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. Several SOHIC resistance test methods have been reported, but none of the test methods is currently standardized.
Within this work SOHIC tests using the newly developed “twist and bend” test, which is currently under NACE standardization, were performed on specimens machined from large-diameter pipes of Grade B, X52 and X65. Within a load range between 50 % and 85% of the specified minimum yield strength of the respective grades, additional twist between 2 and 5 degrees was applied. The SOHIC tests were performed in NACE TM0177 Test Solution A at 1 bar H2S for 14 days. For comparison, also standard four-point bend tests without additional twisting were carried out. The specimens were evaluated visually, by magnetic particle inspection and metallographic examination.
The SOHIC performance is discussed based on grade, microstructure and hardness of the investigated pipe materials.