Steel pipes, as a type of economic steel material, play a crucial role in modern industry. They are not only widely used for transporting fluids and powdery solids, exchanging thermal energy, but also serve as important materials for manufacturing mechanical parts and containers. Since the development of oil in the early 19th century, through the manufacturing of ships, boilers, and airplanes during the two World Wars, to the rise of the chemical industry and the drilling and transportation of oil and natural gas, each technological revolution has greatly promoted the leap in the variety, output, and quality of the steel pipe industry.
The production methods of steel pipes can be divided into two main categories: seamless steel pipes and welded steel pipes. Among them, welded steel pipes can be further divided into straight - seam welded pipes and spiral - seam welded pipes.
There are various production methods for seamless steel pipes, including hot - rolled seamless pipes, cold - drawn pipes, precision pipes, hot - expanded pipes, cold - spun pipes, and extruded pipes.
These steel pipes are all carefully made of high - quality carbon steel or alloy steel and processed through hot rolling or cold rolling (drawing) and other processes.
Welded steel pipes are classified according to their welding processes, including furnace - welded pipes, electric - welded (resistance - welded) pipes, and automatic arc - welded pipes.
According to the welding form, welded steel pipes can be divided into straight - seam welded pipes and spiral - seam welded pipes. In addition, according to the different end shapes, welded steel pipes can be further divided into round welded pipes and special - shaped (such as square, flat, etc.) welded pipes.
In terms of manufacturing methods, steel pipes can be classified into welded steel pipes for low - pressure fluid transportation, spiral - seam electric - welded steel pipes, direct - rolled welded steel pipes, and electric - welded pipes, etc. Seamless steel pipes are widely used in liquid and gas pipelines in various industries. Welded pipes are suitable for water supply pipes, gas pipes, heating pipes, and electrical pipes, etc.
In addition, steel pipes can also be classified according to their pipe - making materials, including carbon steel pipes and alloy steel pipes. Carbon steel pipes can be further divided into ordinary carbon steel pipes and high - quality carbon steel structural pipes. Alloy steel pipes cover various types such as low - alloy pipes, alloy structural pipes, high - alloy pipes, and high - strength pipes.
In terms of connection methods, steel pipes can be divided into plain pipes and threaded pipes. Threaded pipes can be further divided into ordinary threaded pipes and thickened - end threaded pipes. The latter also includes externally thickened, internally thickened, and internally and externally thickened threaded pipes. At the same time, if classified according to the thread type, there are ordinary cylindrical or conical threads and special threads on threaded pipes.
Moreover, according to the surface coating characteristics, steel pipes can be divided into black pipes and coated pipes. Coated pipes include galvanized pipes, aluminized pipes, chromized pipes, etc., while coated pipes are divided into externally coated pipes, internally coated pipes, and internally and externally coated pipes. The commonly used coatings include plastics, epoxy resins, coal - tar epoxy resins, and various glass - type anti - corrosion coating materials.
Finally, steel pipes can also be classified according to their uses.
Pipes for pipelines: These steel pipes are mainly used for transporting water, gas, steam, etc. For example, the application of seamless pipes in oil transportation and natural gas trunk systems, as well as the faucet hoses and sprinkler pipes in agricultural irrigation.
Pipes for thermal equipment: These steel pipes are widely used in general boilers, locomotive boilers, and high - temperature and high - pressure boilers and other thermal equipment, such as boiling water pipes and superheated steam pipes.
Pipes for the machinery industry: These steel pipes have important applications in fields such as aviation, automobiles, and tractors, such as aviation structural pipes, automobile half - shaft pipes, and tractor oil cooler pipes.
Pipes for petroleum and geological drilling: These steel pipes are specially designed for petroleum and geological drilling, including petroleum drilling pipes, drill collars, and various pipe joints.
Pipes for the chemical industry: These steel pipes are mainly used for heat exchangers and pipelines in chemical equipment, as well as for transporting chemical media, such as stainless acid - resistant pipes and high - pressure pipes for fertilizers.
Pipes for other departments: These steel pipes cover a wide range of fields, including pipes for containers, pipes for instruments and meters, and pipes for medical devices.
In addition, steel pipes can also be classified according to their cross - sectional shape, including round steel pipes and special - shaped steel pipes. Special - shaped steel pipes refer to steel pipes with various non - circular cross - sections, such as square pipes and rectangular pipes.
