surface by the separating hydrogen ions.  The speed of this reaction depends i n the  f i r s t instance upon the escaping tendency of the iron i t s e l f , measured by the so-called Nernst "solution pressure" or more acceptably the electrode potential;  i n the second instance, upon the concentrations  of the hydrogen ions, increasing as t h i s concentration i s increasedj and i n the t h i r d instance, upon the ease with which the deposited hydrogen ions can assume a gaseous state and escape or can be removed from the metallie surface. The presence of the hydrogen f i l m prevents further corrosion by two means: f i r s t l y , the hydrogen has an increasing tendency to re-enter the solution as i t builds up on the metal surface and secondly, by insulating the metal from the solution. For the corrosion to proceed, the hydrogen f i l m must be removed either by forming bubbles of hydrogen or by forming water with oxygen.  The reactions taking place are: 2H  Atoms  +  JO,  ^ZZ±  Dissolved 2H  Atoms  ^  H0 2  (2)  Liquid H  2  Gas  and  (3)  Wilson (75) pointed out that i n the ease of i r o n , reaction (1)  i s very much faster than either (2) or (3).  (2)  Reaction  (71),  dominates i n neutral or alkaline solutions as shown by Walker Speller (63) and Dey (23).  In acid solutions reaction (3) dominates  (64).  I t i s p a r t i c u l a r l y important that the results of corrosion tests should be considered i n r e l a t i o n to time of exposure, and that the form of the corrosion-time relationship for a particular metal, and the conditions of exposure should be borne i n mind.  Four main  types of corrosion-time equations based on assumed mechanism have been suggested (3, 4, H ,  12, 13, 26, 49) and can be stated as:  (1)  The r e c t i l i n e a r equation  y = k^t  (2)  The parabolic equation  y  (3)  The logarithmic equation  y = kjlog^t +  (4)  The exponential equation  y = 1^(1  +  kg  = kjt +  k  2  - e~ 2^ k  k^) " *o^)  where y i s the corrosion observed after exposure time t , and k^, k j are constants.  k^,  The units of the constants are not similar f o r a l l  four equations, but the suffixes 1, 2, 3 have been chosen f o r simplicity.  I t i s evident therefore, that the form of the corrosion-  time curve must be considered i f reliable assessment of the corrosion and i t s mechanism i s to be made. The electrode potential of the iron i n a water medium i s related directly to the free energy change for any of the corrosion reactions that go on.  These values presuppose an exact knowledge of  7 the reactions and reversible conditions.  Under these assumptions  the relationship of the electrode potential of i r o n under different circumstances can be calculated.  A recent productive approach to  t h i s i s i n terms of the pH-potential diagram developed by Pourbaix (52).  However, actual conditions involve many i r r e v e r s i b l e effects  and the exact equating of potential to the free energy change i s not valid.  Nonetheless, the measurement of potential i t s e l f can give  some indication of the i r r e v e r s i b l e reactions going on, and provide a means of analysis helpful i n elucidating the important factors i n any corrosion mechanism.  Johnson and Babb (38) have developed the  thermodynamics of i r r e v e r s i b l e corrosion process and applied i t t o an examination of the corrosion of s t e e l i n d i l u t e potassium chloride solutions, i n order to obtain a measure of the corrosion  current.  E a r l i e r work of Mears (47) and Gatty and Spooner (33) has been often used also as a means of elucidating the corrosion mechanism through a study of the potential as i t changes with amount of i r r e v e r s i b i l i t y (corrosion current).  The electrode potentials of any corroding metal  are therefore important even i f they usually provide l i t t l e i f any information on the specific rate of corrosion.  They do provide a  means of predicting general changes i n the characteristics or state of repair of protective or passive films on metal surfaces. this they can be of considerable importance.  Because of  8  Velocity The effects of velocity, l i k e a l l factors influencing corrosion, are varied and often apparently conflicting.  Cox and  Roetheli (19), Passano and Nagley (51) and several others (15,  32,  42, 54, 57, 62, 66, 69, 78) showed that the i n i t i a l effect of increasing v e l o c i t y i s to increase the corrosion rate.  However, at  higher v e l o c i t i e s some investigators (15, 32, 42, 57, 66) have found that the corrosion rate decreases, while others have found i t to continue to increase (19, 62, 66, 69, 7#),  The former experience  was explained i n part by the fact that at low velocities the increase i n oxygen transfer i s the determining factor and therefore the corrosion rate increases.  At higher velocities the increased; rate of  oxygen transfer i s overcome by the resistance of the corrosion products to the transfer of oxygen.  The resistance to oxygen transfer by the  corrosion product films formed on the s t e e l surface varies as the films change.  The alteration of the films chiefly depends on the  a v a i l a b i l i t y of oxygen. Brown (28),  This has been noted by Forrest, Roetheli and  The net effect of these two opposing conditions would thus  be expected to follow the curve as indicated i n Figure 1. At s t i l l higher velocities another factor becomes effective that of carrying away of the corrosion products by erosion.  This leads  to higher corrosion rates as found by Roetheli and Brown (56)  and  Rickers  (55). Groesbeck and Waldron (35) showed that the effect of oxygen  and v e l o c i t y are interrelated.  This could be anticipated, i n that an  Figure 1  E f f e c t of Increasing Oxygen D i f f u s i o n and Increasing F i l m Resistance on Corrosion Rate.  increase i n the v e l o c i t y of water •iDast'. a corroding s t e e l surface would increase the rate of oxygen d i f f u s i n g to the surface thereby advancing the corrosion rate.  However, as shown above, the data i n  the l i t e r a t u r e are decidedly contradictory,  Russell, Chappell and  White (57) found that the surface condition of the specimen affected the results obtained and reached the two following conclusions: (1)  The amount of corrosion of s t e e l under water increased with increasing water v e l o c i t y over the range commonly encountered i n practice, provided the metal surface was i n i t i a l l y coated with rust.  (2) By suitably altering the surface condition of a s t e e l specimen i t i s possible to reproduce the conflicting data which have appeared i n the l i t e r a t u r e . These conclusions were also demonstrated quite clearly by Streicher (66), who found i n his tests on the effect of water quality that the films formed under the different conditions gave the same result as that explained by Russell, Chappell and White (57). Types of Apparatus Used A rotor technique has been used by Wormwell (77), Larson (43) and several others (18, 19, 25, 29, 30, 41, 50, 56, 72, 73, 78).  By  t h i s method the specimens, usually of the coupon type, were suspended by rods i n an aqueous surrounding environment and rotated by means of a motor drive at various revolutions per minute (rpm).  Although  these types of tests are r e l a t i v e l y simple to perform, simple rotation of the specimens i s not i d e a l because the l i q u i d tends to move with the specimen and the actual rate of movement with respect to the metal surface i s not d e f i n i t e l y known.  Furthermore, the leading edge of the  specimens caused a turbulence as they passed through the water and thus destroyed the f l o w p a t t e r n .  Blum and Rawdon (5) used a f i x e d  specimen and a separate s t i r r e r .  Here again however, i t i s v e r y  d i f f i c u l t t o determine the a c t u a l v e l o c i t y o f the l i q u i d passed the specimen surface.  F r i e n d (32) and R u s s e l l et a l (57) located the  specimens i n glass tubes or beakers and water was allowed t o pass over the specimens.  The main objections t o these t e s t s were t h e  l a c k of close c o n t r o l over the r a t e o f motion and t h e concentration o f d i s s o l v e d gases i n the water.  Not only do the r e s u l t i n g motion and  mixing vary i n d i f f e r e n t experiments, and at d i f f e r e n t points i n the same experiment, but a l s o the magnitude o f these f a c t o r s i s never known w i t h any degree of accuracy.  I n the arrangement o f Passano and  Nagley (51) specimens were mounted along the a x i s of glass tubes w i t h the f r o n t end o f the specimen streamlined t o avoid turbulence.  One  specimen was located i n each o f a s e r i e s of glass tubes which were f e d from a header supplied from a constant l e v e l . A s i m i l a r apparatus t o Passano and Nagley (51) was t h a t o f Cohen (16) i n which a specimen was placed i n a h o r i z o n t a l g l a s s tube one end of which was connected t o a s t a t i o n a r y r e s e r v o i r .  The other  end was connected by a f l e x i b l e rubber tube t o a r e s e r v o i r which was r a i s e d or lowered t o cause the l i q u i d t o flow back and f o r t h over the specimen.  S i m i l a r disadvantages t o those stated above can be seen  to apply here. Rawdon and Waldron (54) b u i l t short lengths ( 5 i inches) o f pipes o f d i f f e r e n t s t e e l s i n t o a continuous pipe w i t h T-section rubber washers separating adjoining specimens, the whole being held together  12  'by external t i e rods. up to eight fps.  High rates of flow were easily obtained of  Kendall and Speller (62) used an apparatus which  consisted of coils of 200 feet i n length.  | and V4 inch diameter steel pipe up t o The coils were placed i n a steel drum, heated by  steam, and then water at a constant temperature and constant velocity was passed through the c o i l s . pipe cut into four inch lengths.  Laque (40) used two inch diameter steel The specimens, i n groups of ten,  were assembled into sections using bakelite impregnated fibre for insulating! couplings between specimens.  Thirty sections were prepared  and were set up on top of a sea water supply distributor i n f i v e rows of s i x sections each.  The water discharged from each row of s i x  columns was collected i n troughs, through which i t flowed to a main discharge trough into the sewer. The equipment was not designed, however, to adequately study the effects of velocity.  As Laque states, " I t i s the most convenient  arrangement for the study of galvanic behaviour of metals and alloys i n flowing l i q u i d s " . Eliassen et a l (24) used an apparatus with ^A- inch diameter mild steel specimens approximately f i v e inches long.  The specimens were  separated by acrylic washers and then they were clamped together by means of rubber hoses and hose clamps. l a i d horizontally. specimens.  Four such columns were constructed and  A pump was used to circulate the water through the  Some fresh water was fed into the system to prevent excessive  b u i l d up of corrosion products i n solution. Although the apparatus such as the rotor, fixed specimen with  mixer and tube i s easier to instal,the d i f f i c u l t i e s encountered i n knowing with any degree of accuracy the variables such as velocity and gas content of f l u i d mitigated against their use i n the present investigation.  Because of the desire to obtain accurate control and  good knowledge of a l l the variables i t was decided to b u i l d a system similar to those of Eliassen, Laque and Waldron.  Although the  approach i s empirical i t i s easily adapted to the investigation of theoretical aspects as noted by Laque ( 4 0 ) .  APPARATUS P r e l i m i n a r y Testing Apparatus The purpose of the p r e l i m i n a r y t e s t was t o see i f an adequate general t e s t set-up could be constructed along the l i n e s of the l a t t e r i n v e s t i g a t o r s (24, 40, 54) but with some m o d i f i c a t i o n s . Three, s i x inch p i e c e s , of one inch diameter mild s t e e l pipe were machined at both ends, weighed and assembled i n t o a s i n g l e pipe section.  P l a s t i c washers were used f o r separating purposes.  The  section was held together by means of three t i e - r o d s connected through two standard 5 inch f l o o r f l a n g e s .  The s e c t i o n was then connected  v e r t i c a l l y t o the r e g u l a r l a b o r a t o r y water supply l i n e w i t h a rotameter (.5 t o 8 gallons per minute) f o r f l o w measurement. sewer was connected t o the rotameter.  A l i n e t o the  The arrangement of the apparatus  i s shown i n Figure 2. Wires were soldered on t o the i n d i v i d u a l specimens before weighing so t h a t the p o t e n t i a l s w i t h respect t o a S i l v e r - S i l v e r Chloride Electrode (ACE) could be recorded.  The electrode was a  cube of s o l i d s i l v e r c h l o r i d e , t h a t had been subjected t o e l e c t r o l y t i c reduction i n hydrochloric a c i d s o l u t i o n t o provide an a c t i v e s i l v e r and s i l v e r c h l o r i d e surface.  These electrodes have been shown t o be  h i g h l y r e v e r s i b l e t o both hydrogen and c h l o r i d e ions (59).  The  electrode was i n s t a l l e d through a rubber stopper i n s e r t e d i n t o one end of a one i n c h standard  tee.  The wires from the specimens l e d t o a speedomax equipped w i t h a cathode f o l l o w e r t o enable the r e l a t i v e l y high readings obtained t o be recorded on the speedomax. shown i n Figure 3.  The c i r c u i t diagram of the f o l l o w e r i s  15  city water \ line  to s e w e r  specimen  rotameter  WW  to recorder  Figure 2  silver-silver chloride lead  P r e l i m i n a r y Apparatus.  Figure 3  Cathode Follower.  17  Main Test Apparatus On the basis of the results from the preliminary apparatus above i t was decided to build a much larger size test apparatus which would hold several sections each with eight to ten specimens of % inch diameter pipe, four inches long.  A circular design was planned  i n order to provide good access, simple design f o r a distributor to a number of test sections and minimum space.  