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Effect of Surface Hardness Distribution on SSC Propagation Behavior in Grade X65 Linepipe

Picture for Effect of Surface Hardness Distribution on SSC Propagation Behavior in Grade X65 Linepipe
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Application of sour linepipes has expanded toward severe sour environment regions including higher H2S partial pressure conditions. In 2013, actual sour gas pipeline failure occurred due to SSC (Newbury et al., 2018). One of the possible root cause of SSC was assumed to be a formation of hard spots in a
surface region of steel. Fairchild et al. investigated and proposed three hard zone formation mechanisms including carbon contamination, dual phase microstructure and heat transfer variation in a recent paper (Fairchild et al., 2019; Newbury et al., 2019).

Product Number: 51323-19238-SG
Author: Junji Shimamura, Daichi Izumi, Mitsuhiko Hakoda, Joe Kondo, Mohammed A. Alanezi, Yasser S. AlSubhi, Satoshi Yamaguchi
Publication Date: 2023
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UOE linepipe has been long used for high-strength and severe sour application, however, recently hard-zone issue has been often discussed regarding sulfide stress cracking (SSC) in severe sour environment containing H2S gas. One of the possible root cause of SSC was assumed by formation of hard-zones in the steel pipe inner surface. Advanced-OLAC-based cooling rate control for surface and mid-thick area can achieve uniform and low hardness at the surface portion while maintaining sufficient tensile properties. By improving cooling homogeneity as well as surface cooling rate control, homogeneous granular bainite microstructure can be obtained, resulting in stable low surface hardness even in the inner surface of Grade X65 pipe. SSC propagation behaviors were investigated using Grade X65 samples with two different artificial hard-zones. One is the hard-zones with shallower depthless than 0.5 mm made by the laser heat treatment. The other is the hard-zones with depth of approx. 1.2 mm made by the accelerated cooling with intentionally high surface cooling rate. Using these samples, four-point bend (4PB) SSC tests were conducted under 1 bar H2S condition. As the result, when the hard-zone depth was less than 0.5 mm, crack arrested regardless of the hard-zone width or length. On the other hand, when the hard-zone depth was approx. 1.2 mm, crack propagated. It was found that the deeper the hard-zone, the easier the crack propagates. In the mill trial tests of Grades X60 and X65 UOE pipes, it was found that lowering the surface hardness to less than 240HV0.5 led to no SSC appearance in 1 bar H2S condition.

UOE linepipe has been long used for high-strength and severe sour application, however, recently hard-zone issue has been often discussed regarding sulfide stress cracking (SSC) in severe sour environment containing H2S gas. One of the possible root cause of SSC was assumed by formation of hard-zones in the steel pipe inner surface. Advanced-OLAC-based cooling rate control for surface and mid-thick area can achieve uniform and low hardness at the surface portion while maintaining sufficient tensile properties. By improving cooling homogeneity as well as surface cooling rate control, homogeneous granular bainite microstructure can be obtained, resulting in stable low surface hardness even in the inner surface of Grade X65 pipe. SSC propagation behaviors were investigated using Grade X65 samples with two different artificial hard-zones. One is the hard-zones with shallower depthless than 0.5 mm made by the laser heat treatment. The other is the hard-zones with depth of approx. 1.2 mm made by the accelerated cooling with intentionally high surface cooling rate. Using these samples, four-point bend (4PB) SSC tests were conducted under 1 bar H2S condition. As the result, when the hard-zone depth was less than 0.5 mm, crack arrested regardless of the hard-zone width or length. On the other hand, when the hard-zone depth was approx. 1.2 mm, crack propagated. It was found that the deeper the hard-zone, the easier the crack propagates. In the mill trial tests of Grades X60 and X65 UOE pipes, it was found that lowering the surface hardness to less than 240HV0.5 led to no SSC appearance in 1 bar H2S condition.

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The Effect of Crack Start Positions on NACE TM0177 DCB Elastic Compliance

Product Number: 51319-12842-SG
Author: Jun Nakamura
Publication Date: 2019
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The Double Cantilever Beam (DCB) test method standardized in ANSI NACE TM0177 is increasingly applied as a quality assurance test to specify the performance of carbon and low alloy steels for sour service. The DCB test method has been modified and specified tightly from the view point of specimen geometry test environment and initial stress intensity factor controlled by arm displacement to obtain highly repeatable test results.NACE TM0177 2016 method D has various types of starter notch configurations on DCB specimens. Crack start position shifted change specimen of EDM notch has been in accordance with NACE TM0177 since 2016 and the distance from a pin hole to a crack starter has been different.Previous research the influence of crack starter position on K1SSC has been revealed using Finite Element Analysis (FEA) and DCB tests. In this paper in order to clarify the applicability of compliance curve in TM0177-2016 and propose the new compliance curves FEA and experimental approach was performed. K1SSC of DCB tests should be evaluated in the same crack start positions from the view point of a fracture mechanics.
Picture for High strength steel SSC evaluation in mild sour environments at ambient and high temperatures
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51318-10920-High strength steel SSC evaluation in mild sour environments at ambient and high temperatures

Product Number: 51318-10920-SG
Author: James Wei / Manuel Gonzalez / Brian Chambers / Boris Thomas
Publication Date: 2018
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There is an increasing need to define the operating envelope for materials typically used as oil country tubular goods. This paper reports results of sulfide stress cracking (SSC) tests that were performed in mild sour environment at temperatures below 107°C.
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51312-01202-Selective Dissolution and Stress Corrosion Cracking Susceptibility of Austenitic and Duplex Stainles

Product Number: 51312-01202-SG
ISBN: 01202 2012 CP
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