The longitudinal cross - sectional shape of steel pipes is also diverse, mainly divided into two categories: equal - cross - section steel pipes and variable - cross - section steel pipes. Variable - cross - section steel pipes, as the name implies, refer to steel pipes whose cross - sectional shape, inner and outer diameters, and wall thickness change periodically or non - periodically along the pipe length. These steel pipes include externally conical pipes, internally conical pipes, externally stepped pipes, internally stepped pipes, periodic - cross - section pipes, corrugated pipes, spiral pipes, steel pipes with heat - dissipation fins, and guns with rifling.
In terms of component inspection, the standards for different types of steel pipes vary. For example, according to GB3087 - 2008 "Seamless Steel Pipes for Low and Medium Pressure Boilers", chemical composition tests shall comply with the relevant provisions in GB222 - 84 and GB223 "Methods for Chemical Analysis of Iron and Steel and Alloys". Similarly, GB/T5310 - 2008 "Seamless Steel Pipes for High Pressure Boilers" also sets corresponding standards for chemical composition tests. For imported boiler steel pipes, chemical composition inspections shall be carried out in accordance with the relevant standards specified in the contract.
In addition, the methods for identifying different types of steel pipes are also diverse and depend on the use and characteristics of the steel pipes.
Inferior steel pipes often have folding defects.
Folding refers to various fold lines on the surface of steel pipes. This problem usually runs through the entire length of the steel pipe longitudinally. The occurrence of folding is often because inferior - quality manufacturers pursue production speed and set the reduction amount too large, resulting in the formation of ears, which then leads to folding in the next rolling process. Steel pipes with such folding are prone to cracking after bending, seriously reducing the strength of the steel.
The surface of inferior steel pipes often shows a pitted appearance.
Pitting is caused by excessive wear of the rolling groove, resulting in irregular bumps and depressions on the surface of the steel. In order to pursue profits, manufacturers of inferior steel pipes often let the rolling grooves over - roll, thus causing the pitted appearance.
The surface of inferior steel pipes often has scabbing phenomena.
This is mainly caused by two reasons: (1) The material of inferior steel pipes is uneven and contains many impurities; (2) The guide and guard equipment used by manufacturers of inferior materials is relatively simple, which is easy to adhere to steel materials during the rolling process. These impurities, after being bitten into the rolls, are likely to form scabs.
The surface of inferior steel pipes often has cracks, which are mainly attributed to the use of earthen billets as their billets. Since earthen billets have many pores, these billets will be affected by thermal stress during the cooling process, thus producing cracks. After the rolling process, these cracks are transformed into cracks on the surface of the steel pipes.
Inferior steel pipes are easily scratched, which is mainly because the equipment of their manufacturers is simple, resulting in burrs on the surface of the steel. These burrs will reduce the strength of the steel and thus affect its service performance.
Inferior steel pipes usually lack metallic luster and appear light red or similar to pig iron in color. This is mainly because their billets are earthen billets and the rolling temperature is non - standard. Earthen billets have many pores, and it is difficult to reach the specified austenitic region during the rolling process, thereby affecting the properties of the steel.
The transverse ribs of inferior steel pipes are thin and not fully filled, which is often caused by excessive reduction of the finished product by manufacturers in pursuit of a large negative tolerance. A small iron mold and unfilled holes in the die will lead to substandard steel properties.
The cross - section of inferior steel pipes is elliptical, which is also because manufacturers over - roll the finished product to save materials. The strength of this kind of deformed steel is greatly reduced and does not meet the appearance size standards.
The composition of high - quality steel is uniform, the cut end face is smooth and neat, while inferior materials have the phenomenon of "meat dropping" on the end face due to poor material quality. In addition, manufacturers of inferior materials may have less cut - off at the ends of products, and large ears may appear at the head and tail, further affecting the quality of the steel.
Inferior steel pipes have more impurities, lower density, and serious size over - tolerance. By weighing and checking, we can preliminarily judge whether they are inferior steel materials. For example, for deformed steel bar No. 20, the national standard stipulates a maximum negative tolerance of 5%, and the theoretical weight of a single product with a fixed length of 9M is 120 kilograms. If the actual weight is less than 114 kilograms (i.e., 95% of the theoretical weight), it may be inferior steel.
The inner diameter size of inferior steel pipes fluctuates greatly, mainly due to unstable steel temperature, uneven composition, and simple equipment. Such steel pipes are unevenly stressed and prone to quality problems such as fractures.
The trademarks and imprints of high - quality pipes are relatively standardized and clear, while inferior steel materials may have blurred or non - standard situations.