The apparatus complete  with several test sections i s i l l u s t r a t e d i n Figure 4.  A flow of up  to eight gallons per minute was available so that turbulent as well as laminar flow i n \ inch pipe could be studied. A schematic representation of the pipe-line network i s shown i n Figure 26 .  Cold tap water entering from the building supply i s  piped through a \ inch diameter rubber hose to the head tank where i t was heated under controlled conditions to 130 — «8°F or 90 "±".5°F. The control l i m i t s were quite adequate for the present investigation (9, 20).  From the bath the water was fed by positive suction head t o  a centrifugal pump and then pumped to the lower distributor tank through two inch diameter polyethylene l i n e s .  The distributor tank fed the  water into ten % inch diameter l i n e s , each with a \ inch Saunders-type diaphragm valve^to a rotameter with a range of .5 to 4 gallons per minute (gpm), or .5 to 8 gpm equivalent to ,3 to 3 fp$ or .3 to 6 fps for \ inch pipe. test section.  The water under a positive head passed through the Connecting the top of the t e s t section to the top  distributor tank was an eight inch length of % inch diameter f l e x i b l e rubber pressure hose connected to the top distributor tank by a three inch kralastic ( a c r y l o n i t r i l e copolymer) nipple.  When a section was  19  not i n place a plug (two inch length of \ inch k r a l a s t i c pipe with one end sealed) was inserted i n the hose to stop water from flowing. From the top distributor tank the water flowed through a two inch diameter kralastic pipe to discharge just below the l e v e l of water (controlled bymeans of a f l o a t attached to the i n l e t l i n e ) i n the head tank. In t h i s l i n e provision was made for a quantity of water to be withdrawn to prevent the excessive buildup of the corrosion products i n the water. This flow was approximately 60 and 120 gallons per day for the 90 and 130°F temperatures respectively. A more detailed description of the apparatus follows.  FLOW APPARATUS Head Tank The head tank was an insulated (four inches of mineral wool) 45 gallon steel drum lined inside with heresite (baked phenolicformaldehyde coating).  Two openings were available one being l g  inches i n diameter and the other \ inch i n diameter.  The former was  used for the i n l e t l i n e to the pump while the l a t t e r opening was used for an emergency overflow l i n e ( 5 inch i n diameter) i n case the l e v e l controller stopped controlling.  The l i q u i d l e v e l controller was a  fibre-glass f l o a t attached to a f l o a t valve.  Because of the constant  overflow t h i s valve was always s l i g h t l y open and controlled the l e v e l of the water adequately. Heating was accomplished with a 1000 and a 2000 watt stainless steel immersion type e l e c t r i c heating rods. The temperature was controlled on anqn-off basis through the 1000 watt heater by an Aminco  mercury-switch- mechanical r e l a y , operating through an aminco mercury thermoregulator.  At  90°F  the  1000 watt  c o n t r o l the temperature but a t 130°F the  heater was s u f f i c i e n t t o  2000 watt  heater was l e f t  on a l l the time and the temperature was again c o n t r o l l e d by the 1000 watt heater.  Adequate mixing was provided by the r a t e of c i r c u l a t i o n  of the water. Pump The pump was a Paramount Type B side s u c t i o n c e n t r i f u g a l pump, w i t h a s i n g l e b a l l bearing.  Attached t o a one horse-power motor  and a t 1750 r e v o l u t i o n s per minute the pump could d e l i v e r 60 gpm against a 35 foot head according t o the manufacturer's (Pump and Power Ltd.) s p e c i f i c a t i o n s . The pump was machined t o a l l o w f o r a coating of h e r e s i t e t o be a p p l i e d . D i s t r i b u t o r Tanks Two c y l i n d r i c a l d i s t r i b u t o r tanks, 23 inches i n t e r n a l diameter and 9 inches deep, were designed t o hold the t e n separate l i n e s of the t e s t s e c t i o n s .  The tanks were of welded construction and made  from standard £ inch m i l d s t e e l b o i l e r p l a t e .  The top p l a t e s ,  attached by bolted flanges t o the main tank body, were 27 inches i n diameter and £ inch t h i c k .  Twenty £ i n c h b o l t holes were equispaced  on a 2kk inch b o l t c i r c l e .  Also on the p l a t e s t e n % inch holes f o r  the t e s t sections were d r i l l e d equispaced on a c i r c l e of 20 inches. Over these holes were welded % inch m i l d s t e e l couplings.  At the  center of the head an \ inch hole was d r i l l e d , w i t h an \ inch coupling welded over i t , t o a l l o w the i n s e r t i o n of the ACE w i t h which p o t e n t i a l s were t o be taken.  I t a l s o allowed a thermometer  to be i n s t a l l e d .  At the centre of the bottom of the tanks was a l g  inch hole with a I5 inch coupling welded externally to provide for the circulation of the water through the system. The inside of the distributor tanks including flange areas was; coated with  inch neoprene rubber l i n i n g .  Any bare metal  surface i n the couplings was painted with several coats of l i q u i d neoprene. Control Valves The control valves were % inch flanged cast steel Saunderstype diaphragm valve with  natural rubber diaphragms.  The bodies of  the valves were coated with heresite. Lines and F i t t i n g s Connecting l i n e s were a l l Carlon type EF (polyethylene) and kralastic of sizes described above, and connecting f i t t i n g s were either carlon or k r a l a s t i c .  F i t t i n g s were a l l sleeve type with external steel  collars. Test Sections The test sections were composed of from eight to ten % inch diameter mild steel pipe specimens four inches long. specimens were machined smooth.  The test specimens were separated i n  the test section by l u c i t e washers. diameter and ^/B of an inch thick.  The ends of the  The washers were 1^/8 inches i n Grooves on both sides were  machined i n the middle washers, ^"/32 of an inch deep, to a diameter just equal to the outside diameter of the specimens. the ends were grooved on one side only. against a standard floor flange.  The washers at  The other side was placed  The specimens f i t t e d into these  grooves aneU-were held together by compressing the assemblage between two "V4  inch standard f l o o r flanges by means of three £ inch diameter  s t e e l rods. MEASURING APPARATUS Thermometers A mercury i n glass l a b o r a t o r y thermometer reading from - 10°C  t o 110°C  was used.  I t was i n s t a l l e d i n the centre opening of  the top of the bottom d i s t r i b u t o r tank.  This allowed the temperature  reading of the water j u s t before i t entered the t e s t s e c t i o n s .  The  thermometer was checked with a c a l i b r a t e d thermometer and was found t o be w i t h i n -.2°C  of the c a l i b r a t e d thermometer between 0°C and 100°C.  Potentiometers and electrode The reference electrode used was the s i l v e r - s i l v e r c h l o r i d e electrode (ACE) p r e v i o u s l y described.  The ACE was i n s t a l l e d through  a 5 inch k r a l a s t i c cap i n t o the 5 inch coupling i n the centre of the top d i s t r i b u t o r tank.  From here a lead wire was connected t o one  side of a Leeds and Northrup type G Speedomax equipped w i t h a cathode follower.  This f o l l o w e r ivas mentioned p r e v i o u s l y i n p r e l i m i n a r y  apparatus.  I t enabled recordings of the r e l a t i v e l y high p o t e n t i a l  from the system.  The speedomax was c a l i b r a t e d w i t h a Leeds and  Northrup type K potentiometer using a General E l e c t r i c type G-3 galvanometer and a standard c e l l w i t h an N.B.C. c e r t i f i c a t e , f o r measurements t o - .1  mv.  Rotameters Two types of rotameters were used. flo\raieter model number 2001-v with a range of  One was a Brooks-Mite  .4  to  4  gallons of water  per minute.  This type of rotameter has a tapered metering tube  machined d i r e c t l y i n t o a c l e a r a c r y l i c p l a s t i c block. s t a i n l e s s s t e e l type 316.  The f l o a t was  Five of these were used.  The second type used was a Brooks rotameter (Flow-View type number 1110)  f o r flows between .5 and 8 gallons of water per minute.  This type has a p r e c i s i o n bore pyrex metering tube, w i t h a mild s t e e l float.  Two of these rotameters were used.  A u x i l i a r y Flow System Measurements At the s t a r t of the study two pressure gauges (0-100 p s i g ) were i n s t a l l e d , one i n each d i s t r i b u t o r tank through a  inch  coupling, t o help determine the pressure drop between the two tanks. Balance and Weights A l l weighing measurements were made on a L o e r t l i n g balance w i t h a load l i m i t of three pounds. l i m i t was 1.6  The s e n s i t i v i t y w i t h no load  s c a l e d i v i s i o n s per m i l l i g r a m .  Nivoc weights i n  e x c e l l e n t c o n d i t i o n were used t o weigh the specimens t o a p r e c i s i o n of -.0003 gram. No c a l i b r a t i o n nor buoyancy c o r r e c t i o n s were a p p l i e d . Microscope To a i d w i t h the examinations of the c o r r o s i o n products and the specimens themselves a R e i c h e r t Stereoscopic microscope was used w i t h v a r y i n g powers of magnification of 10, 40 and  100.  S pectrophot omet er For use i n the a n a l y s i s f o r the i r o n i o n concentration of the t e s t water and t a p water, a Beckman model DU, quartz spectrophotometer was used.  The wave length was 5100 A* and a blue f i l t e r w i t h a  hydrogen lamp was employed.  24  MATERIALS Water The corroding medium was Vancouver tap water taken from the c o l d water supply t o the U n i v e r s i t y . This i s obtained from the Greater Vancouver Water Board's Capilano R i v e r watershed, whose c h i e f r e s e r v o i r i s above Cleveland Dam.  An average a n a l y s i s f o r the water f o r 1958,  as supplied by the Greater Vancouver Water Board's laboratory, i s shown i n Table 1. Test Pipe The pipe specimens used f o r a l l t e s t s were standard hot r o l l e d , welded, schedule 40, f i n c h m i l d s t e e l pipe.  The specimens  were a l l cut t o f o u r inches i n l e n g t h . Two l o t s of pipe were obtained.  Type A was a r e g u l a r  commercial v a r i e t y obtained i n 20 f o o t lengths through r e g u l a r purchasing channels and had been i n the U n i v e r s i t y stores f o r a considerable p e r i o d of time.  No corrosion s c a l e was evident, however, and the i n s i d e  surface was f a i r l y smooth except f o r a q u i t e prominent seam. Type B was a high q u a l i t y product manufactured by Western Canadian Pipe M i l l s and obtained d i r e c t l y from them w i t h i n a few days of i t s fabrication.  Lengths as obtained v a r i e d from 10 t o 20 f e e t .  The  i n s i d e surface was smoother than type A, and the seam was n o t i c e a b l y much l e s s protruding and much more uniform.  The mechanical and chemical  d e t a i l s supplied f o r i t are given i n Table I I . Chemicals f o r A n a l y s i s Oxygen Determination Manganese Sulphate CP  25  Potassium Iodide CP Sodium Thiosulphate CP Concentrated Sulphuric Acid CP Starch Technical Grade Iron Determinations a a Dipyridyl CP Concentrated Acetic Acid CP Sodium Bisulphite Technical Grade Iron Solution containing 200 milligrams of Iron per l i t r e  TABLE I Greater Vancouver Water D i s t r i c t Physical and Chemical Analysis of Water Supply Average f o r 1958 Appearance  Clear  Odor  None  Highest Water Temperature  57°F  Lowest Water Temperature  37°F  Turbidity ppm S i l i c a scale  Less than 5  pH  6.6 t o 7»1  Total Solids ppm  20.7  Total Volatile Solids  8.2  Total Fixed Solids  12.5  Phenolphthalein A l k a l i n i t y as CaCO^ ppm  Nil  Total A l k a l i n i t y as CaCC\j ppm  10.3  Total Hardness as CaCO^ ppm Chloride as C l ppm  4.8 .5  Fluoride as F ppm  Less than ,.  Calcium as Ca ppm  1.7  Copper as Cu ppm  .14  Iron as Fe ppm  .16  Ammonia Nitrogen as N ppm  Less than •<  N i t r i t e Nitrogen as N ppm  Nil  Nitrate Nitrogen as N ppm Oxygen Concentration % of Saturation  .05 92.1  TABLE I I Chemical A n a l y s i s and P h y s i c a l P r o p e r t i e s of Type B Pipe (ASTM S p e c i f i c a t i o n SAE 1012)  Chemical A n a l y s i s  C  .13  Mn  .47  S  .033  P  .005  Physical Properties M i l d s t e e l s t r i p before welding, two t e s t s Ultimate p s i  55,300  60,100  Yield psi  44,700  39,700  35.9  37.5  Elongation %  M i l d s t e e l pipe as welded, high and low of four t e s t s High  Low  Ultimate p s i  65,700  59,000  Yield psi  64,500  58,500  35.1  32.8  Elongation %  PROCEDURE Preliminary Tests Measurement of the potentials was started with the beginning of the water flow and the potentials were recorded frequently during the f i r s t eight hours and thereafter once a day.  The water velocity  was changed quite rapidly while a reading was being recorded to note any shift i n potential due t o the water velocity.  No change could be  noted and i t would seem that the potential was independent of the water v e l o c i t y .  The specimens were removed after a time interval of  nine days. Main Tests Iron Analysis Iron i n the water was determined according t o the a a dipyridyl method supplied i n ( l ) .  In t h i s procedure any iron  dissolved i n the water i s reduced to the ferrous state by sodium bisulphite and then treated with a a dipyridyl.  The coloured  solution thus derived obeys Beers Law between a pH of three t o nine, and i t s optical transmission can be obtained by the use of a spectrophotometer.  Figure 24 presents the calibration of the  spectrophotometer using a known concentration of iron solutions. The standard iron solution was made by dissolving 2 grams of iron #  wire i n 30 m i l l i l i t e r s of concentrated sulphuric acid and then d i l u t i n g t o one l i t e r with d i s t i l l e d water. Daily samples for iron analysis of 50 m i l l i l i t e r s of water were obtained, after flushing for one minuts, through a valve i n  the lower d i s t r i b u t o r tank.  