Effect of stress-related pipe cracking remedies on low-temperature sensitization of welds in stainless steel

The low temperature sensitization (LTS) phenomenon in weld joints of 12 inch Type 304 stainless steel pipes was investigated. The program consisted of two major tasks: Task I, Quantify the degree of sensitization (DOS) as a function of aging time and temperature. Task II, Determine the effect of induction heating stress improvement (IHSI) and heat sink welding (HSW) on the subsequent rate of LTS. The DOS level of the head affected zones of weldments measured by the electropotentiokinetic reactivation (EPR) method did not change significantly by LTS heat treatments of various temperatures and time combinations designed to allow extrapolation to BWR service conditions. Task II results indicated that ISHI did not accelerate the LTS phenomenon. The pipe joint made by HSW showed no sensitization in the as-weld condition, but a LTS heat treatment (5000C x 24h) increased sensitization to the level of a conventional butt weld. It was concluded from weld simulation studies, and microstructure observations that the welding heat input defines a LTS seeded area in the HAZ, and thus determines the subsequent LTS occurrence