For large deformed steel pipes with a diameter of more than 16, the distance between the two trademarks of high - quality products is usually more than 1m, while inferior products may have insufficient spacing.
The longitudinal ribs of inferior deformed steel bars often appear wavy, affecting their service performance and appearance quality.
Due to the lack of equipment such as cranes, the packaging of inferior steel pipe manufacturers may be relatively loose, and the side is elliptical, further exposing their quality deficiencies.
In addition, in import and export trade, the specification requirements of spiral steel pipes are also one of the very important contract terms. It usually includes various indicators such as the standard grade, nominal diameter of the reinforcing bar, nominal weight, specified length, and tolerance values. China's standards recommend using a series of spiral steel pipes with nominal diameters of 8, 10, 12, 16, 20, 40mm, and stipulate the corresponding supply length ranges. Understanding these specification requirements helps to ensure that both parties in the trade can clearly understand the product quality and performance requirements, thereby ensuring the smooth progress of the trade.
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(2) Appearance quality requirements:
① Surface quality: Relevant standards have clearly stipulated the surface quality of deformed steel bars, requiring that the ends must be cut flat, and at the same time, there should be no harmful defects such as cracks, scabs, and folds on the surface.
② Allowable deviation values of appearance size: The bending degree of deformed steel bars and the geometric shape of reinforcing bars are strictly controlled. For example, China's standards stipulate that the bending degree of straight reinforcing bars should not exceed 6mm per meter, and the total bending degree should not exceed 0.6% of the total length of the reinforcing bar. -
Plate inspection:
After the steel plate enters the production line, the first step is to conduct a full - plate ultrasonic inspection to ensure its quality. -
Edge milling:
Use an edge milling machine to mill both sides of the steel plate to achieve the predetermined width, parallelism, and bevel shape. -
Pre - bending of edges:
Use a pre - bending machine to pre - bend the edges of the plate to give it the required curvature. -
Forming:
On a JCO forming machine, first press half of the pre - bent steel plate into a "J" shape, and then press the other half into a "C" shape to finally form an "O" shape. -
Pre - welding:
Join the seams of the formed straight - seam welded pipes and use gas - shielded welding for continuous welding. -
Inner welding and outer welding:
Use longitudinal multi - wire submerged arc welding to weld on the inner and outer sides of the straight - seam steel pipe respectively. -
Ultrasonic inspection I:
Conduct 100% ultrasonic inspection of the inner and outer welds and the base metal on both sides of the straight - seam welded pipes. -
X - ray inspection I:
Use an X - ray industrial television to conduct 100% inspection of the inner and outer welds and cooperate with the image processing system to ensure the sensitivity of flaw detection. -
Expansion:
Expand the submerged arc welded straight - seam steel pipe to improve dimensional accuracy and optimize the distribution of internal stress. -
Hydrostatic test:
Inspect each steel pipe on a hydrostatic test machine to ensure that it reaches the standard test pressure and has an automatic recording function. -
Beveling:
Process the ends of the inspected and qualified steel pipes to achieve the predetermined bevel size. -
Ultrasonic inspection II:
Conduct ultrasonic inspection again for each steel pipe to check for possible defects after expansion and hydrostatic test. -
X - ray inspection II:
Conduct X - ray industrial television inspection and end - weld radiography on the steel pipes after expansion and hydrostatic test. -
Magnetic particle inspection of pipe ends:
Detect defects at the pipe ends. -
Anti - corrosion and coating:
Finally, carry out anti - corrosion and coating treatment on qualified steel pipes according to user requirements.
Next is the process flow of spiral - seam welded pipes:
(1) Raw material preparation: It includes steel strips, welding wire, and flux, all of which need to undergo strict physical and chemical inspections before being put into use.
(2) Steel strip butt welding: Use single - wire or double - wire submerged arc welding technology to butt the heads and tails of the steel strips and perform automatic submerged arc welding for repair welding after rolling into a steel pipe.
(3) Pre - forming treatment: The steel strip needs to go through processes such as leveling, edge trimming, edge planing, surface cleaning and conveying, and pre - bending.
(4) An electric contact pressure gauge is used to precisely control the pressure of the pressing cylinders on both sides of the conveyor to ensure the smooth and unobstructed transportation of the steel strip.
(5) The roll - forming technology is adopted, including external control and internal control, to meet different production requirements.
(6) A weld gap control device is carefully configured to ensure that the weld gap strictly meets the welding standards and to comprehensively monitor the pipe diameter, misalignment, and weld gap.
