API 5L LSAW Welded Steel Pipe

What LSAW Pipe Is and Where It Is Used

LSAW stands for longitudinal submerged arc welding. Steel plate is formed into a cylinder and the longitudinal seam is welded from both sides using the submerged arc process, in which the arc is buried under a layer of granular flux. This shields the weld from the atmosphere and produces a clean, ductile weld with excellent toughness. Because the process starts from plate rather than coil, wall thickness is not limited by coil gauge, which is why LSAW pipe is the normal choice for large diameter, heavy wall, high pressure transmission mains from 16 inch up to 60 inch. Two forming routes are common: UOE, where the plate is pressed into a U then an O shape and finally expanded, and JCOE, where the plate is progressively pressed into a J shape. Both produce pipe with excellent dimensional consistency.

LSAW vs SSAW – Choosing the Right Welded Pipe

SSAW (spiral submerged arc welded) pipe is made from coil wound at an angle, producing a helical seam. It is cheaper to produce in very large diameters and is excellent for lower pressure water and slurry lines. LSAW pipe has a straight longitudinal seam that runs parallel to the pipe axis. The practical difference is in the stress field: in an LSAW pipe the seam is oriented in the same direction as the principal hoop stress, but the weld is short and can be fully inspected; in an SSAW pipe the helical seam is longer and crosses the hoop stress direction, and the weld length per metre of pipe is roughly 1.5 to 2 times greater. For high pressure gas transmission where fracture control matters, LSAW is generally preferred. For large diameter, moderate pressure water mains, SSAW is usually more economical.