LSAW pipe — longitudinal submerged arc welded pipe — is the material of choice for large-diameter, high-pressure oil and gas transmission pipelines. Where ERW pipe serves the gathering and distribution world in diameters up to 24 inches, LSAW takes over from 16 inches upward, handling the heavy-wall, high-grade applications that require a deep-penetration weld, tight dimensional control, and full non-destructive examination of every seam.
ZC Steel Pipe manufactures LSAW pipe to API 5L and ISO 3183 standards at our Hai'an City facility. We supply large-diameter line pipe for onshore and offshore pipeline projects in Africa, the Middle East, and South America, with DSAW capability for wall thicknesses up to 40 mm and grades through X70.
CONTENTS
What Is LSAW Pipe?
LSAW vs DSAW — What's the Difference?
Manufacturing Process
API 5L LSAW Specifications & Grades
Size Range & Dimensions
Non-Destructive Testing Requirements
LSAW vs SSAW vs ERW — Comparison
Coating Options for LSAW Pipe
Applications
Frequently Asked Questions
1. What Is LSAW Pipe?
DEFINITIONLSAW — Longitudinal Submerged Arc Welded — pipe is manufactured from steel plate that is formed into a tube and joined along a single longitudinal seam using the submerged arc welding (SAW) process. The weld arc operates beneath a blanket of granular flux, which shields it from atmosphere, stabilizes the arc, and contributes to producing clean, high-quality weld metal.
The "longitudinal" designation means the weld seam runs parallel to the pipe axis — in a straight line from one pipe end to the other. This distinguishes it from SSAW (spiral submerged arc welded) pipe, where the seam runs at an angle around the pipe. The straight-seam geometry of LSAW provides more predictable stress behavior under internal pressure and is preferred for high-pressure gas transmission and offshore applications.
2. LSAW vs DSAW — What's the Difference?
DSAW (Double Submerged Arc Welded) is not a separate process from LSAW — it is the standard technique used when manufacturing LSAW pipe in heavy walls. The distinction is in the number of weld passes:
LSAW (Single Pass)
Passes: 1 — outside only
Wall thickness: Typically ≤14 mm
Application: Light- to medium-wall pipe
Use case: Lower pressure, shorter pipelines
DSAW (Double Pass)
Passes: 2 — inside then outside
Wall thickness: ≥6 mm, typically 10–40+ mm
Application: Heavy-wall high-pressure pipe
Use case: Gas transmission, offshore, X65–X70
In DSAW, the inside weld (IW) is made first, then the pipe is rotated and the outside weld (OW) is completed. This two-pass sequence fills the full joint thickness with weld metal, producing a through-thickness fusion zone that is inspected by both ultrasonic testing and radiographic testing (X-ray). The terms LSAW and DSAW are often used interchangeably in project specifications and commercial documentation — in practice, nearly all heavy-wall LSAW pipe for pipeline service is DSAW.
3. Manufacturing Process
LSAW pipe manufacturing starts with plate rather than coil — this is what enables the heavy wall thicknesses and large diameters that distinguish LSAW from ERW:
Plate preparation — Steel plate (typically TMCP or normalized) is inspected by UT for laminations, then edge-milled to precise bevel geometry for the weld joint.
Pre-bending (J-ing or U-O-E) — The plate edges are pre-bent, then the full plate is formed into a U-shape, then pressed into an O-shape (round tube) in a large press. This is the UOE (U-O-Expand) or JCOE (J-C-O-Expand) process depending on the mill.
Tack welding — The formed cylinder is tack-welded at intervals to hold its shape before the main SAW weld.
Inside weld (IW) — Submerged arc welding from inside the pipe, one or more passes.
Outside weld (OW) — Submerged arc welding from outside the pipe, completing the double-pass DSAW seam.
Cold expansion — The finished pipe is expanded by an internal mechanical expander (UOE) or hydraulically to final OD, improving roundness and relieving residual stresses.
Non-destructive testing — Full weld seam UT, pipe-body UT, and radiographic testing (RT) of weld ends.
Hydrostatic testing — Every pipe is pressure-tested to the required test pressure.
End preparation and marking — Beveled ends per API 5L, marked with heat number, grade, dimensions, and standard.