As reported by Moss and M e l l i o n (48)  the measurement of i r o n concentration i n the range found i n t h i s study by t h i s method i s s a t i s f a c t o r y w i t h an approximate d e v i a t i o n of two per cent. Oxygen A n a l y s i s In analysing the oxygen content of the water the Winkler method (76)  was employed.  I n t h i s method the determination of  d i s s o l v e d oxygen depends upon the formation of a p r e c i p i t a t e of manganous hydroxide i n a glass-stoppered b o t t l e completely f i l l e d w i t h the water under examination.  The oxygen d i s s o l v e d i n the water i s  r a p i d l y absorbed by the manganous hydroxide, forming a mixture of higher oxides which on a c i d i f i c a t i o n i n the presence of an i o d i d e releases iodine i n a q u a n t i t y chemically equivalent t o the oxygen content of the sample.  The l i b e r a t e d i o d i n e i s then t i t r a t e d w i t h a  standard s o l u t i o n of sodium thiosulphate using starch as an i n d i c a t o r . A water sample was obtained from the overflow l i n e d a i l y and then analysed f o r oxygen content.  The r e s u l t s were then compared t o  the s o l u b i l i t y of oxygen i n water as a f u n c t i o n of temperature presented i n Figure 25 (69).  as  The determination of oxygen by t h i s  method i s quite s a t i s f a c t o r y f o r such water as t h a t used i n t h i s study as stated by Young (80). I n s t a l l a t i o n of the Test Sections The t e s t s e c t i o n s composed of e i g h t t o t e n , f o u r i n c h long pipe specimens w i t h machined ends were numbered using metal punches. They were cleaned w i t h a s o f t h a i r e d b r i s t l e brush i n carbon  t e t r a c h l o r i d e and then i n acetone*  This was a l l the treatment  apparently required t o remove any grease or small areas of m i l l  scale.  Some specimens, not t o be used i n the experimental runs, were cleaned i n the above manner t o determine i f any appreciable weight l o s s r e s u l t e d from t h i s cleaning operation.  However, the  weight l o s s i n each instance was i n s i g n i f i c a n t ( l e s s than .002  grams)  and was t h e r e f o r e disregarded i n the weighing of the specimens used i n t h i s study. A f t e r weighing, the specimens were mounted on an aluminum rod; w i t h an outside diameter almost equal t o the i n s i d e diameter of the specimens.  A c r y l i c washers (described i n the apparatus s e c t i o n )  were l o c a t e d between the specimens t o prevent any d i r e c t contact.  The  t e s t sections were compressed together between two f l o o r flanges by means of the three t i e rods as described p r e v i o u s l y . of a completed t e s t s e c t i o n i s shown i n Figure 5-  An i l l u s t r a t i o n A f t e r assembling  the t e s t s e c t i o n , the i n s i d e rod was rotated s e v e r a l times t o smooth the i n s i d e of the pipe specimens and the washers.  The rod was then  removed and the i n s i d e surface examined v i s u a l l y .  I f discontinuities  were i n evidence the rod was again i n s e r t e d , the t i e rods slackened, and revolved again.  This procedure was repeated u n t i l the i n s i d e  surface was smooth and uniform and no d i s c o n t i n u i t i e s were i n evidence to the naked eye. To i n s t a l l the t e s t s e c t i o n i n t o the equipment, the top hose connection from the top d i s t r i b u t o r head was pinched t i g h t w i t h a hose clamp and the plug removed.  The t e s t s e c t i o n was then i n s e r t e d i n t o  the hose approximately one inch of i t s l e n g t h .  On the bottom end of  Figure 5  D e t a i l of Test Section Assembly  32  the t e s t s e c t i o n a rotameter was p o s i t i o n e d and t h a t i n t u r n was secured t o the valve by the use of f l a n g e s .  The whole s e c t i o n was  adjusted t o a t r u e v e r t i c a l p o s i t i o n w i t h i n f i v e degrees.  The t o p  hose clamp was then removed and the valve opened t o t h e desired f l o w . P r i o r t o the weighing and i n s t a l l a t i o n of the specimens, wires approximately three inches i n length were soldered t o the sides of the specimens ( s e l e c t e d t o cover a l l the possible p o s i t i o n s from one t o t e n at l e a s t once i n a l l the t e s t sections used i n t h i s i n v e s t i g a t i o n ) whose p o t e n t i a l s were t o be determined. coated w i t h l i q u i d neoprene. wires l e a d i n g t o the speedomax.  The connection was then  Figure 6 shows the connections and the The p o t e n t i a l of the t e s t specimens  was taken immediately a f t e r the water f l o w was s t a r t e d and then was recorded d a i l y f o r approximately one minute u n t i l the end of the r u n . The water flows used i n the experiment were .75, 1.5, 3.0 and 4.5 f e e t per second. The water i n the system was renewed once a day a t 90°F and twice a day a t 130°F by means of an overflow l i n e i n the exhaust side o f the pump.  The overflow was c o n t r o l l e d by a pinched clamp on the l i n e  and the r a t e was checked each day when the water f o r the oxygen sample was c o l l e c t e d . At the conclusion of the t e s t time selected (5, 10, 15 or 25 days) the s e c t i o n was removed from the system and v i s u a l and microscopic examinations made i n l o n g i t u d i n a l cross sections of specimens selected at random.  This permitted an e x c e l l e n t i n s p e c t i o n of the c o r r o s i o n  products on the i n s i d e of the specimens. The remaining specimens o f the t e s t s e c t i o n were cleaned by means  33  of brushing under a stream of water.  A f t e r the corrosion products  had been removed the specimens were d r i e d with acetone and b u i l d i n g a i r supply.  They were then weighed immediately.  P o t e n t i a l Check on Electrode To compare the reading from the ACE used i n t h i s study w i t h a saturated calomel e l e c t r o d e , a mild s t e e l coupon was i n s e r t e d i n t o a glass c e l l (23) f i l l e d w i t h Vancouver c i t y water. of the coupon was then recorded with both e l e c t r o d e s .  The p o t e n t i a l From t h i s  study i t was found that the ACE gave a p o t e n t i a l of .020 v o l t s l e s s than the saturated calomel e l e c t r o d e .  RESULTS P r e l i m i n a r y Run V i s u a l examination  showed the i n s i d e s of the specimens t o be  r e l a t i v e l y clean w i t h l i t t l e c o r r o s i o n products on the i n s i d e s u r f a c e . The colour of the c o r r o s i o n products which d i d adhere t o the w a l l was rust-red. The r e s u l t s of the determination of the amount of corrosion f o r the p r e l i m i n a r y run are presented i n Table I I I based on the amount of corrosion as measured i n m i l l i g r a m s per square decimetre The data i s shown i n Table XXII.  (md).  In Figure 23 the r e s u l t s f o r the  p r e l i m i n a r y run i s included i n the r e s u l t s f o r the main t e s t run as md p l o t t e d against temperature i n degrees Fahrenheit. The p o t e n t i a l s obtained, at the end of the t e s t time, r e l a t i v e t o the ACE are presented i n Table IV. i n p o t e n t i a l w i t h time.  Table X X I I I shows the change  In Figure 10 the data are p l o t t e d as p o t e n t i a l  ( i n v o l t s r e l a t i v e t o the ACE) against time i n days. Main Test  Run  The v i s u a l and microscopic inspections of the c o r r o s i o n products r e v e a l that the products consisted of a porous rust-coloured p r e c i p i t a t e underlaid by a f i n e , dense, granular black f i l m .  The products adhered  to the surface of the specimens more s t r o n g l y at the higher temperatures and contained a greater amount of the black f i l m .  The c o r r o s i o n  products covered the e n t i r e area of the specimens t o a thickness of approximately /32 1  of an inch at low v e l o c i t i e s .  At the higher  v e l o c i t i e s the l a y e r of corrosion products was decreased s l i g h t l y i n thickness.  The surface of the products was i n the form of waves.  At the low v e l o c i t i e s the peaks were l a r g e and sharp whereas at the higher v e l o c i t i e s the peaks were smoothed over.  The contours formed  at the d i f f e r e n t v e l o c i t i e s are shown i n Figure 7> a, b, c, d, e and f . The r e s u l t s of the determination of the amount of corrosion during a l l phases of the i n v e s t i g a t i o n are presented i n Tables V t o XIV based on the amount of c o r r o s i o n as measured i n milligrams per square decimetre (md) along w i t h the average standard d e v i a t i o n s from the mean f o r the i n d i v i d u a l specimen i n any p a r t i c u l a r t e s t The data are presented i n Tables XXIV t o XXXIII.  section.  In Figures 8 and 9  the r e s u l t s are shown as md p l o t t e d against time i n days. By s e l e c t i o n of parameters the e f f e c t s of temperature and v e l o c i t y can be i l l u s t r a t e d .  I n F i g u r e 19 i s shown the e f f e c t s of  v e l o c i t y on a p l o t of amount of c o r r o s i o n (md) versus v e l o c i t y ( f p s ) w i t h temperature as a parameter.  In F i g u r e 23 the e f f e c t of  temperature i s i n d i c a t e d by graphing the amount of corrosion  (md)  against temperature (°F) w i t h v e l o c i t y ( f p s ) as parameter. The p o t e n t i a l s obtained, r e l a t i v e t o the ACE, at the end of the specimens t e s t time are presented i n Table XVI.  Tables XXXIV  t o XLI show the change i n p o t e n t i a l of the corroding specimen w i t h time.  These data are p l o t t e d as p o t e n t i a l ( i n v o l t s r e l a t i v e t o the  ACE) against time i n days i n F i g u r e s 10 t o 18. In a l l of the above figures and t a b l e s , specimens numbered from 1 t o 74 are type A pipe and those numbered from 75 t o 216 are type B pipe.  PRELIMINARY RUN TABLE I I I V e l o c i t y 4,5 fps Temperature 48 °F.  Results of Weight Loss Tests; Test Run # 1-A Sample #  Velocity fps  1 2  4.5  3 Totalaverage  Time 9 Days.  Weight loss grams  md  Deviation r  r  .3052  237  12  144  .4288  333  84  7056^  .2269  178  71  5041  .9609 .3203  748 249  Standard deviation  78  12241  TABLE IV P o t e n t i a l s at the end of the Test. Sample #  Velocity fps  1 2 3  Potential v o l t s vs Ag Ag C l  -.1980 4.5  -.2600 -.3000  MAIN TEST RESULTS TABLE V Results o f Weight Loss Tests j V e l o c i t y 4.5 fgs and 3.0 fps Temperature 90 F. Test Run #1 Time 15 days Specimen # V e l o c i t y fps  Weight loss grams  md  Deviation r  r  11  .8144 1220  65  4225  12  .9112 1360  75  5625  13  .7879 1180  105  11025  14  .8918 1335  50  2500  1.0360 1550  265  70225  16  .7839 1172  113  12769  17  .7781 1165  120  I44OO  18  .8694 1300  15  225  15  4.5  Total  6.8727 10282  Average  .8591 1285  120994  Test Run #2 Time 15 days 2  1.0999  3  2209  I.O723 1608  47 10  4  1.1822 1735  137  18769  5  .9650 1440  158  24964  47  2209  7  1.1014 1645 1.2154 1820  222  49284  8  1.0249  1534  4096  9  1.0221  1530  64 68  4624  .9522 1430  168  28224  6  3.0  10 Total Average  1645  9.6354 14387 1.0706  1598  100  134479  Standard Deviation  131  39  TABLE VI Results of Weight Loss Tests; Velocity .75 fps Temperature 90°F. Test Run #3 Time 15 days Specimen #  Felocity fps  2  Weight loss grams  md  Deviation r  r  19  1.0688  1600  330  108900  20  1.1340  1700  230  52900  21  1.2845 1.3062  1920  10  100  1951  21  441  23  1.4984  2240  310  96100  24  1.3104  I960  30  900  25  1.5645  2350  420  176400  26  1.1564  1720  210  44100  Total  10.3232  15492  Average  1.2904  1930  22  .75  479841  Test Run #4 Time 15 days 27  .4557  689  145  21025  28  .3509  525  95481  29  .6948  1040  309 206  30  .7135  1068  54756  .6392  956  234 122  14884  .4989  746  88  7744  33  .4826  722  112  12544  34  .6191  926  4.4547 .5568  6672  31 32  .75  Total Average  834  92  42436  8464 257330  -Standjard Deviation  262  40 TABLE VII Results of Weight Loss Tests;  Velocity .75 fps and 1,5 fps Temperature 90°F.  Test Run #5 Time 15 days Specimen #  Velocity fps  Weight loss grams  md  Deviation r  2  r  .6595 .4426  987  20  400  662  .6389  956  .7905 .8066  1183  305 11 216  93025 121 46656  1207  240  57600  40  .4582  282  79524  41  .4264  685 638  108241  42  .8347 .8920  329 282 368  135424  35 36  37 38 39  1.5  43 Total Average  5.9494 .6610  1249 1335 8702  79524 600515  967  Test Run #6 Time 5 days •93 94 95 96  .75  .0353 .0343 .0323 .0310 .0390  97 98  .0273 .0352 .0420  99 100 Total Average  .2769 .0346  264 256  7 15  241 232 292  30  204  67 96  367 314 2170 271  39 21  43  49 225 900 1521 441 4489 9216 1849 18690  Standard Deviation  274  41  TABLE VIII Results of Weight Loss Tests;  Velocity .75 fps and 1.5 fps Temperature 90 F. G  Test Run #7 Time 25 days 2  Weight loss grams  md  161  2.2092  3300  25  625  162  1.9300  2881  444  197136  163  2.4700  3704  379  143641  164  2.3394  3502  177  31329  2.3078  3454  129  16641  167  2.2446  3360  35  1225  168  2.1371  3193  132  17424  169  2.2235  3328  3  9  170  2.3409  3504  179  32041  20.2065  29926  2.2452  3325  Specimen #  166  Velocity fps  .75  Total Average  Deviation r  r  440061  Test Run #8 Time 25 days 171 172  2.4506  3668  35  1125  2.4843  3718  173  2.4195  3622  85 11  7225 121  174  2.4765  74  5476  175 176  2.4025  3707 3596  37  1369  2.4019  3596  1369  2.3789  3561  37 72  2.2504  3369  264  55884 69696  2.4575  3679  46  2116  3815  182  Total  2.5487 24.2708  36331  33124 126905  Average  2.4271  3633  1.5  177 178 179 180  Standard Deviation  235  42  TABLE IX Results of Weight Loss Tests;  V e l o c i t y 3*0 fps and 4.5 fps Temperature 90°F.  