Spiral welded pipe manufacturing process

Spiral welded pipes, also known as SSAW pipes, are manufactured by rolling low-carbon structural steel or low-alloy structural steel strips into a tube blank at a specific helical angle (forming angle) and then welding the seams. This process allows the production of large diameter pipes from narrower strips.

Applications and Specifications of Spiral Welded Pipes

Spiral welded pipes are primarily used for oil and natural gas transmission pipelines. Their specifications are denoted by outer diameter and wall thickness. The pipes can be produced with either single-sided or double-sided welding, ensuring that the welds meet hydraulic test standards, tensile strength requirements, and cold bending performance regulations.

Manufacturing Process of Spiral Welded Pipes

Raw Materials:

Strip coil, welding wire, and flux are the primary raw materials, which must pass strict physical and chemical inspections before use.

Initial Welding:

The head and tail of the strip are butted using single-wire or double-wire submerged arc welding. After the steel pipe is rolled, automatic submerged arc welding is used for repair.

Pre-Forming Preparation:

The strip is leveled, trimmed, planed, surface cleaned, and pre-bent before forming.

Pressure Control:

An electric contact pressure gauge controls the pressure of the cylinder on both sides of the conveyor to ensure smooth strip conveying.

Forming:

External control or internal control roll forming is used to shape the pipe.

Weld Gap Control:

A weld gap control device ensures that the weld gap meets welding requirements. The pipe diameter, misalignment, and weld gap are strictly controlled.

Submerged Arc Welding:

Both internal and external welding are performed using single-wire or double-wire submerged arc welding with American Lincoln welding machines to obtain stable welding specifications.

Ultrasonic Flaw Detection:

Online continuous ultrasonic automatic flaw detection is conducted to ensure 100% non-destructive testing coverage of the spiral welds. Defects trigger an automatic alarm and marking for process adjustment.

Cutting:

An air plasma cutting machine cuts the steel pipe into single pieces.

Inspection:

Each batch of steel pipes undergoes a strict first inspection system to check mechanical properties, chemical composition, weld fusion status, surface quality, and non-destructive testing before production.

Defect Repair and Re-Inspection:

Welds with continuous sonic flaw detection marks are re-examined by manual ultrasonic and X-ray methods. Defective areas are repaired and re-tested until defects are eliminated.

X-ray Inspection:

The strip butt weld and T-joint intersections with the spiral weld are inspected by X-ray television or filming.

Hydrostatic Pressure Test:

Each steel pipe undergoes a hydrostatic pressure test, with parameters controlled and recorded by a microcomputer detection device.

Pipe End Machining:

The pipe ends are machined to ensure the verticality of the end face, bevel angle, and blunt edge are accurately controlled.