Spiral steel pipes (SSAW)
will undergo mechanical performance test, flattening test and flaring test before leaving the factory, and must meet the requirements of the standard. The quality inspection methods of common spiral steel pipes are as follows:
1. Appearance inspection
Judging from the surface, that is, in appearance inspection. The appearance inspection of welded joints is a simple and widely used inspection method. It is an important content of finished product inspection, mainly to find defects and dimensional deviations on the weld surface. It is generally inspected by naked eyes, with the help of tools such as standard templates, gauges and magnifying glasses. If there are defects on the surface of the weld, there may be defects inside the weld.
2. Inspection of physical methods
Physical inspection methods are methods that use some physical phenomena to measure or inspect. The inspection of internal defects of materials or workpieces generally adopts non-destructive testing methods. Non-destructive testing includes ultrasonic testing, radiographic testing, penetrating testing, magnetic testing, etc.
3. Strength inspection of pressure vessel
In addition to the tightness test, a strength test is also required. There are two common types: hydraulic test and pneumatic test. They can test the tightness of welds of vessels and pipes that work under pressure. The air pressure test is more sensitive and faster than the water pressure test, and the product after the test does not need to be drained, which is especially suitable for products with difficult drainage. But the risk of the test is greater than that of the hydraulic test. When conducting the test, the corresponding safety technical measures must be followed to prevent accidents during the test.
4. Denseness inspection
For welded containers that store liquid or gas, the non-compact defects of the welds, such as penetrating cracks, pores, slag inclusions, incomplete penetration and loose structure, can be found by the compactness test. The tightness test methods include: kerosene test, water-carrying test, water wash test, etc.
5. Hydrostatic test
Each steel pipe should be subjected to hydrostatic pressure test without leakage. The test pressure is calculated by pressing P=2ST/D where S—the test stress of hydrostatic test Mpa, and the test stress of hydrostatic test shall be in accordance with the corresponding steel strip standard 60% of the minimum yield (Q235 is 235Mpa) is selected. Stabilization time: D<508 test pressure holding time is no less than 5 seconds; D≥508 test pressure holding time is no less than 10 seconds.
6. Non-destructive testing
X-ray or ultrasonic inspection shall be carried out for repair welding seams of steel pipes, butt weld seams of steel strips and circumferential seams. 100% SX-ray or ultrasonic inspection should be carried out for the steel-direction spiral welds used for the transportation of flammable ordinary fluids, and the spiral welds of the steel pipes used for the transportation of water, sewage, air, heating steam and other common fluids should be X-ray or Ultrasonic inspection spot check (20%).
According to the quality inspection results of spiral steel pipes, spiral steel pipes are usually divided into three categories: qualified products, repaired products and waste products. Qualified products refer to spiral steel pipes whose appearance and internal quality meet the relevant standards or technical requirements for delivery and acceptance; repaired products refer to the appearance and internal quality that do not fully meet the standards and acceptance criteria, but are allowed to be repaired and can meet the standards and acceptance conditions after repair. Spiral steel pipes; Scrap refers to spiral steel pipes whose appearance and internal quality are not up to standard and are not allowed to be repaired or fail to meet the standards and acceptance conditions after repair.
Waste products are divided into internal waste and external waste. Internal waste refers to the waste spiral steel pipe found in the foundry or foundry; the external waste refers to the waste found after delivery of the spiral steel pipe, which is usually exposed during machining, heat treatment or use, and the economic losses caused by it are far Bigger than internal waste. In order to reduce external waste, batch-produced spiral steel pipes should be sampled for experimental heat treatment and rough processing before they leave the factory. Potential spiral steel pipe defects should be discovered in the spiral steel pipe factory as far as possible, so that necessary remedial measures can be taken as soon as possible.
Tips: Welded steel pipes can be divided into straight seam welded pipes and spiral welded pipes according to the weld form.Straight seam welded pipe is a steel pipe whose weld seam is parallel to the longitudinal direction of the steel pipe. Straight seam steel pipes can be divided into high-frequency straight seam steel pipes (ERW Pipe) and submerged arc welded straight seam steel pipes (LSAW Pipe) according to the production process. Straight seam welded pipe has simple production process, high production efficiency, low cost and rapid development.