Temperature monitoring criteria and evaluation of fatigue damage due to thermal stratification in nuclear plant piping

Thermal stratification has been reported as being responsible for pipe support damage and has likely been the cause or a contributing cause of pipe cracking. The root cause of stratification in safety injection piping was found to be a cold leakage through the isolation valve. A periodic leakage and turbulent penetration heating may result in significant fatigue damage. In this paper, thermal stress analysis was performed on the stratified SI piping and fatigue usage was obtained at the most critical area, valve outlet weld according to ASME Section 3 Code. Finally, temperature monitoring criteria could be suggested to ensure piping integrity in the field.=20