(7) Both the inner and outer welding processes use American Lincoln electric welders, supporting single - wire or double - wire submerged arc welding to ensure high stability of the welding specifications.
(8) The weld quality is strictly inspected by an online continuous ultrasonic automatic flaw detector, achieving 100% non - destructive testing coverage. Once a defect is detected, the system will automatically alarm and spray a mark so that production personnel can adjust the process parameters in time to eliminate it.
(9) An air plasma cutting machine is used to accurately cut the steel pipe into single pieces to meet the subsequent processing and delivery requirements.
(10) Each batch of steel pipes will undergo a strict first - inspection system before being put into production, covering multiple aspects such as the mechanical properties of the welds, chemical composition, fusion condition, and surface quality of the steel pipes to ensure the qualification of the pipe - making process.
(11) For the parts marked by continuous ultrasonic flaw detection on the welds, manual ultrasonic and X - ray re - inspections will be carried out. If defects are found, repairs will be made and re - inspected until the defects are completely eliminated.
(12) The steel pipes with butt - welded seams of steel strips and the T - joints intersecting with the spiral welds will all undergo X - ray television or radiographic inspection to ensure welding quality.
(13) Each steel pipe will undergo a hydrostatic test using a radial sealing method and be strictly controlled for test pressure and time by a steel pipe hydrostatic microcomputer detection device. The test parameters will be automatically printed and recorded to ensure the traceability of product quality.
(14) In the mechanical processing of pipe ends, the dimensional accuracy of end - face perpendicularity, bevel angle, and blunt edge will be strictly controlled to meet subsequent usage requirements.
In addition, the steel pipe standards also stipulate the mechanical property indicators of steel, including tensile properties, hardness, toughness, and high - and low - temperature properties. These indicators are crucial for ensuring the final service performance of steel pipes.
① Tensile strength (σb)
In a tensile test, when the specimen is broken, the ratio of the maximum force (Fb) it bears to the original cross - sectional area (So) of the specimen, that is, the stress (σ), is called the tensile strength (σb), and its unit is N/mm² or MPa. This indicator reflects the ability of metal materials to resist damage when subjected to tension. The calculation formula is as follows:
Tensile strength (σb) = Maximum force (Fb) / Original cross - sectional area (So)
Among them, Fb represents the maximum force when the specimen is broken, with the unit of Newton (N); So is the original cross - sectional area of the specimen, with the unit of square millimeter (mm²). Through this indicator, we can understand the strength performance of metal materials during the stretching process.
② Yield point (σs)
For metal materials with a yield phenomenon, there is a specific stress point, that is, the yield point, during the stretching process. When the stress on the specimen reaches this value, it can continue to elongate without an increase in force. If the force decreases during this process, it is necessary to further distinguish between the upper yield point and the lower yield point. The upper yield point refers to the maximum stress before the first decrease in force during yielding, and the lower yield point is the minimum stress in the yielding stage without considering the initial instantaneous effect. The units of both are N/mm² or MPa. The calculation formula is as follows:
Yield point (σs) = Yield force (Fs) / Original cross - sectional area (So)
Among them, Fs represents the constant yield force of the specimen during the stretching process, with the unit of Newton (N); So is the original cross - sectional area of the specimen, with the unit of square millimeter (mm²). Through this indicator, we can understand the plastic deformation behavior of metal materials during the stretching process.
③ Elongation after fracture (σ)
After the tensile test is completed, we can calculate the elongation after fracture by measuring the change in the gauge length before and after the specimen is broken. This indicator reflects the ability of metal materials to extend during the stretching process. The calculation formula is as follows:
Elongation after fracture (σ) = (L1 - L0) / L0 × 100%
Among them, L1 represents the gauge length of the specimen after being broken, and L0 is the original gauge length of the specimen. By calculating this percentage, we can evaluate the degree of deformation of metal materials when subjected to tension.
④ Reduction of area (ψ)
After the tensile test is completed, what we focus on is the change in the cross - sectional area of the necked - down part at the broken end of the specimen. The reduction of area, represented by ψ, reflects the proportion of this change. Specifically, it represents the percentage of the maximum reduction in the cross - sectional area at the necked - down part after the specimen is broken compared with the original cross - sectional area. This indicator is also crucial for evaluating the properties of metal materials. The calculation formula is as follows:
Reduction of area (ψ) = (S0 - S1) / S0 × 100%
Among them, S0 represents the original cross - sectional area of the specimen, and S1 is the minimum cross - sectional area at the necked - down part after the specimen is broken. By calculating this percentage, we can further understand the deformation and fracture characteristics of metal materials during the stretching process.
