The use of a solution of the inverse heat conduction problem to monitor thermal stresses

Jan Taler,Dawid Taler,Karol Kaczmarski,Magdalena Jaremkiewicz,Marcin Trojan,Piotr Dzierwa,M Dudek,W Suwała,S Łopata,J Leszczyński

doi:10.1051/e3sconf/201910801003

Abstract

Thick-wall components of the thermal power unit limit maximum heating and cooling rates during start-up or shut-down of the unit. A method of monitoring the thermal stresses in thick-walled components of thermal power plants is presented. The time variations of the local heat transfer coefficient on the inner surface of the pressure component are determined based on the measurement of the wall temperature at one or six points respectively for one- and three-dimensional unsteady temperature fields in the component. The temperature sensors are located close to the internal surface of the component. A technique for measuring the fastchanging fluid temperature was developed. Thermal stresses in pressure components with complicated shapes can be computed using FEM (Finite Element Method) based on experimentally estimated fluid temperature and heat transfer coefficient

Highlights

The lifetime of pressure elements and damage-free operation of the boiler can be reduced by high-rate heating or cooling of the boiler during its start-up or shutdown
The fluid temperature measured with high accuracy is necessary for determining transient thermal stresses in cylindrical pressure elements [9] or other elements with more complicated shapes
Boiler manufacturers determine thermal stresses on the inner surface of the pressure element based on the temperature measurement in the middle of the wall thickness and near the inner surface of the element

Summary

Introduction

The lifetime of pressure elements and damage-free operation of the boiler can be reduced by high-rate heating or cooling of the boiler during its start-up or shutdown. If the allowable temperature variations of the wall determined with Eq(3) are not exceeded, this means that thermal stress on the inner surface of the element, given by Eq(6) does not exceed the allowable value This indirect method of stress control is approximate due to the assumption of quasisteady state in the pressure component. Another popular method of controlling thermal stresses in pressure elements used by boiler manufacturers is to measure the temperature difference between the average temperature on the wall thickness and the temperature at a point located several millimeters from the inner surface of the component

The stress concentration factor for circumferential thermal stress

Conclusions