The manufacturing process of pipe is determined by the material, diameter, wall thickness, and quality for a specific service. Carbon steel piping is classified according to the manufacturing methods as follows:
- Electric resistance weld (ERW)
- Spiral-Submerged arc weld (SAW)
- Double submerged arc weld (DSAW)
- Furnace weld, butt-welded or continuous weld
Seamless Steel Pipe
Seamless pipe is formed by piercing a solid, near-molten, steel rod, called a billet, with a mandrel to produce a pipe that has no seams or joints. Figure below depicts the manufacturing process of seamless pipe.
ERW Steel Pipe
ERW pipe is made from coils that are cupped longitudinally by forming rolls and a thin-pass section of rolls that brings the ends of the coil together to form a cylinder.
The ends pass through a high-frequency welder that heats the steel to 2600 °F and squeezes the ends together to form a fusion weld. The weld is then heat-treated to remove welding stresses and the pipe is cooled, sized to the proper OD, and straightened.
ERW pipe is produced either in individual lengths or in continuous lengths that are then cut into individual lengths. ERW is supplied according to ASTM A53 and A135 and API Specification 5L.
ERW is the most common type of manufacturing process due to its low initial investment for manufacturing equipment and the process’ adaptability in welding different wall thicknesses.
The pipe is not fully normalized after welding, thus producing a heat-affected zone on each side of the weld that results in non-uniformity of hardness and grain structure, thus making the pipe more susceptible to corrosion.
Therefore, ERW pipe is not as desirable as SMLS pipe for handling corrosive fluids. However, it is used in oil and gas production facilities and transmission lines, after normalized or cold expanded, for 26″ (660.4 mm) OD and larger lines.
SSAW Steel Pipe
Spiral-welded pipe is formed by twisting strips of metal into a spiral shape, similar to a barber’s pole, then welding where the edges join one another to form a seam. This type of pipe is restricted to piping systems using low pressures due to its thin walls.
SAW or DSAW pipe ?
SAW and DSAW pipes are produced from plate (skelp’s), which are either formed into a “U” and then an “O” and then welded along the straight seam (SS) or twisted into a helix and then welded along the spiral seam (SW). DSAW longitudinal butt joint uses two or more passes (one inside) shielded by granular fusible materials where pressure is not used.
DSAW is used for pipe greater than 406.4 mm nominal. SAW and DSAW are mechanically or hydraulically cold expanded and are supplied according to ASTN Specifications A53 and A135 and API Specification 5L. It is supplied in sizes 16″ (406.4 mm) OD to 60″ (1524.0 mm) OD.
LSAW Steel Pipe
LSAW (LSAW) in leaflets plate as raw material, the steel plate in the mold or molding machine pressure (volume) into using double-sided submerged arc welding and flaring from production.
A wide range of the finished product specifications, weld toughness, ductility, uniformity and dense, with a large diameter, wall thickness, high pressure resistance, low-temperature corrosion resistance, etc.. Required steel pipe in the construction of high-strength, high toughness, high-quality long-distance oil and gas pipelines, mostly large diameter thick wall LSAW.
API standard provisions, in the large-scale oil and gas pipelines, when 1, Class 2 areas through the alpine zone, the bottom of the sea, the city densely populated area, LSAW only applied specifically casts.