⑤ Hardness indicators
The ability of metal materials to resist the indentation of hard objects on the surface is called hardness. According to different test methods and applicable scopes, this indicator can be divided into Brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness, micro - hardness, and high - temperature hardness, etc. In the routine testing of pipes, Brinell, Rockwell, and Vickers hardness are the three more commonly used types.
A. Brinell hardness (HB)
The Brinell hardness test uses a steel ball or cemented carbide ball of a certain diameter to press into the surface of the specimen with a specified test force. After maintaining the force for a specified time, the test force is removed, and then the diameter of the indentation on the surface of the specimen is measured. The Brinell hardness value is calculated by dividing the test force by the spherical surface area of the indentation, represented by HBS (steel ball), and the unit is N/mm² (MPa).
Although the Brinell hardness determination is accurate and reliable, this method is mainly suitable for metal materials with a strength below 450N/mm² (MPa). For harder steels or thinner plates, the Brinell hardness may not be applicable. In the steel pipe standards, the Brinell hardness is usually represented by the indentation diameter d. This representation method is both intuitive and convenient for operation.
For example, 120HBS10/1000/30 means that the Brinell hardness value measured after a 10mm steel ball and a 1000Kgf (9.807KN) test force are applied and maintained for 30 seconds is 120N/mm² (MPa).
B. Rockwell hardness (HK)
The Rockwell hardness test is similar to the Brinell hardness test and is also an indentation test method. However, the difference is that it measures the depth of the indentation. Under the action of the initial test force and the total test force, the indenter is pressed into the surface of the specimen. After a specified time, the main test force is removed, and then the increment of the residual indentation depth is measured to calculate the hardness value. Its value is represented by HR, and the commonly used scales are A, B, C, etc. In the steel hardness test, scales A, B, and C, that is, HRA, HRB, and HRC, are the most commonly used.
Welded steel pipes, also known as welded pipes, are made by rolling and forming steel plates or steel strips and then welding them. This kind of steel pipe has a simple production process, high efficiency, and a wide variety of specifications, and requires relatively little investment in equipment. Although its strength is usually slightly lower than that of seamless steel pipes, since the 1930s, with the rapid development of strip continuous rolling technology and the progress of welding and inspection technologies, the quality of welded steel pipes has been continuously improved, and their application fields have become increasingly wide.
Welded steel pipes are mainly divided into two categories: straight - seam welded pipes and spiral - seam welded pipes. Straight - seam welded pipes occupy a place in the market with their simple production process, high production efficiency, and low cost. Spiral - seam welded pipes, although having a longer weld length and a relatively slower production speed, usually have higher strength than straight - seam welded pipes. They can produce welded pipes with larger diameters from narrower billets and can make welded pipes with different diameters from billets of the same width. Therefore, in the field of small - diameter welded pipes, straight - seam welded pipes are more popular, while large - diameter welded pipes are mostly made of spiral - seam welded pipes.
In addition, welded steel pipes for low - pressure fluid transportation (GB/T3091 - 2008), commonly known as general welded pipes or black pipes, are an ideal choice for transporting low - pressure fluids such as water, gas, air, oil, and heating steam. This kind of steel pipe can be divided into ordinary steel pipes and thickened steel pipes according to the wall thickness, and can be divided into plain pipes without threads and threaded pipes according to the pipe end form. In addition to being directly used for fluid transportation, it is also often used as the original pipe for galvanized welded steel pipes.
Galvanized welded steel pipes for low - pressure fluid transportation (GB/T3091 - 2008), also known as galvanized electric - welded steel pipes or white pipes, are specially designed for transporting low - pressure fluids such as water, gas, air, oil, heating steam, and warm water. This kind of steel pipe is treated by hot - dip galvanizing to enhance its corrosion resistance, and is divided into ordinary and thickened wall thickness specifications, as well as threaded and non - threaded pipe end forms. Its specifications are usually expressed in nominal diameters, customarily in inches, such as 1/2, 3/4, 1, 2, etc.
Ordinary carbon steel wire conduits (YB/T5305 - 2006) are an ideal choice for protecting wires in electrical installation projects and are widely used in industrial and civil buildings and the installation of machinery and equipment.
