Coal conversion processes offer a partial solution to the problem of meeting an increasing demand for energy supplies.1 Although the commercial use of coal conversion for the generation of substitute natural fuels may not be a reality for many years, several pilot plants for demonstrating the feasibility of these methods are already in the final stages of assembly or early stages of operation.2 The processes which are being considered are high and low BTU coal gasification and coal liquefaction.3 A common requirement for all of these processes is the need for welded steel pressure vessels to operate continuously and safely under conditions of high temperatures, high pressures and in potentially hostile environments. These hostile environments in combination with the high pressures and temperatures could have a pronounced detrimental effect on the rate at which cracks could initiate and propagate in the pressure vessels, ultimately resulting in a structural failure. Considering the complex geometry and fabrication difficulties of large welded structures, it is reasonable to assume that some of these pressure vessels may contain defects prior to field service inherent in the manufacturing processes of the vessels.4 The reliability of these vessels will largely be governed by the behavior of these defects under the loading and environmental conditions encountered during service.
