Analytical Assessment and Mitigation Strategies for Vibration in High-Pressure and Temperature Piping Subjected to Wall Thinning

Abstract Critical high energy piping lines such as the Main Steam Lines of a Nuclear Power Plant are subject to high pressure, temperature, and flow rates. Operational activities on these lines can produce large dynamic loads that can cause vibration problems resulting in high stresses. High vibration in these critical lines can lead to leakages, support failures, small bore piping failures, or a main steam line break. In aging nuclear power plants, wall thinning due to corrosion can be a significant factor to consider in piping lines that are known to experience vibration. This paper provides recommendations and mitigation strategies to reduce vibration problems in large-bore piping by assessing a typical layout of a main steam line utilizing a piping analysis software. Iterations are carried out to determine type and location of pipe supports to reduce piping code stresses and displacements. Areas of the piping known to experience wall thinning are also considered. In load cases where code stresses exceed code allowable limits, a Level 3 Fitness for Service Assessment per API 579-1/ASME FFS 2021 Code edition is performed via 3D finite element analysis. The analysis results show that the piping stresses and displacements due to dynamic loads can be reduced effectively with the addition of supports in appropriate locations. It can also be seen that the generalized wall thickness due to aging piping lines can have a significant impact on the code stresses. Finally, modeling local thinning area in the FEA model in the Level 3 FFS assessment resulted in a less conservative analysis that allowed the corroded component to operate without repair until the next planned outage.