Definition and meaning of seamless steel pipe
Seamless steel pipes are made of a whole round steel perforated. Steel pipes with no 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, jacked pipes, etc. According to the cross-sectional shape, seamless steel pipes are divided into two types: round and special-shaped. Special-shaped pipes come in square, oval, triangle, hexagonal, melon-shaped, star-shaped, and finned pipes in various complex shapes. The maximum diameter is 900mm and the minimum diameter is 4mm. According to different uses, 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.
In the field of industrial materials, seamless steel pipes are a testament to engineering excellence and offer countless applications in different fields. Known for their strength, durability and versatility, these pipes play a vital role in various industries such as oil and gas, construction, automotive and manufacturing. In this comprehensive exploration, we delve into the intricacies of seamless steel pipes, revealing their manufacturing processes, their advantages, applications and their significant impact on modern infrastructure.
Classification of seamless steel pipes
A steel pipe without seams along the perimeter of its cross-section. According to different production methods, they are divided into hot-rolled pipes, cold-rolled pipes, cold-drawn pipes, extruded pipes, pipe jacking, etc., all of which have their own process regulations.
The materials include ordinary and high-quality carbon structural steel (Q215-A ~ Q275-A and 10 ~ 50 steel), low alloy steel (09MnV, 16Mn, etc.), alloy steel, stainless acid-resistant steel, etc.
According to the purpose, it is divided into two categories: general purpose (for water transmission, gas pipelines and structural parts, mechanical parts) and special purpose (for boilers, geological exploration, bearings, acid resistance, etc.).
Manufacturing Process of Seamless Steel Pipes
The manufacturing process of seamless steel pipes is a complex yet fascinating journey that involves several stages, each contributing to the final product's quality and integrity. Let's break down the process into key steps:
Steel Billet Preparation:
The process begins with the selection of high-quality raw materials, typically in the form of solid round steel billets. These billets serve as the foundation for the seamless pipe and are carefully inspected to ensure they meet the required standards for composition and quality.
Heating and Piercing:
The selected billet undergoes intense heating to forge it into a malleable state. Once heated, the billet is pierced at its center using a mandrel mill or a piercing machine. This piercing creates a hollow tube, known as a shell, with the desired diameter.
Rotary Piercing:
The pierced billet is then elongated and reduced to achieve the desired outer diameter and wall thickness. Rotary piercing mills play a pivotal role in shaping the shell into a pipe with precise dimensions.
Mandrel Mill Process:
The hollow shell is elongated further using a mandrel mill, which employs a mandrel rod to control the internal diameter of the pipe. This process ensures uniformity in thickness and diameter along the length of the seamless pipe.
Stretch Reduction:
To refine the dimensions and enhance the pipe's properties, the pipe is subjected to a stretch reduction process. This involves elongating the pipe through a series of rollers to achieve the final size and wall thickness.
Annealing:
The seamless pipe undergoes annealing, a heat treatment process that imparts crucial properties such as hardness and toughness. Annealing also relieves internal stresses, ensuring the pipe's structural integrity.
Surface Treatment:
The final step involves surface treatment, which may include pickling, passivation, or coating, depending on the intended application. This treatment enhances corrosion resistance and protects the seamless pipe during transportation and storage.
①Main production processes of hot-rolled seamless steel pipes (△Main inspection processes):
Preparation and inspection of tube blank △ → heating of tube blank → perforation → pipe rolling → steel pipe reheating → diameter determination (reduction) → heat treatment △ → finished pipe straightening → finishing → inspection △ (non-destructive, physical and chemical, Taiwan inspection) → warehousing
②The main production processes of cold-rolled (drawn) seamless steel pipes:
Blank preparation→pickling and lubrication→cold rolling (drawing)→heat treatment→straightening→finishing→inspection
The production process of general seamless steel pipes can be divided into two types: cold drawing and hot rolling. The production process of cold-rolled seamless steel pipes is generally more complicated than hot rolling. The tube blanks must first be subjected to three-roll continuous rolling, and then extruded. After the sizing test, if there is no response crack on the surface, the round pipe will be cut by a cutting machine and cut into a blank of about one meter in length. Then enter the annealing process. Annealing requires pickling with acidic liquid. When pickling, pay attention to whether there is a large amount of bubbling on the surface. If there is a large amount of bubbling, it means that the quality of the steel pipe cannot meet the corresponding standards. In appearance, cold-rolled seamless steel pipes are shorter than hot-rolled seamless steel pipes. The wall thickness of cold-rolled seamless steel pipes is generally smaller than hot-rolled seamless steel pipes, but the surface looks brighter than thick-walled seamless steel pipes, and the surface is not too thick. It's quite rough, and there aren't many burrs in the diameter.
The delivery state of hot-rolled seamless steel pipes is generally in a hot-rolled state after heat treatment. After passing the quality inspection, the hot-rolled seamless steel pipe must undergo strict manual selection by the staff. After the quality inspection, the surface must be oiled, followed by multiple cold-drawing experiments. After the hot-rolling treatment, a perforation experiment must be performed. , if the diameter of the perforation is too large, it needs to be straightened and corrected. After straightening, it is transferred by the transmission device to the flaw detection machine for flaw detection experiments. Finally, it is labeled, arranged in specifications, and placed in the warehouse.
Round tube blank → heating → piercing → three-roll cross rolling, continuous rolling or extrusion → tube removal → sizing (or diameter reduction) → cooling → straightening → hydraulic test (or flaw detection) → marking → warehousing seamless steel pipe It is made of steel ingots or solid tube blanks through perforation and then hot-rolled, cold-rolled or cold-drawn. The specifications of seamless steel pipes are expressed in terms of outer diameter * wall thickness in millimeters.
