Shakedown Behavior Of Butt Welded Joints For Pressure Piping

Welding is the main connection method of pressure vessels and pipelines. However, due to the complex work environment and the imperfections and residual stress of welding structures, the welded pressure vessels and pipelines often break down in the welding zone or to be invalid because of the excessive plastic deformation. This paper focus on the most common failure type of thermal ratchet and do the comprehensive analysis for the discontinuous welding model that is under the cycle thermo-mechanical loadings, the study and conclusions are as follows:Based on the classical Bree shakedown diagram, the butt welded model is researched for its stability by adopting Abdalla Finite Element Method (hereafter referred to as FEM). What’s more, compared with the different FEMs to work out the stability, the accuracy of shakedown analysis of welding structure under the cyclic themo-mechanical loading is verified by direct cycling method. Through observing the stress-strain changes and in comparison with different FEMs, it shows that the Abdalla Method can analyze shakedown behavior of the welded structure accurately, so we can draw a conclusion that the shakedown analysis method is reliable。The text establishes six butt welding models in welded groove form with different thickness:UV, Double U, X, U-shaped, single-side welding and V-shaped, and then furthers comparative analysis the influence of different groove form on the stability of butt welding structure. The result shows that the shakedown region of U-shaped groove (welding thickness of20mm≤t≤60mm) and the double U-shaped groove (welding thickness t>60mm) are preferable when being connected as the welding joints have enough shakedown behavior, and they have a better bearing capacity under cyclic thermo-mechanical loading. What’ more, the property of welding material also affects the shakedown of welded structure, the paper analyzes the shakedown behaviors of different welding materials. The welding structure can have a better capacity under the cycle thermo-mechanical loading by the selection of welding materials, which has a critical guidance to adopt the materials of welding structures.This paper researches the connection between the cylinder and the welded pipes, thereby set up a relationship between the cylinder and the weld pipes, the shakedown behavior of weld pipe can be figured out by the calculation of shakedown behavior of non-welded cylinder conveniently, a suitable simplified calculation method is summarized for engineering shakedown assessment.Considering the effects of high temperature heat source, the welded residual stress of welded structures becomes the main factor that affects the shakedown behavior of welded structures. In particular, the dissimilar welding structure fails easily under cyclic loading. Transition welding method is a common welding method of the dissimilar welded, this paper established dissimilar welding butt welding model and simulate the welding process, the welded residual stress distribution and welded residual stress relaxation under cyclic loading was researched. The results showed that dissimilar welded residual stress was significantly greater than the welding of same steel. What’s more, the welded residual stress relaxes under cyclic loading and the welded structure stress relaxation is obvious with5cycles.