Abstract: An underwater pipeline is repaired by cutting away a defective section thereof and replacing the defective section with another length of pipe. The replacement is joined to the exposed ends of the pipeline by welded ball-and-socket joints. Those welds that it is necessary to perform under water are made in a gaseous environment created in a chamber having an open base through which water may be displaced by gas and at least one transparent side panel which is displaceable to form a gap in the side of the chamber. A diver may insert a welding gun or welding rod through this gap. The chamber has outer tubular flanges which receive the lengths of pipe extending through the chamber. Tubular members of flexible or elastomeric material are used to seal each flange to the length of pipe passing there through. Each tubular member of flexible or elastomeric material is positioned around the flange and length of pipe which it is to seal.