Structural integrity assessment of superheater outlet penetration tubeplate

In recent years, the Linear Matching Method (LMM) has been well developed for the integrity assessment of the component subjected to cyclic thermal and mechanical loads. In this paper, the fatigue damage of a superheater outlet penetration tubeplate is assessed in detail using the LMM with an ABAQUS 3D finite element model. The significant thermal transients of the component are due to the out of phase steam temperature oscillations. The primary loading on the component is from pressure (steam and gas) and system moment on the penetration and tail pipes. A transient thermal analysis is performed in the first step to determine the component temperature history during the cycle. Then these temperature solutions are used as an input to the structural analysis to obtain the elastic stress history caused by these temperature loads. A shakedown analysis is thereafter carried out and the evaluation of the steady cyclic behaviour of tubeplate during the steady state cycle is then achieved using the LMM. The elastic, plastic and total strain ranges over the steady state cycle are evaluated for the fatigue damage assessment. Both the constant and changing residual stress solutions associated with the steady state cycle are obtained. The comparisons of stress and strain range calculations for out of phase temperature oscillations by the LMM and other methodologies are given in the paper. Finally, a LMM ratchet limit analysis is carried out to assess the capacity of the component subjected to the existing thermal transients to withstand an additional primary loads including both pressure and moment. The temperature dependent elastic-plastic properties are adopted throughout the LMM assessment.