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Seamless steel pipes are rolled from solid tube blanks after being perforated.

 

    1. Production and manufacturing methods

    According to different production methods, it can be divided into hot-rolled pipe, cold-rolled pipe,cold drawn tube, extruded tubes, etc.

 

    1.1. Hot-rolled seamless pipes are generally produced on automatic pipe rolling units. The solid tube blank is inspected and surface defects are removed, cut into the required length, centered on the perforated end of the tube blank, and then sent to the heating furnace for heating and piercing on the punching machine. It continues to rotate and advance during piercing holes. Under the influence of the rollers and the end, the tube blank is hollow gradually, which is called gross pipe. Then it is sent to the automatic pipe rolling machine to continue rolling. Finally, the wall thickness is evened by the leveling machine, and the diameter is determined by the sizing machine to meet the specification requirements. The use of continuous pipe rolling units to produce hot-rolled seamless steel pipes is a more advanced method.

 

    1.2. If you want to obtain seamless pipes with smaller size and better quality, you must use cold rolling, cold drawing or a combination of the two methods. Cold rolling is usually carried out on a two-roll mill, and the steel pipe is rolled in an annular pass composed of a variable cross-section circular groove and a fixed conical head. Cold drawing is usually performed on a 0.5 to 100T single-chain or double-chain cold drawing machine.

 

    1.3. The extrusion method is to place the heated tube blank in a closed extrusion cylinder, and the perforation rod and the extrusion rod move together to make the extrusion part extruded from the smaller die hole. This method can produce steel pipes with smaller diameters.

 

    2. Purpose

 

    2.1. Seamless pipes are widely used. General-purpose seamless pipes are rolled from ordinary carbon structural steel, low alloy structural steel or alloy structural steel, with the largest output, and are mainly used as pipes or structural parts for transporting fluids.

 

    2.2. It is supplied in three categories according to different uses: a. Supplied according to chemical composition and mechanical properties; b. Supplied according to mechanical properties; c. Supplied according to hydraulic pressure test. If the steel pipes supplied according to categories a and b are used to withstand liquid pressure, they must also undergo a hydrostatic test.

 

    2.3. Special-purpose seamless pipes include seamless pipes for boilers, seamless pipes for geology, and seamless pipes for petroleum.

 

    3. Type

 

    3.1. Seamless steel pipes can be divided into hot-rolled pipes, cold-rolled pipes, cold-drawn pipes, extruded pipes, etc. according to different production methods.

    3.2. According to the shape, there are round tubes and special-shaped tubes. In addition to square tubes and rectangular tubes, special-shaped tubes also include oval tubes, semi-circular tubes, triangular tubes, hexagonal tubes, convex-shaped tubes, plum-shaped tubes, etc.

    3.3. According to different materials, they are divided into ordinary carbon structural pipes, low alloy structural pipes, high-quality carbon structural pipes, alloy structural pipes, stainless steel pipes, etc.

    3.4. According to special purposes, there are boiler pipes, geological pipes, oil pipes, etc.

 

    4. Specifications and appearance quality

    Seamless pipes are in accordance with GB/T8162-87

 

    4.1. Specifications: hot-rolled pipe outer diameter 32~630mm. Wall thickness 2.5~75mm. The outer diameter of cold rolled (cold drawn) pipe is 5~200mm. Wall thickness 2.5~12mm.

    4.2. Appearance quality: The inner and outer surfaces of the steel pipe must not have cracks, folds, roll folds, separation layers, hair lines and scarring defects. These defects should be completely removed, and the wall thickness and outer diameter should not exceed negative deviations after removal.

 

    4.3. Both ends of the steel pipe should be cut at right angles and removed from burrs. Steel pipes with wall thickness greater than 20mm are allowed to be cut by gas cutting and hot sawing. It is also possible not to cut the head after agreement between the supply and demand parties.

    4.4. The "surface quality" of cold-drawn or cold-rolled precision seamless steel pipes shall refer to GB3639-83.

 

    5. Chemical composition inspection

 

    5.1. The chemical composition of domestic seamless pipes supplied according to chemical composition and mechanical properties, such as No. 10, 15, 20, 25, 30, 35, 40, 45 and 50 steel, should comply with the regulations of GB/T699-88. Imported seamless pipes are inspected according to relevant standards stipulated in the contract. The chemical composition of 09MnV, 16Mn, and 15MnV steel should comply with the regulations of GB1591-79.  

 

    5.2. For specific analysis methods, please refer to the relevant parts of GB223-84 "Chemical Analysis Methods for Steel and Alloys".

    5.3. The analysis deviation refers to GB222-84 "Permissible deviations of chemical composition of samples and finished products for chemical analysis of steel".

 

    6. Physical performance inspection

 

    6.1. Domestic seamless pipes and ordinary carbon steel supplied according to structural performance are manufactured according to Class A steel of GB/T700-88 (but the sulfur content must not exceed 0.050% and the phosphorus content must not exceed 0.045%), and their mechanical properties should comply with the values ??specified in the GB8162-87 table.  

 

    6.2. Domestic seamless pipes supplied according to the hydraulic pressure test must ensure the hydraulic pressure test stipulated in the standard.

    6.3. The physical performance inspection of imported seamless pipes shall be carried out in accordance with the relevant standards stipulated in the contract.

 

    7. Main import and export situations

 

    7.1. Generally, the import volume of seamless pipes is large. The main importing countries are Germany and Japan. European countries such as Romania, Russia, Switzerland, France, Spain, Czech Republic, Yugoslavia, Hungary and other countries all import. There are also small quantities imported from Argentina, Mexico and other countries in South America.  

 

    7.2. According to the different requirements of my country’s consumer units, there are more than 100 specifications of imported seamless pipes. Common specifications are 15922mm, 1595mm, and 15918mm. 114.38mm, 114.310mm, 114.313mm. The length generally ranges from 5 to 8m or 4 to 7m. Mainly hot-rolled carbon structure, steel grades are ST35, ST45 and ST65. The smallest diameter of imported specifications is 305mm, and the largest is 47813mm.  

 

    7.3. A small amount of seamless pipes with smaller diameters and thin walls have been imported from France and Spain, such as 183mm, 223mm, 26.93mm, etc. The general rules of the German Mannesmann Steel Pipe Works apply.

    7.4. Seamless pipes imported from Hungary and Japan often refer to DIN2448 and DIN1629.

    7.5. In import claim cases, the main quality problems of imported seamless pipes include: unqualified chemical composition, splitting in the flattening test, low tensile strength, severe corrosion and pits, etc.

 

    8. Packaging

    According to GB2102-88. There are three types of steel pipe packaging: bundling, boxing, oiled bundling or oiled boxing.