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pipe manufacturing 1

The Four Methods of Manufacturing Pipes
manufacturing refers to how the individual pieces of pipe are made in a pipe mill; it does not refer to how the pieces are connected in the field to form a continuous pipeline. Each piece of pipe produced by a pipe mill is called a joint or a length (regardless of its measured length). In some cases, pipe is shipped to the pipeline construction site as "double joints," where two pieces of pipe are pre-welded together to save time. Most of the pipe used for oil and gas pipelines is seamless or longitudinally welded, although spirally welded pipe is common for larger diameters.

Four Types of Manufacturing
Longitudinally Welded SAW Pipe
Welded pipe (pipe manufactured with a weld) is a tubular product made out of flat plates, known as skelp, that are formed, bent and prepared for welding. The most popular process for large diameter pipe uses a longitudinal seam weld. Double submerged arc welded (DSAW) pipe is welded pipe whose longitudinal butt joint is welded in at least two passes, one of which is on the inside of the pipe; the welds are made by heating with an electric arc between the bare metal electrode. Pressure is not used. Filler metal for the welds is obtained from the electrodes. For diameters above 36 inches, double seam welded pipe is specified as an alternative in API 5L. This has two longitudinal seams 180° apart, formed by the SAW process. Finished pipes are normally 40 feet (12 m) and occasionally 60 feet (18 m) long, depending on the capacity of the pipe mill and the ease of transport to the pipeline.

Spiral Welded Pipe
As an alternative process, spiral weld construction allows large diameter pipe to be produced from narrower plates or skelp. The defects that occur in spiral welded pipe are mainly those associated with the SAW weld, and are similar in nature to those for longitudinally welded SAW pipe. An additional problem with early spiral welded pipe was poor dimensional accuracy, particularly out of roundness at the pipe ends. This led to problems of poor fit-up during field girth welding. Spiral linepipe gained a poor reputation in some companies as a result of these early experiences, and it was considered suitable only for low pressure applications such as water pipe. However, modern spiral linepipe from a premium quality supplier is of a quality equivalent to straight seam welded pipe, and it has been used extensively in Canada and Europe for high pressure gas pipelines in grades up to API X70.