Spiral welded pipe (SSAW/SAWH) is also called spiral steel pipe: a low carbon carbon structural steel or low alloy structural steel strip is rolled into a tube blank at a certain spiral angle (forming angle), and then the tube seam is welded together. It can produce large-diameter steel pipes from narrower strips of steel. Its specifications are expressed as outer diameter * wall thickness. The welded pipe should ensure that the hydraulic pressure test, tensile strength and cold bending performance of the weld meet the regulations.
To ensure product quality, we have formulated a complete quality plan, on-site work procedures and inspection and test plans.
Raw material inspection—leveling inspection—butt welding inspection—forming inspection—internal welding inspection—external welding inspection—pipe cutting inspection—ultrasonic inspection—groove inspection—external dimension inspection—X-ray inspection—hydraulic test—final inspection
Quality assurance
According to the regulations of the spiral welded pipe production standard, the main inspection/control items of spiral welded pipe include:
1. Dimensions: steel pipe outer diameter, wall thickness, ovality, curvature, pipe end perpendicularity,
2. Length and appearance quality: weld reinforcement, wrong edge, steel pipe surface, delamination, inclusions, weld defect judgment
3. Chemical composition
4. Tensile test of welded joint
5. Hydrostatic pressure test
6. Acid etching inspection
7.
Non-destructive inspection
Generally, the spiral welded pipe unit adopts the online continuous inspection method to ensure the welding quality of the weld. This is another important feature that distinguishes the spiral welded pipe production from the straight seam welded pipe production. Continuous inspection is beneficial to the monitoring of welding defects, the stability of welding quality, and the guarantee of welding grade. Due to the limitation of the production process, it is extremely difficult to achieve continuous and uninterrupted inspection of the longitudinally welded pipe. This will increase the probability of welding hidden dangers and quality problems, and even affect the overall working reliability of future pipeline operations.
Spiral welded pipe is also a kind of welded pipe. Its strength is generally higher than that of straight seam welded pipe. It can produce welded pipes with a larger pipe diameter from a narrower blank, and can also produce welded pipes with different pipe diameters from the same width blank. However, compared with the straight seam pipe of the same length, the weld length is increased by 30-100%, and the production speed is lower. Therefore, most of the smaller diameter welded pipes adopt straight seam welding, and the large diameter welded pipes mostly adopt spiral welding.
Spiral welded pipe manufacturing process:
1. The raw materials are strip steel coils, welding wire, and flux. Strict physical and chemical tests are required before investment.
2. The strip head and tail are connected by single wire or double wire submerged arc welding, and automatic submerged arc welding is used for repair welding after coiling into steel pipe.
3. Before forming, the strip undergoes leveling, edge trimming, edge planing, surface cleaning and conveying, and pre-bending treatment.
4. The electric contact pressure gauge is used to control the pressure of the cylinders on both sides of the conveyor to ensure the smooth transportation of the strip.
5. Adopt external control or internal control roll forming.
6. The welding seam gap control device is adopted to ensure that the welding seam gap meets the welding requirements, and the pipe diameter, the amount of misalignment and the welding seam gap are all strictly controlled.
7. Both internal welding and external welding adopt American Lincoln electric welding machine for single-wire or double-wire submerged arc welding to obtain stable welding specifications.
8. The welded seams after welding are inspected by an online continuous ultrasonic automatic flaw instrument, which guarantees 100% non-destructive testing coverage of 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 to eliminate the defect in time.
9. Use an air plasma cutting machine to cut the steel pipe into individual pieces.
10. After cutting into single steel pipes, the first three of each batch of steel pipes shall undergo a strict first inspection system to check the mechanical properties, chemical composition, fusion status of the welds, the surface quality of the steel pipes and pass non-destructive inspections to ensure that the pipe manufacturing process is qualified Later, it can be officially put into production.
11. The parts with continuous sonic flaw detection marks on the weld are re-examined by manual ultrasonic and X-ray. If there are defects, after repairing, they will go through non-destructive inspection again until the defects are confirmed.
12. The pipes where the strip steel butt welding seams and the D-shaped joints intersecting with the spiral welding seams are all inspected by X-ray television or filming.
13. Each steel pipe undergoes hydrostatic pressure test, and the pressure adopts radial seal. The test pressure and time are strictly controlled by the steel pipe hydraulic microcomputer detection device. The test parameters are automatically printed and recorded.
14. The pipe end is machined to accurately control the verticality of the end face, bevel angle and obtuse edge.
Price analysis
Due to the high requirements on the material technical performance and production technology of hot rolled coils, on the one hand, there are fewer domestic manufacturers that meet the standards than steel plate manufacturers. On the other hand, its production technology and quality level determine that its market price is also higher than that of hot rolled steel sheet. This is the main reason why the market price of spiral welded pipe is higher than that of
straight seam welded pipe. For the composition of the steel pipe sales price, the material price is the dominant or even the decisive factor.
Cut-to-length length and price
The yield rate of the production of fixed-length pipes is much lower than that of normal-length pipes, and it is reasonable for the manufacturer to raise the price. The rate of price increase varies from company to company. Generally, the price increase is about 10% on the base price. The fixed-length length should be within the usual length range, which is a certain fixed length dimension required in the contract. However, it is impossible to cut out the absolute fixed-length length in actual operation, so the standard specifies the allowable positive deviation value for the fixed-length length. If there is no double-length deviation and cutting allowance in the standard, it should be negotiated by the supplier and the buyer and indicated in the contract. The double-length scale is the same as the fixed-length length, which will bring about a substantial reduction in the yield rate of the manufacturer. Therefore, it is reasonable for the manufacturer to raise the price, and the price increase is basically the same as the fixed-length length.
Spiral welded pipe unit
The spiral welded pipe unit is used to produce large-diameter steel pipes with a diameter of (89～2450)mm×(0.5～25.4)mm and a length of 6～35m. The production method is continuous and discontinuous. The unit adopts spiral forming, and the welding adopts two steps of pre-welding and final welding. Forming and pre-welding (spot welding) are performed on a spiral former first, and then internal and external submerged arc welding is performed on the final welding equipment.
Spiral welded pipe is formed by a spiral former, which can be divided into two types: roll forming and roll forming. The current spiral welded pipe shaper structure can be summarized in three basic forms:
(1) Sleeve type spiral former. It is only suitable for the forming of small diameter welded pipes. It has low cost and easy operation.
(2) Roller spiral former. The roller former is made according to the working principle of the three-roller bending machine. The contact surface of the former and the strip steel is in rolling friction, with low resistance, long tool life, and almost no scratches on the product surface.
(3) Mandrel spiral former. This shaper is suitable for forming small diameter, thin-walled high-quality spiral welded pipes. However, the inner surface of the steel pipe may be scratched due to friction.
