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Surface Hard Zone Phenomenon In TMCP Line Pipe For Sour Service: A State Of The Art Review

Product Number: 51321-16563-SG
Author: Ali Smith/ Carlo Spinelli
Publication Date: 2021
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$20.00
$20.00

Carbon steel line pipes for sour service are required to exhibit hardness levels less than 250 HV10. The hardness of the inner pipe surface is especially critical, since sulphide stress cracking (SSC) may initiate at hardened surfaces. In recent years, high profile failures in sour environments were attributed to the presence of identified hard zones on TMCP pipe inner surfaces, and located far from welds. To help define the SSC limits of such material it is critical to know how these areas form. Based on these considerations, the European Pipeline Research Group has launched at the end of 2017, a research project aiming to reproduce these hard zones via lab scale TMCP, aiming to identify the root cause. This work deals with the first phase of this project, namely a state of the art review covering potential hard zone formation mechanisms in TMCP pipes. From the analyses performed, several mechanisms were found to be potentially relevant for hard zone formation during TMCP plate manufacture. First, possible carbon contamination from the casting phase. Second, the use of intense accelerated cooling equipment. Third, the effect of oxide scale in enhancing cooling power with standard accelerated cooling.

Key words: Hard spot, hard layer, TMCP, Line pipe, sour service

Carbon steel line pipes for sour service are required to exhibit hardness levels less than 250 HV10. The hardness of the inner pipe surface is especially critical, since sulphide stress cracking (SSC) may initiate at hardened surfaces. In recent years, high profile failures in sour environments were attributed to the presence of identified hard zones on TMCP pipe inner surfaces, and located far from welds. To help define the SSC limits of such material it is critical to know how these areas form. Based on these considerations, the European Pipeline Research Group has launched at the end of 2017, a research project aiming to reproduce these hard zones via lab scale TMCP, aiming to identify the root cause. This work deals with the first phase of this project, namely a state of the art review covering potential hard zone formation mechanisms in TMCP pipes. From the analyses performed, several mechanisms were found to be potentially relevant for hard zone formation during TMCP plate manufacture. First, possible carbon contamination from the casting phase. Second, the use of intense accelerated cooling equipment. Third, the effect of oxide scale in enhancing cooling power with standard accelerated cooling.

Key words: Hard spot, hard layer, TMCP, Line pipe, sour service

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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
$20.00

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.