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Double Submerged Arc Welded straight-seam pipe
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DSAW STEEL PIPE

Double Submerged Arc Welded straight-seam pipe for heavy industrial and structural applications.

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DSAW STEEL PIPE: WHAT IS IT? & SPECS

DSAW (Double Submerged Arc Welded) pipe is a straight-seam product manufactured from raw steel plates. Unlike ERW pipe, which is continuously rolled from coil, DSAW is formed by rolling single plates into cylinders and welding the longitudinal seam from both the inside and the outside, ensuring a high-strength, full-penetration joint.

The "Double Submerged" Advantage

The term "Double" refers to the welding passes—once from the inside, and once from the outside. "Submerged" means the welding arc is completely buried under a blanket of granular flux. This protects the molten weld pool from atmospheric contamination (oxygen/nitrogen) and prevents sparks and spatter, resulting in an incredibly pure, high-penetration weld.

The U-O-E Manufacturing Process

The production of DSAW pipe typically follows the "U-O-E" method, which refers to the three stages of forming the heavy steel plate using massive hydraulic presses:

U
U-ing Press

The flat steel plate is crimped and pressed into a U-shape.

O
O-ing Press

The U-shape is crushed closed into an O-shape (cylinder) and tack-welded.

E
Expansion

The pipe is mechanically expanded from the inside to meet exact diameter tolerances.

The Two Types of DSAW Pipe

When buyers specify DSAW, they are usually referring to the welding method. However, DSAW comes in two distinct forms depending on the seam layout:

  • 1. LSAW (Longitudinal Submerged Arc Welded)

    Manufactured with a single, straight seam running down the length of the pipe (created via the U-O-E process). It is the gold standard for offshore oil rigs and extreme high-pressure lines. Learn more about LSAW.

  • 2. SSAW / HSAW (Spiral Submerged Arc Welded)

    Manufactured from hot-rolled steel coils, featuring a helical (spiral) seam. It is highly cost-effective for large diameters and is widely used for water transmission and deep foundation piling. Compare SSAW vs. LSAW.

Key Specifications & Applications

Feature Details
Size Range Typically 18.00” O.D. through 60.00” O.D.
Length Single and Double Random lengths up to 60 ft.
Grades API 5L (Grade B through X70), ASTM A252 (Grades 2 & 3), A572
Conditions New, Surplus, Mill Reject, and Used

Due to its massive diameter and structural integrity, DSAW pipe is the preferred choice for:

  • 🛢️
    High Pressure Pipelines
    Oil and gas transmission lines requiring thick walls.
  • 🏗️
    Structural Piling & Columns
    Heavy support for bridges, marine docks, and offshore platforms.
  • 🛣️
    Road Casing & Sign Poles
    Protecting utility lines under highways and supporting massive billboards.

DSAW Technical FAQ

Common questions regarding the manufacturing and inspection of Double Submerged Arc Welded pipe.

The term "Double" refers to the welding passes. In the DSAW process, the longitudinal seam is welded first from the inside of the pipe, and then a second pass is made from the outside. These two weld beads penetrate the steel to overlap slightly, ensuring 100% fusion through the wall thickness without the need for a filler strip.
The main difference is the orientation of the weld seam. DSAW has a single straight (longitudinal) seam. Spiral Weld (SSAW) has a seam that spirals down the length of the pipe. While Spiral pipe is cost-effective for water transmission and piling, DSAW is preferred for high-pressure lines because the shorter, straight seam is easier to inspect and has fewer geometric imperfections.
After welding, the pipe may not be perfectly round. "Mechanical Expansion" involves inserting a hydraulic tool inside the pipe that pushes outwards. This cold-works the steel, ensuring the pipe meets strict roundness tolerances (ovality) and also relieves residual stresses from the welding process, increasing the pipe's dimensional stability.
Critical DSAW pipe undergoes rigorous Non-Destructive Testing (NDT). This typically includes Ultrasonic Testing (UT) of the entire seam to check for internal flaws, and X-Ray (Radiographic) inspection of the pipe ends. Most specifications (like API 5L) also require a hydrostatic pressure test to guarantee leak integrity.
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Related Services
Pipe Coating (FBE/Galv)Precision CuttingSplicing & Welding
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