Significance of weld defects in pressure vessels under fatigue loading

The paper describes work on the significance of defects under fatigue loading in three particular areas where additional information was needed to formulate a rational defect acceptance standard for pressure vessels. In the low cycle fatigue area, tests on small scale specimens containing slag, porosity and lack of fusion defects showed that existing information can be extrapolated back to endurances of 102 provided strain range is used. Tests on model cylindrical and spherical vessels, with similar defects in seam and nozzle welds, showed that there was no significant effect of scale and the results from small scale specimens can be used safely. Crack propagation studies at elevated temperatures, but below the creep range, of various materials showed similar growth rates as for ambient temperature. A parallel study of the costs and frequency of repairs showed that significant savings could be made if rational defect acceptance standards were used in pressure vessel codes. (author)