Teach you to know steel pipe

What is a steel pipe?

Steel pipe has hollow section and its length is much larger than the diameter or circumference of steel. According to the sectional shape, it can be divided into round pipe, square pipe, rectangular pipe and special-shaped steel pipes; According to the material is divided into carbon structural steel pipe, low alloy structural steel pipe, alloy steel pipe and composite steel pipe; According to the purpose, it can be divided into conveying pipeline, engineering structure, thermal equipment, petrochemical industry, machinery manufacturing, geological drilling, high pressure equipment and so on. According to the production process is divided into seamless steel pipe and welded steel pipe, which is divided into hot rolled and cold rolled (pull) two kinds of seamless steel pipe, welded steel pipe and straight seam welded steel pipe and spiral seam welded steel pipe.

202203121647069859185194 - Teach you to know steel pipe

Steel pipe is not only used to transport fluids and powdery solids, exchange heat, manufacture mechanical parts and containers, it is also an economical steel. It can reduce the weight, save 20 ~ 40% of the metal, and realize the industrial mechanized construction. Using steel pipe to manufacture highway bridge can not only save steel, simplify construction, but also greatly reduce the area of protective coating and save investment and maintenance cost.

Classification of steel pipes

Classification by production method

Steel pipe can be divided into two categories according to the production method: seamless steel pipe and welded steel pipe, welded steel pipe is referred to as welded pipe.
  1. According to the production method, seamless steel pipe can be divided into: hot rolled seamless pipe, cold drawn pipe, precision steel pipe, hot expansion pipe, cold spinning pipe and extrusion pipe. Seamless steel tube is made of high quality carbon steel or alloy steel, hot rolled, cold rolled (drawn) points.

  2. Welded steel pipe is divided into furnace welding pipe, electric welding (resistance welding) pipe and automatic arc welding pipe because of its different welding form is divided into straight seam welding pipe and spiral welding pipe, because of its end shape is divided into round welding pipe and shaped (square, flat, etc.) welding pipe. Welded steel pipe is made of rolled tubular steel plate welded to the seam or spiral seam. In terms of manufacturing methods, it can be divided into welding steel pipe for low-pressure fluid transportation, spiral seam welding steel pipe, direct coil welding steel pipe, electric welding pipe and so on. Seamless steel pipe can be used in various industries, such as liquid pressure pipe and gas pipe. Welded pipes can be used for water pipelines, gas pipelines, heating pipes, electrical pipes and so on.

Classification by material

Steel pipe can be divided into carbon steel pipe, alloy steel pipe, stainless steel pipe and so on.
Carbon pipe can be divided into ordinary carbon steel pipe and high quality carbon structure pipe.
Alloy tube can be divided into: low alloy tube, alloy structure tube, high alloy tube, high strength tube. Bearing tube, heat and acid resistant stainless tube, precision alloy (such as cutting alloy) tube and high temperature alloy tube, etc.

Classification by connection mode

Steel pipe can be divided into light pipe (pipe end without thread) and wire pipe (pipe end with thread) according to the connection mode of pipe end.
Wire tube is divided into: ordinary wire tube and tube end thickened wire tube.
Thickening wire pipe can also be divided into: outer thickening (with external thread), inner thickening (with internal thread) and inner and outer thickening (with internal and external thread) and other ground wire pipe.
If the thread type can also be divided into: ordinary cylindrical or conical thread and special thread and other ground thread tube.
In addition, according to the needs of users, wire pipes are generally equipped with pipe joints delivery.

Classification by plating characteristics

According to the surface coating characteristics of steel tube can be divided into: black tube (not coated) and coated tube.
Galvanized pipe, aluminum pipe, chromium pipe, aluminized pipe and other alloy layer of steel pipe.
Coating pipe has outer coating pipe, inner coating pipe, inner and outer coating pipe. Commonly used coatings are plastic, epoxy resin, coal tar epoxy resin and a variety of glass anti-corrosion coating materials.
Galvanized pipe is divided into: KBG pipe, JDG pipe, threaded pipe and so on.

