Comparison of Existing Methods for Studying Compatibility of Pipeline Steels with Compressed Hydrogen

One of the key challenges hindering the safe transportation of compressed hydrogen and its mixtures with natural gas through existing pipeline systems is the potential hydrogen embrittlement (HE) of steel pipe materials. At the same time, there is no universally accepted method for screening pipeline steels for hydrogen resistance. The existing testing methodologies used to assess the suitability of steels for operation in contact with compressed hydrogen have been analyzed. The results of comparative experiments conducted by the authors using various methods demonstrate that the outcomes of screening pipeline steels for hydrogen compatibility, obtained through testing in aqueous hydrogen sulfide solutions versus compressed hydrogen environments, do not correlate with each other. For example, when testing two pipeline steels with strength classes K52 and X70 for stress corrosion cracking in an aqueous hydrogen sulfide solution, both steels showed negative results and were classified as non-resistant. However, when tested in a gaseous hydrogen environment, they were categorized according to conditional resistance levels to hydrogen degradation as "resistant" and "satisfactorily resistant," respectively. The satisfactory resistance of the analyzed steels to hydrogen embrittlement was further confirmed by the authors' experiments evaluating these materials' resistance to crack propagation in a compressed hydrogen environment, which allowed both steels to be classified as "suitable" for operation in hydrogen-containing conditions. It is concluded that the acceptability of a given steel for pipelines transporting compressed hydrogen and its mixtures with natural gas should be determined based on testing results in the actual operational environment of the gas pipeline.