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SSC Limits Of TMCP Line Pipes

Product Number: 51321-16516-SG
Author: Hervé Marchebois/ Christoph Bosch/Ali Smith
Publication Date: 2021
$20.00
$20.00
$20.00

Large diameter TMCP (Thermo-Mechanically Controlled Process) pipelines have recently shown detrimental local variations in mechanical properties. Additionally, industry experience demonstrated that API(1) 5L / ISO(2) 3183 and NACE MR 0175 / ISO 15156 compliant TMCP linepipe presented increased ID surface hardness, commonly known as hardspots or hard layers. These surface anomalies are difficult to detect as standard QA/QC included in API/ISO standards do not cover this matter sufficiently. In cases where hard spots are present (e.g. as it has been observed on API 5L X60, X65 grades) this may lead to rapid SSC failures in severe sour service environments. Thus, the European Pipeline Research Group (EPRG)(3) launched at the end of 2017 a research program to define the SSC (Sulfide Stress Cracking) limits of TMCP pipes, to do a literature survey on Non-Destructive Techniques (NDT) able to detect surface hardness anomalies, and finally to reproduce hard layers through a “lab scale TMCP rolling” and point out the potential root cause of surface hardening. The current paper highlights work in progress with a specific focus on SSC limits of both API 5L X52 and X65 grades suitable for sour service and for natural gas applications in compliance with NACE MR0175/ISO 15156 - SSC Region 3 requirements. Threshold stress is determined using NACE TM0316 four-point bend testing in environments ranging from 1 to 17 bar of partial pressure of H2S. Results are discussed with respect to the through wall hardness of materials and recommendations are then proposed to be considered in general for sour service line pipe projects.

Key words: sulfide stress cracking, SSC, hydrogen induced cracking, HIC, blistering, ThermoMechanically Controlled Process, TMCP, linepipe, hardness

Large diameter TMCP (Thermo-Mechanically Controlled Process) pipelines have recently shown detrimental local variations in mechanical properties. Additionally, industry experience demonstrated that API(1) 5L / ISO(2) 3183 and NACE MR 0175 / ISO 15156 compliant TMCP linepipe presented increased ID surface hardness, commonly known as hardspots or hard layers. These surface anomalies are difficult to detect as standard QA/QC included in API/ISO standards do not cover this matter sufficiently. In cases where hard spots are present (e.g. as it has been observed on API 5L X60, X65 grades) this may lead to rapid SSC failures in severe sour service environments. Thus, the European Pipeline Research Group (EPRG)(3) launched at the end of 2017 a research program to define the SSC (Sulfide Stress Cracking) limits of TMCP pipes, to do a literature survey on Non-Destructive Techniques (NDT) able to detect surface hardness anomalies, and finally to reproduce hard layers through a “lab scale TMCP rolling” and point out the potential root cause of surface hardening. The current paper highlights work in progress with a specific focus on SSC limits of both API 5L X52 and X65 grades suitable for sour service and for natural gas applications in compliance with NACE MR0175/ISO 15156 - SSC Region 3 requirements. Threshold stress is determined using NACE TM0316 four-point bend testing in environments ranging from 1 to 17 bar of partial pressure of H2S. Results are discussed with respect to the through wall hardness of materials and recommendations are then proposed to be considered in general for sour service line pipe projects.

Key words: sulfide stress cracking, SSC, hydrogen induced cracking, HIC, blistering, ThermoMechanically Controlled Process, TMCP, linepipe, hardness

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Sulfide Stress Cracking Test of TMCP Pipeline Steels in NACE MR0175 Region 3 Conditions

Product Number: 51320-14446-SG
Author: Xin Yue, Weiji Huang, Andrew J. Wasson, Jamey A. Fenske, Timothy D. Anderson, Brian D. Newbury, Doug P. Fairchild
Publication Date: 2020
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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.  

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