An Engineering Basis for Establishing Radiographic Acceptance Standards for Porosity in Steel Weldments

Radiographic acceptance standards, such as those found in the ASME Unfired Pressure Vessel Code are critically reviewed. Limits on the size and distribution of porosity in steel welds are analyzed from the viewpoint of susceptibility to failure in service. In large part, present standards for porosity appear to have been established on a “good workmanship” basis rather than on setting sound conservative limits for the maximum size, and distribution of flaws which can be tolerated without decreasing the reliability of the product. Radiographic acceptance standards in use today do not reflect the significant advances being made in (1) the fracture mechanics approach to designing for prevention of failure; (2) theoretical studies of the stress-concentration effects of holes in close proximity to one another; and (3) the possible use of complementary nondestructive testing techniques. Considerable emphasis is placed on the proposition that radiographic acceptance standards for weldments must be designed specifically for each particular application. Considerations applicable to welds in the 120-in-dia rocket motor case are cited as an example of how standards for acceptable porosity and inclusions can be established.