Spiral steel pipe(ssaw) is a steel pipe with spiral seam, which is made of strip steel coil as raw material, often warmly extruded, and welded by automatic double-wire double-sided submerged arc welding process. It is mainly used in pipeline transportation of oil, natural gas, bridges, docks, roads, buildings and other projects. Welding is the most common connection method for steel pipes, so how are spiral steel pipes generally welded?
Spiral steel pipe generally adopts advanced double-sided submerged arc welding process, which can realize welding in the best position, and is not prone to defects such as misalignment, welding deviation and incomplete penetration, and it is easy to control the welding quality.
1) The raw materials are strip coil, welding wire and flux. It has to undergo a rigorous physical and chemical inspection before it is put into use.
2) For the butt joint of the strip steel, single wire or double wire submerged arc welding is used, and active submerged arc welding is used for repair welding after rolling into a steel pipe.
3) The electric contact pressure gauge is used to control the pressure of the cylinders on both sides of the conveyor to ensure the smooth conveying of the strip.
4) Before forming, the strip is leveled, trimmed, planed, surface cleaned and conveyed and pre-bending.
5) Use external control or internal control roll forming.
6) The welding seam gap control equipment is selected to ensure that the welding seam gap meets the welding requirements, and the steel pipe dimension, the amount of misalignment and the welding seam gap are strictly controlled.
7) Both internal welding and external welding are used for single wire or double wire submerged arc welding by American Lincoln welding machine, so as to obtain stable welding quality.
8) The welded seams are all inspected by the online continuous ultrasonic automatic flaw tester, which ensures 100% non-destructive testing coverage of the spiral welds. If there is a defect, it will automatically alarm and spray the mark, and the production workers can adjust the process parameters at any time accordingly to eliminate the defect in time.
9) Use an air plasma cutting machine to cut the steel pipe into single pieces.
10) After cutting into a single steel pipe, each batch of steel pipes must undergo a strict first inspection system to check the mechanical properties, chemical composition, fusion status of the weld, the surface quality of the steel pipe and non-destructive testing to ensure that the pipe making process is qualified. , can be officially put into production.
11) The parts with continuous sonic flaw detection marks on the welds shall be re-examined by manual ultrasonic wave and X-ray. If they are indeed defective, they shall be repaired and subjected to non-destructive inspection again until it is confirmed that the defects have been eliminated.
12) The tube where the strip butt weld and the T-joint intersecting with the spiral weld are all inspected by X-ray television or filming.
13) Each steel pipe is tested by hydrostatic pressure, 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.
14) The pipe end is machined so that the verticality of the end face, the bevel angle and the blunt edge are accurately controlled.
When welding, be sure to control the size of the weld gap. If the weld gap of the spiral steel pipe is too large, the proximity effect will be reduced, the eddy current will lack heat, the weld seam will be poorly crystallized, and incomplete fusion or cracking will occur indirectly; It will form welding seam burning; perhaps by kneading the welding seam, it will form a pit after rolling, which will affect the welding surface quality of the steel pipe.