Describes procedures for the examination of butt welds in carbon and low alloy steel vessels, the procedures being designed to detect imperfections which generally lie parallel to the axis of the weld. Whereas the procedures apply to all thicknesses of material in the case of flat welds, the limiting parameters as regards longitudinally welded seams are: (i) the ratio of the outside diameter of a vessel to its thickness, which will ensure that, with the types of probe available, the ultrasonic beam will reach the under surface of the weld remote from the probe position; (ii) whether the material is such that an ultrasonic beam can be propagated through it. In the case of circumferential welds only the second parameter described above applies. The standard does not cover the detection of imperfections lying transverse to the weld, such imperfections being detected by additional agreed manual or automatic scanning techniques, nor does the standard specify levels of acceptance based on the results obtained from the described procedures.