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Creep rate assessment in function of stress and temperature for P91 steel

Osocha P., Duda P.

Journal of Energy Science

2012

Vol. 1, nr 2

71--82

Many coal-powered power stations uses equipment that have worked for over 20 years. Farther operation of the units involve large costs due to efficiency and reliability loss. Predicting the residual life of elements that have been in service for many years is especially important, when existing installations can not be replaced for economical or technological reasons. Accurate residual life assessment is the key for optimization of expenses due to unscheduled outages and unnecessary replacements. For power stations’ elements operating in high temperatures for very long time, understanding and mathematical description of creep phenomena is of utmost importance. It allows on FEM modeling of the elements behavior in time and assessment of worn degree. This paper presents methods for a creep strain and rate modeling. The main aim is to prepare an equation modeling creep rate of P91 steel in function of time, stress and temperature based on test data. For this reason, a creep phenomenon will be presented together with significant equations. Then, sample calculations, leading to the creep rate model establishment, will be performed. The paper finishes with the presentation of the equation describing the creep rate of P91 steel in dependence on time and stress and temperature.

Modelowanie zjawisk pełzania na przykładzie grubościennego ciśnieniowego trójnika widlastego wykonanego ze stali P91

Węglowski B., Osocha P.

Rynek Energii

2009

nr 6

140-145

Przedstawiono analizę cieplno-wytrzymałościową grubościennego elementu rurociągu parowego o złożonej geometrii - trójnika widlastego. Element wykonany jest ze stali P91 przeznaczonej do pracy w warunkach nadkrytycznych. Opracowano i przedstawiono matematyczny model pełzania specyficzny dla stali P91. Na bazie opracowanego modelu pełzaniowego i obliczeń MES oszacowano stopień zużycia elementu i jego pozostały czas pracy. Wyznaczono przebieg od-kształceń i naprężeń z uwzględnieniem pełzania.

This paper presents methods for residual life prediction of thick-walled pressure elements operating in power plants. The main aim is to show the finite element analysis based on uniaxial creep strain test data approximated with three dimensional mathematical model. For this reason, equations will be proposed with the description of creep strain dependence on time and stress for selected temperature, and the equations coefficients will be given in a table. Then, sample calculations based on the proposed model will be performed. The paper finishes with the FE simulation of thick-walled element creep behavior.