What SSAW Pipe Is and How It Is Made
SSAW stands for spiral submerged arc welded. A steel strip is fed into the forming machine at an angle to the pipe axis and formed into a helix, while the inside and outside of the spiral seam are welded in a continuous submerged arc pass. Because the strip runs diagonally, one strip width can produce a whole family of diameters simply by changing the forming angle, which is why SSAW is the economical route to very large diameter pipe, typically from about 400 mm up to 3000 mm and beyond. The pipe is then expanded and hydrostatically tested.
The Main Disadvantages of SSAW Pipe
Longer weld seam. The spiral seam is significantly longer than the longitudinal seam of an LSAW pipe of the same diameter and length. Every metre of seam is a potential defect location, so inspection coverage must be higher and the cost of that inspection offsets part of the saving.
Higher residual stress. The helical forming and the long weld introduce residual stress in the wall, which can affect dimensional stability and ovality, particularly after cutting or in elevated temperature service.
Geometry control. Roundness, straightness and end squareness are harder to hold than with LSAW pipe, and the step or mismatch at the spiral seam can affect the quality of the field girth weld.
Sensitivity to process drift. Spiral welding depends on precise strip edge tracking. If the tracking or the welding parameters drift, lack of fusion, porosity or inclusions can run along the seam for a considerable distance.
Appearance. The prominent spiral seam is considered less clean visually than a longitudinal seam, which matters for exposed piping and for some project specifications.
Field welding geometry. The spiral seam meets the girth weld at an angle, and that crossing point demands extra care during field welding and inspection.
LSAW and the Other Pipe Types Compared
LSAW stands for longitudinal submerged arc welding. Heavy plate is formed into a cylinder so that the main seam runs parallel to the pipe axis, and the seam is welded by the submerged arc process. The defining forming route is JCOE: the plate edges are first pressed into a J shape, the middle of the plate into a C shape, the shape is then closed into an O, and finally the pipe is expanded to achieve roundness, relieve internal stress and even out mechanical properties. That expansion step is the reason LSAW pipe achieves tighter diameter tolerance and better roundness than SSAW pipe.
Steel pipe is usually grouped into three types by manufacturing route. Seamless pipe is pierced from a solid billet and has no seam at all, giving uniform strength for high pressure and high temperature duty. Welded pipe is made from plate or coil and includes ERW, submerged arc welded pipe in both the LSAW and SSAW forms, and electric fusion welded pipe, and it is the economical choice for large diameters. Cast pipe is poured into a mould and is used for special components and fittings rather than for line pipe.
The difference between ERW and EFW follows the same logic. ERW heats the strip edges by resistance and forges them together without filler metal, and modern high frequency ERW produces a very clean weld. EFW covers arc welding processes that use filler metal, so submerged arc welded pipe, both LSAW and SSAW, belongs to the EFW group.
Where SSAW Is Still the Right Choice
SSAW pipe remains the standard solution for large diameter water transmission mains, dredging and piling pipe, slurry lines, low pressure oil and gas gathering lines, structural piles and outfall pipelines, where large diameter and cost per metre matter more than the last increment of dimensional accuracy. The disadvantages listed above are manageable when the design pressure is modest, the pipe is expanded after welding, and full length seam inspection is specified and actually carried out.
Inspection and Process Controls That Offset the Disadvantages
Automatic strip edge tracking with continuous recording of the welding parameters for each pipe.
Full length ultrasonic inspection of the spiral seam on both the inside and the outside, supported by radiographic sampling.
End dimension checks for diameter, ovality, straightness and end squareness before the field girth weld is made.
Hydrostatic testing of every pipe to the specified pressure and duration.
Expansion after welding to improve roundness and reduce residual stress.
Strip edge preparation and cleanliness control to reduce the risk of inclusions along the seam.
FAQ
Q: What does SSAW stand for?
Spiral submerged arc welded. The strip is formed into a helix and the inside and outside of the spiral seam are welded by the submerged arc process in a continuous pass.
Q: What are the main disadvantages of SSAW pipe?
A longer weld seam than LSAW, higher residual stress from helical forming, tighter process control needed for roundness and end squareness, and greater sensitivity to strip tracking and welding parameter drift.
Q: Is LSAW better than SSAW pipe?
LSAW has a shorter seam and is expanded after welding, which gives better roundness and tolerance and suits high pressure transmission lines. SSAW is more economical at very large diameters and is adequate for lower pressure water, slurry and structural service.
Q: What is the JCOE process?
JCOE is the forming sequence used for LSAW pipe. The plate edges are pressed into a J shape, the middle into a C shape, the shape is closed into an O, and the pipe is then expanded to final dimensions.
Q: What is the difference between ERW and EFW pipe?
ERW welds the strip edges by resistance heating without filler metal, while EFW covers arc welding processes that use filler metal. Submerged arc welded pipe, including LSAW and SSAW, belongs to the EFW group.
Q: What are the three types of steel pipe?
Seamless pipe pierced from a solid billet, welded pipe made from plate or coil by ERW, submerged arc or electric fusion welding, and cast pipe poured into a mould for special components and fittings.
