Research Of Burn-through During In-service Welding Onto Running Pipelines

Welding repair onto in-service pipelines has good economic efficiency and application trend, because it is much quick and has little effect to normal run of pipeline. But it is also very dangerous because burn-through might happen during welding.In this paper, the device was designed and set up to simulate the in-service welding. The thesis mainly analyzes the effect of pipe thickness, inside pressure of pipe, heat input and the way of cooling which are related to burn-through. According to the experiment result, different cooling ways have great effect to burn-through, comparing to air-cooling, the way of water-cooling requires much more heat input. When the pipe wall becomes thicker, burn-through requires higher heat input. convex deformation from outside wall to inside wall of pipe happened during normal welding, and concave deformation from outside wall to inside wall of pipe happened during in-service welding because of the pressure inside the pipe. Burn-through requires higher heat input when pressure inside the pipe changes from 0.5MPa to 2.5MPa. It requires lower heat input when pressure inside the pipe changes from 0.5MPa to 2.5MPa.The paper analyzes the process of in-service welding with non-linearity analytical software SYSWELD, and simulates the three-dimensional model of in-service welding by pressing evenly on the pipe wall. Simulating the in-service welding process with different models of different pipe wall thickness, and analyzing the temperature field and stress field of in-service welding, by changing the conditions such as method of cooling, heat input, pressure inside the pipe. The results show that: comparing to water-cooling, the peak temperature of inside wall is much higher with the way of water-cooling; when the pipe wall becomes thicker, the peak temperature of inside wall becomes lower; when the heat input becomes higher, the peak temperature of inside wall becomes higher, and instantaneous stress becomes higher; when the pressure inside the pipe becomes higher, instantaneous stress of the inside wall becomes higher. Comparing with the experiment data, there are some errors in the simulation results. In the further research, we should amend the boundary conditions to make it more close to the welding operation.The researches in this paper provide theoretical supporting for the repairing of in-service welding, are helpful for the development and application of the repairing technology in-service welding of gas-oil pipes.