What Is A SAW Pipe?
SAW, or Submerged Arc Welded, are so-called because they are pipes made by fusing steel plates via the arc welding method. They are also known as JCOE pipes because these tubes are shaped in the form of the letters "J," "C," and "O" to adjust their dimensions during arc welding.
How Are SAW Pipes Made
Unlike ERW pipes, SAW tubing uses metal fillers and a conductive flux during the welding process. These substances are deposited on the steel coil edges to help close the seam. In its solid or unheated state, the flux cannot conduct currents.
However, once heated, it easily acts as a conductor to pass electricity between the electrode and the seam. This flux also helps cover the sparks and fumes usually emitted during the welding process.
Meanwhile, the filler material to close the seam is usually a wire up to 6mm thick. This material is fed to the open seam of the steel coil at a regulated speed and heated by the current conducted by the flux; it helps weld the edges together.
This filler is usually copper coated to prevent corrosion and rust of the steel pipe. The seam may be closed from the outside, inside, or on both sides. A SAW pipe made via an interior and exterior double seaming is also known as a DSAW pipe.
Types Of Saw Pipes
Longitudinal Submerged Arc Welded Or LSAW
The Longitudinal Submerged Arc Welding is the preferred process when making pipes larger than 10 inches. Unlike seamless pipes, which use whole metal billets, steel plates are used when making LSAW pipes.
The steel is bent and welded into creating wider diameter pipes- these are the types of lines used in the oil and gas industry. The major difference between LSAW pipes and other types of Submerged Arc
Welded pipes is that the welding here is done in a straight seam via a double-sided submerged arc welding. DSAW, or doubled seamed pipes, is another variant of LSAW pipes, with the only difference being that both the former's interior and exterior feature a seam weld.
Spiral Submerged Arc Welded Or SSAW
Unlike LSAW pipes which use steel plates, steel coils form the base production material for Spiral Submerged Arc Welded Pipes. In addition, these coils are welded helicoidally or in a spiral shape instead of being longitudinally welded.
Using coils over plates and spiral welding contributes to the cost-effectiveness of Spiral Submerged Arc Welded pipes. As a result, these pipes are preferred for transporting low-value substances like water.
If the line is not involved in transporting energy products like gas and oil, it is most probably a Spiral Submerged Arc Welded pipe.
Characteristic Features Of SAW Pipes
- SAW pipes use a filler metal for welding. These are usually copper coated to avoid rust.
- Most commercial pipes above 24 inches are LSAW because seamless pipe sizing is limited to smaller diameters.
- SAW pipes are made by the "submerged" arc welding method, which uses a flux mixture to help close the seam between the steel coils.
- Due to their large size, SAW pipes are most commonly used in oil and gas pipeline lines.
- Submerged Arc Welded pipes are more accessible and have more application than seamless pipes.
- SAW pipes are also known as JCOE pipes because of their manufacturing process.
Difference Between SAW and ERW Pipes
| ERW Pipes | SAW Pipes | |
| Seam | The seam in ERW pipes is invisible as the edges are fused by passing an electrical current through the steel. | SAW pipes have a visible seam as the submerged arc welding uses filler metals to fuse the steel seams. |
| Material Used | These pipes are made using steel plates. | These pipes are made using steel coils. |
| Applications | Seamless pipes are used in projects that require tubing that can withstand pressure and corrosion, such as power generation and pharmaceuticals. | SAW pipes transport medium to low-pressure commodities like oil and natural gas. |
Differences Between LSAW and SSAW Pipes
|
LSAW Pipes |
SSAW Pipes | |
|
Production/ Welding Process | Steel is fused at longitudinal seams when making LSAW pipes. | SSAW pipes are made by welding steel coils in a spiral formation. |
|
Applications | LSAW pipes transport gas and oil due to their large diameter. | SSAW pipes are mostly used to transport non-critical substances, like water. |
SAW Pipes Specifications
American Petroleum Institute- API 5L Grade B Pipe Specification
Chemical Properties
| Elements | Maximum Content in % |
|---|---|
| Carbon | 0.26% |
| Manganese | 1.20% |
| Sulfur | 0.030% |
| Phosphorous | 0.030% |
| Vanadium | 0.15%, unless specified |
| Niobium | 0.15%, unless specified |
| Titanium | 0.15%, unless specified |
Tensile Properties
|
Properties |
Minimum % |
|
Yield Strength |
35,500 psi |
|
Tensile Strength |
60,200 psi |
|
Weld Seam Tensile Strength |
60,200 psi |
Applications Of SAW Pipes
- SAW pipes, particularly LSAW pipes, are most commonly used in the oil and gas industry to transport flammable and non-flammable fuel.
- These pipes also have applications as carrier lines in the chemical and petrochemical industries.
- SSAW pipes are more affordable than LSAW pipes, making them a great fit for mining projects. This tubing is used to ferry water and slurry from the sites.
- SAW pipes are popular materials in on and offshore piping projects.
- SAW pipes can also be used as plumbing in building constructions
.
Advantages Of SAW Pipes
- The welding process for SAW pipes uses a flux powder made of substances like manganese oxide, silica, and more. This molten/heated flux helps conduct the current to the steel edges without causing arc light, splatter, welding fume, noise, or even the UV radiation associated with traditional welding.
- Since the production uses a filler metal to close the edges of the metal coils, the weld penetration is deeper than usual. This process also leads to better welding control and high deposition rates.
- Submerged Arc Welding has a high deposition rate of 45 kg/hr and can weld up to 5 m of thin sheet steel per minute.
- Using metal fillers ensures that the steel edges do not have to be extensively prepared for the welding process.
- In Submerged Arc Welding, only the lower flux portions have direct with the edge to get molten. The upper half of the substance remains unaffected. As a result, only a minimal portion of the flux has to be disposed of as slag. The remaining portion can be reused again for the next set of welding. This helps conserve almost 90% of the materials, leading to cost conservation.
- SAW pipes have a lot of potential in mechanized applications and can be used in indoor and outdoor projects.
- Submerged Arc Welding produces pipes with larger diameters, increasing their application as transport lines in the gas and oil industry.
Disadvantages Of SAW Pipes
- Unlike seamless or ERW pipes, SAW tubing requires several post-production works. Flux and filler material is used to join the edges of the steel coil, leading to the production of weld beads and slag. Before the pipe is ready for delivery, these must be removed from the product.
- Submerged Arc Welding has limited application as it can be used in producing only steel/iron or nickel-based alloys.
- To make SAW pipes, the steel coils must be submerged in "flux" consisting of substances like silica, lime, and calcium fluoride. Though it can be administered using a flux hopper and a welding head, it cannot be easy to operate with every welding batch.
- SAW pipes are more prone to corrosion and rusting than seamless or ERW pipes as they have a tangible welded area. This may also result in a lower pressure capacity and strength, limiting application to low to medium-pressure lines.