The Numerical Simulation On Welding Residual Stresses Of The Ethylene Spherical Tank Steel

Ethylene spherical tanks are becoming increasingly huge along with the rapid advancement of the world oil economy and the unceasing enhancement of ethylene's output. However, the existence of welding residual stresses seriously threatens an ethylene spherical tank's service life and even might result in severe security disaster; therefore it is imminent to solve this problem. This paper focuses on the numerical simulation of welding residual stress in ethylene spherical tanks, where SYSWELD (a finite element software) is utilized to dynamically simulate the entire welding process and to quantitatively analyze the distribution of welding residual stresses and their values. The influence of welding parameters and preheat temperature over welding residual stresses is examined through the simulation of disparate welding processes with different welding parameters and preheat temperature. The application of ethylene spherical tanks in practical manufacturing will be theoretically based on such an examination. The distribution of welding residual stresses in welding joints during welding is obtained from the combination of a few experiments and abundant numerical simulations.The welding process of ethylene spherical tanks is simulated with SYSWELD, where a model is applied in the form of double ellipsoid heat source. Curves of welding heat circulation in coarse grain zone are attained under various welding parameters, whose impact over the heat circulation is discussed thereafter. In addition, the multilayer welding process of ethylene spherical tanks is also simulated with SYSWELD, in which the non-lineal relationship is taken into consideration between welding material's thermophysical property and temperature. Besides, influence of latent heat in phase transformation over temperature field is taken into account in the simulation as well. The distribution law is concluded of residual stress in multilayer welding joint, and so is the influence of postweld heat treatment over the distribution of welding residual stress as a result of the simulation of three coupling fields: welding temperature field, metallurgical structure field and stress-strain field.