Thermomechanical Analysis of a Pressurized Pipe Under Plant Conditions

Abstract

This paper is concerned with the development of a methodology for thermomechanical analysis of high temperature, steam-pressurized P91 pipes in electrical power generation plant under realistic (measured) temperature and pressure cycles. In particular, these data encompass key thermal events, such as “load-following” temperature variations and sudden, significant fluctuations in steam temperatures associated with attemperation events and “trips” (sudden plant shut-down), likely to induce thermomechanical fatigue damage. An anisothermal elastic-plastic-creep material model for cyclic behavior of P91 is employed in the transient finite element (FE) model to predict the stress–strain-temperature cycles and the associated strain-rates. The results permit characterization of the behavior of pressurized P91 pipes for identification of the thermomechanical loading histories relevant to such components, for realistic, customized testing. This type of capability is relevant to design and analysis with respect to the evolving nature of power plant operating cycles, e.g., associated with more flexible operation of fossil fuel plant.

A dislocation-based model for high temperature cyclic viscoplasticity of 9–12Cr steels

“…This change is driven by (i) a requirement to reduce emissions from fossil fuel plant, (ii) the control of energy cost by continuous mixing of energy sources and (iii) the intermittent nature of renewable energy. The complex operational cycles [1,2] which current and future plant must endure, therefore, leads to thermo-mechanical fatigue (TMF) and creep-fatigue (CF) failure. These failures commonly occur within the heat affected zone (HAZ) of welded connections (Type IV cracking) [3], sometimes as early as 5-10% of the plant design life.…”

Multiaxial cyclic viscoplasticity model for high temperature fatigue of P91 steel

“…4, illustrates the ability of the model to operate across a broad range of strain-rates. This result enables reliable extrapolation from accelerated laboratory test conditions to the strainrates typically observed in modern plant [8,9,22]. Fig.…”

“…P91 steel is a 9Cr martensitic steel typically used for plant header and piping systems due to its high creep strength [3]. A number of material models capable of simulating the constitutive behaviour of candidate materials already exist, including the unified Chaboche model [4][5][6][7] and the twolayer viscoplasticity model [8,9]. However, a hyperbolic sine material model has been chosen as it is more representative of the key mechanisms of deformation [10], enabling strain-rate independence of the material parameters and offers greater accuracy through the full stress regime [1,2,11].…”

Modelowanie wpływu parametrów eksploatacyjnych na stan naprężenia rur grubościennych w kotłach o parametrach nadkrytycznych

“…W rzeczywistych warunkach podczas uruchamiania bloku występują chwilowe gwałtowne zmiany temperatury uwarunkowane procedurą włączania poszczegól-nych elementów instalacji, związane z działaniem systemu sterowania. Pojawiają się wówczas oscylacje temperatury pary [1][2][3][4][5]. Szybkość zmian temperatury pary w krótkich przedziałach czasu może osiągać znaczne wartości.…”