The environmental fatigue evaluation for piping is performed based on conservative formulas and environmental correction factors (Fen) calculation because of the difficulty of finding transient strain history and to reduce the cost of the analysis. Therefore, more sophisticated analyses using a finite element model of piping would be required to meet Code requirement (cumulative fatigue usage factor including the environmental effects, CUFen < 1).
The environmental fatigue evaluation was performed considering the transient stress history for pressurizer surge and spray piping. The stress histories due to the thermal moment and thermal gradient through the wall thickness were evaluated using a three-dimensional piping system model. The strain rate for Fen calculation was calculated in accordance with draft Code Case 10-293 and 14-1177.
For the purpose of comparison, environmental fatigue usage factors and Fen are calculated based on the ASME Code NB-3600 rules. The differences of Fen, CUF, and CUFen are reviewed between the methods using NB-3200 rule and NB-3600 rule.
Finally, this paper shows that environmental fatigue evaluation considering transient history is an effective method in lowering the environmental CUF value of the piping.