Straight - seam electric - welded steel pipes (GB/T13793 - 2008) have the characteristic that the weld is parallel to the longitudinal direction of the steel pipe and are suitable for general structural purposes, including various types such as metric electric - welded steel pipes and electric - welded thin - walled pipes.
Spiral - seam submerged - arc welded steel pipes for pressure fluid transportation (SY/T5037 - 2000) use hot - rolled steel strip coils as billets, are formed by cold - rolling in a spiral shape at room temperature, and are welded by double - sided submerged - arc welding. They are specially designed for pressure fluid transportation and have excellent pressure - bearing capacity and welding performance.
Spiral - seam high - frequency welded steel pipes for pressure fluid transportation (SY/T5038 - 2000) also use hot - rolled steel strip coils as billets, are manufactured by cold - rolling in a spiral shape at room temperature and high - frequency lap welding processes, and are also suitable for pressure fluid transportation, and also have excellent pressure - bearing capacity and plasticity.
General spiral - seam high - frequency welded steel pipes for low - pressure fluid transportation (SY/T5039 - 2000) are a type of steel pipe suitable for general low - pressure fluid transportation and are made by high - frequency lap welding.
Spiral - seam welded steel pipes for piling (SY/T5768 - 2000) are specially made for the design of foundation piles such as civil construction structures, docks, and bridges. They use hot - rolled steel strip coils as billets and are manufactured by cold - rolling in a spiral shape at room temperature and double - sided submerged - arc or high - frequency welding processes.
In addition, seamless steel pipes are also an important type of steel material. They have the characteristics of a hollow cross - section and no joints around the periphery and are widely used in manufacturing structural parts and mechanical parts. Compared with solid steel materials such as round steel, seamless steel pipes are lighter in weight when having the same bending and torsional strength, and are an economic - section steel material. Their cross - sectional shape is mostly circular, but other special - shaped cross - section steel pipes are also manufactured according to specific uses.
Structural seamless steel pipes (GB/T8162 - 2008) are seamless steel pipes specially designed and manufactured for general structures and mechanical structures.
Seamless steel pipes for fluid transportation (GB/T8163 - 2008) are suitable for transporting fluids such as water, oil, and gas and are a type of seamless steel pipe with strong versatility.
Seamless steel pipes for low - and medium - pressure boilers (GB/T3087 - 2008) are specially designed for manufacturing superheated steam pipes, boiling water pipes, etc. of various low - and medium - pressure boilers and are made of high - quality carbon structural steel.
Seamless steel pipes for high - pressure boilers (GB5310 - 2008) are suitable for the heating surfaces of water - tube boilers with high pressure and above, and the materials include high - quality carbon steel, alloy steel, and stainless heat - resistant steel.
High - pressure seamless steel pipes for fertilizer equipment (GB6479 - 2000) are suitable for chemical equipment and pipelines and can withstand relatively high working pressures and temperature ranges.
Seamless steel pipes for petroleum cracking (GB9948 - 2006) are specially designed for petroleum refining plants and are used for furnace tubes, heat exchangers, pipes, and other parts.
Geological drilling steel pipes (YB235 - 70) are specially provided for the geological department, including various types such as drill rods and drill collars, to meet the needs of core drilling.
Carbon steel seamless steel pipes for ships (GB5312 - 2009) are used to manufacture the pressure - resistant pipe systems, boilers, and superheaters of ships to ensure the safe operation of ships.
Seamless steel pipes for automobile half - shaft sleeves (GB3088 - 82) are specially designed for automobile manufacturing, with excellent material quality to meet the requirements of high strength and high precision.
High - pressure oil pipes for diesel engines (GB3093 - 2002) are specially designed for the injection system of diesel engines to ensure the stability and safety of the high - pressure oil circuit.
Precision inner - diameter seamless steel pipes for hydraulic and pneumatic cylinders (GB8713 - 88) have precise inner - diameter dimensions and are suitable for the manufacture of hydraulic and pneumatic cylinders to ensure the accuracy and performance of the cylinders.
Cold - drawn or cold - rolled precision seamless steel pipes (GB3639 - 2000) are suitable for mechanical structures and hydraulic equipment and have the characteristics of high precision and high surface finish.
Stainless - steel seamless steel pipes for structures (GB/T14975 - 2002) are widely used in industrial and petrochemical fields and have excellent corrosion resistance.
Stainless - steel seamless steel pipes for fluid transportation (GB/T14976 - 2002) are also suitable for fluid transportation. The material is stainless steel to ensure long - term corrosion resistance.
