Root cause analysis of the folding deformation for the expansion joint in the nuclear power station

In the nuclear power station, the expansion joint of moisture separator re-heater (MSR for short) was founded locally folding deformation under the outage condition. Folding deformation increasing will lead expansion joint leak, it would cause emergency stop when leaking seriously. To solve these problems, this paper analysis mainly on three aspects: the material organization performance, the expansion joint installation and the stress characteristic of expansion joint. Both the verticality deviation in the process of installation and the material hardness value exceed standard are the root cause of these problems. At the end of the paper, the improvements have been put forward for this problem.