Thermal Analysis And Temperature Control Of Gas Pipelines In-service Welding

During long-term working, the high-pressure gas pipelines are prone to partial leakage because of corrosion or human damage. At present, in-service welding is the main method to repair leaking gas pipeline. The gas pipeline can keep on serving while the welding happens, so it makes enormous benefits and has prospects. However, during the in–service welding, fast and high-pressure gas flow in the pipe. So the welding joint is prone to burn-through or hydrogen caused cracking. Controlling the welding heat input and mastering the law of welding temperature field are the focus of in-service welding.This thesis basing on the basic principles of heat transfer of welding, considering the relationship between material properties and temperature, analyzing the characteristics of the heat-exchange process between gas and pipe-wall, use ANSYS to establish the multi-channel welding model of steel patch and simulate the dynamic temperature filed of this 3D model.Following is the main conclusions of this thesis:(1)Welding with the four kinds of parameters introduced in this thesis, the maximum temperature of internal wall is between 280℃and 600℃which is lower than 980℃, so the burn-through can not happen.(2)With the increase of flowing-speed and internal pressure, the heat-exchange coefficient increase, so the maximum temperature of internal wall and the t8/5 decreases.(3)When the line-energy is the same, the temperature of pipe wall by discontinuous welding is more lower than continuous welding.Through the simulation, we know, when the in-service welding happens with the parameters of this thesis under this environment, the burn-through can not happen. Therefore, the pressure relief and flowing-speed control are reasonable and the welding parameters are all feasible.