Classification by purpose

  • 1. Pipes for pipelines. Such as: water, gas pipe, steam pipe seamless pipe, oil transmission pipe, oil and gas trunk pipe. Agricultural irrigation faucet with pipe and sprinkler irrigation pipe.
  • 2. Pipes for thermal equipment. Such as general boiler with boiling water pipe, overheated steam pipe, locomotive boiler with heat pipe, big smoke pipe, small smoke pipe, arch brick pipe and high temperature and pressure boiler pipe.
  • 3. Pipes for mechanical industry. Such as aviation structure tube (round tube, elliptical tube, flat elliptical tube), automobile half shaft tube, axle tube, automobile tractor structure tube, tractor oil cooler tube, agricultural machinery with square tube and rectangular tube, transformer tube and bearing tube, etc..
  • 4. Petroleum geology drilling pipe. Such as: oil drilling pipe, oil drill pipe (kelly and hexagonal drill pipe), drilling, oil pipe, oil casing and all kinds of pipe joint, geological drilling pipe (core pipe, casing, active drill pipe, drilling, hoop and pin joint, etc.).
  • 5. Tubes for chemical industry. Such as: petroleum cracking pipe, chemical equipment heat exchanger and pipe with pipe, rust acid resistant pipe, chemical fertilizer with high pressure pipe and transport chemical medium with pipe.
  • 6. For other departments. Such as: container tube (high pressure gas cylinder tube and general container tube), instrument instrument tube, hand case tube, injection needle and medical instrument tube.

Classification by section shape

Steel pipe products are of various types and specifications, and their performance requirements are also various. All of these should be differentiated as user requirements or working conditions change. Generally, steel pipe products are classified according to section shape, production method, pipe material, connection mode, coating characteristics and uses.
Steel pipe can be divided into round steel pipe and special-shaped steel pipe according to the shape of cross section.
Special-shaped steel pipe refers to the steel pipe of various non-circular annular section.
The main ones are:
Square tube, rectangular tube , The elliptical tube, Flat elliptic tubes, Semicircle pipe, Hexagonal pipe, Hexagonal inner pipe, Unequilateral hexagonal pipe, Equilateral triangle tube, Pentagonal tube, Octagonal tube, Convex pipe, Double convex pipe, Double concave tube, Polyconcave tube, Melon seed tube, Flat tube, Diamond tube, Star pipe,parallelogram Pipe, Ribbed tube, Dropwise tube, Inner fin tube, Twisted vision tubes, B type tube, D type pipe and multilayer pipe.
Steel pipe according to the longitudinal section shape is divided into: equal section steel pipe and variable section steel pipe. Variable section (or variable section) steel pipe refers to the steel pipe whose section shape, internal and external diameter and wall thickness change periodically or non-periodically along the direction of pipe length. It mainly includes: outer conical tube, inner conical tube, outer ladder tube, inner ladder tube, periodic section tube, corrugated tube, spiral tube, steel tube with heat sink and gun barrel with multiple lines, etc.

Chemical composition inspection of steel pipe

  • (1) GB3087 “Seamless steel tube for low and medium pressure boiler” provisions. Chemical composition test method according to gb222-84 and GB223 “Methods for chemical Analysis of Steel and Alloy” relevant part.
  • (2) GB/T5310 “Seamless steel tubes for high pressure boilers” provisions. Chemical composition test method according to GB222-84 and “Method for Chemical Analysis of Iron and Steel and Alloy”, GB223 “Method for chemical analysis of Iron and Steel and Alloy”.
  • (3) Chemical composition inspection of imported boiler steel pipe shall be carried out according to relevant standards stipulated in the contract.
  • (4) Other standards such as GB/T8162, GB/T8163, GB9948, GB6479.

Production method of steel pipe

Steel tubes are divided into seamless steel tubes and welded steel tubes. Seamless steel tube production process is the solid tube billet or steel ingot into hollow capillary, and then rolled into the desired size of the steel tube. Different methods of perforating and rolling are used to produce seamless steel tubes. The production process of welded steel pipe is to bend the steel billet (steel plate or strip) into a tube shape and then weld the gap to become steel pipe. Because of the different forming and welding methods used, different methods of producing welded steel pipe are formed.
Seamless steel tubes are mainly produced by hot rolling. The extrusion method is mainly used in the production of difficult to perforate low plastic high alloy steel pipe or special-shaped steel pipe and composite metal pipe. The hot rolled pipe can be processed into small diameter and thin wall steel pipe by cold rolling and cold drawing. The welding steel pipe process is simple, the production efficiency is high, the cost is low, the product variety expands day by day. Main production methods of seamless and welded steel tubes are shown in Table 1 and 2.

