Large-diameter spiral steel pipe is a general name, generally refers to a spiral steel pipe with a diameter greater than 1 meter. Spiral steel pipes are formed by bending steel strips and then welded. The steel pipe needs to be tested for water pressure, bending and flattening, and has certain requirements on the surface quality. Usually, the delivery length is 12 meters, and it is often required to deliver to a fixed length. The specification of the spiral steel pipe is expressed by the nominal diameter (mm). Edit the classification of the steel number representation method of large-diameter spiral steel pipe in this paragraph


The steel number representation method of large diameter spiral steel pipe: 1. Carbon structural steel ①It is composed of Q+number+quality grade symbol+deoxidation method symbol. Its steel number is prefixed with "Q", which represents the yield point of the steel, and the following number represents the yield point value in MPa. For example, Q235 represents a carbon structural steel with a yield point (σs) of 235 MPa. ②When necessary, symbols indicating quality grade and deoxidation method can be marked behind the steel number. The quality grade symbols are A, B, C, D, respectively. Deoxidation method symbol F means boiling steel, B means semi-stabilized steel, Z means stabilized steel, TZ means special stabilized steel, and the symbol for stabilized steel can be omitted, that is, ZT and TZ can be omitted. For example Q235-AF means A-grade boiling steel. ③Special purpose carbon steel, such as bridge steel, marine steel, etc., basically adopts the representation method of carbon structural steel, but the letter indicating the purpose is added at the end of the steel number.


 2. High-quality carbon structural steel ① The two digits at the beginning of the steel number indicate the carbon content of the steel, expressed in ten thousandths of the average carbon content. For example, the steel with an average carbon content of 0.45% has a steel number of "45", which is not a sequence number. , so it cannot be read as 45 gauge steel. ②For high-quality carbon structural steel with high manganese content, the manganese element should be marked, such as 50Mn. ③ Boiling steel, semi-stabilized steel and high-quality carbon structural steel for special purposes shall be specially marked at the end of the steel grade.


3. Carbon tool steel ①The steel number is crowned with "T" to avoid mixing with other steels. ②The number in the steel number indicates the carbon content, expressed in thousandths of the average carbon content. For example "T8" means a uniform carbon content of 0.8%. ③For those with higher manganese content, mark "Mn" at the end of the steel grade, such as "T8Mn". ④The phosphorus and sulfur content of high-quality carbon tool steel is lower than that of general high-quality carbon tool steel. The letter "A" is added at the end of the steel number to show the difference, such as "T8MnA". Edit this paragraph analysis of the causes of the wrong side of the large-diameter spiral steel pipe


The reasons for the misalignment of the large-diameter spiral steel pipe: During the production of the large-diameter spiral steel pipe, the misalignment occurs from time to time, and there are many influencing factors. In production practice, the steel pipe is often degraded by the wrong side and out of tolerance. Therefore, it is necessary to analyze the reasons for the misalignment of large-diameter spiral steel pipes and their preventive measures. 1. The sickle bend of the steel strip is the most important factor causing the misalignment of the steel pipe. In the forming of the spiral welded pipe, the camber of the steel strip will continuously change the forming angle, resulting in the change of the weld gap, resulting in seam opening, misalignment or even overlapping. The quality of the steel pipe is seriously affected. Therefore, the camber bending of the steel strip after uncoiling is observed. By controlling the vertical roller, the disc shear can cut off part of the camber and the continuous control and correction of the forming angle is to reduce the camber of the steel strip in the production process. An effective way to generate errors. 2. Due to the poor shape and dimensional accuracy of the head and tail of the non-trimmed steel strip, it is easy to cause the steel strip to bend hard and cause misalignment when docking. 3. When the excess height of the butt welding seam of the head and tail of the steel strip is large, if it is not handled properly during overforming, it is easy to cause a large misalignment. 4. The poor condition of the edge of the steel strip is another important reason for the misalignment. In the production process of the large-diameter spiral steel pipe in this section, the spiral steel pipe is made of strip steel coils as raw materials, often warmly extruded, and made of automatic double-wire double-sided Spiral seam steel pipe welded by submerged arc welding process. The main production process is as follows: (1) The raw materials are strip steel coil, welding wire and flux. They must undergo strict physical and chemical inspections before being put into use. (2) The head and tail of the strip steel are butted by single wire or double wire submerged arc welding, and automatic submerged arc welding is used for repair welding after rolling into a steel pipe. (3) Before forming, the strip is leveled, trimmed, planed, surface cleaned and conveyed and pre-bending. (4) The electric contact pressure gauge is used to control the pressure of the cylinders on both sides of the conveyor to ensure the smooth conveying of the strip. (5) Adopt external control or internal control roll forming. (6) The weld gap control device is used to ensure that the weld gap meets the welding requirements, and the pipe diameter, the amount of misalignment and the weld gap are strictly controlled. (7) Both internal welding and external welding use the American Lincoln welding machine for single-wire or double-wire submerged arc welding, so as to obtain stable welding specifications. (8) The welded seams are all inspected by an online continuous ultrasonic automatic flaw tester, which ensures 100% non-destructive testing coverage of the spiral welds. If there is a defect, it will automatically alarm and spray the mark, and the production workers can adjust the process parameters at any time accordingly to eliminate the defect in time. (9) Use an air plasma cutting machine to cut the steel pipe into single pieces. (10) After cutting into a single steel pipe, each batch of three steel pipe heads shall undergo a strict first inspection system to check the mechanical properties, chemical composition, fusion condition of the weld, the surface quality of the steel pipe and non-destructive testing to ensure the pipe making process. Only after passing the test can it be officially put into production. (11) The parts with continuous sonic flaw detection marks on the welds shall be re-examined by manual ultrasonic wave and X-ray. If they are indeed defective, they shall be repaired and subjected to non-destructive inspection again until it is confirmed that the defects have been eliminated. (12) The tube where the strip butt welding seam and the T-joint intersecting with the spiral welding seam are located shall all be inspected by X-ray television or filming. (13) Each steel pipe is tested by hydrostatic pressure, and the pressure is radially sealed. The test pressure and time are strictly controlled by the steel pipe water pressure microcomputer detection device. The test parameters are automatically printed and recorded. (14) The pipe end is machined, so that the verticality of the end face, the bevel angle and the blunt edge are accurately controlled. Edit this paragraph of large diameter spiral steel pipe material The commonly used domestic materials are: Q235A, Q235B.Q23b, 0Cr13, 1Cr17, 00Cr19Ni11, 1Cr18Ni9, 0Cr18Ni11Nb. Q345 L245 L290 X42 X46 X70 X80 , chemical industry, electric power industry, agricultural irrigation, urban construction, is one of the twenty key products developed in my country. For liquid transportation: water supply, drainage. For gas transportation: gas, steam, liquefied petroleum gas. For structural purposes: for piling pipes, for bridges; for wharves, roads, building structures, etc.