Main Production Process
a. Uncoiling and Plate Inspection. After uncoiling, the steel plate is about to get into the production. The first step is to conduct the ultrasonic inspection for the whole plate.
b. Flattening and Edge Milling. Through pressing anvil machine, the original curved steel plate is flattened. And then, the two edges of the steel plate are conducted with double milling via the edge milling machine. After that, the steel plate can get the required width, plate edge parallel degree and groove shape.
c. Curling Forming. The steel plate is rolled up spirally along with the outer edge into tubular shape through the production line.
d. Butt Welding and Cutting. The sophisticated double submerged arc welding technology is employed for preliminary welding, inside welding and outside welding. Then, the welded steel pipe is cut in terms of the standard length via the plasma cutter.
e. Visual Check. The professional technical staff would check the basic parameters of the steel tube.
f. Ultrasonic Examination. The inside and outside welding seam as well as the basic metal on two sides of the welding seam are inspected 100%.
g. X Ray Flaw Detection. The inside and outside welding seams are checked 100% via the X ray industrial TV inspection. The image processing system is used to ensure the sensitivity of the flaw detection.
h. Hydrostatic Test. Use the hydrostatic test machine to test each steel pipe to make sure that the steel tube can reach the standard required test pressure.
i. Chamfering and End Facing. Process the tube end of the qualified steel tube to make it achieve the required groove size.
j. Final Check. Conduct the ultrasonic test, X ray flaw detection as well as the tube end magnetic particle examination again to check whether there is welding problem and tube end defect.
k. Anti-rust Oil and Marking. Paint the oil outside of the steel tube for corrosion resistance and mark the product according to the requirements of customers.
In addition to the above inspection items, the steel plate and steel pipe should also go through the damage inspection and other inspection in line with the API standard, other related standard and the special requirements of some customers, including random inspection of physical and chemical property for the incoming raw material, 100% steel plate appearance inspection, etc.
The spiral steel tube has spiral welding seam. Taking usage of steel strip and coiled plate as the raw material, it is formed through cold extrusion and welded via the automatic double wire double sided submerged arc welding technology.
1. The raw material including strip coil, welding wire and welding flux must pass the strict physical and chemical inspection before being put to use.
2. Make butt joint of the head and tail of the steel strip and adopt single wire or double wire submerged arc welding. After the material being rolled into the steel pipe, the automatic submerged arc welding is taken for repair welding.
3. Before forming, the steel strip is processing with flattening, edge shearing, edge planning, surface cleaning, conveying and preliminary rolling.
4. The electric contact pressure gauge is put to use for controlling the pressure of hydraulic push-up cylinder on the two sides of the conveyor to ensure the steady conveyance of the steel strip.
5. The external or internal control roller type is adopted for forming.
6. The weld gap can meet the welding requirements through weld gap control device. The diameter, alignment tolerance and weld gap can be controlled strictly.
7. The inside and outside welding adopt the American Lincoln electric welding machine to achieve single wire or double wire submerged arc welding to ensure stable welding specification.
8. The finished welding seam is inspected through the online continuous automatic ultrasonic flaw detector, ensuring 100% nondestructive detection coverage rate for spiral welding seam. If there is a defect, the system would alarm automatically and make a mark through spraying. Taking this as the basis, the production worker adjusts the process parameters timely to eliminate the defect.
9. The whole steel pipe is cut into the single one by using the air plasma cutter.
10. After the cutting, each batch of the steel tube should be approved by the strict first inspection involving the mechanical property, chemical composition and fusion state of the welding seam, surface quality of the steel tube as well as nondestructive inspection. The tube manufacturing technology must be ensured to be qualified before starting the formal production.
11. If the welding seam has the continuous ultrasonic inspection mark, it should be reexamined via the manual ultrasonic and X ray. It the welding seam does have the defect, after the repair, the nondestructive inspection is carried out again until the confirmation of defect elimination.
12. The steel pipe, which has the T-shaped joint formed through the crossing of the butt weld seam and spiral weld seam of the steel strip, should go through the X ray TV or film examination.
13. The hydrostatic pressure test is taken for each steel pipe. The pressure is sealed along with the radial direction. The test pressure and time are controlled accurately via the steel tube hydrostatic microcomputer detection device. The test parameters are recorded and printed automatically.
14. The tube end machining makes the end face verticality, groove angle and root face obtain accurate control.
1. Surface Quality. The steel pipe surface is not allowed to have crack, scar and fold. The convex block is allowed to appear on the surface of the steel tube but cannot exceed the height of the traverse rib. The height and depth of other defects on the steel tube surface cannot outnumber the allowable deviation of the dimension of the position that the defect locates.
2. Dimension, External Form, Weight and Allowable Deviation
1. Length and Allowable Deviation.
a. Curvature and the End
The curvature of the straight steel pipe should be controlled in the range of not affecting the normal use. The total curvature cannot be greater than 40% of the total length of the reinforcing steel bar. The end of the steel tube should be sheared with high verticality and flatness. The local deformation should not affect the normal use.
b. Length. The steel tube is generally delivered in accordance with the specified length. The concrete delivery length should be indicated in the contract. If the steel pipe is delivered in the form of reel, each reel should be a steel tube. It is allowed that 5% of the steel tube reels can be composed of two steel tubes. If 5% of the total steel tube reels is less than two, then two steel tube reels can be formed with two steel tubes. The weight and the diameter of the steel tube reel are confirmed through the negotiation of both parts.
2. Surface Shape and Allowable Dimension Deviation of the Ribbed Steel Pipe
The transverse rib of the steel tube should conform to the following provisions.
a. The intersection angle β of the transverse rib and the axis of the steel tube should not be less than 45°. When β is not more than 70°, the direction of the transverse rib on two opposite sides should be the opposite.
b. The total gap of the end of the transverse rib on the opposite two sides including the width of the longitudinal rib cannot exceed 20% of the nominal perimeter.
c. When the nominal diameter is no greater than 12mm, the specific projected rib area should not be less than 0.055.
d. The specific projected rib area should be greater than or equal to 0.060 when the nominal diameter is 14mm and 16mm.
e. When the nominal diameter outnumbers 16mm, the specific projected rib area cannot be less than 0.065.
3. Reverse Bending Performance.
If the customer has the needs, the reverse bending performance test can be conducted for the steel pipe. The bend diameter in the reverse bending performance test is larger than that of the bending test by the value of diameter of steel tube. The bending sequence is first 45° in forward direction, then 23° in opposite direction and lastly 23° in reverse. After the reverse bending test, the surface of the bent part of the steel tube cannot generate crack.