Application of pre-heating in the reduction of residual stress in the repair welds of steel pipes

In this paper, the study application of pre-heating on the repair welds in the steel pipes and analysis of thermo-elastic-plastic molding of this process was investigated using finite element method. In order to verify the model, experimental data for repair welding of carbon steel pipe, obtained by deep hole drilling method, were utilized. Good agreement was observed between the finite element and experimental data. The results indicated that the developed computational method is an effective tool to predict the residual stress of pipes in the repair welded. The present finite element model was developed in repair welded carbon steel and stainless steel pipes to consider the effect of preheating. It was observed that by increasing the preheating temperature in the repair welded pipes, tensile axial residual stresses on the inner surface and outer surface of the carbon steel and stainless steel pipes decreased 35 and 50 percent respectively, but the compressive axial residual stresses on the outer surface have small variation. Moreover, by increasing the preheating temperature tensile hoop residual stresses on the outer surface on the stainless steel side and tensile hoop residual stresses on the inner surface on the carbon steel side decreased, but only a small variation was observed on the compressive hoop residual stresses. In general, there is no significant effect on the magnitude and distribution of hoop residual stresses on the inner surface of the stainless steel pipe. Also, high preheating temperatures will have wider distribution of axial residual stresses.