A test which can determine the presence of porosity in any particular weld or welded assembly. Radiography is the most effective and reliable non-destructive
test method, but it cannot detect porosity smaller than a minimum size. Radiographs taken from two different angles can establish the depth of the porosity from a surface. See RADIOGRAPH.
Fine porosity and other fine voids which extend to a free surface can be detected by a dye penetrant or fluorescent penetrant which is applied to a surface, soaks into voids and finally bleeds out of the voids after the excess is removed.
Another type of porosity test is used to test the ability of a welder to produce welds which are satisfactory for oil, water, or gas containers. A test weld joint can
be clamped over a pressure box against a rubber gasket and the box pressurized with air. Liquid soap is applied to the weld joint, and porosity or voids are indicated by the appearance of bubbles on the surface.