Test Run #9 Time 25 days icimen #  md  181  2.0968  3138  22  484  183  2.1406  3150  10  100  184  2.0281  3036  164  26896  185  2.2592  3382  222  49284  2.1179  3170  10  100  187  2.0908  3129  31  961  188  2.0834  3113  42  1764  189  2.0615  3086  74  5476  190  2.1619  3235  75  5625  Total  19.0042  28444  Average  2.1116  3160  3.0  Deviation r  2  Weight loss grams  186  Velocity fps  r  90690  Test Run #10 Time 25 days 191  1.9860  2974  3  9  192  2.0308  3040  69  4761  193  1.7793  2663  308  94864  2.1488  3216  245  60025  196  1.9518  2921  50  2500  197  2.1220  3176  205  42025  198  1.8736  2804  167  27889  13.8923  20794  1.9846  2971  195  4.5  Total Average  232073  Standard Deviation  106  43 TABLE X Results of Weight Loss Tests] Velocity 1.5 fps Temperature 90°F. Test Run #11 Time 5 days 2  Weight loss grams  md  .0841  126  78  6084  .2387 .1088  357 162  153 42  23409  .1046  156 350  205  .2333 .0898  48 146  134  ,70  2304 21316 4900  206  .0831  80  6400  207  .1535  124 230  26  676  Specimen #  Velocity fps  199 201 202 203  1.5'  204  Total Average  1.0963 .1370  Deviation r  r  1764  66851  1639 204  Test Run #12 Time 15 days 208  1.4297 1.3012  209 210  1.2764  211 212  1.5  1.3657 1.3290  213  1.4137  214  1.4499 1.5158  215 216  1.4887 Total  12.5701  Average  1.3967  2140  50  2500  1946 1910  144 180  20736 32400  2044  46 101  2116 10201  26  676  2170  80  6400  2269 2228  179 138  32041  1989 2116  18812 2090  Standard Deviation  19044 127114  97  TABLE X I Results o f Weight Loss Tests;  V e l o c i t y 3.0 f p s and 1.5 f p s Temperature 130°F.  Test Run #13 Time 15 days •ecimen #  Velocity fps  137 138 139 140  3.0  md  3.2687  4891  16  256  3.2695  4897  22  3.2991 3.4090  4941  66  484 4356  5104 4803  229 72  52441  4612  263  69169 131890  142  3.2104  143 Total  3.0833 19.5900  29248  Average  3.2566  4875  Deviation r  2  Weight loss grams  r  5184  Test Run #14 Time 25 days  101  3.3616  5038  66  4356  102  3.3686  62  3844  103  3.1172  5042 4666  438  191844  104  3.2130  4809  87025  3.5463  5309  3.5541  5320  295 205 216  46656  3.2574  4876  228  51984  3.6487 3.6160  5462  358  128164  5413  309  95481  Total  30.6819  45935  Average  3.4091  5104  105  1.5  107 108 109  *  110  42025  651379  Standard Deviation  162  TABLE X I I Results o f Weight Loss Testsj  V e l o c i t y 4.5 f p s and 3.0 fps Temperature 130°F.  Test Run #15 Time 25 days md  112  2.8952  4332  74  5476  113  3.0603  4586  180  32400  2.9476  4415  9  81  116  3.0255 .  4534  128  16384  117  2.9378  4393  13  169  118  2.7980  4181  225  50625  Total  17.6644  26439  Average  2.9441  4406  114  Velocity fps  4.5  Deviation r  2  Weight loss grams  Specimen #  r  Standard Deviation  148  105135  Test Run #16 Time 25 days 119  3.1356  4694  272  73984  120  3.2702  4895  71  5041  121  3.1676  47a  225  50625  122  3.3770  5055  89  7921  3.3683  5042  76  5776  125  3.4750  5202  236  55696  126  3.4380  5146  180  32400  12?  3.2582  4877  89  7921  128  3.3722  5048  82  6724  Total  29.8621  44700  Average  3.3180  4966  123  3.0  246088  175  46  TABLE XIII Results of Weight Loss Tests;  V e l o c i t y .75 f p s and 1.5 fps Temperature 130°F.  Test Run #17 Time 15 days md  64  3.3947  5081  5  65 66  3.2212  4822  264  25 69696  3.5613  5331  245  60025  3.5556  5323 5162  237  56169  76  5776  4945 5080  141 6  19881  4955  131  17161  67  Velocity fps  .75  69  3.4482  70  3.3032  71 72  3.3935 3.3102 Total Average  27.1879 3.3985  Deviation r  2  Weight loss grams  Specimen #  r  Standard Deviation  181  36 228769  40699 5086  Test Run #18 Time 10 days  3.2465 2.9356  4860  362  131044  4394  104  10816  4849  351 453  123201 205209  131  3.2393 3.3076 2.9536  77  5929  132  2.9601  4431  67  4489  134  2.5617 2.8318  3835  663  4239  259  439569 67081  Total  23.9062  35980  Average  2.9895  4498  73 74 129 130  1.5  135  4951 4421  987318  376  47  TABLE XIV Results of Weight Loss Testsj  Velocity ,75 fps and 4.5 fps Temperature 130°F.  Test Run #19 Time 10 days scirnen #  2  Weight loss grams  md  Deviation r  r  145  2.3927  3432  299  89401  146  2,6024  3895  164  26896  147  2.5354 2.3600  3795  64  4096  3532  199  39601  38  1444  79  6241  154  23716  149  Velocity fps  .75  150  2.5177  151  2.5465  3769 3810  152  2.5955  3885  17.5502  26118  2.5072  3731  Total Average  191395  Test Run #20 Time 10 days 153  1.7013  2546  143  20449  154  1.8988  2842  153  23409  155  1.7852  2672  17  289  1.6840  2520  169  28561  158  1.8405  2755  66  4356  159  1.7778  2661  28  784  160  1.8897  2828  137  18769  12.5773  18824  1.7969  2689  157  4.5  Total Average  96617  Standard Deviation  178  48  V a r i a t i o n o f Water during Tests The maximum, minimum and median o f pH, oxygen concentration and i r o n concentration f o r the c i t y water and the system water are shown i n Table XV.  TABLE XV Maximum, minimum and median f o r pH, oxygen and i r o n concentrations f o r d u r a t i o n of t e s t s . Temp. °F city  system  water  water  Oxygen Concn. ppm city system water  90°  water >  130°  max.  42  12.0 7.2  min.  39  10.8 6.8  5.1 4.2  median  41  11.2 7.1  5.0  90±.5 130i.75  PH city  system  water  water  7.1  7.2  6.7 6.9  6.7 6.9  I r o n Concn. ppm c i t y system water  water  .52  .97 .10  .08  .28  .30  TABLE XVI P o t e n t i a l s o f Specimens at the End o f t h e i r Test Times;  Temperature  90°F and 130°F. P o t e n t i a l s at 90°F.  Velocity fps Specimen #  .75  20  .7700  24  .7420  26  .7300  162  .4400  167  .4500  1.5  173  .3900  179  .3720  3.0  1  .6000  5  .5900  184  .2100  190  .2600  4.5  4  .7150  7  .6750  195  .4000  196  .3850 P o t e n t i a l s at 130°F.  67  .6250  70  .6700  105  .7600  109  .6950  121  .3840  126  .4000  140  .6300  113  .5750  157  .5480  159  .5320  -40  b o >  < rZ LU H O CL  Specimens O 20 • 24 3 26 e 162 € 167  -90 -I 0 0  0  2  4  6  8  10  12 TIME  Figure 11  Potential-Time Curves.  14  16  18  20  22  24  26  28  DAYS  V e l o c i t y .75 f p s Temperature 90°F.  H  '.V  TIME Figure 12  Potential-Time Curves.  DAYS  V e l o c i t y 1.5 f p s Temperature 90°F.  Specimens O I • 5 © 184 f ) 190 0  2  8  10  12  14  TIME Figure 13  Potential-Time Curves.  16  18  20  DAYS  V e l o c i t y 3 0 f p s Temperature 90°F. e  22  24  26  28  I  0  2  I  1  4  i  6  1  8  i  10  I  12 TIME  Figure 14  Potential-Time Curves.  I  14  I  16  I  18  I  20  I  22  J  24  1  26  1  28  DAYS  V e l o c i t y 4»5 f p s Temperature 90°F.  -P-  Figure 15  Potential-Time Curves.  V e l o c i t y .75 f p s Temperature 13QO . F  TIME DAYS Figure 16  Potential-Time Curves.  V e l o c i t y 1.5 f p s Temperature 130°F. ON  10  12  T4  16  TIME DAYS Figure 17  Potential-Tijne Curves.  V e l o c i t y 3.0 f p s Temperature 130°F.  24  26  28  TIME Figure 18  Potential-Time Curves.  DAYS  V e l o c i t y 4.5 f p s Temperature 130'°^ 0>  DISCUSSION OF RESULTS P r e l i m i n a r y Run The range i n weight l o s s of the three specimens was almost two-fold*  This was p a r t l y ascribed t o the considerable c o r r o s i o n  t a k i n g place on the outside of the specimens due t o moisture condensation (water temperature 45°P and room temperature approximately 72°F).  The weight l o s s e s while thus i n considerable e r r o r , d i d show  t h a t a small weight l o s s could be detected i n s p i t e of the heavy specimen, and f a i r r e p r o d u c i b i l i t y expected.  On t h e b a s i s of these  r e s u l t s i t was decided that the specimens t o be used i n the main t e s t i n g would be made 2/3 t h i s length. The p o t e n t i a l , measured against t h e AGE, moved toward a more p o s i t i v e (cathodic) value (from an average of -.5 t o -.25 v o l t s ) as noted i n Figure 10.  T h i s trend corresponds t o a s i m i l a r one found by  Procupiu (53) and Georghiu (34).  This r e s u l t i s more than l i k e l y due  to the a c c e l e r a t i n g supply of oxygen t o t h e i n t e r f a c e , r e s u l t i n g from the  r e l a t i v e movement between the specimen and the water.  The  increased supply of oxygen causes cathodic area d e p o l a r i z a t i o n along w i t h anodic p o l a r i z a t i o n , both of which r e s u l t i n a more p o s i t i v e (cathodic) p o t e n t i a l . The p o t e n t i a l s of the i n d i v i d u a l t e s t pieces increased n e g a t i v e l y from the t o p t o the bottom specimen of the t e s t s e c t i o n . This d i f f e r e n c e could be due t o the l a c k of a f u l l water supply i n the top t e s t piece as the water flowed from the t o p t o the bottom and i t was not t h r o t t l e d s u f f i c i e n t l y t o ensure keeping the pipe f u l l .  With t h i s  l a c k of water the t o p section more than l i k e l y received a greater supply  of. oxygen thus i n c r e a s i n g the reduction process a t the cathodes and reducing cathodic p o l a r i z a t i o n . The p o t e n t i a l s found here w i t h c i r c u l a t i n g water were p o s i t i v e (cathodic) compared t o the p o t e n t i a l s p r e v i o u s l y determined (23)  i n s t a t i c water.  results.  Table XVII i l l u s t r a t e s t h i s w i t h s e l e c t e d  This can be explained i n t h i s manner.  The e f f e c t of  r e l a t i v e motion between the e l e c t r o l y t e and the electrode areas i n the t e s t piece was t o increase the r a t e of t r a n s f e r of reactants and products g i v i n g r i s e t o e i t h e r : (1)  anodic area d e p o l a r i z a t i o n  (2)  anodic area p o l a r i z a t i o n  (3)  cathodic area d e p o l a r i z a t i o n  The d i r e c t i o n of the electrode change produced by the movement depends on the r e l a t i v e magnitude of 1,  2 or 3,  thus,  predominance of 1 gives a more negative (anodic) p o t e n t i a l while a predominance of 2 or 3 gives a more p o s i t i v e (cathodic) p o t e n t i a l . I t was evident i n t h i s t e s t that 2 or 3 had predominated r e s u l t i n g i n a more p o s i t i v e (cathodic) p o t e n t i a l . shown by Gatty and Spooner (33)  and Cohen  This has been  (15).  TABLE XVII Comparison of P o t e n t i a l under S t a t i c and Dynamic Conditions Condition  P o t e n t i a l v o l t s vs  S t a t i c end of 10 days (average)  -.7055  Dynamic end of 9 days (average)  -.2500  ACE  Main Test  Run  Water The choice of Vancouver tap water as corroding medium has been discussed p r e v i o u s l y as based on i t s i n d u s t r i a l importance.  I t should  a l s o be added that n a t u r a l waters have most o f t e n been chosen f o r c o r r o s i o n s t u d i e s , and t h a t while the use of a s y n t h e t i c water i n an i n v e s t i g a t i o n w i l l allow study of the e f f e c t s of a multitude of t r a c e c o n s t i t u e n t s , i t i s common and accepted p r a c t i c e t o take e i t h e r composition as constant, or only v a r i a b l e w i t h respect t o a l i m i t e d number of components.  The use of a n a t u r a l water does introduce the  a d d i t i o n a l hazard of compositional changes o c c u r r i n g , sometimes over wide ranges, as e f f e c t e d by seasonal, water r e s e r v o i r or water treatment changes.  While such changes are exceedingly d i f f i c u l t t o  take i n t o account both i n reproducing previous work, or i n trends w i t h time i n an i n v e s t i g a t i o n such as t h i s which proceeded over four consecutive months, i t may be emphasized t h a t "constant  composition"  of the corroding medium may be assumed subject t o the f o l l o w i n g qualifications: (a)  The various t e s t runs, w i t h v e l o c i t y , temperature  and duration as main v a r i a b l e s , were spaced i n a random fashion throughout the t e s t period as shown c l e a r l y i n the calendar of t e s t runs presented as Figure 27 i n Appendix I I I .  This involved random  d i s t r i b u t i o n of both v e l o c i t y l e v e l s and t e s t duration times. Temperature l e v e l s were checked only by running 90°F t e s t at two separated calendar periods. of the r e s u l t s were apparent.  I n a l l cases no i n c o n s i s t e n c i e s i n any Even though e x a c t l y d u p l i c a t e t e s t  runs were not made, the v a r i a b l e of d u r a t i o n of t e s t was chosen at l e v e l s close enough together t h a t i n c o n s i s t e n c i e s would have become obvious. (b)  Vancouver tap water does vary w i t h time i n respect  of a l l the v a r i a b l e s mentioned i n Table 1.  Only l i m i t e d data i s  a v a i l a b l e however and the average values are assumed t o be a p p l i c a b l e . The exceptions t o t h i s are the ones chosen f o r regular a n a l y s i s throughout the t e s t p e r i o d , i . e . , pH, oxygen content, and i r o n content. As shown i n Table XV these v a r i a b l e s show some v a r i a t i o n .  There was  no n o t i c e a b l e trend vrith time however, and the medians were c l o s e l y i n d i c a t i v e of the general value of the v a r i a b l e .  I t i s c l e a r from  the median value of oxygen concentration t h a t the water was very c l o s e t o the a i r s a t u r a t i o n value at a l l times (e.g. 5»0 ppm at 130°F compared t o a s a t u r a t i o n value of  5.1 ppm).  There was a very s l i g h t  increase i n median i r o n concentration i n the system water, although i t i s doubtful i f t h i s i s significant. I t may t h e r e f o r e be concluded t h a t under t e s t c o n d i t i o n s , Vancouver tap water, aerated t o s a t u r a t i o n c o n d i t i o n s , may be considered a constant composition medium, i n t h a t median or average values of composition v a r i a b l e s represent w e l l the o v e r a l l conditions throughout t e s t periods which v a r i e d from 5 days t o 25 days.  Main Test_Run Corrosion Products The c o r r o s i o n products were approximately the same i n structure and appearance as those encountered by s e v e r a l previous i n v e s t i g a t o r s (4, 10, 19, 28).  These products have been  i d e n t i f i e d as c o n s i s t i n g of a red porous p r e c i p i t a t e , f e r r i c hydroxide, and a b l a c k granular f i l m , magnetite.  The c o r r o s i o n  apparently started along the seam i n the type A pipe as observed from the t e s t runs completed at f i v e days.  In these t e s t s the  corrosion products had covered the seam completely but had not as yet covered f u l l y the remaining s u r f a c e .  Because the seam was l e s s  prominent i n the type B pipe the above was not n o t i c e d i n any of the f i v e day runs using type B pipe. The l a y e r s of c o r r o s i o n products were t h i c k e s t (approximately "V32 of an inch)^at the lower temperature and lowest v e l o c i t i e s used i n t h i s study.  