MS H-SAW (Helical Submerged Arc Welded) and L-SAW (Longitudinal Submerged Arc Welded) pipes are both types of welded steel pipes used in various industries, particularly for transporting oil, gas, and water. The primary difference between them lies in the welding process and the orientation of the weld seam. Here’s a detailed comparison:

1. Welding Process

• MS H-SAW Pipes:
  • The weld seam is helical (spiral) in shape.
  • The pipe is formed by rolling a steel plate at an angle, and the welding is done using the submerged arc welding (SAW) process along the helical seam.
  • Suitable for producing large-diameter pipes.
• L-SAW Pipes:
  • The weld seam is straight (longitudinal) along the length of the pipe.
  • The steel plate is rolled into a cylindrical shape, and the welding is done along the longitudinal seam using the submerged arc welding (SAW) process.
  • Typically used for medium to large-diameter pipes.

2. Weld Seam Orientation

• H-SAW Pipes:
  • The helical weld seam allows for uniform stress distribution along the pipe, making it more resistant to certain types of stress.
  • The spiral shape of the weld can accommodate larger diameters and thicker walls.
• L-SAW Pipes:
  • The straight weld seam is simpler and easier to inspect and repair.
  • The longitudinal orientation is better suited for high-pressure applications.

3. Applications

• H-SAW Pipes:
  • Commonly used in oil and gas transmission pipelines, water pipelines, and structural applications.
  • Ideal for projects requiring large-diameter pipes with high strength.
• L-SAW Pipes:
  • Widely used in oil and gas transportation, water pipelines, and industrial applications.
  • Preferred for high-pressure applications due to the straight weld seam.

4. Advantages

• H-SAW Pipes:
  • Can produce pipes with larger diameters and thicker walls.
  • Better stress distribution due to the helical weld.
  • Efficient for long-distance pipelines.
• L-SAW Pipes:
  • Easier to manufacture and inspect.
  • Better suited for high-pressure applications.
  • Cost-effective for medium to large-diameter pipes.

5. Limitations

• H-SAW Pipes:
  • More complex manufacturing process.
  • Higher production costs compared to L-SAW pipes.
• L-SAW Pipes:
  • Limited to certain diameter ranges.
  • Less efficient for very large-diameter pipes compared to H-SAW.

Summary Table

In summary, the choice between H-SAW and L-SAW pipes depends on the specific requirements of the project, such as diameter, pressure, and stress conditions. Both types are widely used in the pipeline industry, and each has its own advantages and limitations.

Pipe Types

The required thickness of a pipe is affected by the type of pipe selected. There are three main pipe types:

• Seamless – a pipe with no weld lines.
• Longitudinally welded – a pipe with one or more longitudinal weld lines.
• Spiral welded – spiral shaped weld.

Pipe Types: Seamless, Longitudinally Welded, Spiral Welded

Seamless

This pipe is formed by thrusting a piercing plug through a metal billet whilst it is retained between rollers, or, by pressing a mandrel into a billet that is held within a die. The result of both operations is a pipe with no weld lines (it is seamless).

Seamless Pipe Manufacturing Process

Longitudinally Welded

Flat metal plate can be hot rolled to produce the circular shape of a pipe. It is then necessary to weld the two ends of the plate together to complete the pipe shape in its entirety. Longitudinally welded pipes may have one weld, or multiple welds. As a rough guide, pipes up to approximately 1,000mm in diameter will have only a single weld, whilst larger pipes will require more than one weld.

Single Weld Longitudinally Welded Pipe

Longitudinally welded pipes are not preferred for critical systems if seamless welded pipes can be used. There are several reasons for this:

1. The weld must be proven before its integrity can approach/near that of a seamless pipe. For critical systems, the aim is always to make the piping system as reliable as possible.
2. Proving of a weld takes time and adds financial cost.
3. The use of longitudinally welded pipe creates additional stresses within the piping system (during the design stage, stress calculations are performed extensively).

Tip – if the manufacturing process for a longitudinally welded pipe is hard to visualise, take a piece of paper in two hands and bend it lengthwise into a circular tube shape, then place tape along the joining edges to maintain the tube shape. Now imagine that the paper is metal plate and the tape is the weld, that is generally how longitudinally welded pipe is manufactured.

Spiral Welded

For systems operating with very high volumes and low pressures, a spiral welded pipe may be used. The manufacturing method is similar to that of a longitudinally welded pipe, but the metal plate is rolled at an angle which gives the pipe its spiral shape. Although this type of piping is the cheapest to manufacture, it is the least popular of the three. A typical application for spiral welded pipe would be for power station cooling water systems (non-toxic, high volume, low pressure).

Spiral Welded Pipe Manufacturing Process

Because spiral welded pipes are welded, they are also not favoured for critical systems for the same reasons as mentioned previously when discussing longitudinal welded pipes (weld integrity must be proven, cost of proving the weld, stress raising characteristics within the piping system).