Numerical Simulation Of Welding To Repair The Pipeline In Service

The in-service welding technology in China started lately and its basic theory hasn't been systemetic yet, so there were very few reports on it in China. However, the importance of in-service welding technology is increasing greatly, since pipeline operators request this kind of thechnology intensively, which will become a big promotion for the development of in-service welding technologh. Under this background, this paper made a simulation of factors on burnthrough and HIC(hydrogen-indued cracking) problems which may occur during in-service welding, resulting in some conclusions which are instructive to practice. Procedure and results of this study are as follows:The simulation of plate test not only proved the reliability of SYSWELD on in-service welding simulation, but also showed the procedure of application of this software. Since in in-service welding the way to prevent burnthrough is to control the maximum temperature of inner surface, while the way to prevent HIC is to control the maximum hardness and residual stress of weldment, the emphasis of the study was on the inner surface temperature, HAZ maximum hardness and the maximum residual stress of weldment. This paper established a model on the basis of SYSWELD to simulate the procedure of in-service welding, and analyzed single-fator and multi-factor effects on burnthrough and HIC.After the simulation finished, the result showed that the main factors those have a high effect on burnthrough and HIC are heat input and pipe thickness. The temperature of inner surface will increase as the heat input increasing, so there is a limited upper heat input for specified pipe thickness and operation condition (the limited upper heat input is 1300J/mm when pipe thickness is 8mm in this study), further more, a graphic of maximum heat inputs corresponding to different pipe thicknesses can be drawn to figure out the safe area of in-service welding:It also should be pointed out that heat input increasing is favorable for the prevention of HIC. It obvious that pipe thickness increasing is good for burnthrough prevention and decreasing the hardness of HAZ (heat affected zone), but it will increase the residual stress of weldment.This paper studied the relationship between some factors and burnthrough and HIC as well as convection coefficient's effect on both, pointing out that it also need to do more research on the convection coefficient of inner surface.