Opening Contribution 5: Collaborative Approach to Weld Quality by Designer and Inspector

Abstract

Most engineering components are subject to inspection at some stage, particularly those incorporating welded joints. Often the task of the welder and inspector is hampered by the location of joints in positions difficult of access. This is just one aspect of poor design which could be eliminated by collaboration between designer and inspector at the outset. Up to the present, insufficient attention has been paid by designers to important features such as the weldability of materials, joint geometry, siting of welds, feasibility of heat treatment, and surface finish. The increasing use of non-destructive testing, particularly ultrasonics and radiography, has highlighted inspection problems, and as a result, designers are becoming more aware of their ultimate influence on inspection. Although the aims of the designer and inspector are the same—adequate service performance at lowest cost without danger of shutdown—the designer's interest appears to wane as the inspector's functions become more significant. A prolific cause of weld failure is fatigue cracking caused by stress-concentration at welded joints, yet how many designers realize that the external contour of a weld cannot approach the neat appearance indicated on drawings unless expensive grinding or machining is done? The paper will attempt to explore, with the aid of examples, the avenues where more co-operation is needed between designer and inspector. In addition the paper will present a new concept in the designer/inspector relationship in the form of a ‘failure index’ calculated from a number of variables known at the outset. This is a scheme to enable the designer to anticipate the relative amounts of inspection to be applied to various parts of complicated welded fabrications like those in conventional and nuclear power stations. The index system was devised specially as a collaborative link between designer and inspector in a field where the cost of failure in service can be enormous.