Special - shaped seamless steel pipes are non - circular seamless steel pipes, including various types such as equal - wall - thickness, unequal - wall - thickness, and variable - diameter ones, and are widely used in the manufacture of various structural parts and mechanical components.
B. Actual size: The actual size obtained during the production process may be larger or smaller than the nominal size. This phenomenon is called deviation.
C. Weight per meter calculation: The weight per meter can be calculated by the formula 0.02466 × wall thickness × (outer diameter - wall thickness).
Deviation and tolerance
A. Definition of deviation: Since the actual size often cannot completely match the nominal size, the standard allows a certain difference between the actual size and the nominal size. This difference may be a positive value (positive deviation) or a negative value (negative deviation).
B. Explanation of tolerance: Tolerance is the sum of the absolute values of the positive deviation and the negative deviation stipulated in the standard, also known as the "tolerance zone". It should be noted that deviation is directional, while tolerance is not. Therefore, it is inappropriate to call the deviation value "positive tolerance" or "negative tolerance".
Delivery length
The delivery length, also known as the user - required length or contract length, is stipulated in the standard as follows:
A. Usual length: Steel pipes within the length range specified by the standard and without a fixed length requirement are called usual lengths. For example, the length range of standard hot - rolled (extruded, expanded) steel pipes for structural pipes is 3000mm - 12000mm, and that of cold - drawn (rolled) steel pipes is 2000mm - 10500mm.
B. Fixed length: This is a certain fixed length size required in the contract and should be within the usual length range. Since it is difficult to achieve an absolute fixed length in actual operation, the standard allows a certain positive deviation. Taking structural pipes as an example, the yield of fixed - length pipes is lower than that of usual - length pipes, so production enterprises may propose a price increase.
C. Multiple length: This should also be within the usual length range, and the single - multiple length and the multiple constituting the total length need to be indicated in the contract. In actual operation, the total length needs to be added with the allowable positive deviation of 20mm, and the cutting allowance of each single - multiple length needs to be considered. Taking structural pipes as an example, the cutting allowance of steel pipes with an outer diameter of less than or equal to 159mm is 5 - 10mm, and that of those with an outer diameter greater than 159mm is 10 - 15mm.
If the standard does not clearly stipulate the deviation and cutting allowance of the multiple length, the supply and demand parties should negotiate and agree on it in the contract. The multiple length, similar to the fixed length, will cause a significant decrease in the yield of production enterprises. Therefore, the price increase proposed by enterprises is reasonable, and the price increase range is usually similar to that of the fixed length.
D. Range length: When users hope to obtain a specific range of lengths within the usual length range, it needs to be clearly indicated in the contract. For example, the usual length is 3000 - 12000mm, and the range - fixed length may be set as 6000 - 8000mm or 8000 - 10000mm. It should be noted that compared with the fixed length and multiple length, the range length is more relaxed, but compared with the usual length, it is more strict, and it may also reduce the yield of production enterprises. Therefore, the price increase proposed by enterprises is also reasonable, and the price increase range is usually about 4% of the base price.
Uneven wall thickness: The wall thickness of steel pipes is not uniform, and there are objectively differences in wall thickness on the cross - section and longitudinal body of the steel pipe, that is, uneven wall thickness. To control this non - uniformity, some steel pipe standards stipulate the allowable indicators for uneven wall thickness, which usually do not exceed 80% of the wall thickness tolerance. The specific implementation needs to be negotiated by the supply and demand parties.
Ovality: On the cross - section of a circular steel pipe, there may be a difference between the maximum outer diameter and the minimum outer diameter, that is, ovality (or non - circularity). To ensure quality, some steel pipe standards stipulate the allowable indicators for ovality, which generally do not exceed 80% of the outer diameter tolerance. Similarly, this needs to be determined through negotiation by the supply and demand parties.
Bending degree: The steel pipe may be curved in the length direction, and the degree of bending is the bending degree. The standard stipulates two methods for measuring the bending degree: one is the local bending degree, which uses a one - meter - long straightedge to measure the chord height at the maximum bending of the steel pipe; the other is the total bending degree of the whole length, which uses a thin rope to tighten from both ends of the pipe to measure the maximum chord height and convert it into a percentage of the length. Both methods are suitable for measuring the bending degree at the end of the pipe.