The h i l l s and v a l l e y s formed a t the d i f f e r e n t  v e l o c i t i e s are shown i n Figure 7, a, c, d, e and f .  The contours  were more prominent i n the low v e l o c i t y t e s t s and were more or l e s s i n rows as can be seen i n F i g u r e 7, c, d as compared t o F i g u r e 7, e, f . No d i f f e r e n c e could be noted i n c o r r o s i o n product appearance between type A and type B pipe f o r s i m i l a r v e l o c i t i e s .  However, a  d i f f e r e n c e showed up on the cleaned side of the specimens. shown i n Figure 7, c, d, e, and f;  This i s  c and d are type A pipe at  v e l o c i t i e s .75 and 1©5 f p s r e s p e c t i v e l y .  The dark areas are cathodic.  Figure 7, e and f are type B pipe a t v e l o c i t i e s 3.0 and 4»5 f p s and the absence of any large cathodic areas i s c l e a r l y shown.  Figure 7 b  Specimen showing Corrosion Product and Cleaned Side at a V e l o c i t y of .75 fps and Temperature 130°F.  Figure 7 c  Corrosion Product formed a t a V e l o c i t y of .75 f p s and a Temperature of 130°F. Type A pipe.  Figure 7 d  Corrosion Product formed at a V e l o c i t y of 1.5 f p s and a Temperature of 130°F. Type A pipe.  Figure 7 e  Corrosion Product formed a t a V e l o c i t y of 3.0 f p s and a Temperature of 130°F. Type B pipe.  Figure 7 f  Corrosion Product formed at a V e l o c i t y of 4.5 f p s and a Temperature of 130°F. Type B pipe.  Figure 7,b shows the c o r r o s i o n product and the clean side of a specimen subjected t o a v e l o c i t y of .75 f p s . The distance between the peaks and v a l l e y s was approximately 3  /64 of an inch at .75 f p s and decreased w i t h i n c r e a s i n g water  velocity.  This smoothing apparently r e s u l t e d from the increased  turbulence wearing away the products i n the pipe..;  However, the  turbulence was of i n s u f f i c i e n t f o r c e t o cause an increase i n amount of c o r r o s i o n ( a t l e a s t up t o 4.5 f p s the highest v e l o c i t y used) i n t h e 25 day period t e s t s , due t o erosion of the products, and b a r i n g of new surface f o r the c o r r o s i o n r e a c t i o n s . Time At any given v e l o c i t y and e i t h e r temperature the c o r r o s i o n e f f e c t may be noted as a t o t a l amount up t o a c e r t a i n time, or as a rate ( c a l c u l a t e d as the amount f o r a c e r t a i n time period d i v i d e d by the p a r t i c u l a r time p e r i o d ) .  These can then be portrayed as a  f u n c t i o n of time on any d e s i r e d scale ( l i n e a r , p a r a b o l i c , logarithm or exponential) as noted i n the l i t e r a t u r e review above. The l i m i t e d time period of t h i s i n v e s t i g a t i o n has meant that the amount of c o r r o s i o n and time increments used f o r p l o t t i n g Figures 8 and 9 are r e l a t i v e l y l a r g e .  In a d d i t i o n t e s t times of  l e s s than f i v e days d i d not give very reproducible r e s u l t s and hence the very important i n i t i a l amount of c o r r o s i o n i s not s p e c i f i c a l l y determined here, but can only be given as an average amount f o r the lowest time used, t h a t of f i v e days.  A l l of the r e s u l t s , w i t h these  experimental l i m i t a t i o n s , are given i n Figure 8 and 9 on a l i n e a r time s c a l e .  5000  o  4000  o  3000  o o  2000 O -745 • 1-49 3 2- 9 8 O 4- 4 7  1000  10  TIME Figure 8  Amount of Corrosion.  20  15 DAYS  Temperature 90°F.  25  ft/sec ft/sec ft/sec ft/sec  30  7500  TIME Figure 9  Amount of Corrosion.  DAYS  Temperature 1 3 0 ° F . ON  I t i s obvious that the r e s u l t s reported here a l l o w no i n t e r p r e t a t i o n of the mechanism f o r the i n i t i a l stages of corrosion ( i . e . below f i v e days exposure) and that the f i v e day amount of c o r r o s i o n reported i s an o v e r a l l average f o r that period of time. During that time the i n i t i a l l a y e r s of corrosion products are l a i d down, a process which w i l l most c e r t a i n l y proceed by a d i f f e r e n t r a t e mechanism.  However, an i n v e s t i g a t i o n i n t o t h i s time period i s  outside the scope of t h i s p r o j e c t . Figures 8 and 9 show the expected decrease of „rate. of c o r r o s i o n w i t h time of exposure due t o the p r o t e c t i v e e f f e c t of the i n c r e a s i n g depth of the corrosion products.  The amount of c o r r o s i o n  found i n these t e s t s under constant v e l o c i t y conditions are undoubtedly higher than those i n commercial equipment where the f l o w would not n e c e s s a r i l y be continuous and the oxygen supply c o n s i d e r a b l y reduced.  Rawdon and Waldron (54) i n t h e i r t e s t s found a f a c t o r of  approximately two between t h e i r t e s t s and those f o r commercial l i n e s . E l i a s s e n (24)  has suggested the f o l l o w i n g equation f o r the  amount of c o r r o s i o n . C = K (1 where  e  - k t  )  C = amount of corrosion t = s p e c i f i c time K = c o e f f i c i e n t u n i t s of md k = c o e f f i c i e n t u n i t s of ^"/time.  This equation i s based on the r e s u l t s he obtained i n h i s i n v e s t i g a t i o n s and represents the exponential type of c o r r o s i o n equation.  I t could be shown i n Figure 9  how w e l l the equation f i t s  the l i n e s f o r v e l o c i t i e s of ,75, 3»0 and 4»5 f p s .  However, because  of t h e l a r g e increments used i t i s not j u s t t o say the corrosion-time curves are exponential u n t i l f u r t h e r points have been obtained. From the equation i t can be noted that C would approach K as t becomes l a r g e , and thus a f t e r a s u f f i c i e n t period of time the amount of corrosion would be e s s e n t i a l l y independent of time. I f a system a f t e r a s u f f i c i e n t period of time assumes a constant c o r r o s i o n r a t e i t i s evident that the above equation would not apply.  L i k e l y a l i n e a r corrosion-time  curve would best s u i t the  amount of corrosion expected a f t e r a constant r a t e i s e s t a b l i s h e d , VELOCITY Actual E f f e c t s In most t e s t s p r e v i o u s l y reported where the v e l o c i t y of n a t u r a l water, the corroding medium, <past . the metal surface has been :  v a r i e d the amount of corrosion passed through a maximum.  However,  t h i s maximum v a r i e d considerably with each experiment because of the l a r g e v a r i a t i o n i n the experimental apparatus.  Friend (32) found a  maximum at ,15 f p s , another i n v e s t i g a t o r (55) at 1 f p s , E l i a s s e n (24) at approximately 1 f p s , R u s s e l l , Chappell and White (57) at ,19 f p s f o r polished s t e e l and ,824 f p s f o r rough s t e e l ,  R o e t h e l i and Brown  (56) found a maximum a t an unstated v e l o c i t y , Rawdon and Waldron (54) also found a decreasing amount of corrosion.  However, S p e l l e r and  Kendall (62) d i d not obtain any maximum i n t h e i r i n v e s t i g a t i o n s and instead they obtained a corrosion versus v e l o c i t y curve which tended t o become h o r i z o n t a l w i t h i n c r e a s i n g v e l o c i t y up t o t e n f p s .  These t e s t s were c a r r i e d out on t e s t sections c o n s i s t i n g of a c o i l of pipe up t o 200 feet i n l e n g t h .  This type of apparatus i s completely  divorced from any of the above i n v e s t i g a t o r s excluding perhaps that of E l i a s s e n (24) and Rawdon and Waldron (54) who used m i l d s t e e l specimens four t o s i x inches long formed i n t o a pipe l i n e . Another i n v e s t i g a t o r Wormwell (78) found t h a t the c o r r o s i o n rate of m i l d s t e e l i n f l o w i n g sea water (up t o 1.2 with increasing v e l o c i t y .  f p s ) increased  Other t e s t s (69) have shown an increase  up t o 25 fps i n sea water. S t r e i c h e r (66) i n h i s study on the e f f e c t s of water q u a l i t y on corrosion of m i l d s t e e l encountered a maximum amount of c o r r o s i o n between 4 to 6 f p s depending on the temperature.  However, he a l s o  encountered i n the same studies r e s u l t s s i m i l a r t o those of S p e l l e r and Kendall mentioned above.  These apparent d i s c r e p a n c i e s of t h i s  and those above can however be q u a l i t a t i v e l y explained. A comparison of the r e s u l t s of some of the previous i n v e s t i g a t o r s w i t h those of the present study i s shown i n Table  xrai. At high \*ater v e l o c i t i e s (the exact v e l o c i t y depending on which type of apparatus was used) s u f f i c i e n t oxygen i s brought t o the metal surface t o cause p a s s i v i t y i n the same manner as the high concentration of d i s s o l v e d oxygen i n water passivates i r o n .  This  was noted i n experiments c a r r i e d out by Groesbeck and Waldron  (35)  who i n s e r t e d coupons i n t o a pipe and c i r c u l a t e d varying oxygen concentrated d i s t i l l e d water (pH7) past the coupons.  Bauer,  Krohnke and Masing (2) gave an example of i r o n passivated by oxygen,  TABLE XVIII  Comparison of Results of Previous Work to the Present Study Water  Temperature Range °F  Velocity Range fps  Velocity f o r Maximum Corrosion  Reference  .15  32  Metal  Type of Apparatus  Iron  Foil i n Beakers  Natural  Black Iron  Coupons  Treated Colorado River  51 - 60  1-15  4-6  66  Black Iron  Coupons  Untreated  51 - 60  1-15  -  66  Mild Steel  Coupons i n Tubes  Natural  70  1-4  57  Mild Steel  Cylinders  Natural  -  Mild Steel Pipe Network  Synthetic  68  Mild Steel Pipe Network  Natural  -  60 - 150  .02-8  .2-8.4 40-340 rpm .125*4 .1-8  HO rpm 1  -  56 24 62  Mild Steel  Coupons Rotated  Natural  -  0-1.2  Iron  Rods  Natural  60  3-15  6  51  Cast Iron  Coupons  Natural  .2-2  .2  42  0-12  4.5  15  -  68 - 100  Mild Steel Tube Network  Natural  Mild Steel  Cylinder  Sea Water  -  Mild Steel  Cylinder  Distilled  70  .5-7.5  90 - 130  .75-4.5  Mild Steel Pipe Network  Natural  0-250 rpm  19  -  .95 .75 - 1.5  78 55  Present  72  as shown by a p o t e n t i a l of -.22 t o + ,08 v o l t s (ACE scale) f o r i r o n i n water containing the higher oxygen concentration as compared w i t h -.7 t o -.8 v o l t s i n water normally saturated with a i r . Further evidence i n t h i s d i r e c t i o n i s shown by the f a c t that the presence of c h l o r i d e ions (3,5$ sodium c h l o r i d e ) i n s o l u t i o n e f f e c t i v e l y retards p a s s i v a t i o n as shown by weight l o s s determinations, and i r o n then corrodes a t i n c r e a s i n g rates f o r oxygen concentration above those f o r which the rate decreased i n d i s t i l l e d water (31).  This explains why Wormwell and others d i d not obtain  a maximum amount of corrosion i n t h e i r sea water experiments w i t h increasing v e l o c i t y . The apparent c o n t r a d i c t i o n of Kendall and S p e l l e r (62) r e s u l t s and the r e s u l t s of S t r e i c h e r (66) are explained by t h e d i f f e r e n t f i l m s on the specimens as p r e v i o u s l y discussed i n the l i t e r a t u r e review. In t h i s i n v e s t i g a t i o n the amount of c o r r o s i o n increased t o a maximum between .75 and 1,5 f p s , f o r the temperature range i n v e s t i g a t e d , as shown i n Figure 19.  This corresponds c l o s e l y w i t h the r e s u l t s of  E l i a s s e n (24) whose apparatus most c l o s e l y resembles that of the present  study. For s i m i l a r time periods and a t 90°F the amount of c o r r o s i o n  was a maximum a t a v e l o c i t y about 1,5 f p s .  Apparently above t h i s  v e l o c i t y s u f f i c i e n t oxygen was brought t o the surface, i n terms of the mechanism described l a t e r , t o cause p a s s i v i t y i n the same manner as high concentrations of d i s s o l v e d oxygen i n n a t u r a l water passivates i r o n .  The d i f f e r e n t type of corrosion a t t a c k due t o  6000h  2  4500h  O  CO  o or or o o  3000r-  I  500  2  3 VELOCITY  Figure 19  ft/sec  E f f e c t of Water V e l o c i t y on Amount of Corrosion.  v e l o c i t y was quite i n evidence on the type A pipe.  Up t o 1.5 f p s  the attack was very uniform and covered the e n t i r e surface of the specimen.  As the v e l o c i t y increased f u r t h e r corrosion a t t a c k became  more l o c a l i z e d and a t 4.5 f p s p i t s became n o t i c e a b l e . seen by examining Figure 20.  This can be  The dark areas are cathodic.  It  would seem that because of the i n c r e a s i n g oxygen a v a i l a b l e , the anodic s e l f p o l a r i z a t i o n increased and the cathodic s e l f p o l a r i z a t i o n decreased, thus i n c r e a s i n g the e f f e c t i v e cathodic area and consequently decreasing the anodic area under a t t a c k .  This  leads t o l o c a l i z i n g the s e v e r i t y of the a t t a c k on a l e s s e r area which causes p i t t i n g as explained by Mears and Evans (46).  Figure 20, L o c a l i z i n g of c o r r o s i o n attack caused by changing v e l o c i t y on type A pipe.  75  The maximum amount of corrosion f o r a d e f i n i t e time period at 90°F which occurred at a v e l o c i t y intermediate i n the range explored (1,5 f p s ) e x i s t e d i n a s i m i l a r f a s h i o n a t 130°F, a t a v e l o c i t y of about ,75 f p s .  This e f f e c t was apparently due  p r i m a r i l y t o the increased ease of oxygen t r a n s m i s s i o n a t the higher temperature,even though the s a t u r a t i o n concentration i s l e s s , and the decreased thickness of the laminar l a y e r next t o the c o r r o s i o n products.  The net r e s u l t would therefore be f o r a supply of oxygen  s u f f i c i e n t t o cause p a s s i v a t i o n t o be reached a t a lower v e l o c i t y than would occur at 90°F, No d i f f e r e n c e i n corrosion a t t a c k w i t h change i n v e l o c i t y was noticed on the surface of t h e type B pipe a t 130°F a f t e r removal of corrosion products i n d i s t i n c t i o n t o type A pipe.  