A Life Assessment for Steam Turbine Casing Using Inelastic Analysis

Abstract

An important characteristic of a fossil power plant is its ability to maintain reliability and safety of the plant against frequent start-ups and load changes. Unstable states arising during start-ups, shutdowns and load changes give rise to unsteady temperature distribution with time in steam turbine innercasing (HP/IP), which results in non-uniform strain and stress distribution. The rapid increase of temperature during starts-ups, especially, causes susceptible to failure and reduction of expected life for steam turbine components. Thus accurate knowledge of thermal stresses is required for the integrity and lifetime assessment for the turbine components. In this paper, the fatigue damage is calculated of steam turbine inner casing was calculated by combining the stress analysis based procedure and Neuber's rule. By substituting the material cyclic stress-strain relationship into the Neuber equation, the inelastic total strain range was obtained. Using this study, life consumption of steam turbine inner-casing can be obtained and a guideline for effective maintenance was proposed.

Thermo-mechanical Analysis of Gas Turbine Casing to Enhance Fatigue Life

“…Gas turbines essentially consist of stationary and rotary components which are being encased in a structure called "casing" generally a steel structure or steel casing. It is one among the major components of engine stator and its appropriate design efficiently controls the radial displacement of rotor and stator and the weight which indirectly improves the efficiency of engine and reliability [1], [2].The major issue with casing is that it has to be designed in such a way that it must be safeguarded from thermal stresses. During starting, shutting down and load variation in many turbines component, unstable condition arises that leads to distribution of transient temperature [3]- [5].…”

“…Nozzle fit corner was chosen for the analysis as it is often exposed to cracking due to thermo-mechanical low-cycle fatigue [1]. Choi woosung and Hyun jungseob calculated fatigue damage of steam turbine casing by stress analysis/ neubersrule [2]. Schwingshackl and Petrovinvestigated different non-linear models for dynamic flange behavior using non-linear dynamic analysis of casing [17].…”

Thermal Stress Analysis in Structural Elements of HRSG Casing

“…Also, the casing of HRSG can be easy to damage during the start-up. However, researches related with these problems have not been conducted as much as the gas turbine or steam turbine casings which have the same cases of failure [12][13][14][15].…”