Spiral steel pipe is mainly used in tap water engineering, petrochemical industry, chemical industry, electric power industry, agricultural irrigation, urban construction, is one of the 20 key products developed in China.
For liquid transportation: water supply, drainage. For gas transportation: gas, steam, liquefied petroleum gas. For structural use: for piling pipes, Bridges; Pipe for wharf, road, building structure, etc.
1. Carbon structural steel
① by Q+ number + quality grade symbol + deoxidation method symbol. Its steel number is prefixed with “Q”, which represents the yield point of the steel, followed by the yield point value in MPa. For example, Q235 represents a carbon structural steel with a yield point (σ S) of 235 MPa.
(2) If necessary, the symbol of quality grade and deoxidation method can be marked behind the steel number. The quality grade symbols are A, B, C and D respectively. Deoxidization method symbol F for boiling steel, B for semi-stabilized steel, Z for stabilized steel, TZ for special stabilized steel, stabilized steel symbol is optional, namely ZT and TZ are optional. For example, Q235-AF stands for class A boiling steel.
③ Carbon steel for special purposes, such as bridge steel, Marine steel, etc., basically uses the method of carbon structural steel, but at the end of the steel number additional letters to indicate the use.
2. High quality carbon structural steel
(1) The two digits at the beginning of the steel number represent the carbon content of the steel, in order to represent the ten thousandths of the uniform carbon content, for example, the uniform carbon content of 0.45% of the steel, the steel number is “45”, it is not the serial number, so it can not be read as 45 steel.
② High quality carbon structural steel with high manganese content should be marked with manganese element, such as 50Mn. ③ Boiling steel, semi-stabilized steel and high quality carbon structural steel for special purposes should be specially marked in the last steel number, such as semi-stabilized steel with uniform carbon content of 0.1%, and its steel number is 10B.
3. Carbon tool steel
The steel number is prefixed with “T” to avoid mixing with other steels.
② The number in the steel number represents the carbon content, expressed in thousandths of the uniform carbon content. For example, “T8” indicates a uniform carbon content of 0.8%.
③ If the manganese content is higher, mark “Mn” at the end of the steel number, such as “T8Mn”.
④ The 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”.
In the production of large diameter spiral steel pipe, the wrong edge often occurs, which is affected by many factors. In production practice, the spiral steel pipe is often degraded due to out-of-tolerance of the wrong dry side. Therefore, it is necessary to analyze the causes of misalignment of large diameter spiral steel pipe and its preventive measures.
1. The sickle bend of steel belt is the main factor causing the wrong side of steel pipe. In the spiral steel pipe forming, the sickle bend of the steel strip will constantly change the forming Angle, resulting in the change of the weld gap, resulting in seam opening, staggered edge and even edge lap. It seriously affects the quality of steel tube, so it is an effective method to reduce the wrong side of steel strip scythe by observing the scythe after unwinding, cutting part of scythe by controlling the vertical roller and continuously controlling and correcting the deviation of forming Angle.
2. Due to the poor shape and dimensional accuracy of the uncut steel head and tail, it is easy to cause hard bending of the steel belt during docking and cause wrong side.
3. When the welding seam height of steel head and tail butt welding is large, it is easy to cause a large wrong side if it is not handled properly during overforming.
4. Poor edge condition of steel strip is another important reason for wrong edge