Multiple cracks were found in S32168 austenitic stainless steel welding seam and base material of conversion gas three-way pipe in 2# hydrogen manufacturing unit after it has been in use for more than a year.Samples were taken from the cracked welding seam and base material.By adopting research approaches like chemical composition analysis,metallographic observation,fracture observation and hardness testing analysis,it is found that there is stress corrosion cracking sensitive medium at the fractures such as chloride ions and sulfur ions.The crack is transgranular extension with less forks at the tip and it's relatively round and blunt.There are also obvious shell patterns on the fracture surface.It is proved that the three-way pipe cracking is result from stress corrosion cracking and fatigue which caused by chloride ions,and hydrogen sulfide in the medium accelerated the cracking process.
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