Table 1: Seamless and welded steel tubes production methods

Production methods
The basic process
Wear a hole
Pipe mill
On the automatic pipe rolling line
Round tube billet in two high punch
On the perforation
Two high rolling in back feed roll
Pipe machine with short end rolling
On the cycle pipe rolling line
Round steel ingot or tube billet in two – roll type
Perforating machine;
Square or polygonal ingot in water
Press punch
The period of the pass with variable section
Pipe rolling machine with long mandrel
In continuous tube rolling mill
The rolling
Round tube billet in three or two high type
Perforating machine;
Continuous casting billet or ingot in two
Punch on roller pressure punch
Long on 7 ~ 9 continuous pipe mills
Mandrel rolling;
Attached tension reducing machine
On the three high pipe rolling set
Round tube billet in two high punch
The perforation;
Continuous casting billet in three roller punch
On the perforation
Strip length on three high skew mill
Mandrel rolling
On the extension pipe rolling line
Punch a hole in a two-roll punch
In a disc – shaped tension guide roller
Two high skew mill with long mandrel
In the planetary type pipe rolling set
The rolling
Adopt casting hollow tube billet
Rolling on a planetary pipe mill

Table 2: Seamless and welded steel tubes production methods

Production methods
The basic process
Wear a hole
Pipe mill
Pipe jacking method
Cup hair on a hydraulic press
Jacking on the pipe jacking machine
Squeezing method
The tube blank is heated on the extruder
Can continue rolling or drawing
Cold rolling method
Use hot rolling tube material in cold rolling mill
The rolling
Cold drawn method
Use hot rolled or cold rolled tube material in cold
Drawing machine drawing system
The furnace
The chain furnace welding
The heated tube blank passes through the welded tube mold
The molding
Simultaneous forming welding
Continuous furnace welding
The heated tube billet is formed in roller form
Welding machine bending molding
Simultaneous forming welding
Resistance welding
Continuous bending on roller forming machine
Curved shape
Weld on resistance welding pipe machine
Arc welding
To press or form on a press
On a roll bending machine
Type B (straight seam), connected on the forming machine
Continuous bending forming (spiral seam)
Weld on submerged arc automatic pipe welder
Pick up
Inductive welding
Continuous bending on roller forming machine
Curved shape
Weld on inductance welding machine

Specification of spiral steel pipe

(1) Specification: the specification requirements of spiral steel pipe should be listed in the import and export trade contract. Generally, it should include the standard brand number (type code), the nominal diameter of the steel bar, the nominal weight (mass), the specified length and the allowable value of the above indicators. Our country standard recommends spiral steel pipe series with nominal diameters of 8, 10, 12, 16, 20, 40mm. Supply length is divided into fixed length and double length. China’s export rebar length selection range is 6 ~ 12m, Japanese rebar length selection range is 3.5 – 10m.

(2) Appearance quality: 

  • ① Surface quality. The surface quality of rebar is stipulated in the relevant standards, requiring that the end should be cut flat and straight, the surface shall not have cracks, scarring and folding, and there shall be no harmful defects in use; 
  • Allowable value of dimension deviation. The bending degree of rebar and the requirements of steel bar geometry are specified in the relevant standards. As stipulated in Chinese standards, the bending degree of straight bar is not greater than 6mm/m, and the total bending degree is not greater than 0.6% of the total length of bar.

Related terms of steel pipe

Size of steel pipe

  • A. Nominal size: the nominal size stipulated in the standard, the ideal size desired by users and manufacturers, and the order size indicated in the contract.
  • B. Actual size: the actual size obtained in the production process, which is usually greater than or less than the nominal size. This phenomenon of greater or less than the nominal size is called deviation.
  • C. Meter weight: weight per meter =0.02466* wall thickness * (outer diameter – wall thickness)

Deviation and tolerance of steel pipe

  • A. Deviation: in the production process, because the actual size is difficult to meet the requirements of the nominal size, that is, often greater than or less than the nominal size, so the standard stipulates that there is A difference between the actual size and the nominal size. A positive difference is called a positive bias, and a negative difference is called a negative bias.
  • B. Tolerance: the absolute sum of positive and negative deviation values specified in the standard is called tolerance, also called “tolerance zone”.
Deviation is directional, that is, “positive” or “negative”; Tolerances are non-directional, so it is wrong to call the value of the deviation a “positive tolerance” or a “negative tolerance”.

