Many previous studies have presented results on the relaxation of residual stress in a welded component as a result of post weld heat treatment. Techniques such as neutron diffraction and deep hole drilling have been used to measure the residual stress after the heat treatment and compare this with the residual stress for the component in the as-welded condition. The work described in this paper is novel: neutron diffraction is used to measure the relaxation of residual stress continuously as the heat treatment is being carried out. Residual stresses are measured in a butt-welded ferritic steel pipe as the pipe is heat treated to 650°C and then cooled to room temperature. The results identify those parts of the heat treatment that lead to significant stress relaxation and the mechanisms responsible for this relaxation. The techniques developed during this work allow future heat treatments to be optimised to achieve the low levels of residual stress in welded components.

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This paper describes a study of the ability of the DHD technique to measure the spatial distribution of residual stresses. A two dimensional finite element model of a metal plate has been generated together with a representative state of residual stress. A simulation of the DHD technique is then carried out to provide a series of measurements of the residual stress which can be compared with the known residual stress. This simulation allows the effect of the varying trepan diameters on the accuracy of the DHD technique to be explored. The results of the simulation show that the DHD technique can be used to measure residual stress with a high accuracy, but the increase in the trepan diameter introduce some errors. Suggestions and techniques for reducing these errors are presented.