Study Of In-service Welding Burn-through Mechanism

Compared to other pipeline repair techniques, in-service welding repair technology has many advantages such as high efficiency, less cost, environmental protection benefits,etc. All the advantages make it a promising pipeline repair technique.However, in-service welding repair is a huge risk thing to do, many defects may be caused during the repair. Weld Burn-through is one of the difficult problem to overcome in the first place. This article is based on simulation used simulation and in-service welding experiment, to explore the mechanism of in-service weld burn-through. Using the thermal elastoplastic model to find out how various factors will influence equivalent stress under molten pool and the distribution of the yield strength.Result shows that the internal stress and welding heat input are the main factors influencing radial deformation. The equivalent stress under molten pool increases with internal pressure,and so as radial deformation. The increase of welding heat input can make equivalent stress under molten pool decreases slightly, meanwhile instantaneous yield strength loss increase sharply, eventually causes the increase of radial deformation. By establishing the head instantaneous model, I found that the effect of medium flow rate on the radial deformation is very slight. The increase of wall thickness can make both equivalent stress distribution and yield strength loss under molten pool decreases, this causes the scale of radial deformation smaller.Simulation and experimental results show that using highest temperature to conclude whether burn-though happens or not is improper when internal pressure changes, while radial deformation below molten pool can precisely predict it.As the lining of the radial deformation reaches a certain size, burn through will occur. As for this article experiment, burn-though will occur when radial deformation reach 0.2 mm when using 4 mm thickness Q235 steel.This is proven both by welding experiment and simulation.