ANALYSIS OF CRACKED PIPING SYSTEMS SUBJECTED TO THERMAL STRESS, RESIDUAL STRESS AND DYNAMIC LOADING.

摘要

This study is divided into two major parts: (i) analysis of the cracked pipe behavior under normal service loads such as the pressure, thermal and weld residual stress loadings; and (ii) evaluation of structural integrity of the cracked piping system subjected to a dynamic loading.;The role of residual stresses in propagating stress corrosion cracks is investigated. It is shown that in the absence of any other applied loading, the growth of a circumferential stress corrosion crack in the weld residual stress field will eventually slow down resulting in crack arrest.;The equivalence of the weld residual and thermoelastic stress problems is shown to provide an effective approach for the determination of stress intensity factors for cracks in complex weld residual stress fields. Its use is demonstrated in obtaining stress intensity factors for a flaw in a typical weld residual stress field of butt-welded pipe using finite element methods. The propagation behavior is examined for a stress corrosion crack located in the heat affected zone of a welded pipe. One of the conclusions is that the larger diameter pipes are inherently safer from the viewpoint of stress corrosion cracking.;In the second part, a methodology is developed for structural failure analysis of a cracked pipe under dynamic loading. It is shown that the failure analysis based upon the net section collapse criterion utilizing the dynamic loads determined by a nonlinear analysis of the cracked piping system represents an effective engineering approach for the evaluation of its structural integrity. Analytical predictions are shown to be in reasonable agreement with experimental results thus verifying the approach. Finally, an application of the developed methodology is discussed for a cracked piping system in a nuclear power plant.;The evaluation of a flaw under normal service loads deals primarily with the linear elastic fracture mechanics calculations to determine the crack extension over a specified time period. For the determination of fatigue crack growth due to thermal transients, stress intensity factor solutions for axisymmetric circumferential flaw under arbitrary thermal stress loading are developed.