Quality Control of Spiral Welded Pipe

Welded pipes are round pipes welded by steel plates, which are divided into high-frequency electric resistance welded pipes (ERW pipes), straight seam arc welded pipes (LSAW), and spiral welded pipes.

Industrial TV internal inspection equipment: inspect the appearance quality of internal welding seams.
Magnetic Particle Flaw Detector: To inspect near-surface defects of large-diameter steel pipes.
Ultrasonic automatic continuous flaw detector: inspect the transverse and longitudinal defects of the full-length weld of the spiral steel pipe.
Ultrasonic manual flaw detector: re-inspection of large-diameter steel pipe defects, inspection of repaired welds and weld quality after hydraulic pressure.
X-ray automatic flaw detector and industrial TV imaging equipment: inspect the internal quality of the full-length weld of the spiral steel pipe, with a sensitivity of not less than 4%.
X-ray filming equipment: inspect the original weld seam and repair welding seam, the sensitivity is not less than 2%.
2,200-ton hydraulic press and computer automatic recording system: to test the pressure-bearing quality of each large-diameter steel pipe.

In order to ensure product quality, we have formulated a comprehensive quality plan, on-site work procedures and inspection and test plans:

Raw material inspection—leveling inspection—butt welding inspection—forming inspection—inner welding inspection—outer welding inspection—pipe cutting inspection—ultrasonic inspection—groove inspection—dimension inspection—X-ray inspection - hydrostatic test - final inspection

Anti-corrosion

The anti-corrosion requirements of this project are quite different from those of other domestic projects. The main differences are:

Internal anti-corrosion materials generally use cement mortar in China, and this project uses non-toxic epoxy paint (thickness 0.4mm).

The electric spark test voltage of the external anti-corrosion coating is generally 3000 volts in China, and the maximum is not more than 5000 volts. This project is 10 kV. In response to the above requirements, we focus on the following two aspects of work:

Strict sandblasting work procedures to ensure the quality of rust removal, and complete the spraying of internal and external primers within 1 hour, which is the basis for ensuring the quality of anti-corrosion. When formulating the anti-corrosion process, we specifically require that the glass cloth be soaked with epoxy coal tar pitch paint, semi-mechanically rolled, and the glass cloth is manually pushed flat with a roller to ensure the uniformity and fineness of the outer coating. The inner and outer anti-corrosion pipes should be inspected in the open storage yard for 4 months. The inner coating has no yellow spots and other bad phenomena, and the electric spark test of the outer anti-corrosion layer can still meet the requirements of 10 kV.

Spiral welded pipe unit

The spiral welded pipe unit is used to produce large-diameter steel pipes with a diameter of (89-2450)mm×(0.5-25.4)mm and a length of 6-35m. Its production methods are continuous and discontinuous. The unit adopts spiral forming, and the welding adopts two steps of pre-welding and final welding. Forming and pre-welding (spot welding) takes place on a spiral former, followed by internal and external submerged arc welding on the final welding machine.

The spiral welded pipe is formed by a spiral former, which can be divided into two types: upper coil forming and lower coil forming. Recently, there are three basic forms of the structure of the former of the spiral welded pipe:
(1) Sleeve-type spiral former. It is only suitable for the forming of small-diameter welded pipes. It is low in cost and easy to operate.
(2) Roller spiral forming and deleting device. The roll former is made according to the working principle of the three-roller bending machine. The contact surface between the former and the steel strip is rolling friction, which has low resistance, long tool life, and almost no scratches on the product surface.
(3) Mandrel screw former. This former is suitable for forming small-diameter, thin-walled high-quality spiral welded pipes. However, the inner surface of the steel pipe may be scratched due to friction.

The use of spiral welded pipe

Spiral welded pipes are mainly used in water supply projects, petrochemical industry, chemical industry, electric power industry, agricultural irrigation and urban construction in China. Used for liquid transportation: water supply and drainage. For gas transportation: gas, steam, liquefied petroleum gas. For structural purposes: as piling pipes, as bridges; pipes for wharves, roads, building structures, etc.