Use of FEA Software in Diagnosing Valve Performance Degradation
Author: Gregory Kramer, Robert Stakenborghs, Sean Moles, Lindsey Dziuba
A case study is presented using the commercial FEA (finite element analysis) software package Autodesk Simulation Mechanical to analyze a leaking 10″ double disk gate valve used in the nuclear power industry. This particular valve experiences adverse environmental conditions in normal operation: closed with main steam on the upstream side and ambient conditions on the downstream side. Maintenance and repair attempts performed on the valve were only found to temporarily fix the leakage and the root cause of the leakage was not discovered using traditional techniques. The location and environment of the valve made inspections and repairs difficult and costly. FEA software allowed multiple loading cases and simulations to be performed without affecting plant operations or personnel. These loading conditions included thermal, pressure, and simulated pipe movements. The results showed that after thermal transients, different thermal expansions between the valve body and valve stem could lead to decreased, or in some cases, increased seat force, depending on the initial conditions. The decreased seat force could make the valve prone to leakage while the increased seat force could increase the torque required to open the valve beyond specifications.