The weight  l o s s was s i m i l a r f o r type A and B pipes used as specimens i n the same t e s t s e c t i o n and under i d e n t i c a l c o n d i t i o n s . Theoretical Velocity Effects V e l o c i t y p r i m a r i l y a f f e c t s the amount of corrosion through i t s i n f l u e n c e on d i f f u s i o n phenomena.  The influence of v e l o c i t y on  c o r r o s i o n w i l l thus vary markedly w i t h the type of surface, c h a r a c t e r i s t i c s of the f l o w and nature of the medium through which oxygen d i f f u s i o n must take p l a c e .  In r e l a t i v e l y low v e l o c i t i e s such  as encountered i n the present i n v e s t i g a t i o n , e r o s i o n and c a v i t a t i o n are not of major importance. Under the conditions of pH and temperature used i n t h i s study the oxygen content and the d i f f u s i o n of oxygen through the laminar l a y e r and the corrosion products were the c o n t r o l l i n g f a c t o r s (23).  I t has been shown by Stern (67)  as i l l u s t r a t e d i n Figure 21  t h a t the change i n anodic and cathodic p o l a r i z a t i o n curves w i t h v e l o c i t y r e s u l t e d i n the corrosion current represented by the i n t e r s e c t i o n of these two curves at point A, and therefore the corrosion r a t e , being p r o p o r t i o n a l t o the v e l o c i t y of the s o l u t i o n . The change of v e l o c i t y from v^ t o v^ (Figure 21) from i ^ t o i ^ and so on up t o point A.  changed the current  A f t e r t h a t point was reached  the c o r r o s i o n r a t e was independent of v e l o c i t y and remained so u n t i l i n c r e a s i n g turbulence caused disturbances t o change the shape and p o s i t i o n of the l o c a l p o l a r i z a t i o n curves. Assuming that the laminar sublayer e x i s t e d at the  beginning  of the t e s t on the r e l a t i v e l y smooth specimens, and the c o r r o s i o n r a t e was determined by the d i f f u s i o n of oxygen, then the i n i t i a l r a t e should have been p r o p o r t i o n a l t o a f r a c t i o n a l power, n, of the Reynolds number (24).  I f the logarithm of the c o r r o s i o n r a t e was  p l o t t e d against the logarithm of the v e l o c i t y , a s t r a i g h t l i n e of slope n should r e s u l t . Kendall's and S p e l l e r ' s data (62),  which shows the amount  of oxygen uptake from water f l o w i n g at various v e l o c i t i e s through a c o i l up t o 200 f e e t i n length of rusted s t e e l p i p e , has therefore been p l o t t e d i n t h i s type of graph, Figure 22,  w i t h the logarithm of  oxygen uptake as the ordinate and the logarithm of the v e l o c i t y (fps) as the abscissa. number was .79  The n which i s the f r a c t i o n a l power of the Reynold  i n t h i s case.  At v e l o c i t i e s higher than 8 fps the  rate no longer increased as v e l o c i t y r a i s e d t o the ,79 power. would be i n agreement w i t h passing point A i n Figure 21 where an increase i n v e l o c i t y had no longer any s i g n i f i c a n t e f f e c t .  This  Figure 21  E f f e c t of the P o s i t i o n of the L o c a l Anodic P o l a r i z a t i o n Curve on the Influence of V e l o c i t y on Amount of Corrosion.  78  T  1  1 I I I M|  1  1  1  II I II|  1  "  O Moss Transfer Correlation _ : •I  • Speller a Kendall (62)  i i i i i i nl  .  i  I VELOCITY  i i i 1111 fps  : i  10  Figure 22 Comparison of S p e l l e r and Kendall Results w i t h Mass Transfer C o r r e l a t i o n .  The d i f f u s i o n of oxygen i s l i m i t i n g whether the oxygen i s used t o reduce cathodic p o l a r i z a t i o n or t o p a r t i c i p a t e i n the anodic polarization.  Since magnetite i s present a t a l l but the  initial  stages of corrosion, then i t would appear p l a u s i b l e t o consider a zero oxygen a v a i l a b i l i t y as being maintained w i t h i n the magnetite zone.  The o v e r a l l d r i v i n g force f o r oxygen d i f f u s i o n i n from the  water would therefore be the concentration of the d i s s o l v e d the bulk of the s o l u t i o n .  oxygen i n  This would be the a i r s a t u r a t i o n value.  The v e l o c i t y e f f e c t i s apparently important up t o the point where i t i s s u f f i c i e n t t o a t t a i n and maintain the maximum supply of oxygen (equal t o the a i r saturation value) f o r d i f f u s i o n through t h e laminar l a y e r and l a y e r s of c o r r o s i o n products.  Above t h i s value  of v e l o c i t y the maximum o v e r a l l d r i v i n g force f o r oxygen d i f f u s i o n w i l l e x i s t , assuming the oxygen content of the water i s maintained, and any f u r t h e r l i m i t i n g f a c t o r w i l l be due t o some step i n the d i f f u s i o n process such as d i f f u s i o n through some part of the corrosion products. Below t h i s c r i t i c a l v e l o c i t y * t h e o v e r a l l d r i v i n g force f o r oxygen d i f f u s i o n , w h i c h i s c o n t r o l l e d by the average oxygen concentration a v a i l a b l e i n the "source", that i s the f l o w l a y e r s (viscous or t u r b u l e n t ) outside the laminar l a y e r , w i l l be reduced below the maximum possible t o a degree d i r e c t l y dependent on the v e l o c i t y . Because of the rough surface nature of the corrosion products i t i s c l e a r that turbulence w i l l e x i s t t o a high degree, t h a t the laminar water l a y e r w i l l be very small, and t h a t the main c o n t r o l l i n g f a c t o r w i l l undoubtedly be the rate o f d i f f u s i o n through the product l a y e r s .  corrosion  Figure 22 a l s o shows a p l o t of the c o r r e l a t i o n f o r mass transfer  (17). k^.d  f (vL/ ,  )  5  where  k^ =  mass t r a n s f e r c o e f f i c i e n t i n concentration u n i t s moles/hr. sq. f t . moles cu f t  (  d,L  =  diameter of pipe  D  &  -  d i f f u s i v i t y of gas through l i q u i d  v  =  v e l o c i t y f e e t per second d e n s i t y of l i q u i d  f  —  v i s c o s i t y i n centipoises  I t has been shown In Treybal (68)  that the powers f o r the Reynold and  Schmidt numbers are .8 and .33 r e s p e c t i v e l y and t h a t the constant i s .023.  This assumes that the c o r r o s i o n products have no e f f e c t on the  t r a n s f e r of oxygen and t h a t a l l the r e s i s t a n c e t o t r a n s f e r i s i n the laminar l a y e r .  I t a l s o assumes t h a t the oxygen concentration at the  surface of the metal i s zero. S p e l l e r and Kendall (62)  c o r r e l a t e d t h e i r work i n terms of a  s p e c i f i c corrosion r a t e , K, which as shown by Wilson (79) can be expressed i n terms as f o l l o w s : K_  cc. of O2 consumed per year x 3.32  x l i t r e s of water/year  area of i r o n surface i n sq. cm. x av. conc'n. of oxygen  Comparing K w i t h k  n  one can see they are very s i m i l a r .  Figure 22  shows that the a c t u a l r a t e of corrosion as determined by Kendall and S p e l l e r was about l / 4 0 that found from the c o r r e l a t i o n .  This appears  t o i n d i c a t e that the mass t r a n s f e r of oxygen from the water on to the surface of the metal through the laminar l a y e r accounted f o r very l i t t l e of the t o t a l r e s i s t a n c e , and t h a t the main f a c t o r would appear to be the resistance t o oxygen d i f f u s i o n i n the c o r r o s i o n products and the t r a n s f e r of corrosion products away from the surface of the metal. Since i n the present i n v e s t i g a t i o n a maximum amount of corrosion f o r a s p e c i f i e d time period occurred at a r e l a t i v e l y low v e l o c i t y of .75 to 1,5 same manner as above.  f p s , the r e s u l t s could not be c o r r e l a t e d i n the Further r e s u l t s would have to be obtained  at  lower v e l o c i t i e s than .75 f p s to determine i f at the lower v e l o c i t i e s the r e s u l t s could be c o r r e l a t e d i n a s i m i l a r f a s h i o n .  The reasons f o r  t h i s apparent d i f f e r e n c e between the r e s u l t s of Kendall and S p e l l e r and those reported here may be assumed t o be twofold.  In the f i r s t place  Kendall and S p e l l e r began with "rusted" pipe and the properties of the " r u s t " as f a r as oxygen demands, p o r o s i t y e t c . are unknown.  Certainly  the s i t u a t i o n i n t h i s regard would not be a t a l l comparable.  In the  second place they measured oxygen uptake and t h i s introduces f u r t h e r d i f f i c u l t i e s of i n t e r p r e t a t i o n because of the p o s s i b l e oxygen demand t h a t would e x i s t i n the " r u s t " already present i r r e s p e c t i v e of f u r t h e r corrosion r e a c t i o n , and because of the decrease i n the o v e r a l l oxygen d i f f u s i o n d r i v i n g f o r c e by the reduction i n oxygen concentration.  TEMPERATURE Increased temperat lire caused a marked increase i n amounts of c o r r o s i o n f o r i d e n t i c a l v e l o c i t i e s as was a n t i c i p a t e d and i s shown i n Figure 23.  Skaperdas and U h l i g (61) show t h a t i n s t a t i c t e s t s the  weight l o s s almost doubles f o r a 55°E r i s e i n temperature.  Under open  c i r c u l a t i n g c o n d i t i o n s such as those used here, the c o r r o s i o n rate increased up t o about 175°F (36) then f e l l t o a v e r y low value at the b o i l i n g point (64). In t h i s i n v e s t i g a t i o n the e f f e c t of the i n t e r a c t i o n between temperature and v e l o c i t y helped t o increase the c o r r o s i o n process t o a f a c t o r of about two f o r a 40°F r i s e i n temperature. POTENTIALS The p o t e n t i a l measurement data p l o t t e d i n Figures 10 t o 18 show the anodic or negative values i n c r e a s i n g downward on the ordinate axis. The electrode p o t e n t i a l of any i r o n specimen at any i n s t a n t i s determined by: (1)  The r e l a t i v e magnitudes of the anodic and cathodic areas on the specimen  (2)  The anodic and cathodic p o t e n t i a l s of these areas.  I t therefore f o l l o w s t h a t the electrode p o t e n t i a l changed depending upon which of the possible anodic and cathodic processes was i n c o n t r o l . A more noble or more p o s i t i v e (cathodic) p o t e n t i a l i s the r e s u l t o f : (1)  Increase i n anodic area s e l f p o l a r i z a t i o n  (2)  Decrease i n cathodic area s e l f p o l a r i z a t i o n .  83  TEMPERATURE Figure 23  °F  E f f e c t of Temperature on Amount of Corrosion.  A l e s s noble or more negative (anodic) p o t e n t i a l i s t h e r e s u l t o f :  The  (3)  Decrease i n anodic area s e l f p o l a r i z a t i o n  (4)  Increase i n cathodic area s e l f p o l a r i z a t i o n .  corrosion rate of a metal increases i f processes 2 and 3 above  occur, and therefore i t cannot be s a i d t h a t the corrosion rate decreases i f the p o t e n t i a l becomes more noble (cathodic) unless the conditions under which the experiment i s conducted are known and understood. The main e f f e c t of v e l o c i t y i s t o increase t h e t r a n s f e r of reactants thereby r e s u l t i n g i n one or a l l of the f o l l o w i n g e f f e c t s : (1)  Cathodic area  (2)  Anodic area p o l a r i z a t i o n  (3)  Anodic area d e p o l a r i z a t i o n .  depolarization  Therefore, the d i r e c t i o n of the p o t e n t i a l change w i l l depend on which f a c t o r i s a f f e c t e d the most by an increase i n v e l o c i t y . Consideration of t h e f i n a l p o t e n t i a l s of the t e s t specimens as obtained a t the end of the 25 day runs and given i n Table XIX, shows the e f f e c t of v e l o c i t y t o be l e s s noticeable  at 90°F than 130°F.  However, a t both temperatures the most e l e c t r o p o s i t i v e or noblest p o t e n t i a l was encountered a t 3.0 f p s .  I t would seem then that the  cathodic area d e p o l a r i z a t i o n ( e f f e c t (1)) was more predominant than that of e f f e c t (2) a t t h i s v e l o c i t y because the corrosion amount was not the lowest recorded.  At 4.5 fps where the lowest amount of corrosion  occurred the p o t e n t i a l s ranked second and t h i r d i n n o b i l i t y at 90°F and 130°F r e s p e c t i v e l y .  The higher v e l o c i t y apparently caused an increased  amount of oxygen t o be brought t o the surface and e f f e c t (2) became the major f a c t o r .  The anodic area p o l a r i z a t i o n of mild s t e e l due t o  85  increased oxygen has been shown by s e v e r a l i n v e s t i g a t o r s (2, 35, 58, 64). I t i s quite evident from the r e s u l t s t h a t the conditions under which corrosion t e s t i n g i s performed must be c l e a r l y stated and understood.  Table XIX shows some cases of a more noble p o t e n t i a l w i t h  a greater corrosion amount than that of a l e s s noble p o t e n t i a l . TABLE XIX Comparison of P o t e n t i a l s and Amounts of Corrosion  Potential (at 25 days) v o l t s vs.ACE (45°F) 90°F  130°F  Static  -.7055  -.7055  Flow: .75 f p s  -.4950  1.5 fps  Corrosion Amount (at 25 days) md 90°F  130°F  -.6500  3325  (5560)  -.4350  -.7450  3633  5104  3.0 f p s  -.2750  -.3950  3160  4966  4.5 fps  -.4850  -.6000  2971  4406  The p o t e n t i a l d i f f e r e n c e s determined experimentally f o r the i r o n specimens against the ACE have i n t h i s case been adjusted t o a common temperature base i n an attempt t o make the r e s u l t s f o r d i f f e r e n t temperatures comparable.  The temperature c o e f f i c i e n t f o r the ACE has  been given by Champion (14) and t h i s has been applied t o the r e s u l t s f o r 90°F and 130°F t o correct them t o 45°F.  As has been p r e v i o u s l y  noted the ACE gives a constant p o t e n t i a l d i f f e r e n c e from the saturated  86  calomel electrode i n t a p water of .020 v o l t s a t 70°F. The p o t e n t i a l s a t 130°F increased i n a negative (anodic) d i r e c t i o n from those at 90°F.  I n t h i s case, t h i s corresponded t o  the e f f e c t of i n c r e a s i n g temperature on i n c r e a s i n g the amount of corrosion.  