Leakage occurred on tin brass cooling plate tubes of emergency ventilation system in a nuclear power plant.Thus

several investigations were carried out

such as the macroscopic examination

broken tube material analysis

corrosion product analysis

electrochemical analysis

macro and micro analysis of crack and fracture

and the fracture SEM analysis.The results showed that

stress corrosion cracking(SCC) occurred on the tin brass in nitrite environment in the cooling medium was considered as the major reason.One of the reason is the NH4+ formed by nitrite made the tin brass tube particularly sensitive to the SCC.On the other hand

residual stress on the tin brass tube exacerbated the stress corrosion tendency.Several measurements were put forward

like replacing the broken cooling plate tubes for red copper tubes

increasing the TTA content in corrosion inhibitor from 1.0 mg/kg to 10-20 mg/kg

and so on.