Open Collections

Effects of blended hydrogen enriched natural gas on the microstructure and mechanical properties of a X42 steel pipeline and Grade 290 weld

University of British Columbia

The objective of this thesis was to investigate the effects of hydrogen-enriched natural gas (HENG) blend on the microstructure and mechanical properties of an API 5L X42 pipeline that is currently being used in FortisBC’s infrastructure. The seam welded X42 pipeline is a commonly used material in North America’s natural gas infrastructure and is manufactured through hot rolling and connected with submerged arc welding (SAW) along the seam. A decommissioned Vintage Grade 290 pipe was manufactured in the same way as the X42 material which was also used for this study. The introduction of hydrogen gas into other X-series pipeline systems has shown the potential to cause hydrogen embrittlement (HE) which can lead to premature failure. This embrittlement could degrade the mechanical properties and be one of the main reasons for a shortened life cycle, causing repairs to occur more frequently. In this study, the ultimate tensile strength, yield strength, percent elongation, area reduction, fracture surface, microhardness, and phase compositions were all tested on both the X42 base and Vintage Grade 290 welded material. These properties were obtained through tensile tests, Vickers hardness testing, and analysis on a scanning electron microscope. Tensile test samples were obtained in the longitudinal direction in the pipe wall with the welded samples in the hoop direction perpendicular across the weld. These samples were induced in various hydrogen and natural gas blends for different prolonged periods. Induction blends consisted of 0%, 5%, and 20% hydrogen concentration by molar mass mixed with natural gas. The samples were then held in these enriched environments for periods of 2 weeks, 2 months, and 6 months. The results revealed that both the hydrogen concentration and time of exposure have small impacts on various properties of the material in the X42 base material. As for the Grade 290 weld, the hydrogen concentration and exposure time did not impact the mechanical properties of this material. To iii analyze the hydrogen susceptibility of the material, a 2% and 3% factor of embrittlement was determined for the X42 and Grade 290 respectively. Microstructural analysis of the pipeline at various locations was conducted utilizing an optical microscope, scanning electron microscope, and energy dispersive X-ray spectroscopy. These revealed the phases and chemical composition present in the X42 base material and the Vintage Grade 290 fusion zone (FZ), heat affected zone (HAZ), and base metal (BM) regions. Micro-hardness testing on the X42 showed that hydrogen could diffuse into the material and increase the hardness near the exposed surface. This hardness increase was not present in the Vintage Grade 290 HAZ and FZ.

Text

2020-12-14

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/76796

Mechanical Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/