Fractures occurred at the root of valve body connection thread during the use of three-valve manifold of differential pressure transmitter in diesel hydrogenation unit reactor of a petrochemical company.Through disassembly,testing and failure analysis of the fracture parts,the survey revealed that there is widening trend of grain boundary at cracking area and presence of intergranular corrosion.Under the long-term influence of intergranular corrosion,intergranular stress corrosion cracking is apt to develop.In addition,the material of valve body can't meet the standard requirements;strip carbides in organization further ac-celerate the cracking.In view of the situation,specific protection strategies were advised.
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