The movement of the p o t e n t i a l i n t h i s d i r e c t i o n , as a  r e s u l t of change of temperature, has a l s o been observed by Laque (40). From Figures 10 t o 18 i t can be observed t h a t the p o t e n t i a l s , as measured, a l l moved e v e n t u a l l y i n a more noble d i r e c t i o n .  Usually  the p o t e n t i a l i n a moving s o l u t i o n i s more noble than that i n a s t a t i c solution.  This i s because cathodic area d e p o l a r i z a t i o n and anodic  area p o l a r i z a t i o n are affected greater than anodic area d e p o l a r i z a t i o n as has been shown by Gatty and Spooner (33), Procopui (53) and Georghui (34),  However, an exception t o t h i s has been noted here (Table XIX).  At a v e l o c i t y of 1,5 f p s and 130°F the p o t e n t i a l was more anodic than that i n a s t a t i c t e s t .  This was another example of the n e c e s s i t y of  having the conditions of the i n v e s t i g a t i o n thoroughly understood before decisions are made. Most of the specimens showed a r a p i d drop i n p o t e n t i a l at the s t a r t of the t e s t period i n d i c a t i n g a r a p i d breakdown of any f i l m present before water flowed, (Figures 10 t o 18). so a t the higher temperature.  This was p a r t i c u l a r l y  However, a t 90°F some specimens a t the  higher v e l o c i t i e s showed a r i s e i n p o t e n t i a l i n d i c a t i n g that the increased oxygen a t the i n t e r f a c e had increased the p r o t e c t i o n of the film.  L a t e r , the oxygen concentration was apparently depleted by the  l o c a l a c t i o n process since the p o t e n t i a l s decreased.  Although the  oxygen t r a n s f e r t o the surface would be increased g r e a t l y a t 130°F, the  corrosion r e a c t i o n occurred more r a p i d l y and no increase i n p o t e n t i a l was noticed a t the s t a r t of the experiments. A l l p o t e n t i a l curves of twenty f i v e days extent showed a plateau between approximately eight t o twelve days where the c o r r o s i o n r e a c t i o n i s occurring at a r e l a t i v e l y high r a t e .  However, a t 130°F  the formation of the c o r r o s i o n products l i k e l y began t o hinder the t r a n s f e r of oxygen and products t o and from the surface of the metal and the corrosion r a t e and the p o t e n t i a l then dropped quite r a p i d l y . Table XX exemplifies t h i s change between f i f t e e n and twenty f i v e day corrosion r a t e s .  At 90°F though, the c o r r o s i o n products have not  decreased the r a t e below t h a t of f i f t e e n days i n d i c a t i n g that t e s t s of longer duration may be r e q u i r e d . TABLE XX Comparison of Corrosion Rates 90°F  130°F  15  25  15  25  128  133  340  208  1*5  140  U$  330  208  3o0  106  124  305 ' 198  4.5  86  116  220  Tjjne days Velocity fps .75  176  The reason f o r the p o t e n t i a l becoming more noble despite the increase i n corrosion rate i s not c l e a r .  The p o s s i b i l i t y of the  corrosion r a t e being greater a t some time between f i f t e e n and twenty f i v e days and then decreasing does e x i s t .  88  When a constant r a t e of corrosion has developed, the p o t e n t i a l should vary very l i t t l e from the value obtained when the constant r a t e was reached. The greater i n s i d e w a l l roughness of the type A pipe compared to the type B c o r r e l a t e s with the more negative p o t e n t i a l of the former. As Bryan (7) stated, the l o c a l a c t i o n of the corrosion process w i l l occur more r a p i d l y on a rough surface than on a smooth surface, and would l i k e l y correspond t o a more anodic p o t e n t i a l .  This decrease i n  n o b i l i t y of a rough surface compared t o a smooth surface has been found by Gatty and Spooner ( 3 3 ) . STATISTICAL DESIGN Frequently i n s c i e n t i f i c i n v e s t i g a t i o n s , p a r t i c u l a r l y where an e m p i r i c a l approach has t o be adopted, problems a r i s e i n which the e f f e c t s of a number of d i f f e r e n t f a c t o r s on some property or process r e q u i r e evaluation.  For a long time the approved method would be t o v a r y each  of the f a c t o r s one a t a time keeping the others constant. take a l o n g and tedious amount of work.  This would  Such problems can u s u a l l y be  most economically i n v e s t i g a t e d by arranging the experiments according t o an ordered plan i n which a l l the f a c t o r s are v a r i e d i n a regular way. Several i n v e s t i g a t o r s ( 6 , 27, 39, 74) have shown how t h i s type of an experiment can be designed.  Designs of t h i s sort lend themselves  very  w e l l t o s t a t i s t i c a l a n a l y s i s , and unplanned experimental work i s l i a b l e to confuse the e f f e c t s sought i n such a way t h a t much of the information which would otherwise be a v a i l a b l e i s s a c r i f i c e d . The type of experiment c a r r i e d out i n t h i s study i s adaptable  to a f a c t o r i a l design.  I n t h i s design a set of v a l u e s , or l e v e l s ,  f o r each f a c t o r t o be studied i s decided and then one or more t r i a l s of the process i s c a r r i e d out w i t h each of t h e p o s s i b l e combinations of the l e v e l s of the f a c t o r s . When these t r i a l s have been run the r e s u l t s are then analysed by an appropriate method (22) t o determine the l e v e l s of the f a c t o r s which give an optimum response. In t h i s study t h r e e main f a c t o r s have been chosen, temperature (A),  v e l o c i t y (B) and time ( C ) .  Each of these f a c t o r s w i l l be i  associated w i t h two l e v e l s .  This leads t o a design as shown i n Table  XXI. TABLE XXI A 7? F a c t o r i a l Design Trial  Factor l e v e l A  1 2 3 5  6  7 8  B  C  + -  +  +•  -  +  +  +  +  -+-+  The minus term i n Table XXI corresponds t o the low l e v e l of t h e p a r t i c u l a r f a c t o r while the p l u s term i s the high l e v e l . By using t h i s design the l e a s t time required f o r a maximum amount of corrosion can be obtained w i t h as few as eight t o t e n possible t r i a l s .  A l s o the conditions required f o r a maximum c o r r o s i o n  r a t e can be determined.  An a n a l y s i s on the r e s u l t s of the present study has been done, but unfortunately the l e v e l s were too f a r apart ( i . e . temperature 90°F t o 130°F).  They d i d show that the temperature l e v e l should be r a i s e d  several degrees (between 170°F and 180°F) as could be a n t i c i p a t e d from the r e s u l t s of previous i n v e s t i g a t o r s , and t h a t the v e l o c i t y conditions f o r a maximum amount of corrosion i n the l e a s t time should be approximately 1,2 f p s , at t h i s temperature range. I t i s sometimes convenient t o v i s u a l i s e the r e l a t i o n between response and the f a c t o r i a l l e v e l s g e o m e t r i c a l l y . response surface as shown by Spinks (65).  This leads t o a  A study of the response  surface may a l s o provide information on the basic mechanism of the process.  CONCLUSIONS 1.  The corrosion of m i l d s t e e l pipes i n Vancouver t a p water  i n a continuous c i r c u l a t i n g system reaches a maximum amount o f corrosion between a v e l o c i t y of .75 and 1.5 f p s a t 90°F and 130°F respectively. 2.  The amount of corrosion then decreases up t o 4*5 f p s .  Determination of corrosion r a t e s without a s u i t a b l e passage  of time can give very misleading r e s u l t s as i l l u s t r a t e d i n Table XX. 3.  With a knowledge of the system under observation, p o t e n t i a l  time studies can be used t o a s c e r t a i n .the type of c o n t r o l under which the system i s operating. 4.  Most of the c o n t r a d i c t o r y r e s u l t s i n the l i t e r a t u r e are due  to the d i f f e r e n c e s i n apparatus.  With s i m i l a r apparatus r e s u l t s can  be duplicated quite c l o s e l y . 5.  Although oxygen u s u a l l y increases the amount of corrosion  i t can a l s o apparently a c t as a passivator thereby reducing c o r r o s i o n .  RECOMMENDATIONS 1.  A design of the experiment has been drawn up t o a s s i s t i n the  e x p l o r a t i o n of corrosion on the e x i s t i n g apparatus.  Of immediate  i n t e r e s t are the conditions necessary t o obtain a maximum amount of corrosion i n the shortest time. 2.  At some f u t u r e date, t o overcome the l e a k i n g which occurred  w i t h low temperatures a t the p l a s t i c s t e e l connections i n the d i s t r i b u t o r tanks, due t o the deformation caused by the high temperatures, the p l a s t i c n i p p l e and flange w i l l have t o be replaced w i t h a h e r e s i t e or other s u i t a b l e l i n i n g m i l d s t e e l n i p p l e or f l a n g e . 3.  An i n v e s t i g a t i o n i n t o the e f f e c t of c y c l i n g of the water  from on t o o f f should a l s o be of i n t e r e s t .  The r e s u l t i n g amount of  corrosion should be c l o s e r t o t h a t i n a c t u a l water l i n e s . 4.  A probe i n t o the e f f e c t of i n h i b i t o r s on the c o r r o s i o n of  m i l d s t e e l would a l s o a f f o r d an i n t e r e s t i n g experiment. 5.  An examination i n t o the i n f l u e n c e of d i f f e r e n t metal  surfaces on p o t e n t i a l s could provide f u t u r e work.  Furthermore,  research i n t o the e f f e c t of impressed currents and the  determination  of the p o l a r i z a t i o n curves from these currents should a l s o produce u s e f u l information.  93 LITERATURE CITED  1.  AWWA, APHA Standard Methods f o r Examination of Water and Sewage Waverly Press i n c . 1955.  2.  Bauer F., Krohnke H. and Massing A. Die Korrosion M e t a l l i s c h e r Werkstoffe 1, S. H i r z e l L e i p z i g 1936•  3.  Bengough G. D., Stuart J . M. and Lee A. R. Proc. Roy. Soc. A 127, 42 1930.  4.  Bengough G. D., Lee A. R. and Wormwell F. Proc. Roy. Soc. A 134, 312 1931.  5.  Blum W. and Rawdon H. S. Trans. ELectrochem. Soc. 52 , 403  1927.  1  6.  Box G. E. P. and Youle P. V. Biometrics 11, 287 1955.  7.  Bryan R. Trans. Faraday Soc. 2£,  209.  1933  1198  30, 1059 1934 3JL> 1714  1935  8.  Burch B. Corrosion of M i l d S t e e l i n Vancouver Tap Water B.A.Sc. Thesis U n i v e r s i t y of B r i t i s h Columbia 1956.  9.  C a l c o t t W. S., Whetzel J . C. and Whittaker H. F. Monograph on Corrosion Testing and M a t e r i a l s of Construction f o r Chemical Engineering Apparatus. Von Nostrand New York  10.  Carius C. Korr Met. 7,  11.  1923.  186  1931.  Champion F. A. Trans Faraday Soc. 40 #10  12.  Champion F. A.  13.  Metal Ind. (London) 72 440 Champion F. A. I b i d 74 7 19.50.  14.  593  1945. 1948.  Champion F. A. Corrosion Testing Procedures Chapman and H a l l London 1952.  94 15. Cohen M. " - - - J . Electrochem. Soc. £3, 26 16.  1943.  Cohen M. Trans. Electrochem. Soc. 8 J , 1255  1945.  17.  Coulson J . M. and Richardson J . F. Chemical Engineering V o l . I page 244 Pergamon Press London 1954.  18.  Cox G. L. Ind. Eng. Chem. 23, 902  1931.  19.  Cox G. L. and R o e t h e l i B. E. Ind. Eng. Chem. 23_, 1012 1931.  20.  Crompton D. K. and M i t c h e l l N. ¥. ASTM Symposium on Corrosion T e s t i n g Procedure page 74  21. 22.  Cushman A. Corrosion of Iron  1937.  1907.  Davies 0. L. et A l . The Design and A n a l y s i s of I n d u s t r i a l Experiments O l i v e r and Boyd Edinburgh 1954.  '  23.  Dey W. R. Corrosion of M i l d S t e e l i n Vancouver Tap Water B.A.Sc. Thesis U n i v e r s i t y of B r i t i s h Columbia 1957.  24.  E l i a s s e n R. et A l . J.A.W.W.A. 48, 1005 1956.  25.  Evans U. R. Ind. Eng. Chem. 17, 370  26.  1925.  Evans U. R. Trans. Electrochem. Soc. P r e p r i n t 91-95  1945.  27.  F i s h e r R. A. The Design of Experiments 0 O l i v e r and Boyd Edinburgh 1949.  28.  Forrest H. D., R o e t h e l i B. E. and Brown R. H. Ind. Eng. Chem. 23, 650 1931*  29.  Forrest H. D», R o e t h e l i B. E. and Brown R. H. I b i d 22, 1197 1930.  30.  Fraser 0. B., Ackerman D. E. and Sands J . W. I b i d 12, 332 1927.  31.  Frese F. G. I b i d 30, 83 1938.  95 32.  F r i e n d J . N. J . Iron S t e e l I n s t . 11, 62, 128 1922.  33•  Gatty 0 . and Spooner E. C. R. Electrode P o t e n t i a l Behaviour of Corroding Metals i n Aqueous S o l u t i o n s . Oxford 1938.  34«  Georghiu R. Ann. S c i . Univ. Jassy 18, 337 1933.  35.  Groesbeck E. C. and Waldron L. J . Proc. Am. Soc. Test. Mat. 3 1 , 279 1931.  36.  H e l l e r D. Corrosion of M i l d S t e e l i n Vancouver Tap Water B.A.Sc. Thesis U n i v e r s i t y of B r i t i s h Columbia 1958.  37.  I s f e l d V. L. Cathodic P r o t e c t i o n Measurements B.A.Sc. Thesis U n i v e r s i t y of B r i t i s h Columbia 1955.  38.  Johnston P. A. and Babb A. L. Ind. Eng. Chem. 46, 518 1954.  39.  Kempt home 0 . . The Design and A n a l y s i s of Experiments John Wiley and Sons Inc. New York 1952.  40.  Laque F. L. Am. Sc. Test. Mat. 4 0 , 640 1940.  41.  Larson E. L. and Skold R. V. J.A.W.W.A. £0, 1429 1958.  42.  Larson E. L. and Skold R. V. I b i d 42, 1294 1957.  43.  Larson T. E. and King R. M. Corrosion 10, #3, 110 1954.  44.  McKay R. and Worthington G. Corrosion Resistance of Metals and A l l o y s Reinhold Publishing Co. New York 1936.  45.  Maxwell H. E.' Mech. Eng. 58, #12, 803 1936.  46.  Mears R. B. and Evans U. R. Proc. Roy. Soc. A 146, 153 1934.  47.  Mears R. B. and Brown R. H. J . Electrochem. Soc. 22, 75 1950.  96  48. 49.  Mellon M. G. and Mass M. L. Ind. Eng. Chem. Anal. Ed. 14, 862 M i l e y H. A. Trans. Electrochem. Soc. 81, 391  1942. 1942.  50.  Nurse T. J . , Ison H. C. K. and Wormwell F. J . Iron S t e e l I n s t . 160, #3, 247 1948.  51.  Passano R. F. and Nagley F. R. Proc. Am. Soc. Test. Mat. 33_, 387  1933.  52.  Poubaix M. J . N. Thermodynamics of D i l u t e Aqueous Solutions E. Arnold & Co. London 1949.  53.  Procopiu F. Ann. Chim. Phys. 1£, 121  54.  1921.  Rawdon H. S. and Waldron L. J . P r o c Am. Soc. Test. Mat. 35 , 233  1935.  55.  R i c k e r s W. M.Sc. Thesis M.I.T. 1923.  56.  R o e t h e l i B. E. and Brown R. H. Ind. Eng. Chem. 23_, 1010 1931.  57.  R u s s e l l R. P., Chappell E. L. and White A. Ind. Eng. Chem. 1£, 65 1927.  58.  Schikorr G. Korr U Met. 4, 244,  59. 60.  1928.  