2021 wholesale price 20cr Hot Rolled Thick Wall Seamless Pipe - Spiral steel pipe is of high quality and low price – Weichuan

Spiral steel pipe is a spiral seam steel pipe made of strip steel coil as raw material, often formed by warm extrusion and welded by automatic double wire double-sided submerged arc welding process. The spiral steel pipe sends the strip steel to the welded pipe unit. After rolling by multiple rollers, the strip steel is gradually rolled up to form a circular pipe blank with opening gap. Adjust the reduction of the extrusion roller to control the weld gap at 1 ~ 3mm and make both ends of the welded junction flush.

(1) Raw materials, i.e. strip steel coil, welding wire and flux. Strict physical and chemical inspection shall be carried out before input.

(2) The butt joint of strip steel head and tail adopts single wire or double wire submerged arc welding, and automatic submerged arc welding is adopted for repair welding after rolling into steel pipe.

(3) Before forming, the strip steel is leveled, trimmed, planed, surface cleaned, transported and pre bent.

(4) The electric contact pressure gauge is used to control the pressure of the pressing oil cylinder on both sides of the conveyor to ensure the smooth transportation of strip steel.

(5) Adopt external control or internal control roll forming.

(6) The weld gap control device is used to ensure that the weld gap meets the welding requirements, and the pipe diameter, misalignment and weld gap are strictly controlled.

(7) Both internal welding and external welding adopt American Lincoln Electric welding machine for single wire or double wire submerged arc welding, so as to obtain stable welding quality.

(8) All welded welds are inspected by on-line continuous ultrasonic automatic flaw detector to ensure 100% NDT coverage of spiral welds. If there are defects, it will automatically alarm and spray marks, and the production workers will adjust the process parameters at any time to eliminate the defects in time.

(9) The steel pipe is cut into single pieces by air plasma cutting machine.

(10) After cutting into a single steel pipe, each batch of steel pipe shall be subject to a strict first inspection system to check the mechanical properties, chemical composition, fusion condition, surface quality of steel pipe and NDT to ensure that the pipe making process is qualified before it can be officially put into production.

(11) The parts with continuous acoustic flaw detection marks on the weld shall be rechecked by manual ultrasonic and X-ray. If there are defects, after repair, they shall be subject to NDT again until it is confirmed that the defects have been eliminated.

(12) The pipe of butt welding seam of strip steel and T-joint intersecting spiral weld shall be inspected by X-ray television or film.

(13) Each steel pipe is subject to hydrostatic test, and the pressure adopts radial seal. The test pressure and time are strictly controlled by the microcomputer detection device of steel pipe water pressure. Test parameters are automatically printed and recorded.

(14) The pipe end is machined to accurately control the perpendicularity, slope angle and blunt edge of the end face.

1. If the gap is too large, the proximity effect will be reduced, the eddy current heat will be insufficient, and the weld intergranular joint will be poor, resulting in incomplete fusion or cracking.

2. If the gap is too small, the proximity effect will increase, the welding heat will be too large, and the weld will be burned; Or the weld is extruded and rolled to form a deep pit, which affects the surface quality of the weld.

After the two edges of the tube blank are heated to the welding temperature, common metal grains are formed under the extrusion of the extrusion roller, which penetrate and crystallize with each other, and finally form a firm weld. If the extrusion force of spiral steel pipe is too small, the number of common crystals will be small, the strength of weld metal will decrease, and cracking will occur after stress; If the extrusion force is too large, the molten metal will be extruded out of the weld, which will not only reduce the weld strength, but also produce a large number of internal and external burrs, and even cause defects such as welding overlap.