Conditions for execution of the two sided heating method and its control procedure: Development of a residual stress control method for pipe butt-welded joints (2nd Report)

Summary

The previously reported two sided heating method proposed by the authors is an effective residual stress control method for pipe butt-welded joints. This paper describes the non-dimensional parameters controlling this method and the conditions to be fulfilled to ensure sufficient effectiveness in actual applications. The results obtained may be summarised as follows:

1. The previously reported elastic analysis solution is used to investigate the effect of the two sided heating method as well as the effect of the temperature distribution during two sided heating on the stress generated near the weld line. The results show that there are three parameters - the non-dimensional stress K, non-dimensional heating position βℓ, and non-dimensional heating width βW - that control the residual stress effect of the two sided heating method. The relationship between βℓ, βW, and the non-dimensional stress K is defined and plotted graphically. By use of the diagrams presented, it is possible to select the combination of execution parameter ranges to enable the residual stress on the inside surface of pipe butt-welded joints during heating by the two sided heating method to be rendered into a compressive state.

2. An elastic-plastic FEM analysis involving variation in the heating position, heating width, and temperature distribution during two sided heating is run to validate the two sided heating method execution parameter ranges described in conclusion (1). When a temperature difference exists across the plate thickness, this case should be evaluated by the mean temperature. Even where the pipe dimensions differ, provided the non-dimensional heating position βℓ, non-dimensional heating width βW, and non-dimensional stress K are the same, the same residual stress control effect is shown to be exerted. These three non-dimensionalised parameters are those that control the two sided heating method.