How SAW pipe is manufactured: SAWL and SAWH

SAW means submerged-arc welding. In pipe production it is commonly used for large-diameter and/or heavier-wall welded pipe.

The two main geometries are:

• SAWL — submerged-arc welded longitudinally;
• SAWH — submerged-arc welded helically.

Other common commercial terms include LSAW for longitudinal SAW and HSAW/SSAW for helical/spiral SAW.

What submerged-arc welding is

Unlike HFI/ERW pressure welding, submerged-arc welding is a fusion-welding process.

An electric arc melts the joint edges and consumable electrode wire beneath a protective granular flux. The process can achieve high deposition rates and deep penetration, making it well suited to heavy wall thicknesses.

Pipe mills often weld from both the inside and outside to create the required full-thickness longitudinal or helical seam.

SAWL: longitudinal pipe from plate

A typical SAWL route starts with individual steel plate.

1. Plate preparation

The plate is inspected and cut to the width/length needed for the required pipe diameter and length. Plate edges are machined to the weld-joint geometry specified by the mill process.

The properties of the pipe body depend heavily on the plate, including its:

• grade;
• TMCP, normalized or other delivery condition;
• toughness;
• through-thickness properties where specified;
• UT condition.

2. Forming the plate into an open pipe

Common forming routes include:

• UOE — plate is formed into a U shape, then an O shape;
• JCOE — progressive J, C and O forming;
• press-bending or other proprietary plate-forming processes.

These are manufacturing methods, not steel grades.

3. Tack welding

The formed edges are aligned and temporarily held by tack welding so the pipe maintains geometry during the main welding operations.

4. Internal and external SAW

The longitudinal seam is welded, commonly from the inside and then the outside using submerged-arc welding.

5. Expansion/calibration

Many SAWL lines mechanically expand the pipe to improve roundness, dimensional control and residual-stress distribution. This is why the final “E” appears in UOE.

Not every longitudinal SAW mill uses exactly the same sequence, so the buyer should verify the mill's qualified route.

SAWH: helical pipe from coil or strip

SAWH pipe uses coil or strip as the continuous feedstock.

The strip enters the forming machine at an angle and is progressively formed into a helix. The meeting strip edges create a spiral/helical seam, which is submerged-arc welded continuously.

The helix angle allows one strip width to produce several pipe diameters within the mill's range, giving SAWH production useful dimensional flexibility.

SAWL vs SAWH

Neither route should be declared generally “better”. Project specifications may permit only one route because of design philosophy, fatigue considerations, dimensional range, historical qualification or client preference.

Circumferential welds are a separate issue

A pipe can be SAWL or SAWH and still later receive a circumferential/girth weld if cans or pipe sections are joined end-to-end.

That circumferential fabrication weld is not what makes the original pipe SAWL or SAWH. It is an additional fabrication operation with its own WPS/PQR, NDT and acceptance requirements.

This distinction matters for very large structural tubulars assembled from multiple cans.

Inspection after welding

Depending on the product standard and project, a SAW pipe production line can include:

• plate/coil inspection before forming;
• visual and dimensional control;
• automated UT of the weld;
• radiographic testing of specified weld areas;
• hydrostatic testing;
• pipe-body UT;
• weld-end examination;
• mechanical testing;
• Charpy/CTOD or other supplementary testing where required.

For offshore line pipe, see API 5L offshore-service pipe requirements.

SAW vs HFI

The two welded routes should not be confused.

• HFI/ERW generally starts from strip/coil and uses high-frequency pressure welding without conventional filler wire.
• SAW uses fusion welding with electrode wire and flux.
• SAWL generally starts from plate.
• SAWH generally starts from coil/strip.

See How ERW/HFI pipe is manufactured.

Procurement questions

For a SAW-pipe RFQ, clarify:

• SAWL only, SAWH permitted, or either?
• plate/coil grade and delivery condition;
• forming method if restricted;
• weld procedure qualification;
• internal/external weld arrangement;
• maximum permitted repair welding;
• NDT method and acceptance standard;
• hydrostatic test;
• pipe-body UT;
• length range and circumferential weld restrictions;
• bevel/end requirements;
• EN 10204/API documentation and TPI points.

Procurement takeaway

SAWL and SAWH are both submerged-arc welded pipe routes, but they are built around different feedstock and seam geometry.

For project compliance, do not substitute one route for the other merely because OD, wall thickness and grade are the same. The manufacturing route must be expressly permitted by the governing specification and approved for the intended service.

References and verification sources

• EUROPIPE — Production of longitudinal large-diameter pipe
• Welspun Corp — Pipe manufacturing capabilities