What is a seamless steel pipe?

Seamless steel pipes are perforated from whole round steel, and steel pipes without welds on the surface are called seamless steel pipes. According to the production method, seamless steel pipes can be divided into hot-rolled seamless steel pipes, cold-rolled seamless steel pipes, cold-drawn seamless steel pipes, extruded seamless steel pipes, and top pipes. According to the cross-sectional shape, seamless steel pipes are divided into two types: round and special-shaped. Special-shaped pipes include square, oval, triangular, hexagonal, melon seed, star, and finned pipes. The maximum diameter is 900mm and the minimum diameter is 4mm. According to different purposes, there are thick-walled seamless steel pipes and thin-walled seamless steel pipes. Seamless steel pipes are mainly used as petroleum geological drilling pipes, cracking pipes for petrochemical industry, boiler pipes, bearing pipes, and high-precision structural steel pipes for automobiles, tractors, and aviation.

Seamless steel pipes are widely used.

  1. General-purpose seamless steel pipes are rolled by ordinary carbon structural steel, low-alloy structural steel or alloy structural steel, with the largest output, and are mainly used as pipelines or structural parts for conveying fluids.
  2. According to different purposes, it can be supplied in three categories:
    a. Supply according to chemical composition and mechanical properties;
    b. According to mechanical performance;
    c. According to the water pressure test supply. Steel pipes supplied according to categories a and b. if used to withstand liquid pressure, shall also be subjected to a hydraulic test.
  3. Special-purpose seamless pipes include seamless pipes for boilers, chemical and electric power, seamless steel pipes for geology, and seamless pipes for petroleum.

Seamless steel pipes have a hollow section and are used in large quantities as pipelines for transporting fluids, such as pipelines for transporting oil, natural gas, gas, water and certain solid materials. Compared with solid steel such as round steel, steel pipe is lighter in flexural and torsional strength and is an economical section steel. Widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipes, automobile transmission shafts, bicycle frames, and steel scaffolding used in construction. Steel pipes are used to make ring parts, which can improve material utilization, simplify manufacturing procedures, and save materials and processing. Working hours.

How does decarburization and oxidation of seamless steel pipes occur?

How does decarbonization occur?

Decarburizationof seamless steel pipesis a phenomenon that occurs when the oxidation rate of the steel surface is less than the rate of carbon diffusion. Both carbon oxidation and diffusion occur strongly at high temperatures above the transformation point A1. Decarburization can be controlled by the heating atmosphere in the furnace, and the oxidizing atmosphere can cause decarburization or oxidation. Especially when there is water vapor in the furnace, the decarburization of the seamless steel pipe is very serious. Also, in the heat treatment of rough forging, when the scale is removed by urine shot in advance. If the shot peening is excessive, there will be more oxidative decarburization, and attention should be paid to this.

How is oxidation caused?

During heat treatment, such as heat, iron on the surfaceof the seamless steel pipecombines with oxygen in the air to form iron oxide, a phenomenon called oxidation. The film formed by oxidation is converted into oxide flakes. The scale can prevent rapid cooling during cooling, causing so-called cooling soft spots. Generally, when the oxidation rate of oxygen is greater than the rate of expansion of carbon, an oxide scale is generated; On the contrary, decarburization of the seamless steel pipe occurs.

Thus, a coarse oxide scale without decarburizing can be generated in the strongly oxidizing furnace gas whose oxidation rate is significantly higher than the diffusion rate. Therefore, it has become common knowledge that high-carbon (SK) steel must be annealed in a strong oxidizing atmosphere.

In general, the scale of high-carbon steel is dense, and thescale of low-carbon steelis loose and easy to take off. Fe2O3, the bottom layer is Fe3O4, the innermost layer is Fe: and above the transformation point As, the order of the oxide scale from the outer layer to the inner is: Fe2O3, Fe3O4, FeO.

The difference between seamless steel pipe and welded steel pipeis that the forming process is different and the application range is different.

  1. Seamless pipes are made of long steel cylinders. Engineers heat the cylinder first. They then inserted a tool called a mandrel into the center of the cylinder. The cylinder is rolled and stretched until the desired tube size and wall thickness is reached. However, the welded pipe was originally a flat sheet of steel that was molded into a tubular shape. Weld the two sides together. Although this type of pipe appears to have distinct seams that require grinding, many pipes are welded on both sides using high-frequency current welding.
  2. Mainly used for petroleum geological drilling pipes, petrochemical cracking pipes, boiler pipes, bearing pipes and high-precision structural steel pipes for automobiles, tractors, aviation, etc.; Welded steel pipes are widely used in water engineering, petrochemical, chemical, electric power, agricultural irrigation, urban construction and other fields.
  3. There are welding ribs on the inner wall of the welded pipe. The pressure of the seamless steel pipe is relatively high, usually around 10 MPa, and the welded pipe is now seamless. Seamless pipes are made of perforated steel ingots or solid tube billets, and then processed by hot rolling, cold rolling or cold drawing. The seamless pipe specification is expressed as outer diameter * wall thickness in mm. Seamless steel pipes can be divided into hot-rolled and cold-rolled (dial) seamless steel pipes.

Expansion: Hot-rolledseamless steel pipes are divided into ordinary steel pipes, medium pressure boiler steel pipes, high-pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, oil cracking pipes, geological steel pipes and other steel pipes.

In addition to ordinary steel pipes, low and medium pressure boiler steel pipes, high-pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, oil cracking pipes and other steel pipes, cold (stretched) seamless steel pipes also include carbon thin-walled steel pipes, thin alloy steel pipes, thin-walled stainless steel pipes, specially shaped steel pipe.

The outer diameter of hot-rolled seamless pipes is generally more than 32mm, and the wall thickness is 2.5-75mm. The diameter of cold-rolled seamless pipes can reach 6mm, the wall thickness can reach 0.25mm, and the outer diameter ofthin-walled pipescan reach 5mm or less. , cold rolling has higher dimensional accuracy than hot rolling.