Prevention of stress corrosion cracking in piping welds

Stress corrosion cracking in piping welds in boiling water reactors (BWR's) has been observed in stainless steels as well as in low alloyed ferritic steels. Cracks in welded austenitic stainless steel piping in BWR's have been a serious problem in early operational years of nuclear power plants. Intergranular stress corrosion cracking (IGSCC) incidents of large diameter pipes have had an impact on plant availability and economics and defects are considered also as a safety hazard. The number of welds in connection to large diameter pipes is about 250 per unit, with a large wall thickness, about 30 mm in average, making inspection requirements stringent. SCC has been concentrated in the same systems in the power plants all over the world, namely reactor water cleanup systems, core spray and all lines of main re-circulation lines operating at high temperatures. In order to evaluate the rate of failures and the related safety, risk, cracking mechanisms effective in different materials have been analysed and remedial actions have been evaluated.