Spiral Steel Pipe Production Process

Spiral steel pipe is a spiral seam pipe made from strip coil as the raw material, formed by cold extrusion, and welded using the automatic double-wire double-sided submerged arc welding process. The strip is fed into the welding pipe unit, rolled through multiple passes, and gradually coiled to form a circular pipe blank with an open gap. The extrusion reduction is adjusted to control the weld gap between 1-3mm and ensure the weld ends are flush.

Production Process:

(1) Raw materials, namely the strip coil, welding wire, and flux, all undergo strict physical and chemical inspection before being put into use.
(2) The head and tail of the strip are butt-joined using single-wire or double-wire submerged arc welding. After being coiled into a pipe, automatic submerged arc welding is used for repair welding.
(3) Before forming, the strip undergoes leveling, edge trimming, edge planing, surface cleaning, conveying, and pre-bending treatment.
(4) An electric contact pressure gauge is used to control the pressure of the hydraulic cylinders on both sides of the conveyor, ensuring stable feeding of the strip.
(5) External control or internal control roll forming is adopted.
(6) A weld gap control device is used to ensure the weld gap meets welding requirements. The pipe diameter, misalignment, and weld gap are all strictly controlled.
(7) Both internal and external welding are performed using Lincoln electric welders from the USA for single-wire or double-wire submerged arc welding, thereby achieving stable welding quality.
(8) All completed welds undergo online continuous ultrasonic automatic flaw detection inspection, ensuring 100% nondestructive testing coverage of the spiral weld. If defects are found, the system automatically alarms and sprays a mark. Production workers can then adjust process parameters at any time based on this to eliminate defects promptly.
(9) An air plasma cutting machine is used to cut the steel pipe into single lengths.
(10) After being cut into single pipes, each batch of pipes undergoes a strict first-article inspection system. This checks the mechanical properties and chemical composition of the weld, the fusion condition, the surface quality of the pipe, and nondestructive testing. Production officially begins only after ensuring the pipe-making process is qualified.
(11) Sections of the weld marked by continuous ultrasonic flaw detection are rechecked manually using ultrasound and X-rays. If defects are confirmed, they are repaired and then re-inspected nondestructively until the defects are confirmed to be eliminated.
(12) All pipes containing the strip butt weld and the T-joints where it intersects the spiral weld are inspected by X-ray television or filming.
(13) The steel pipes undergo a hydrostatic test using radial sealing. The test pressure and time are strictly controlled by a microcomputer detection device. Test parameters are automatically printed and recorded.
(14) The pipe ends are machined to ensure accurate control of end face perpendicularity, bevel angle, and root face.

Weld Treatment

   If the gap is too large, it reduces the proximity effect, leading to insufficient eddy current heat, poor intergranular bonding in the weld, resulting in lack of fusion or cracking.

   If the gap is too small, it increases the proximity effect, causing excessive welding heat which burns the weld; or the weld forms deep pits after extrusion and rolling, affecting the surface quality of the weld.

After the two edges of the pipe blank are heated to the welding temperature, under the pressure of the squeeze rolls, common metal grains form, mutually penetrating and crystallizing, ultimately forming a strong weld. If the extrusion force is too small, the number of common crystals formed is small, the strength of the weld metal decreases, and cracking may occur under force. If the extrusion force is too large, the molten metal will be squeezed out of the weld, not only reducing weld strength but also generating significant internal and external burrs, or even causing defects like welding overlap.

Main Technical Characteristics of Spiral Steel Pipe

a. During the forming process, the steel plate deforms uniformly with low residual stress, and the surface does not get scratched. Processed spiral pipes offer greater flexibility in the size range of diameter and wall thickness. They have unparalleled advantages, especially in producing high-grade, thick-walled pipes, particularly small and medium-diameter thick-walled pipes, meeting more user requirements regarding spiral pipe specifications.
b. Using the advanced double-sided submerged arc welding process allows welding in the optimal position, making it less prone to defects like misalignment, off-weld, and lack of penetration, and easier to control welding quality.
c. 100% quality inspection of the steel pipes ensures the entire production process is under effective inspection and monitoring, effectively guaranteeing product quality.
d. All equipment on the entire production line can connect with the computer data acquisition system, enabling real-time data transmission. Technical parameters during the production process are managed by the central control room.

Applications

Spiral steel pipes are mainly used in water supply projects, the petrochemical industry, the chemical industry, the power industry, agricultural irrigation, and urban construction. They are one of the twenty key products developed in China.

For liquid transport: Water supply, drainage.
For gas transport: Gas, steam, liquefied petroleum gas.
For structural use: Piling pipes, bridges; piers, roads, building structures, etc.