FRACTURE TOUGHNESS OF HAZS IN STEELS FOR OFFSHORE PLATFORMS

This article is based on a paper presented at a WIC/ISC conference, "Welding in Energy-Related Projects", Toronto, Sept. 1983. Brittle regions within the weld heat-affected zone can have a significant influence on the resistance of a structure to failure by brittle fracture. Although a structure can be designed for crack arrest, the techniques available are scarecely practicable; it is therefore usual to design to prevent fracture initiation, and this aspect forms the main theme of the article. The Authors, of The Welding Institute, discuss the metallurgy of HAZs in carbon-manganese and micro-alloyed steels, including the effects of the material composition, of post-weld heat treatment, and of welding procedure. Measurement of HAZ toughness by Charpy and fracture-mechanics tests, the sectioning of specimens, and the significance of HAZ toughness are considered in some detail. In their concluding remarks, the Authors stress the need to obtain a good assessment of HAZ fracture-initiation resistance before fabrication. Careful consideration should be given to the type of fracture-toughness specimen to be used, so that a balance can be struck between accurate modelling of the service situation and the provision of standard reproducible results. Assessment of results should always include examination of the test specimens by metallographic sectioning to identify which regions of the HAZ have been tested.