Spiral steel pipe is a spiral seam steel pipe made of strip steel coil as raw material, extrusion molding at regular temperature, and welded by automatic double-wire double-sided submerged arc welding process. Spiral steel pipe will be fed into the welded pipe unit, through a number of rolls rolling, the strip steel is gradually rolled up to form a round billet with an open gap, adjust the amount of extrusion rollers under pressure, so that the weld gap is controlled at 1 ~ 3mm, and make the weld ends flush.
Production process:
(1) Raw materials, i.e. strip coil, welding wire and flux. All of them are subjected to strict physical and chemical tests before they are put into use.
(2)The strip steel head and tail are butt-jointed, and single-wire or double-wire submerged arc welding is used, and automatic submerged arc welding is used to make up the weld after it is rolled into a steel pipe.
(3) Before forming, the strip steel is leveled, sheared and shaved, the surface is cleaned and conveyed and pre-bent edges are treated.
(4) Electric contact pressure gauge is used to control the pressure of the press-down cylinder on both sides of the conveyor, which ensures the smooth transportation of the strip.
(5) Adopt external or internal control roll forming.
(6) Weld gap control device is adopted to ensure that the weld gap meets the welding requirements, and the pipe diameter, the amount of misalignment and the weld gap are strictly controlled.
(7) Both internal and external welding are carried out by single-wire or double-wire submerged arc welding with American Lincoln electric welding machine, so as to obtain stable welding quality.
(8)The finished welds are inspected by on-line continuous ultrasonic auto-injury meter, which ensures 100% NDT coverage of the spiral welds. If there are defects, automatic alarm and spray marking, production workers accordingly adjust the process parameters at any time to eliminate defects in a timely manner.
(9) Air plasma cutting machine is used to cut the steel pipe into single one.
(10) cut into a single pipe, each batch of steel pipe should be a strict first inspection system, check the mechanical properties of the weld, chemical composition, dissolution conditions, the surface quality of the steel pipe as well as after non-destructive testing, to ensure that the pipe making process is qualified before officially put into production.
(11) The weld has a continuous acoustic flaw marking of the parts, after manual ultrasonic and X-ray review, such as defects, after repair, and again after nondestructive testing, until it is confirmed that the defects have been eliminated.
(12) Strip steel butt weld weld and intersecting with the spiral weld d joints in the pipe, all through the X-ray television or film inspection.
(13) Each steel pipe is hydrostatically tested, and the pressure is radially sealed. Test pressure and time are strictly controlled by the steel pipe hydrostatic microcomputer testing device. Test parameters are automatically printed records.
(14)Pipe ends are mechanically processed so that end face verticality, bevel angle and blunt edges are accurately controlled.
Welding treatment:
1. If the gap is too large, it will cause the neighborhood effect to be reduced, the eddy current heat is insufficient, and the weld crystals will be poorly integrated, resulting in unfusion or cracking.
2. If the gap is too small, it will cause the neighbor effect to increase, the welding heat is too large, resulting in weld burn; or weld by extrusion, rolling the formation of a deep crater, affecting the surface quality of the weld.
The two edges of the billet heated to the welding temperature, in the extrusion roller extrusion, the formation of *** with the metal grains penetrate each other, crystallization, and ultimately the formation of a solid weld. Spiral steel pipe if the extrusion pressure is too small, the formation of *** with the number of crystals is small, the weld metal strength decreases, the force will produce cracking; if the extrusion pressure is too large, it will make the molten state of the metal is squeezed out of the weld, not only reduces the strength of the weld, but also produces a large number of inside and outside the burr, and even cause defects in the weld lap.