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Quality Inspection of Spiral Steel Pipe

Date:2020-09-04    keywords:spiral steel pipe, quality inspection
Spiral steel pipes should be subjected to mechanical performance test, flattening test and flaring test before leaving the factory, and must meet the requirements of the standard. The quality inspection method of spiral steel pipe is as follows:
1. 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 part 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, the pressure vessel must be subjected to a strength test. 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 weld seam, 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 ordinary 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 scrap 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 that are unqualified in appearance and internal quality 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, the spiral steel pipes produced in batches should be sampled for experimental heat treatment and rough processing before they leave the factory. Potential spiral steel pipe defects should be found in the spiral steel pipe factory as much as possible, so that necessary remedial measures can be taken as soon as possible.

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