Steam Turbine Casing Analyses to Determine Pressure and Temperature Limits – Crossover Piping and Pipe Flanges

Abstract

Abstract To ensure safe and reliable operation, steam turbine casings and piping must have acceptable stresses and maintain sealing when subjected to internal pressures and temperatures. Analysts conduct structural evaluations using finite element analysis (FEA) techniques to show acceptance. This paper outlines the analytical methods used to perform these types of analyses, provides analysis examples, and summarizes the process to create pressure and temperature limit maps. Finite element models determine pipe loads and stresses from static structural analyses for normal operation and hydro test conditions, and transient analyses for heat-up and cool-down conditions. As part of the turbine model, the piping is evaluated for stress acceptability when subjected to internal steam pressure and temperature. The pipe flanges are reviewed for sealing capabilities and consider the effects of bolt stress relaxation at elevated temperatures, joint contact surface separation, and penetration of the internal pressure into the sealing surface. A series of analyses on the pipe and pipe flange models we re used to create pressure and temperature limit maps. These maps allow an engineer to determine the acceptability of the piping for a particular application.