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The Analysis of how to Select the Steel Support Structure, LSAW or SSAW?

Date:2019-05-08    keywords:LSAW,SSAW

Regarding the selection of steel for steel-supported structural steel pipes, is it better to use straight-slit steel pipes or spiral steel pipes? The following analysis gives an introduction from the production process and price comparison of the two steel pipes, which can give the practical person an intuitive understanding of the properties and characteristics of the two steel pipes:


First, the production process comparison of materials:


Straight seam steel pipe process(LSAW):
1. Stencil: After the steel plate used to manufacture the large-diameter LSAW steel pipe enters the production line, the whole board ultrasonic inspection is first carried out;
2. Milling edge: double-sided milling the two edges of the steel plate by the edge milling machine to achieve the required plate width, parallelism of the edge of the plate and the shape of the groove;
3. Pre-bending: pre-bending the edge of the board with a pre-bending machine to make the edge of the board have the required curvature;
4. Molding: On the JCO molding machine, half of the pre-bent steel plate is first stepped and pressed into a "J" shape, and the other half of the steel plate is also bent and pressed into a "C" shape, and finally an opening is formed. "O" shape
5. Pre-welding: the jointed straight seam welded steel pipe is welded and continuously welded by gas shielded welding (MAG);
6. Internal welding: welding by longitudinal multi-wire submerged arc welding (up to four wires) on the inside of a straight seam steel pipe;
7. External welding: welding by longitudinal multi-wire submerged arc welding on the outside of straight seam submerged arc welded steel pipe:
8. Ultrasonic inspection I: 100% inspection of the inner and outer welds of straight seam welded steel pipes and the base metal on both sides of the weld;

9. X-ray inspection I: 100% ray industrial TV inspection of internal and external welds, using image processing system to ensure the sensitivity of flaw detection;

10. Expanding diameter: Expanding the full length of the straight seam submerged arc welded steel pipe to improve the dimensional accuracy of the steel pipe and improve the distribution state of the internal stress of the steel pipe;

11. Hydraulic test: On the hydraulic test machine, the steel pipe after the diameter expansion is tested one by one to ensure that the steel pipe meets the test pressure required by the standard. The machine has automatic recording and storage functions;
12. Chamfering: The steel pipe after passing the inspection shall be processed at the pipe end to achieve the required pipe end groove size;
13. Ultrasonic inspection II: Ultrasonic inspection is carried out again and again to check for defects that may occur after straightening and water pressure of straight seam welded steel pipes;
14. X-ray inspection II: ray industrial TV inspection and pipe end welding filming of steel pipes after expansion and hydrostatic test;
15. Tube end magnetic particle inspection: carry out this inspection to find the tube end defect;
16. Anti-corrosion and coating: The qualified steel pipe is anti-corrosion and coating according to user requirements.


Spiral steel tube forming process(SSAW):

1. Raw materials are strip coils, welding wire, flux. Strict physical and chemical testing is required before input.
2. The steel head and tail are butt jointed, and 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.
3. Before forming, the strip is leveled, trimmed, planed, surface cleaned and pre-bent.
4. 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.
5. Use external control or internal control roll molding.
6. 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.
7. 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.
8. The welded welds 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.
9. Cut the steel tube into a single root using an air plasma cutter.
10. After cutting into a single steel pipe, the first three inspections of 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. After that, it can be officially put into production.
11. The part of the weld with continuous sound wave detection mark, after manual ultrasonic and X-ray review, if there is a defect, after repair, it will pass the non-destructive test again until it is confirmed that the defect has been eliminated.
12. The tube of the butt weld of the strip and the joint of the butt joint intersecting the spiral weld are all inspected by X-ray TV or film.
13. Each steel pipe is subjected to hydrostatic pressure test and the pressure is sealed by radial. The test pressure and time are strictly controlled by the steel pipe water pressure microcomputer detection device. Test parameters are automatically printed and recorded.
14. Pipe end machining, so that the verticality of the end face, the groove angle and the blunt edge are accurately controlled.

Second, product price comparison:

In terms of price, the straight seam steel pipe is slightly higher than the spiral steel pipe. The reason is that the raw material of the two is used. The straight seam steel pipe is directly rolled and fixed in a large steel factory to define the width and length of the plate. Therefore, it is higher in price than spiral steel pipe. The raw material used for spiral steel pipe is steel strip or coiled sheet, which can produce steel pipes of larger diameter with narrower surface plates of various sizes. 

It is easy to see in the above two molding processes that the weld seam of the straight seam steel pipe is expressed in a straight line on the steel pipe; the weld seam of the spiral steel pipe is expressed in the form of a spiral on the surface of the steel pipe, and the two steel pipes are treated in the weld seam and There is no difference in the welding process, but the length of the weld is that the spiral steel pipe is much longer than the straight seam steel pipe; their force points are not nearly the same, the force of the straight seam steel pipe is uniform, and the force of the spiral steel pipe is uniform. It is spread over the entire pipe body, so the straight seam steel pipe should be superior to the spiral steel pipe in strength.

In addition, the straight seam steel pipe is superior to the spiral steel pipe in the appearance of the steel pipe, because the seamless joint of the straight seam steel pipe can achieve the appearance of the seamless steel pipe.

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