Experimental and numerical investigation of the effects of the pre-heating in the modification of residual stresses in the repair welding process

In this paper, the application of pre-heating process on the reduction of residual stress in the repair welding of steel pipes is investigated. In this purpose, a thereto-elastic-plastic molding of the repair welding process is developed using finite element method. In order to verify this modeling method, experimental data of repair welds of a carbon steel pipe, measured by deep hole drilling method, were utilized. The verified results indicated that the developed computational method can be beneficially used as an effective tool to predict the residual stress of the pipes undergo the repair welding. The verified finite element model was utilized in the repair welding of carbon steel and stainless steel pipes to consider the effects of preheating. It was observed that by increasing the preheating temperature in the repair welded pipes, longitudinal residual stress on the inner and outer surfaces of the both carbon and stainless steel pipes decreased about 35-50%, respectively, although the compressive residual stresses on the outer surface have small variations. Moreover, by increasing the preheating temperature, tensile hoop residual stresses on the outer surface of both the stainless steel and the carbon steel pipes decreased, but only a small variation was observed on the compressive hoop residual stress. In general, there are no significant effects on the magnitude and distribution of hoop stresses on the inner surface of the repaired stainless steel pipe. Also, high preheating temperature, leads to a wider distribution of axial residual stresses in repair welded pipes.