Effect of Heat Input Ratio on Residual Stress in Multipass Welding Using Finite Element Method and Ultrasonic Stress Measurement

The presence of residual stresses in components, particularly in those operating in high temperature, can lead to cracking and reduction of fatigue life. The present work is an attempt to study the effect of heat input ratio of multipass welding on the residual stresses. Firstly, the ultrasonic stress measurement technique is carried out in the weldment using specific welding parameters. The stress measurement conducted by ultrasonic method utilizes longitudinal critically refracted waves which are basically promoted parallel to the surface of material at certain depth. Moreover, the hole drilling method is utilized so as to validate the results of ultrasonic method. The finite element analysis is then carried out for the same welding condition so that the residual stress obtained by FEM could be compared and verified with those extracted from ultrasonic method. The different finite element analyses employing different heat input ratios are conducted in the 15Mo3 high strength low alloy steel while two different interpass time are considered. Finally, it has been concluded that heat input of the second pass has significant effect on longitudinal residual stress peak while heat input of the first pass is not much influential on residual stress magnitude if long interpass time is considered. On the other hand, when the second pass is deposited immediately after the first pass, the heat input ratio can be used as a criteria for evaluation of the maximum residual stress.