Criteria for Heated Band Width Based on Through-thickness Temperature Distribution
Hao LU, Jianhua WANG, Hidekazu MURAKAWA
The heated band width is the most important processing parameter for local postweld heat treatment of tubes and pipes.A correct heated band width must be chosen so that the allowable maximum temperature difference in the soak band is maintained and a sufficient degree of stress relaxation is achieved.In this paper, the effects of the geometrical and the thermal parameters in the postweld heat treatment are investigated using axisymmetric FEM.The most severe condition in which the heat input and insulation are only applied to the outside surface of the pipe has been studied in detail. The effect of the geometrical and the thermal parameters on the through thickness temperature gradients is investigated.Through this study, it is found that the required heated band width is mainly influenced by the wall thickness and the heat transfer coefficient on the internal surface.The computed results show that the Hi number is inadequate for practical use under general conditions.A more general Hi number is proposed as a linear function of the thickness. Further, based on the computed results, the authors propose criteria for the heated band width which includes the effect of the geometrical and the thermal parameters.