Abstract
Higher temperatures of the power boiler superheater operation may lead to high strains caused by the creep phenomenon. This paper presents a determination of the maximum allowable operating temperature limited by the creep phenomenon for steam superheater SH3. The calculations are carried out first on the basis of applicable European standards. Then, calculations are performed based on conducted creep tests, a proposed creep model, and a finite element method (FEM) model. A detailed creep phenomenon analysis based on the conducted creep tests shows that stresses that determine the creep process are mainly caused by pressure. Normal stresses resulting from bending are mainly the effect of thermal expansion. These stresses undergo significant relaxation because of creep. The creep phenomenon analysis explains the equations of the European standards. The presented calculations enable estimation of a safe value of the operating temperature which is constant over time. The estimated time of safe operation does not take account of temperature spikes. For this reason, pressure elements working at high temperatures must be inspected regularly to assess their wear state.
Highlights
A procedure aimed at evaluating the relationship between the plant operation strategies and its service life is presented by Stoppato [1]
The paper presents an analysis of creep phenomena in the power boiler superheater SH3 [7]
Maximum stresses are limited to allowable values for the time of 200,000 h under creep conditions, and creep strain should be less than 1% at 100,000 h
Summary
A procedure aimed at evaluating the relationship between the plant operation strategies and its service life is presented by Stoppato [1]. Many failures of elements of the power boiler superheaters are caused by the improper operation and the wrong support method of hanger tubes [5]. The hanger conditions in combination with thermal expansion and pressure loads cause stress concentration zones in superheaters and shorten the period of trouble-free operation. The existing methods of designing pressure equipment according to international standards do not require detailed creep analysis, taking into account this phenomenon as a function of time. The paper presents an analysis of creep phenomena in the power boiler superheater SH3 [7]. Calculations are first carried out on the basis of applicable European standards and with the help of the FEM software to model large structures [8]. Calculations are performed based on conducted creep tests, a proposed creep model, a FEM model, and with the use of the software to analyze the nonlinear material behavior [9]
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