Shemilt L. W. P r i v a t e communication February Simmod M. T. J . Electrochem. Soc. 9J, 31  1950.  61.  Skaperdas G. and U h l i g H. Ind. Eng. Chem. 34, 748 1942.  62.  S p e l l e r F. N. and Kendall V. V. I b i d 15, 134 1923.  63.  S p e l l e r F. N. J . F r a n k l i n I n s t . 1^,  64.  523  1959.  1922.  S p e l l e r F. N. Corrosion Causes and Prevention McGraw H i l l Book Company New York 1935.  97  65.  Spinks J . ¥. T. Chem. i n Canada 10, #3, 36 1958.  66*  S t r e i c h e r L. J.A.W.W.A. 48, 219 1956.  67.  Stern M. Corrosion 13 #11, 775t 1957.  68.  Treybal R. E. Mass Transfer Operations McGraw H i l l Book Company New York 1955.  69.  U h l i g H. Corrosion Hand Book John Wiley and Sons 1948.  70.  Vernon W. H. Chem. and Ind. 21, 314, 1943.  71.  Walker W. H. Trans. Am. Electrochem. Soc. 14, 175 1908.  72.  Wesley V/. A. Proc. Am. Soc. Test Mat. 43_, 649 1943.  73.  Wesley W. A. and Copson H. R. Trans. Electrochem. Soc. j>2, 403 1927.  74.  Wilson E. B. An I n t r o d u c t i o n t o S c i e n t i f i c Research McGraw H i l l Book Company New York 1952.  75.  Wilson R. E. Ind. Eng. Chem. 15_, 127 1923.  76.  Winkler R.  Ber.  21, 2843 1888.  77.  Wormwell F. J. Appl. Chem. 3 #4, 164 1953.  78.  Wormwell F. J . I r o n S t e e l I n s t . 154, 219 1946.  79.  % c h e L. H. Trans. Electrochem. Soc. 82, 265 1945.  80.  Young R. S. I n d u s t r i a l Inorganic A n a l y s i s Chapman H a l l L t d . , London 1953.  TABLE XXII Weight Loss Tests a t 45°F Specimen  Time Days  1 2 3  9  Velocity fps  Weight grams. before after 352.5752 355.1780 353.9262  4.5  352.2700 354.7492 353.6993  TABLE XXIII P o t e n t i a l Time Data f o r Specimens 1, 2, 3 V e l o c i t y 4.5 f p s Temperature 45°F. Time Days  -  P o t e n t i a l (-) V o l t s v s . ACE Specimen 1  0 1 2.1 3.9 5.0 7.1 9.0  .5055 .3460 .2350 .2205 .2436 .2160 .1980  2  3 .5021 .3842 .2870 .2750 .2880 .2800 .2555  .4965 .3886 .3770 .3190 .3200 .3300 .2890  TABLE XXIV Weight Loss Tests at 90°F Test Run #1 • Specimen  Time Days  Velocity fps  Weight grams. before after  11  173.2086  172.3942  12  171.4496  170.5384  13  172.6097  171.8200  172.7458  171.8540  15  172.2350  171.1990  16  17O.9OOI  170.1162  17  173.7402  172.9621  18  173.2532  172.3838  14  15  4.5  Test Run #2 1  171.8552  171.1686  2  172.8999  171.8000  3  173.2971  172.2248  4  172.2950  171.1128  171.8390  170.8548  6  171.0864  169.9850  7  171.1864  169.9710  8  172.2299  171.2050  9  172.4342  171.4121  10  175.0322  174.0800  5  15  3.0  100  TABLE XXV Weight Loss Tests a t 90°F Test Run #3 Specimen  Time Days  Velocity fps  Weight grams before after  19  173.9009  172.8321  20  174.9551  173.8221  21  171.6795  170.3950  172.9472  171.6410  23  172.4650  170.9666  24  173.2014  171.8910  25  171.2013  169.6368  26  170.3062  169.1498  22  15  .75  Test Run #4 27  175.0702  174.6145  28  172.8480  172.4971  29  170.6573  169.9625  171.8485  171.1350  31  171.9612  171.3220  32  171.8096  171.3107  33  172.6826  172.4000  34  172.3969  171.7338  30  10  .75  TABLE XXVI Weight Loss Tests a t 90°F • Test Run #5 Specimen  Time Days  Velocity fps  Weight grams Before After  35  171.7495  171.0900  36  172.2988  171.8562  37  173.9984  173.3595  38  171.7125  170.9220  172.9200  172.1134  40  173.4128  172.9546  41  173.7354  173.3090  42  171.1401  170.3054  43  169.6740  168.7820  39  10  1,5  Test Run #6  93  167.5474  167.5121  94  167.3330  167.2987  95  167.4203  167.3880  167.0175  166.9865  97  168.0691  168.0301  98  167.2141  167.1868  99  166.6066  166.5709  100  167.2800  167.2380  96  5  .75  TABLE XXVII Weight Loss Tests a t 90°F Test Run #7 Specimen  Time Days  Velocity fps  Weight grams Before After  161  177.2992  175.0900  162  177.2300  175.3000  163  176.6245  174.1505  164  176.9197  174.5803  176.2505  173.9427  167  177.8128  174.5682  168  176.6756  173.5385  169  175.8850  172.6615  170  175.0189  172.6780  166  25  .75  Test Run #8 171  177.9289  175.4787  172  178.9605  176.4762  173  180.5700  178.1505  174  179.4100  176.9335  178.9525  176.5500  176  178.6990  176.2981  177  178.5789  176.2000  178  178.3328  176.0824  179  179.3012  176.8437  180  177.9512  175.4025  175  25  1.5  TABLE XXVIII Weight Loss Tests at 90°F Test Run #9 Specimen  Time Days  Velocity fps  Weight grams Before After  181  178.0224  175.9256  183  178.4246  176.3200  184  179.4989  177.4708  185  178.0292  175.7700  177.1200  175.0021  187  178.3511  176.2603  188  178.4262  176.3428  189  178.1505  176.0890  190  179.0824  176.9205  186  25  3.0  Test Run #10  191  178.3885  176.4025  192  178.4000  176.3692  193  178.3793  176.6000  179.3123  177.2635  196  179.5818  177.6300  197  178.6674  176.5854  198  177.5056  175.7320  195  25  4.5  TABLE XXIX Weight Loss Tests a t 90°F Test Run #11 Specimen  Time Days  Velocity fps  Weight grams Before After  199  176.9292  176.4851  201  177.1587  176.9200  202  178.2732  178,1624  178.9802  178.8856  204  178.5537  178.3200  205  176.8700  176.7302  206  177.9268  177.8437  207  177.7486  177.5951  203  5  1.5  Test Run #12 208  178.9700  177.5403  209  179.5012  178.2000  210  176.9500  175.6736  211  178.9121  177.5464  180.1853  178.8563  213  178.2302  176.8265  214  179.6850  173.2351  215  130.3732  178.3624  216  180.4887  179.1000  212  15  1.5  105  TABLE XXX Weight Loss Tests at 130°F Test Run #13 Specimen  Time Days  Velocity fps  Weight grams Before After  101  167,0616  163.7000  102  168.9916  165.6230  103  166.2364  163.1192  166.8882  163.6752  105  168.3498  164.8025  107  165.8194  162.2653  108  168.0995  164.8421  109  168.1982  164.5495  110  168.7393  165.1238  104  25  1.5  Test Run #14  111  167.0030  164.4421  112  167.5772  164.6820  113  167.3408  164.2305  168.9501  166,0025  116  166.8350  163.8905  117  168.1910  165.2532  118  167.6098  164.8118  114  25  4.5  TABLE XXXI Weight Loss Test a t 130°F Test Run #15 Specimen  Time Days  Velocity fps  Weight grams Before After  119  167*3754  164.3398  120  167.7203  164.4501  121  168.9381  164.7705  122  167.6282  164.3512  167.9608  166.5925  125  169.7200  166.2450  126  169.9256  166.4872  127  168.3920  165.0388  128  167.8825  164.5103  64  171.1853  167.7906  65  171.1202  167.8990  66  170.7511  167.1898  171.2533  167.6982  69  170.5846  167.1354  70  172.2685  168.9653  71  170.4358  167.0423  72  170.8082  167.4980  123  25  3.0  Test Run #16  67  15  .75  TABLE XXXII Weight Loss Tests a t 130°F Test Run #17 Specimen  Time Days  Velocity fps  Weight grams Before After  73  170.2489  167.0024  74  169.3084  166.8728  129  168.1478  164.9085  167.3576  164.0500  131  177.6201  174.6645  132  178.0702  175.1101  134  177.6004  175.0387  135  177.3000  174.4682  130  10  1.5  Test Run #18 136  178.6305  176.0575  137  178.2502  175.1815  138  179.4200  176.3505  178.0703  174.9712  140  173.3908  175.1818  142  176.7632  173.7578  143  178,2808  175.3975  139  15  3.0  TABLE XXXIII Weight Loss Tests a t 130°F Test Run #19 Specimen  Time Days  Velocity fps  Weight grams Before After  144  178.9075  175.9881  145  173.3135  175.9253  146  178.5102  175.9078  178.8159  176.2805  149  177.8604  175.5000  150  177.7189  175.2012  151  178.5950  176.0435  152  177.3169  174.7214  153  176.6005  174.8992  154  177.1492  175.2504  155  178.7738  176.3786  179.5268  175.8428  158  173.0905  176.2500  159  173.6988  176.9210  160  173.8902  177.0005  147  10  .75  Test Run #20  157  10  4.5  109  TABLE XXXIV Potential Time Data for Specimens 20, 24, 26, 162, 167. Velocity .75 fps Temperature 90°F Time Days  0 1 2 3 4 5 6 7 rt  O  9 10 11 1 O  13 14 15 16 17 18 19 20 21 22 23 24  Potential (-) Volts vs ACE Specimen 20  24  26  162  167  .7950 .8695 .8645 .8780 •.8250 .8295  .8100 .8520 .8430 .8745 .8705 .8225  .7950 .8315 .8410 .8604 .8230 .8200  .5400 .7400 .6600  .5660 .7500 .6100  .7815  .7720  .7720  .6700 .6700 .7000 .6750  .6300 .6300 .6700 .6300  .7830 .7810 .7502  .7610 .7580 .7501  .7545 .7545 .7305  .6650  .6300  .6720  .6615  .6350  .6050  .6055  .5750  .6000 .5570 .4540  .5850 .5250 .4490  .5060  .4950  110  TABLE XXXV P o t e n t i a l Time Data f o r Specimens 173, 179. V e l o c i t y 1,5 f p s Temperature 90°F Time Days  0 1 2 3 4 5 6 7 8 9 10  P o t e n t i a l (-) v o l t s vs ACE Specimen  #173  #179  .3000 .3550 .2200  .2750 .4780 .3400  .3050 .4100 .4740 .5530  .4830  .6350  .5700  .6465  .5700  .6200  .5110  11  12 13 14  .5200  .5815  15 16 17 18  .5630 .5160  .3550  20 21  .4140 .4540  .3900  19  23 24 25  .4610 .4850  TABLE XXXVI P o t e n t i a l Time Data f o r Specimens 1, 5, 184, 190. V e l o c i t y 3.0 f p s Temperature 90 F P o t e n t i a l (-) v o l t s vs ACE Specimen  1  5  .6350 .8470 .8336  .6845 .7436 .7242  .7248 .6426 .6170 .6090 .6385  ;6945 .6230 .6190 .6070 .6260  .6026  .5791 .5870  .6000  184  .7150 .6100 .3550 .2650 .4390 .5250 .5900 .6150  190 .8200  .6200  .4830  .4540 .5200 .4780 .4290  .6050  .4390  .6200  .4830  .6150 .5160 .4490  .4740  .3870  .2835 .2050 .2150 .2350  .3050  .2800  .3250  .3350 .3340  112  TABLE XXXVII P o t e n t i a l Time Data f o r Specimens 13, 17, 195, 196. V e l o c i t y 4.5 f p s Temperature 90 F Q  Time Days  P o t e n t i a l (-) v o l t s vs ACE Specimen 13  0 1 2 3 4  .9500  17  196  195  .8985 .8732 .8421  .8130 .8190 .7941 .7636 .7320  .7200 .8000 .6300  .6800 .7100 .5660  .6100  .5580  6 7 8' 9 10 11  .8401 .7770 .7100 .7235 .7195  .7270 .6768 .6640 .6890 .6825  ' .6750 .6400  .6700 .6050  13 14 15 16 17 18  .7310  .6830  K J  .9220  12  19  20 21  22 23 24 25  •  .6350  .5900  .6235  .5980  .6600 .6350 .5580  .6350 .5900 .5400  .5250 .4340  .5060 .4290  .4740  .4490  113  TABLE XXXVIII P o t e n t i a l Time Data f o r Specimens 67, 70. V e l o c i t y .75 f p s Temperature 130°F Time Days  P o t e n t i a l (-) V o l t s vs ACE Specimen 67  0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15  16 17 18  19 20 21 22 23 24 25  %  70  .7280 .9560  .7960 .9560  .8400 .8020 .7600 .7740 .7740  .8810 .8500 .8620 .3400 .8300  .8200 .8200  .8410 .8410  .7470 .6830 .6220  .8080 .7470 .6670  TABLE XXXIX P o t e n t i a l Time Data f o r Specimens 105, 109. V e l o c i t y 1.5 f p s Temperature 130°F P o t e n t i a l (-) V o l t s vs ACE Specimen 105  109  .4215 .9020 .9820 .9950  .4590 .8030 .8300 .8300  .9880 1.0400 .9950 .9760  .8400 .8510 .8400 .8350  .9500 .9880  .8300 .8300  .9660 .8560 .7850  .8560 .7850 .7020  .7960  .7340  .7740  .7150  .7400  .6900  TABLE XL P o t e n t i a l Time Data f o r Specimens  121, 126, 140.  V e l o c i t y 3.0 f p s Temperature 130°F P o t e n t i a l (-) V o l t s vs ACE Specimen  121  126  140  .4760 .9260 .7850  .5520 .8690 .8400 1.0220 .7670 .8350  .7340 .7020 .6460 .6180  .6960 .6830 .6590 .6410  .6320 .6220  .6590 .6410  .5650 .4630  .6140 .4900  .4070  .4260  .3870  .3950  .3680  .3680  .3910  .3950  .7600 .7850 .7090 .6260  .6260 .6410  116-  TABLE XL P o t e n t i a l Time Data f o r Specimens  113, 157, 159.  V e l o c i t y 3.0 f p s Temperature 130°F Time Days  0 1 2 3 4 5 6 7 8 9 10 11 12 13 14  P o t e n t i a l (-) V o l t s vs ACE Specimen  113  157  159  .8300 .9880  .7740 .8865 .7340 .7020  .7790 .7910 .6830 .6520  .6520  .6300  .6220 .5440 .5520  .6140 .5270 .5370  1.0560  .9260  .7850 .7470 .7400 .7470 .7340 .7600 .7280  17  .7090 .6220 .5660 .6220  19  .6000  21  .5650  15  16 18  20 22  23 24 25  .5860 .5060  IRON C O N C E N T R A T I O N  ppm  12  TEMPERATURE Figure 25  °F  V a r i a t i o n i n Oxygen Concentration w i t h Temperature. H H  inlet city water S i  5\ constont overflow emergency overflow  head tank  ^ upper ^—distributor \ tank U  LI  U  LX\  rubber hose plug  \\  K-rotameter A — ^  ~>-volve n  n  n  A  N  lower distributor tank "mi  TOY  Figure 26  Schematic Representation of Test Apparatus.  pump rnotoq  119-a  Test Numbers Shown I - 5 8 16 Type A pipe 6 - 1 5 8 1 8 - 2 0 Type 8 pipe 17 T y p e A 8» B p i p e 90°F I30°F~------  Velocity fps I?  75  19  7  12  18 l~4~  1-5  II  8  16 13  3-0  20 10  45  12  27 Sept.  Figure 27  12 Oct.  Calendar of Test Runs.  27 1953  II  26 Nov.  26  13  Dec.  10 Jon. 1959  25  SAMPLE CALCULATIONS C a l c u l a t i o n of amount of corrosion f o r specimen 113 Area of specimen = 2TTrl = 2 x 3.1416 x .412 x 4 - 10.354 i n  2  Area of specimen i n square decimeters = 10.354 x ( 2 . 5 4 ) 100  2  = .669 weight l o s s md  3060.3 mg.  mg weight l o s s area i n square decimeters - 3060.3 .669 - 4586  C a l c u l a t i o n of average standard d e v i a t i o n f o r t e s t run #13 Average standard d e v i a t i o n  =  --  162  Comparison of S p e l l e r and Kendall (62) r e s u l t s w i t h those of mass t r a n s f e r c o r r e l a t i o n Sh=  ,023Re Sc' ,8  Sh number — k d D  33  D  G= 0 - w a t e r = ' D  6  8 2x  1  0  _  1  2  ^ /year 2  d = 5,2 x 1 0 " f t 2  k^—  gram moles 02 consumed yearCft^) ( gram moles) cu f t  The average oxygen concentration was 5.94 c c / l i t e r (62) Therefore  gram moles - 5.94 x 1.4 x 10~3 cu f t 3.2 x 10-1 x 3.44 x 1 0 ~  7.52 x 10"  Let s = gram moles of oxygen consumed per year per square f e e t of c o i l Therefore  k D  1.34 x 1Q s x 5.2 x 10~ _ 1.02 x 1 0 6.32 x 10-J2  ~  2  1  Sc number — (^n-v-water) (Do2~water'' / ' w a t e r 80°F = 6.05 x 10"  l b s / f t sec  4  D  0 -water = 2  6  '  8 2  ^ w a t e r 30^ = ' 6  * lO"  1  *  1  2 4  1  q  l b s  /cu  Sc _ 6.05 xlQ-4 3.15 x 1 0 6.24 x 10 x 6.82 x 10"  f  7  x  1  Sc*33  _  7e  Re number _  =  t  4.5 x 10  2  1  6 d^rf  d = 5.2 x 10 ^ f t  6.24 x i o i = 6.05 x 10-4 l b s / f t sec Therefore Re _  5.2 x 10" x v x 6.24 x 10 - 5.35 x 10 x v 2  6.05 x 10-4 Re* = 8  9.5 x 10 x v 2  ,  S  Therefore using o v e r a l l equation  1  3  122  1.02 x 10 x s 1  s = 1.63 x 10  1  9.5 x 10 x v 2  x v  8  x 7.6 x 2.3 x 10~  2  3  To'change the u n i t s of s t o the u n i t s of K, the s p e c i f i c corrosion r a t e , the u n i t s of f t / s e c must be changed t o l i t e r s / y e a r and sq f t must be changed t o sq cm. s  =  s  =  1.63 x 10 x 1.87 x 10 1  3.03 x 10 x v ' 9.29 x 10^ 7  8 =  6  x v'  -  B  3.3 x IxA x  3.03 x 10 x 7  V  8  Substituting s into K K —  3.3 x lpA- x v ' x 3.32 5.94 8  v 1.0 4.0  v  t 8  . 1.0 3.04  =  1.8 x 10 x v * 4  K  1.80 x 10 5.35 x 10  4  4  8  v'  B  

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