The spiral steel mill feeds the strip into the welded pipe unit. After rolling through multiple rolls, the strip is gradually rolled up to form a circular tube blank with an open gap. The reduction of the pressing roll is adjusted to control the weld gap to 1. ~3mm and make the solder joints flush at both ends.
The treatment method is the same as that of the lsaw steel pipe. If the clearance is too large, the proximity effect is reduced, the eddy current heat is insufficient, and the weld inter-granular joint is poor, resulting in un melting or cracking. If the gap is too small, the proximity effect is increased, the welding heat is too large, and the weld is burnt; or the weld is pressed and rolled to form a deep pit, which affects the surface quality of the weld.
After the two edges of the spiral tube are heated to the soldering temperature, under the extrusion of the pressing roller, common metal crystal grains are mutually infiltrated and crystallized, and finally a firm weld seam is formed. If the pressing force is too small, the number of common crystals formed will be small, the strength of the weld metal will decrease, and cracking will occur after the force is applied; if the pressing force is too large, the molten metal will be extruded out of the weld, not only will it be lowered. The weld strength, and a large number of internal and external burrs, and even weld sews and other defects.
The following is the treatment process of spiral submerged arc welded pipe for pressurized fluid transportation:
Physical and chemical testing
Strict physical and chemical testing is required before input. Raw materials are strip coils, welding wire, flux while the steel head and tail are butt jointed. The single wire or double wire submerged arc welding is used, and the automatic submerged arc welding is used after the steel pipe is rolled.
Before forming, the strip is leveled, trimmed, planed, surface cleaned and pre-bent. The electric contact pressure gauge is used to control the pressure of the cylinder on both sides of the conveyor to ensure the smooth conveying of the strip.
External and internal control roll molding
The weld gap control device is used 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. Both internal and external welding are performed by single-wire or double-wire submerged arc welding using a Lincoln welding machine in the United States to obtain stable welding specifications.
The welded seams are inspected by online continuous ultrasonic automatic injury inspection to ensure the non-destructive testing coverage of 100% spiral welds. If there is a defect, the alarm is automatically alarmed and sprayed, and the production worker adjusts the process parameters at any time to eliminate defects in time.
First inspection system
Cut the steel pipe into a single root using an air plasma cutting machine. After cutting into a single steel pipe, each batch of steel pipe shall be subjected to a strict first inspection system to check the mechanical properties, chemical composition, fusion condition, surface quality of the steel pipe and non-destructive testing to ensure the pipe-making process is qualified. In order to formally put into production.
The part of the weld with continuous acoustic flaw detection mark, after manual ultrasonic and X-ray review, if it is defective, after repair, it will pass the non-destructive test again until it is confirmed that the defect has been eliminated.
The tube of the butt weld and the butt joint that intersects the spiral weld are all inspected by X-ray TV or film. Each steel pipe is subjected to hydro static pressure test and the pressure is radially sealed. The test pressure and time are strictly controlled by the steel pipe water pressure microcomputer detection device. The test parameters are automatically printed and recorded. End machining, which makes the end face vertical, groove angle and blunt edge accurately controlled.