Dimensional over - tolerance, also known as dimensional deviation beyond the allowable range of the standard, mainly refers to the fact that the outer diameter and wall thickness of steel pipes exceed the preset standard range. Although some people are used to calling dimensional over - tolerance "out - of - tolerance of tolerance", this statement that confuses deviation with tolerance is not rigorous. A more accurate statement should be "out - of - tolerance of deviation". This deviation may be a "positive" deviation or a "negative" deviation, and in the same batch of steel pipes, it is relatively rare for both positive and negative deviations to be out of tolerance at the same time.
In addition, we also need to understand the theoretical weight calculation method of commonly used profiles. The calculation formula is: m = F × L × ρ, where m represents the mass, with the unit of Kg; F is the cross - sectional area, with the unit of m²/m; L is the length, with the unit of m; ρ is the density, with the unit of Kg/m³. At the same time, we also need to master the calculation method of the cross - sectional area.
- Calculation of the cross - sectional area of square steel: F = a²
- Calculation of the cross - sectional area of steel pipes: F = 3.1416 × (D - 2 × t) × D, where D is the diameter and t is the thickness.
- Calculation of the cross - sectional area of steel plates and flat steels: F = a × t, where a is the width and t is the thickness.
Steel Pipe Continuous Rolling Technology
The continuous rolling process occupies an important position in steel pipe production. It involves the continuous rolling and diameter - controlling processes of steel pipes. During this process, the steel pipe and the mandrel move cooperatively in multiple stands, and the deformation and movement are jointly affected by the rollers and the mandrel. The movement mode of the mandrel can be free - floating, that is, it moves forward only driven by the metal; or it can be speed - limited, that is, a certain movement speed is set and its degree of freedom is restricted. Throughout the entire continuous rolling process, the mandrel, the rollers, and the steel pipe form an interrelated whole. Any change in any one of them will cause a change in the state of the entire system. Continuous rolling theory is the scientific theory that studies this kind of interrelationship.
Kinematic Characteristics of Steel Pipe Continuous Rolling
A series of complex kinematic phenomena will occur during the continuous rolling of steel pipes. These phenomena not only affect the dimensional accuracy and shape quality of the steel pipes but also have a direct impact on the stability and efficiency of the continuous rolling process. Therefore, in - depth research and understanding of these kinematic characteristics are of great significance for optimizing the continuous rolling process of steel pipes, improving product quality, and reducing costs.
- Kinematic phenomena
- Slip phenomenon and its influence
- Variation law of tension coefficient
Comprehensive Analysis of the Motion State of Continuous - Rolled Tubes
During the continuous rolling of steel pipes, a variety of kinematic phenomena can be observed. Among them, the slip phenomenon is an important characteristic, which has a significant impact on the dimensional accuracy and shape quality of the steel pipes. At the same time, the tension coefficient will also change as the continuous rolling process progresses. This change directly affects the stability and efficiency of the continuous rolling process. Therefore, a comprehensive analysis of the motion state of the continuous - rolled tubes, including an in - depth exploration of the slip phenomenon and the tension coefficient, is of crucial importance for optimizing the continuous rolling process of steel pipes, improving product quality, and reducing costs.
- Relative displacement between the rolled piece and the mandrel
- Setting and function of the stands
- Process analysis of intermittent rolling
- Movement characteristics of the mandrel during single - stand rolling
Deformation and Stress Analysis in the Steel Pipe Continuous Rolling Process
In the continuous rolling process of steel pipes, the relative displacement between the rolled piece and the mandrel is a key factor, which directly affects the forming quality of the steel pipes. At the same time, the setting of the stands is crucial for ensuring the stability and efficiency of the continuous rolling process. As a common process mode, the process characteristics and influencing factors of intermittent rolling need to be deeply analyzed. In addition, the movement characteristics of the mandrel during single - stand rolling are also a major research focus in the continuous rolling process. Finally, this paper will also explore the deformation and stress problems in the steel pipe continuous rolling process, aiming to provide theoretical support for optimizing the continuous rolling process and improving product quality.
- Analysis of internal stress in the steel pipe during the continuous rolling process
- Detailed discussion on sidewall deformation and stress
During the continuous rolling of steel pipes, the distribution and change of internal stress in the pipe are issues that cannot be ignored. At the same time, the deformation and stress state of the sidewall also directly affect the dimensional accuracy and performance of the steel pipes. Therefore, in - depth analysis of these issues is of great significance for optimizing the continuous rolling process and improving product quality.
Sinosteel Stainless Steel Pipe is the Manufacturer and Supplier of Stainless Steel Pipe and Special Alloy Pipe
From : https://www.sinosteel-pipe.com/en/blog-5600349094892099.html
