Stress Oriented Hydrogen Induced Cracking (SOHIC) is recognized as an individual cracking mechanism in NACE MR0175/ISO 15156-2. SOHIC occurrence is rare and the mechanism not fully understood but thought to be restricted to carbon and low-alloy steels with low strength and low hardness. Several SOHIC resistance test methods have been reported, but none of the test methods is currently standardized. The newly developed "twist and bend" test is currently under standardization in NACE TG 536. Within this work, SOHIC resistance tests using the "twist and bend" test method were performed on SAWL large-diameter pipes of grades X52 and X65. All relevant sampling positions (base material, heat-affected zone, longitudinal weld) were investigated and the results were compared to standard four-point bend SSC tests without additional twist. A new test geometry using reduced specimen dimensions that allows testing of smaller specimens containing welds has also been developed. In addition, a finite element method (FEM) simulation comparing both test geometries was also performed. The SOHIC performance is discussed based on grade, microstructure and hardness of the investigated pipe materials. The investigated SAWL large-diameter pipes revealed excellent SOHIC resistance.
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机译：在NACE MR0175 / ISO 15156-2中，应力定向的氢致裂纹（SOHIC）被认为是一种单独的裂纹机理。 SOHIC的发生极少，其机理尚不完全清楚，但被认为仅限于强度低，硬度低的碳钢和低合金钢。已经报道了几种SOHIC电阻测试方法，但是目前尚无标准化的测试方法。 NACE TG 536目前正在对新开发的“扭曲和弯曲”测试进行标准化。在这项工作中，使用“扭曲和弯曲”测试方法对SA52级X52和X65级大口径管道进行了SOHIC电阻测试。研究了所有相关的采样位置（基础材料，热影响区，纵向焊缝），并将结果与标准的四点弯曲SSC测试进行了比较，而没有额外的扭曲。还开发了一种新的测试几何图形，该几何图形使用了减小的样本尺寸，可以测试包含焊缝的较小样本。此外，还进行了比较两种测试几何形状的有限元方法（FEM）仿真。根据所研究管道材料的等级，微观结构和硬度来讨论SOHIC性能。所研究的SAWL大直径管道显示出优异的耐SOHIC性能。
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