Prediction of Weld Penetration in Circular Laser Welds of Ferritic Steel (P91) Material

Any weld designer will always try to design a weld joint with as much low heat input as possible, at the same time obtain a good depth of penetration and in the process maintain minimum heat affected zone. When a tube or a rod has to be welded using a process and if a design analysis can be done, prior to freezing of the design, to find the depth of penetration, then it may raise the confidence level of the weld design. By this way we can avoid wasting time in carrying out random trials. In the present work an approximate method of predicting the depth of penetration during welding over the peripheral of a circular rod has been formulated under Laser Welding Process. This method will be helpful to design the joint with enhanced efficiency and with lesser probability of defects like lack of penetration and excess penetration. In the analysis ‘Thermal Explosion” theory has been used to predict the depth of penetration to map the fusion zone of a circular weld joint on P91 rod. The calculated depth of penetration has been compared with the measured depth of penetration on the weld carried out on a rod using Laser Welding process and the results were found to be nearly matching. It has been found that the depth of penetration increases as the welding progresses over the rod and the difference between the depth of penetration between starting & ending points is around a few microns. This is due to the buildup of heat in the cross section of the rod as the weld progresses.