Session: 21-07 Mechanical Integrity and Materials for Steam Turbines

Paper Number: 101392

101392 - Steam Turbine Casing Analyses to Determine Pressure and Temperature Limits – Crossover Piping and Pipe Flanges 

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.  To show that turbine casings and piping are acceptable, analysts conduct structural evaluations using finite element analysis (FEA) techniques.  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 of the overall steam turbine, including the main casing, steam chest, crossover pipes, and pipe flanges, are used to determine the pipe loads and stresses, and pipe flange sealing.  Static structural analyses are conducted for normal operation and hydro test conditions, and transient analyses are conducted for heat-up and cool-down conditions.  For the heat-up and cool-down evaluations, the results are reviewed to determine the times when the worst stresses occur.  The piping is evaluated for stress acceptability when subjected to internal steam pressure, temperature, and pipe loads.  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.  The acceptance criteria for the bolted joint sealing is based on the minimum width of the contacting surface and the minimum joint contact pressure. 

So that the design can be applied for the appropriate conditions, a series of analyses were conducted on the pipe and pipe flange models to create pressure and temperature limit maps.  These maps plot maximum allowable working pressure (MAWP) versus maximum allowable working temperature (MAWT) and allow an application engineer to determine quickly the acceptability of the casing for a particular application.  The paper presents an explanation of the process used to create the limit maps.  The work documented in this paper is a continuation of the work presented at the 2021 Turbo Expo conference.

Presenting Author: Paul T. Smith Elliott

Presenting Author Biography: Paul Smith, Senior Engineer, Product and Technology, Research and Development, Elliott Group

Paul is a senior mechanical engineer responsible for the finite element analysis (FEA) for the Turbine Development Group for Elliott Company’s Research and Development Department. He has been involved with FEA since 1981 when he started working for Westinghouse, first conducting seismic analyses for equipment for nuclear power plants, and then conducting shock and vibration analyses for shipboard equipment for the U.S. Navy. Paul has been with the Elliott Company since 1998, where he is responsible for the development and analysis of steam turbines. Paul is a professional engineer with a B.S. degree in Mechanical Engineering from Penn State.

Authors:

Paul T. Smith Elliott
Jason Schirato Elliott
Adam R. Neil Elliott
Daniel J. Griffin Engineering USA