engleski

A Contribution to Assessment of Steam Generator Tubes Integrity

Three-dimensional linear and non-linear finite element analyses have been carried out to determine the stress intensity factors, the J-integral and the plastic limit loads for external axial semi-elliptical surface cracks in VVER steam generator tubes under internal pressure. Under the assumption of a small elastoplastic strain, the constitutive law characterizing the material's stress-strain response of the austenitic steel 08X18H10T is represented by the well-known Ramberg-Osgood model. All computations have been performed within the commercial finite element package ABAQUS. Six different crack lengths are considered (5, 10, 20, 30, 40 and 50 mm) and four values of the ratio of the crack depth to the tube thickness are selected (0.2, 0.4, 0.6 and 0.8). The results for the stress intensity factors and J-integral are generated and expressed as the GE/EPRI influence functions to allow comparisons with the values available in literature. As usual in literature, the plastic limit pressure solutions have been developed on the basis of finite element limit load analyses employing elastic-perfectly plastic material behaviour. Using these solutions, a new analytical approximation of the plastic limit pressure has been developed for a wide range of cracks. The proposed stress intensity factors, J-integral and the analytical approximation of limit pressure provide very useful tools for assessing the integrity of pressurized tubes. As an example, the Crack Driving Force (CDF) approach of the SINTAP procedure is applied to the failure analysis of steam generator tubes under internal pressure. The effects of crack depth and length on the failure pressure are evaluated for the tube geometry considered.

finite element method; elastoplastic fracture analysis; structural integrity; steam generator tubes; external axial semi-elliptical surface crack; SINTAP procedure

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