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Impact Of Material Properties Of Thick-Wall X65 TMCP Plate Steel For Sour Service

Low-alloy steel of API(1) 5L grade X65 is commonly used as line pipe material for sour service applications, where, due to stringent operation limits, resistivity to Hydrogen Induced Cracking (HIC), Sulfide Stress Cracking (SSC) and Stress-Oriented Hydrogen Induced Cracking (SOHIC) is required and tested before and after plate into pipe forming. Within recent years more challenging requirements have been introduced, including more severe corrosion test conditions, increased mechanical properties and extended limitations regarding hardness, to enable application to increasingly severe sour service conditions. For steel plants and plate manufacturers this entails the necessity to further improve the quality of their products together with separate improvements and modifications on the production plants and processes that have been implemented anyway.

Product Number: 51322-17917-SG
Author: Thomas Haase, Christoph Bosch, Matthias Frommert, Markus Schürmann, Alexander Voelling, Sven Casper
Publication Date: 2022
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Low-alloy steel of API 5L grade X65 is commonly used as line pipe material for sour service applications. Within recent years more challenging requirements have been introduced, including more severe corrosion test conditions, increased mechanical properties, and extended limitations regarding hardness, to enable application to increasingly severe sour service conditions. Within this study a systematic investigation of material properties related to corrosion resistance was performed for low sulfur X65 TMCP-based steel plates with a thickness of 30 mm and 35 mm. Plate-to-pipe forming simulation to different wall thickness to diameter ratios (t/D) was undertaken and HIC testing according to NACE TM0284 was performed to investigate the HIC resistance after cold forming of heavy plates to SAWL pipes. Wall thickness to diameter ratios of 5 % and above were found to be accomplishable.

Low-alloy steel of API 5L grade X65 is commonly used as line pipe material for sour service applications. Within recent years more challenging requirements have been introduced, including more severe corrosion test conditions, increased mechanical properties, and extended limitations regarding hardness, to enable application to increasingly severe sour service conditions. Within this study a systematic investigation of material properties related to corrosion resistance was performed for low sulfur X65 TMCP-based steel plates with a thickness of 30 mm and 35 mm. Plate-to-pipe forming simulation to different wall thickness to diameter ratios (t/D) was undertaken and HIC testing according to NACE TM0284 was performed to investigate the HIC resistance after cold forming of heavy plates to SAWL pipes. Wall thickness to diameter ratios of 5 % and above were found to be accomplishable.

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Author: Xin Yue, Weiji Huang, Andrew J. Wasson, Jamey A. Fenske, Timothy D. Anderson, Brian D. Newbury, Doug P. Fairchild
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Steel pipelines are sometimes subjected to demanding sour environments resulting from the presence of high H2S contents. Pipeline materials, therefore, must be resilient against sulfide stress cracking (SSC) which is caused by H2S. Beginning in the 1980s, thermo-mechanically controlled processed (TMCP) steels have been widely used for the manufacturing of large-diameter sour service pipelines. The failure of the Kashagan pipelines in 2013 raised concern regarding the use of TMCP steels in sour environments. These concerns arise from the potential for local hard zones (LHZs) to be produced on the surface of the line pipe during TMCP processes, ultimately leading to through-wall SSC failures. In the present study, several X60 - X65 TMCP steels (both with and without LHZs) have been tested under different Region 3 (R3) conditions in the NACE MR0175/ISO15156-2 pH-H2S partial pressure diagram. It can be concluded that the presence of LHZs increases TMCP steels’ sour cracking susceptibility; however, TMCP steels without LHZs pass the SSC tests at even the most severe R3 environments. Traditional HRC or HV10 testing are not able to detect LHZs, and so lower load HV 0.5 or HV 0.1 tests are necessary. For TMCP steels, the current R3 may be further divided into R3-a and R3-b sub-regions. The sour cracking severity of R3-a is less than that of R3-b. Additional actions, like enhanced mill qualification of the TMCP plate, should be considered to ensure that no LHZs exist in steels to be utilized in R3-b environments.