What Are Helical Welded Pipes?
Also called Spiral Submerged Arc Welded or simply SSAW pipes, helical pipes are made by fusing steel plates via submerged arc welding. They are typically made from low-carbon structural steel or low-alloy steel strips.
Unlike Longitudinally Welded pipes, helical piping requires special coiling before fusing the steel coils. These coils are rolled and welded spirally to create a rounded circular tube. The weld gap during coil fusion is maintained around the 1 to 3 mm mark.
Unlike typical Submerged Arc Welded piping, helical welded pipes involve internal and external welding. This process increases rigidity as the two overlapping welds of the pipe increase its bearing potential.
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.
Why Are They Called Helical Welded Pipes?
Unlike LSAW pipes which use steel plates, steel coils form the base production material for Spiral Submerged Arc Welded Pipes (SSAW). These coils are welded helicoidal or in a spiral shape instead of being longitudinally welded, giving it the name of Helical welded Pipes. Using coils over plates and spiral welding contributes to the cost-effectiveness of Spiral Submerged Arc Welded pipes.
Since this piping relies on spirally welded steel coils, it is possible to manufacture helical pipes with varying adjustments. Their production system makes customizations easier as size adjustment, straightening, and diameter adjustments are easier with helical 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 Submerged Arc Welded Helical pipe.
Important Characteristics of Helical Welded Pipes
- These pipes use a filler metal for welding. These are usually copper coated to avoid rust.
- Commercial helical pipes above 24 inches are SAW-based because seamless pipe sizing is limited to smaller diameters.
- These pipes are made by the “submerged” arc welding method, which uses a flux mixture to help close the seam between the steel coils.
- Helical pipes are more accessible and have more application than seamless pipes.
- These pipes are also known as JCOE pipes because of their manufacturing process.
- These pipes are typically welded internally and externally.
- Since slag is used during HSAW pipe production, this piping exhibits improved toughness and low-temperature performance.
- Strips shaped into a helical form are the crux of helical welded pipe production. This system leads to improved versatility as the diameter and length adjustments of the steel are easier.
- The average diameter for helical pipes varies from 20 to 100 inches.
Relevant Specifications for Helical Pipes
API 5 L is the most commonly accepted specification for making helical welded pipes. The common grades under this standard include X42, X52, X60, and X65.
Chemical Properties of API 5L Helical Welded Pipes
|Elements||Maximum Element Content in Percentage (%)|
|Grade A||Grade X42||Grade X46||Grade X52||Grade 56||Garde 60||Gard0e 65||Grade 70||Grade A25|
Tensile Properties of API 5 L Helical Pipes
|Grades||Minimum Yield Strength||Minimum Tensile Strength|
|Grade A25||25 psi||45 psi|
|Grade A||30 psi||48 psi|
|Grade B||35 psi||60 psi|
|Grade X42||42 psi||60 psi|
|Grade X46||46 psi||63 psi|
|Grade X52||52 psi||66 psi|
|Grade X56||56 psi||71 psi|
|Grade X60||60 psi||75 psi|
|Grade X65||65 psi||77 psi|
|Grade X70||70 psi||82 psi|
|Grade X80||80 psi||90 psi|
Helical Pipes: Manufacturing Process
Unlike ERW pipes, Helical welded pipes involve SAW manufacturing or Submerged Arc Welding. Thus, this tubing uses metal fillers and a conductive flux during the welding process to fuse the plates. 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. This 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.
To get the shape, size, and structure correct, manufacturers fold and weld the strips using the helix angle for guidance. Also called the molding angle, this scale impacts the pipe's residual stress. Using this scale correctly also helps improve surface roughness, resistance, and more. The steel strips are bent and welded at this angle to make helical pipes.
Uses of Helical Welded Pipes
Though used in the petrochemical industry, helical pipes are more commonly seen in water engineering and agriculture. These pipes are capable of carrying gas, or LPG, across distances, but they are better suited to transport non-critical substances like water or steam for irrigation, drainage, or supply.
However, helical pipes generally have a lower-than-average physical dimension despite their easy malleability. In some cases, the welding seam length may be longer than the actual pipe length. Poorly made helical pipes may also show defects like cracks, air holes, and partial welding.
Differences Between Helical and Longitudinally Welded Pipes
|LSAW Pipes||Helical Welded Pipes|
|Production/ Welding Process||Steel is fused at longitudinal seams when making LSAW pipes.||Helical welded pipes are made by welding steel coils in a spiral formation.|
|Applications||LSAW pipes transport gas and oil due to their large diameter.||Helical welded pipes are mostly used to transport non-critical substances, like water.|