Skelp End Welding in Helical Pipe Production

The production of large diameter pipe by the helical welding process requires that consecutive coils be welded together to facilitate the advance of each subsequent coil through the forming section of the pipe mill. Traditionally, the skelp ends have been joined by a single-pass submerged arc weld simply designed to join the skelp ends together and provide sufficient strength and ductility to survive the pipe forming operation. Subsequent to pipe forming, the length of pipe containing the skelp end weld (SEW) has been cut off and discarded. This process results in both a substantial yield loss as well as additional processing costs as the shortened pipes are later double jointed to produce full size lengths. To overcome these inefficiencies, a process has been developed for making high quality skelp end welds which meet API and CSA requirements. In this paper, the welding process will be described and evaluation of the integrity of the skelp end weld is discussed. Of particular interest are the properties of both the weld and associated heat affected zone in the vicinity of the “T” where the skelp end weld merges with the helical weld. This paper demonstrates that skelp end welds meeting rigorous integrity specifications can be successfully produced. Incorporation of suitable skelp end welding and inspection procedures in the pipe production process significantly enhances the efficiency of helical pipe production.