How to Carry Out Quality Inspection of Spiral Steel Pipe
Due to its superior performance, spiral steel pipes are now widely used in power industry, agricultural irrigation, tap water engineering, petrochemical industry, chemical industry, urban construction, etc, in order to avoid the circulation of unqualified products in the market, causing many inconveniences to our lives , we need a unified testing method to test the quality of different spiral steel pipes. Next, Permanent Steel Manufacturing Company Ltd will talk about the quality inspection method of spiral steel pipe.
Spiral steel pipe is a spiral seam steel pipe made of strip steel coils as raw materials, often extruded and formed by automatic double-wire double-sided submerged arc welding.
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. Physical inspection: Physical inspection is a method of measuring or inspecting using some physical phenomena. 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 test of pressure vessel: In addition to the tightness test, the pressure vessel must be subjected to 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. Density test: Welding containers that store liquid or gas, the non-compact defects of the weld, such as penetrating cracks, pores, slag inclusion, incomplete penetration and loose structure, can be found by the tightness test. The tightness test methods include: kerosene test, water-carrying test, water wash test, etc.
5. Hydrostatic test Each steel pipe shall be subjected to hydrostatic pressure test without leakage. The test pressure shall be calculated according to P=2ST/D where S – the test stress of hydrostatic test Mpa, and the test stress of hydrostatic test shall be corresponding The steel belt standard stipulates that 60% of the minimum yield (Q235 is 235Mpa) is selected. Stabilisation time: D<508 test pressure retention time is not less than 5 seconds; D≥508 test pressure retention time is not less than ten seconds 4 Non-destructive testing of repair welding seams of steel pipes, steel strip butt welds and circumferential seams should be carried out X-ray or ultrasonic inspection. 100% SX-ray or ultrasonic inspection shall 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 shall 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 they are allowed to be repaired and can meet the standards and acceptance conditions after repair. Spiral steel pipe; Scrap refers to unqualified appearance and internal quality, it is not allowed to rework or spiral steel pipes which still fail to meet the standards and acceptance conditions after rework.
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.
Physical inspection: Physical inspection is a method of measuring or inspecting using some physical phenomena. 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. Strength test 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. At the same time, the product after the test does not need to be drained, which is especially suitable for products with difficult drainage. But the danger 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.
Tightness test: For welded containers that store liquid or gas, the non-compact defects of the weld, such as penetrating cracks, pores, slag inclusion, incomplete penetration and loose structure, can be found by the tightness test. The tightness test methods include: kerosene test, water-carrying test, water wash test, etc.
The strength of spiral welded pipes is generally higher than that of straight seam welded pipes. A narrower blank can be used to produce welded pipes with larger pipe diameters, and a billet with the same width can be used to produce welded pipes with different pipe diameters. Spiral submerged arc welded pipe welds are distributed in a spiral line, and the welds are long, especially when welding under dynamic conditions, the welds leave the forming point before they can cool down, and welding hot cracks are easily generated. The direction of the crack is parallel to the weld and forms a certain angle with the axis of the steel pipe, generally between 30-70°. This angle is exactly the same as the shear failure angle, so its bending, tensile, compression and torsion resistance are far inferior to LSAW pipes. At the same time, due to the limitation of the welding position, the saddle-shaped and fish-ridged welds are affected Beautiful.
In addition, during the construction process, the intersecting line welds at the joints of the spiral welded mother pipe split the spiral seams, resulting in greater welding stress, which greatly weakens the safety performance of the components. Therefore, the non-destructive testing of the spiral welded pipe welds should be strengthened. Ensure the welding quality, otherwise the spiral submerged arc welded pipe should not be used in important steel structure occasions. Straight seam steel pipes are welded under static conditions, with high weld quality, short welds, and low probability of defects. The steel pipe is expanded through the full length, the pipe shape is good, the size is accurate, the steel pipe wall thickness range and the pipe diameter range are wide, and it is suitable for steel structure load-bearing columns such as construction, bridges, dams, offshore platforms, ultra-long span building structures, and those which require wind and earthquake resistance. Electric pole tower mast structure. Spiral steel pipe is a kind of steel commonly used in industry, construction and other industries.
Source: OilVoice