Pipe Types Explained
The oil and gas industry uses three main steel pipe types: Seamless, ERW (Electric Resistance Welded), and LSAW (Longitudinal Submerged Arc Welded).
Seamless pipes are made from solid steel billets that are heated and pushed or pulled over a form to create a hollow tube without any welded seams.
They are commonly used for high-pressure applications in upstream operations like drilling and exploration, midstream fluid transmission, downstream refining, and utility services.
ERW pipes are made using cold-forming, shaping steel coils into cylindrical forms, and the seam is welded together using an electric current.
The weld seam runs along the length of the pipe. ERW pipes are cost-effective for low-to-medium-pressure applications, such as transporting water, oil, and gas.
LSAW pipes are made by bending and welding steel plates along the length, with the seam running straight (longitudinal seam) or in a spiral.
Manufacturing Process for Seamless, ERW, and LSAW Pipes
ERW Pipe Production
ERW pipes are made by cold-forming steel coil and welding the seam:
The appropriate width and gauge steel coil is selected and loaded onto an uncoiler.
The strip passes through rollers, progressively forming it into a round shape.
The longitudinal edges are heated by passing a high-frequency current between them.
Rolls press the edges together to create a fusion weld without adding filler metal.
The welded pipe passes through sizing stands to achieve the final diameter.
The pipe is cut to length, the ends are formed (plain, bevelled, threaded, etc.), and the pipe is tested before shipping.
The entire ERW process is continuous, with the pipe moving at a constant speed through the forming and welding stands.
LSAW Pipe Production
LSAW pipes are made from steel plate that is formed and welded:
Steel plates are selected, and the edges are milled to prepare them for welding.
The plate is pre-bent on a press brake to start forming it into a round shape.
A U-press forms the plate into a U-shape, and an O-press closes the U into a tube.
The longitudinal seam is initially tack welded on the inside to hold the edges together.
The pipe is then passed through automatic welding stations that lay down multiple passes of submerged arc welds inside and outside the seam.
A mechanical expander expands The welded pipe slightly to achieve a proper round shape.
The pipe is cut to length, bevelled, tested hydrostatically, and inspected before shipping.
LSAW pipes are generally used for larger diameters (16" and above) and have thicker walls than ERW pipes.
