Characteristics of spiral welded pipe
Spiral welded pipe is a spiral seam steel pipe with strip steel coil as raw material, which is often warmly extruded and bent into a spiral shape. The raw materials are strip coiling, welding wire, and flux. The quality and performance of the spiral welded pipe are determined according to the needs, and the content and types of different elements must be matched according to the needs. Then, let's learn about the characteristics of spiral welded pipes!
1) Carbon: The more carbon content, the higher the rigidity, but the worse the plasticity and toughness.
2) Sulfur: It is a harmful impurity in steel. Steel with high sulfur content is easy to be brittle and cracked at high temperature, which is usually called hot brittleness.
3) Phosphorus: It significantly reduces the plasticity and toughness of steel, especially the serious phenomenon at low temperature is called cold brittleness. Steel needs to strictly control sulfur and phosphorus, and low carbon steel contains high sulfur and phosphorus, which is easy to cut and helps to improve the machinability of steel.
4) It can improve the strength of manganese steel, weaken and eliminate the adverse effects of sulfur, and improve the hardenability of steel. High-alloy steel with high manganese content (high manganese steel) has excellent wear resistance and other physical properties.
5) Silicon: It can improve the hardness of steel, but reduce its plasticity and toughness. Electrical steel contains a certain amount of silicon, which can improve the soft magnetic properties.
6) Tungsten: It can improve the red hardness and thermal strength of steel, and improve the wear resistance of steel.
7) Chromium: It can improve the hardenability and wear resistance of steel, and improve the corrosion resistance and oxidation resistance of steel.
8) Vanadium: It can refine the grain structure of steel and improve the strength, toughness and wear resistance of steel. Dissolution of austenite at high temperatures increases the hardenability of the steel; conversely, the presence of austenite in the form of carbides reduces the hardenability.
9) It can significantly improve the hardenability and thermal strength of molybdenum:steel, prevent temper brittleness, and improve remanence and coercivity.
10) Titanium can refine the grain structure of steel and improve the strength and toughness of steel.
11) It can improve the strength and toughness of nickel steel and improve the hardenability. When the content is high, some physical properties of steel and alloys can be significantly changed, and the corrosion resistance of steel can be improved.
The rolls must undergo strict physical and chemical inspections before being put into use. Adopt strip steel head-to-tail butt, single wire or two submerged arc welding, and use automatic submerged arc welding repair welding after spiral welded pipe. Before forming, the strip is straightened, cut, scraped, conveyed for surface cleaning and bent. The electric contact pressure gauge is used to control the pressure of the cylinders on both sides of the conveyor belt to ensure the smooth conveying of the strip. The welding seam is evenly distributed on the circumference of the spiral pipe, and the spiral welded pipe has high dimensional accuracy and strong strength. Under the same wall thickness, the screw steel pipe can withstand a lot of pressure. And because it is formed by continuous bending, the size of the spiral tube is not limited, and the length can be freely determined.
After the welding is completed, a radiographic inspection of the spiral welded pipe welding and the cross joint of the spiral welding is carried out. Each steel pipe must undergo the corresponding hydrostatic pressure test, and the pressure is radially sealed. The test pressure and time are strictly controlled by the water pressure microcomputer detection device of the steel pipe, and the test parameters are printed.
The welding defect of spiral welded pipe is "inclined defect". In use, the main stress direction of the steel pipe, that is, the equivalent defect length in the axial direction of the steel pipe is smaller than that of the seamless pipe; secondly, the pipeline steel is all rolled steel plates, so the impact toughness has a large anisotropy, and the CVN value in the rolling direction 3 times higher than the CVN value perpendicular to the rolling direction.
The above are the characteristics of the spiral welded pipe. If you want to know more, please feel free to contact us!