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 B	Grade A	Grade X42	Grade X46	Grade X52	Grade 56	Garde 60	Gard0e 65	Grade 70	Grade A25
Carbon	0.26%	0.22%	0.26%	0.26%	0.26%	0.26%	0.26%	0.26%	0.26%	0.21%
Manganese	1.20%	90%	1.30%	1.40%	1.40%	1.40%	1.40%	1.45%	1.65%	60%
Sulfur	0.030%	0.030%	0.030%	0.030%	0.030%	0.030%	0.030%	0.030%	0.030%	0.030%
Phosphorous	0.030%	0.030%	0.030%	0.030%	0.030%	0.030%	0.030%	0.030%	0.030%	0.030%

 

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.