A numerical estimation of leak-tightness in rolled joint under thermal creep

Abstract

In the present work, a numerical framework is developed to estimate the leak-tightness of tube to end-fitting rolled joint used in various industries under thermal creep. The leak-tightness of the rolled joint depends on the contact pressure (at the contact surfaces of the tube and end-fitting) and residual stresses (on inner and outer tube surfaces) generated during manufacturing through the rolling process. An axisymmetric finite element model is developed and validated (with literature) to accurately determine the contact pressure and residual stresses at the end of the rolling process. The relaxation in contact pressure and residual stress due to thermal creep during the service life of rolled joint (after manufacturing rolling process) is also accounted in the model. Further, to estimate the leak-tightness (leak rate), a radial plane strain model is chosen that yields the same results as the axisymmetric model. The submodelling approach in the plane strain model handles the modelling of micro-sized leakage paths efficiently. From the FE modelling, it is observed that the contact pressure and residual stresses reduce significantly due to thermal creep. The effect of different leak geometries is examined on the leak-tightness of the rolled joint. It is found that an elliptical leak with major axis in radial direction has a more rate of increase in leakage as compared to other geometries.