Straight seam steel pipe strength and steel number representation method

Straight seam steel pipe is a steel pipe whose weld seam is parallel to the longitudinal direction of the steel pipe. It is usually divided into metric electric welded steel pipe, electric welded thin-walled pipe, transformer cooling oil pipe, and so on. The production process of straight seam welded pipe is simple, the production efficiency is high, the cost is low, and the development is rapid. The strength of the spiral welded pipe is generally higher than that of the straight seam welded pipe, and the welded pipe with a larger diameter can be produced with a narrower billet, and welded pipes with different diameters can be produced with the same width billet. But compared with the straight seam pipe of the same length, the weld length is increased by 30~100%, and the production speed is lower.

ERW steel pipes are divided into induction welding and contact welding according to different welding methods. Hot-rolled wide-band steel coils are used as raw materials and undergo pre-bending, continuous forming, welding, heat treatment, sizing, straightening, cutting, and other processes. Compared with the welded pipe, it has the advantages of the short weld seam, high dimensional accuracy, uniform wall thickness, good surface, and high-pressure resistance, but the disadvantage is that it can only produce small and medium-sized thin-walled pipes, and the weld seam is prone to gray spots, incomplete fusion, and groove corrosion. defect. At present, the widely used fields are city gas, crude oil, refined oil transportation, etc.

The welding method of LSAW steel pipe is to use a single medium-thick plate as the raw material, press (roll) the steel plate into a tube blank in a mold or a forming machine, and use double-sided submerged arc welding and expand the diameter for production. It has a wide range of finished product specifications, good toughness, plasticity, uniformity, and compactness of the weld seam, and has the advantages of large pipe diameter, thick pipe wall, high-pressure resistance, low-temperature resistance, and strong corrosion resistance. When constructing high-strength, high-toughness, and long-distance oil and gas pipelines, most of the required steel pipes are large-diameter thick-walled longitudinal submerged arc welded pipes. According to API standards, in large-scale oil and gas pipelines, when passing through Class 1 and Class 2 areas such as alpine regions, seabeds, and urban densely populated areas, LSAW pipes are suitable pipe types. According to different molding methods, it can be divided into:
UOE welded pipe: After the single steel plate is pre-bent at the edge, it undergoes processes such as U forming, O forming, internal welding, external welding, and mechanical cold expansion;
JCOE welded pipe: that is, according to "J-C-O-E" pre-welding, forming, cold expansion after welding and other processes;
HME welded pipe: formed by the mandrel rolling method according to "C-C-O", followed by cold expansion after welding.

The steel number representation method of large diameter straight seam steel pipe:
1. Carbon structural steel:
① It is composed of Q + number + grade symbol + deoxidation method symbol. Its steel number is preceded by "Q", which represents the yield point of the steel, and the number behind it represents the value of the yield point in MPa. For example, Q235 represents a carbon structural steel with a yield point (σs) of 235MPa.
② Symbols indicating grade and deoxidation method can be marked behind the steel number. The grade symbols are A, B, C, and D respectively. The deoxidation method symbol F means boiling steel, B means semi-killed steel, Z means stabilized steel, TZ means special stabilized steel, and the stabilized steel may not be marked with symbols, that is, both ZT and TZ may not be marked. For example, Q235-AF means boiling steel.
③ Carbon steel for special purposes, such as bridge steel, marine steel, etc., basically uses the expression method of carbon structural steel, but the letter indicating the purpose is added after the steel number.
2. Carbon structural steel:
①The 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, for steel with an average carbon content of 0.45%, the steel number is "45". It is not a serial number, so it cannot be read as 45 gauge steel.
② For carbon structural steel with high manganese content, the manganese element should be marked, such as 50Mn.
③The boiling steel, semi-killed steel, and special-purpose carbon structural steel should be specially marked after the steel number, for example, the steel number of semi-killed steel with an average carbon content of 0.1% is 10b.
3. Carbon tool steel:
①The steel number is crowned with "T" to avoid mixing with other steel types.
② The number in the steel number indicates the carbon content, expressed in thousandths of the average carbon content. For example, "T8" means that the average carbon content is 0.8%.
③ For those with higher manganese content, "Mn" is marked after the steel number, such as "T8Mn".
④The phosphorus and sulfur content of carbon tool steel is lower than that of ordinary carbon tool steel. The letter "A" is added after the steel number to show the difference, such as "T8MnA".