Study On Hydrogen-Induced Cracking Of Steels For Transportation Gas Pipeline

To improve Hydrogen-Induced Cracking (HIC) performance of steels fortransportation gas pipeline, NACE standard testing method is adopted to conduct HICperformance on steel plate and pipes made from a variety of steel levels, such as X52,X60, X65 and X70, and several modeling methods, as SSAW, UOE and ERW. Thisresearch program is supported and sponsored by the programs "the nationalizedresearch of the equipment of West-to-East Gas Pipeline project (WEGP)---thenationalized research of the large-diameter gas pipeline of WEGP ---the research ofpipeline material qualification of the large-diameter gas pipeline" ---A researchprogram sponsored by China national economic and trade commission, etc. It showedthat HIC immersion of pipeline steel with NACE TM 0284-1996 standard testingmethod can judge the HIC relative sensibility of different materials. The performanceof pipeline welding line is better than that of mother material. The HIC performance isrelated with the chemical composition, micro-structure and technical level in smeltingand rolling. The material with even, fine micro-structure, without MnS inclusion,without ferrite/pearlite banded microstructure has good HIC performance.After the testing conditions, such as testing liquid, time and size of tested materialare changed, the effect on the testing results are found. The results of comparison intesting liquid A and B suggest that same materials have different performance. The testliquid should be select according specific environment. With the same material, withthe increase of immersion time, the HIC crack because of absorbing hydrogen willcontinue to increase, but not much. The cool flattening does not affect HIC sensitivity.To ensure the accuracy of testing result, it should not be done, if the tested material canmeet the requirement of handling.With Hydrogen pressure theory, the judgment of HIC crack and mathematicalextension model of HIC crack is got, which can predict the length of crack. The resultsof this research have been used for material qualification of the WEGP large-diametergas pipeline and has important academic importance, and practical value tolong–distance pipeline safety.