The outer diameter of hot-rolled seamless steel pipes is generally greater than 32mm and the wall thickness is 2.5-200mm. The outer diameter of cold-rolled seamless steel pipes can be up to 6mm and the wall thickness can be up to 0.25mm. The outer diameter of thin-walled pipes can be up to 5mm and the wall thickness is less than 0.25mm. Rolling has higher dimensional accuracy than hot rolling.
General seamless steel pipes are made of hot-rolled or cold-rolled high-quality carbon structural steels such as 10, 20, 30, 35, 45, 16Mn, 5MnV and other low-alloy structural steels, or 40Cr, 30CrMnSi, 45Mn2, 40MnB and other composite steels. Seamless pipes made of 10 and 20 grade low carbon steel are mainly used for fluid transportation pipelines. Seamless tubes made of medium carbon steel such as 45 and 40Cr are used to manufacture mechanical parts, such as stressed parts of automobiles and tractors. Generally, seamless steel pipes must ensure strength and flattening tests. Hot-rolled steel pipes are delivered in a hot-rolled or heat-treated state; cold-rolled steel pipes are delivered in a heat-treated state.
Hot rolling, as the name suggests, has high temperature, so the deformation resistance is small and large deformation can be achieved. Take the rolling of steel plates as an example. Generally, the thickness of continuous casting billet is about 230mm, and after rough rolling and finish rolling, the final thickness is 1~20mm. At the same time, due to the small width-to-thickness ratio of the steel plate, the dimensional accuracy requirements are relatively low, and plate shape problems are not prone to occur. The main focus is to control the crown. For those with structural requirements, it is generally achieved through controlled rolling and cooling, that is, controlling the opening rolling temperature and final rolling temperature of finishing rolling. Round tube blank → heating → perforation → heading → annealing → pickling → oiling (copper plating) → Multi-pass cold drawing (cold rolling) → billet tube → heat treatment → straightening → hydraulic test (flaw detection) → marking → storage.
Common Specifications and Standards of Seamless steel pipe
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Standard
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Description
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ASTM A106
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For high-temperature service
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ASTM A53
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For structural and pressure purposes
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API 5L
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For pipeline transportation of gas and oil
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DIN 17175
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For boiler tubes
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EN 10216
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For pressure purposes in Europe
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Seamless steel pipe uses
Seamless steel pipes are widely used.
1. General-purpose seamless steel pipes are rolled from ordinary carbon structural steel, low alloy structural steel or alloy structural steel. They have the largest output and are mainly used as pipes or structural parts for transporting fluids.
2. Available 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.
3、Special-purpose seamless pipes include seamless pipes for boilers, chemical and electric power, geological seamless pipes, and petroleum seamless pipes. Seamless steel pipes have hollow sections and are widely used as pipelines for transporting fluids, such as pipelines for transporting oil, natural gas, coal gas, water and certain solid materials. Compared with solid steel materials such as round steel, steel pipes are lighter in weight when the bending and torsional strength is the same, and they are an economical cross-section steel material. It is 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. The use of steel pipes to make ring parts can improve material utilization, simplify the manufacturing process, and save materials and processing. Steel pipes have been widely used for manufacturing.
Advantages of seamless steel pipe
A seamless pipe is a long steel strip with a hollow cross-section and no seams around it. There are more than 5,100 production plants under more than 1,850 companies in more than 110 countries in the world that produce seamless pipes, including more than 260 plants under more than 170 companies in 44 countries that produce oil pipes.
Because of this feature of seamless steel pipes, they are widely used in the transportation of oil, natural gas, coal gas, water and some solid materials. Compared with other steel pipes, seamless steel pipes have a strong advantage in bending resistance. And the quality of seamless steel pipes is also relatively light. It is a very economical cross-section steel.
In addition, seamless steel pipes have the following advantages:
1. Seamless steel pipes are light in weight, and their weight is only 1/5 of that of square steel.
2. Corrosion resistance of seamless steel pipes: resistant to acid, alkali, salt and atmospheric corrosion, resistant to high temperature, good impact resistance and fatigue resistance, no regular maintenance required, and effective service life of more than 15 years;
3. The tensile strength of seamless steel pipes is more than 8-10 times that of ordinary steel, and the elastic modulus is better than that of steel, with excellent creep resistance, corrosion resistance and shock resistance;
4. Seamless steel pipes have excellent mechanical properties and are easy to machine;
5. Seamless steel pipes are highly elastic, can be used repeatedly in mechanical equipment, have no memory, are non-deformable, and are anti-static.
In recent years, seamless steel pipes have been widely used in various industries. The market demand is too large, and more and more companies are producing seamless steel pipes, and the product quality is uneven. So how to judge the quality of seamless steel pipes? The editor of Yinze Steel has something to say.
First of all, we need to know that the wall thickness of high-quality seamless steel will be particularly thick, because the thicker the wall thickness of the product, the more economical and practical it is. If the wall thickness is thinner, its processing cost will increase significantly, and the resource cost will be higher. Secondly, the process of seamless steel also determines its limitations. The general seamless steel has low precision and uneven wall thickness, low brightness inside and outside the tube, high cost of fixed length, and pitting and black spots on the inside and outside are not easy to remove; thirdly, its detection and shaping must be processed offline. Therefore, it demonstrates its superiority in high pressure, high strength, and mechanical structural materials. We will slowly discover it during use.
In fact, seamless steel pipes have only entered the market in recent years. With the increasing market demand, the advantages of seamless steel pipes have also been stimulated, but there are also many counterfeit and shoddy products on the market. I hope everyone must be cautious when choosing.
For high-quality seamless steel pipes backed by expert manufacturing and global service, choose BAOWI Steel — your trusted partner in steel solutions.
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