4. API 5L LSAW Specifications & Grades
The dominant standard for LSAW pipe in oil and gas is API 5L (adopted as ISO 3183 internationally). Both PSL1 and PSL2 are available, with PSL2 being mandatory for most long-distance transmission pipelines.
| Grade | SMYS (MPa) | SMTS (MPa) | Y/T Ratio Max (PSL2) | CVN Test Temp |
| Grade B | 245 | 415 | 0.93 | 0°C (32°F) |
| X42 | 290 | 415 | 0.93 | 0°C (32°F) |
| X52 | 360 | 460 | 0.93 | 0°C (32°F) |
| X60 | 415 | 520 | 0.93 | 0°C (32°F) |
| X65 | 450 | 535 | 0.93 | 0°C (32°F) |
| X70 | 485 | 570 | 0.93 | 0°C (32°F) |
| X80 | 555 | 625 | 0.93 | 0°C (32°F) |
Procurement Note — PSL2 Requirements for LSAW
For most international gas transmission projects, PSL2 is the minimum acceptable specification. PSL2 adds: mandatory CVN impact testing, Y/T ratio controls, weld seam and pipe body UT, and tighter chemistry controls. Always confirm whether your project specification requires PSL2 and at what CVN test temperature — pipelines in cold climates or subsea environments routinely specify −20°C or lower, which affects the steel chemistry and heat treatment your mill must deliver.
Sour Service (LSAW)
For pipelines in sour service (wet H₂S environments per NACE MR0175 / ISO 15156), LSAW pipe must meet additional requirements: maximum hardness in pipe body, weld metal, and HAZ (typically HRC 22 / 250 HBW), and the weld seam must be post-weld heat treated (PWHT) or the chemistry controlled to ensure PWHT is not required. Confirm with your supplier whether NACE-compliant LSAW is in scope for your project.
5. Size Range & Dimensions
| OD Range | WT Range | Length | End Finish | Tolerance OD |
| 406 mm – 1524 mm (16"–60") | 6 mm – 40+ mm | 8 m – 12.2 m (R2/R3) | Beveled per API 5L | ±0.75% for OD ≥ 508 mm |
Common LSAW project sizes for transmission pipelines include:
16" × 9.5 mm to 17.5 mm — gathering trunk lines and medium-pressure transmission
20" × 12.7 mm to 22.2 mm — regional gas transmission
24" × 14.3 mm to 25.4 mm — major gas trunk lines, X65 or X70
30" × 15.9 mm to 28.6 mm — long-distance high-pressure gas transmission
36"–42" × 19.1 mm to 40+ mm — large diameter export pipelines, X70/X80
6. Non-Destructive Testing Requirements
For API 5L PSL2 LSAW pipe, the following NDT is mandatory per the standard:
| Test | Location | Method | Coverage |
| Ultrasonic Testing (UT) | Full weld seam | Automated UT | 100% of seam length |
| Ultrasonic Testing (UT) | Pipe body | Automated UT | 100% of body area |
| Radiographic Testing (RT) | Weld ends | X-ray or gamma | Pipe ends, minimum 200 mm from each end |
| Hydrostatic Test | Full pipe | Hydraulic pressure | Every pipe, 100% |
| Dimensional Inspection | OD, WT, length, squareness | Mechanical gauging | Every pipe or per sampling plan |
Engineering Insight — Why NDT Matters for LSAW
A single missed weld defect in a large-diameter high-pressure pipeline can cause a catastrophic failure affecting hundreds of kilometers of service. Unlike ERW (where defects tend to be small and localized in the narrow HAZ), LSAW weld defects can be larger and more varied (inclusions, lack of fusion, porosity). The mandatory UT + RT combination in PSL2 provides the multi-technique verification needed to ship pipe with documented integrity for critical service.
7. LSAW vs SSAW vs ERW — Comparison
| Feature | LSAW (DSAW) | SSAW (Spiral) | ERW (HFW) |
| Seam orientation | Longitudinal (straight) | Helical (spiral) | Longitudinal (straight) |
| Diameter range | 16"–60" (406–1524 mm) | 16"–120"+ (406–3000+ mm) | ½"–24" (21–610 mm) |
| Wall thickness | 6–40+ mm | 6–25 mm | Up to ~20 mm |
| Max pressure rating | Highest | Moderate | Moderate–High (PSL2) |
| Dimensional tolerance | Tightest | Moderate | Tight (small sizes) |
| Cost per tonne | Highest | Lowest | Moderate |
| High-pressure gas transmission | Preferred | Accepted with limitations | Smaller diameters |
| Offshore pipeline | Standard choice | Rarely used | Rarely used |
8. Coating Options for LSAW Pipe
Large-diameter transmission pipelines almost universally require anti-corrosion coating. The most common systems for LSAW pipe are:
3LPE (Three-Layer Polyethylene) — fusion bonded epoxy primer + adhesive + PE topcoat. Standard for onshore buried pipelines in moderate climates.
