CERT-Untersuchungen an Leitungsrohrstählen über eine Korrosionsgefährdung durch wasserstoffhaltige Gase bei hohen Drücken

CERT tests on line pipe steels for corrosion risks by hydrogen containing gases under high pressure Notched and unnotched round tensile specimens of line pipe steels were subjected to constant extension rate testing in autoclaves. The testing included pulling the specimens at a slow strain rate to fracture as well as slow strain rate cyclic loading. Besides base material, welded joints with varying hardness values ranging up to 400 HV were tested. Testing environments were inert gases (N₂, Ar, air, natural gas), 70 bar H₂ and various mixtures of H₂ and natural gas. In all gases, fracture occurred in the region of highest plastic deformation. When H₂ was present in the environment secondary cracking and fractions of brittle fracture were found on the fracture surface, their extent being reduced by the presence of O₂ and CO. No crack growth occurs in H₂ environment under cyclic loading when there is no plastic deformation. For the range investigated, there is no influence of hardness on the resistance of the materials to cracking, but surface finish and notch acuity exercise a strong influence.