3LPP (Three-Layer Polypropylene) — same three-layer system but with polypropylene topcoat for higher operating temperatures (up to 110°C).
FBE (Fusion Bonded Epoxy) — single-layer epoxy coating, commonly used as primer layer in 3LPE/3LPP or as standalone for bends and fittings.
Concrete Weight Coating (CWC) — applied over 3LPE/3LPP for offshore and subsea pipelines requiring negative buoyancy.
For a detailed comparison of coating systems, see our guide: 3LPE vs FBE vs 3LPP — How to Choose the Right Anti-Corrosion System →
9. Applications
Onshore Gas Transmission
Long-distance natural gas transmission pipelines — the backbone of national gas infrastructure in the Middle East, Africa, and Southeast Asia — are predominantly built with LSAW (DSAW) pipe in X65 and X70 grades, 24" to 48" OD, with 3LPE or 3LPP coating. The combination of high strength, heavy wall, and tight dimensional tolerances supports the high-pressure (70–100 bar) operating conditions of these systems.
Offshore Pipelines
Subsea oil and gas export pipelines specify LSAW pipe almost exclusively. The demanding combination of external hydrostatic pressure, internal process pressure, installation loads, and corrosion environment requires the heavy wall, full-NDT, PSL2 DSAW pipe that LSAW mills deliver. Typical diameters are 8" to 30" with concrete weight coating.
Oil Export Trunk Lines
Crude oil export pipelines from production fields to terminals or refineries use LSAW X60/X65 pipe in 16" to 36" diameters. Operating pressures are typically lower than gas lines (40–80 bar), but the large diameter and pipeline length make LSAW the economic and technical optimum.
Water Transmission
Large municipal water supply pipelines in arid regions (Middle East, North Africa) use LSAW pipe in Grade B and X42 with FBE or cement lining. The combination of low cost (relative to oil and gas grades) and large diameter makes LSAW practical for bulk water transmission over long distances.
10. Frequently Asked Questions
What is LSAW pipe?
LSAW stands for Longitudinal Submerged Arc Welded. It is manufactured from steel plate formed into a tube and welded along a single straight longitudinal seam using the submerged arc welding process, which produces welds beneath a blanket of flux for excellent quality and deep penetration. LSAW pipe is used for large-diameter, high-pressure oil and gas transmission pipelines.
What is the difference between LSAW and DSAW pipe?
DSAW (Double Submerged Arc Welded) is a subset of LSAW. In DSAW, the seam is welded twice — first from inside, then from outside the pipe. This double-pass method fills the full joint thickness and is required for heavy-wall pipe. Most large-diameter high-pressure LSAW pipe is manufactured using the DSAW method; the terms are often used interchangeably in project specifications.
What sizes does LSAW pipe come in?
LSAW pipe is typically produced in the range of 16 inches to 60 inches OD (406 mm to 1524 mm), with wall thicknesses from 6 mm to over 40 mm. Below 16 inches, ERW is more economical. Above 60 inches, spiral (SSAW) pipe is typically used. Random pipe lengths are 8 m to 12.2 m.
What API grades are available in LSAW pipe?
LSAW pipe is available to API 5L in grades from Grade B through X80, in both PSL1 and PSL2. For large-diameter high-pressure gas transmission, X65, X70, and X80 PSL2 are most commonly specified. LSAW pipe can also be made to ISO 3183 and EN 10208 for international projects.
What is the difference between LSAW and SSAW pipe?
LSAW has a straight seam running parallel to the pipe axis; SSAW has a helical seam at an angle. LSAW is preferred for high-pressure service because its straight seam geometry allows more precise weld quality control. SSAW can reach larger diameters and is more economical for lower-pressure large-diameter water or slurry pipelines. For critical oil and gas transmission, LSAW is typically required over SSAW.
Request LSAW Pipe — ZC Steel Pipe
ZC Steel Pipe manufactures LSAW / DSAW pipe to API 5L and ISO 3183 at our Hai'an City facility. We supply 16" to 60" OD in grades Grade B through X70, PSL1 and PSL2. Full NDT package (UT + RT + hydrostatic), coating options available including 3LPE, 3LPP, and FBE. Active supply to pipeline projects in Africa, Middle East, and South America.
Contact us: mandy.w@zcsteelpipe.com | WhatsApp: +86-139-1579-1813
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