Delivery length of steel pipe

Delivery length is also called customer required length or contract length. The standard has the following provisions on delivery length:
A. Ordinary length (also known as irregular length) : where the length is within the standard length range and there is no fixed length requirements, are called ordinary length. For example, structural pipe standards: hot rolled (extruded, expanded) steel pipe 3000mm ~ 12000mm; Cold-drawn (rolled) steel pipe 2000mm ~ 10500mm.
B. Fixed length: the fixed length shall be within the normal length range and is a fixed length specified in the contract. But in practice, it is impossible to cut absolute length, so the standard stipulates the allowable positive deviation value for the length of definite length.
The structural pipe standard is:
The yield of fixed length pipe decreases more than that of normal length pipe, so it is reasonable for the manufacturer to raise the price. Add price range each enterprise is not consistent, add price 10% or so on base price foundation commonly.
C. Length of multiples: the length of multiples shall be within the normal length range, and the single length and the multiple of the total length shall be indicated in the contract (e.g. 3000mm×3, i.e. 3000mm 3x, with a total length of 9000mm). In practice, the allowable positive deviation of 20mm should be added to the total length, plus the incision allowance should be left for each single ruler length. Take the structural pipe as an example, the specified incision allowance: outer diameter ≤159mm is 5 ~ 10mm; Outer diameter >159mm is 10 – 15mm.
If there is no length deviation and cutting allowance in the standard, it shall be indicated in the contract through negotiation between the supply and demand parties. Double ruler length is the same as fixed ruler length, which will greatly reduce the yield of production enterprises. Therefore, it is reasonable for the production enterprises to raise the price, which is basically the same as the fixed ruler length.
D. Range length: the range length is within the usual range. If the user requires a fixed range length, it shall be indicated in the contract.
For example, the length ranges from 3000 mm to 12000mm, and the length ranges from 6000 mm to 8000mm or 8000mm to 10000mm.
It can be seen that the range length is more relaxed than fixed length and multiple length, but it is much stricter than the usual length, which will also reduce the yield of production enterprises. Because this production enterprise puts forward add price is reasonable, its add price range is in base price commonly add price 4% left and right sides.

Uneven wall thickness of steel pipe

Steel tube wall thickness can not be the same everywhere, there is an objective phenomenon of unequal wall thickness in its cross section and longitudinal tube body, that is, uneven wall thickness. In order to control this unevenness, the allowable index of wall thickness unevenness is stipulated in some steel pipe standards. Generally, it is not more than 87.5% of wall thickness tolerance (implemented after negotiation between the supply and demand parties).

Ovality of steel pipe

The phenomenon of unequal outer diameters exists in the cross section of circular steel pipe, that is, the difference between the maximum outer diameter and the minimum outer diameter is ellipticity (or unroundness). In order to control the ovality, some steel pipe standards stipulate the allowable index of the ovality, which is generally not more than 80% of the outer diameter tolerance (implemented after negotiation between the supply and demand parties).

Bending of steel pipe

The length of the steel pipe is curvilinear, and its curvilinear degree is called bending degree. The bending specified in the standard is generally divided into the following two kinds:
A. Local bending: measure the maximum bending point of the steel pipe with A one-meter ruler and measure its chord height (mm), which is the value of local bending. The unit is mm/m and the expression method is as follows: 2.5mm/m. This method also applies to pipe end bending.
B. Total bending of the whole length: measure the maximum chord height (mm) at the bending point of the steel pipe with a thin rope, and then convert the percentage of length (in meters) to the total bending of the length direction of the steel pipe.

For example: the length of steel pipe is 8m, and the maximum chord height measured is 30mm, then the full length bending of the pipe should be 0.03÷8m×100%=0.375%.

Types of steel pipes

Welded steel pipe

Welded steel pipe, also known as welded pipe, is made of steel plate or steel belt after crimping forming welded steel pipe. Welded steel pipe production process is simple, high production efficiency, variety of specifications, less investment in equipment, but the general strength is lower than seamless steel pipe. Since the 1930s, with the rapid development of high quality strip rolling production and the progress of welding and inspection technology, the quality of weld is constantly improving, the variety and specifications of welded steel pipe are increasing day by day, and replaced the seamless steel pipe in more and more fields. Welded steel pipe is divided into straight seam welded pipe and spiral welded pipe according to the form of weld.
Straight seam welded pipe production process is simple, high production efficiency, low cost, rapid development. The strength of the spiral welded pipe is generally higher than that of the straight seam welded pipe, and the welded pipe with larger diameter can be produced with a narrower blank, and the welded pipe with different diameter can also be produced with a blank of the same width. But compared with the straight seam pipe of the same length, the weld length increases by 30~100%, and the production speed is lower. Therefore, small diameter welded pipe mostly use straight seam welding, large diameter welded pipe mostly use spiral welding.
Low pressure fluid transport welded steel pipe (GB/T3091) is also known as general welded pipe, commonly known as black pipe. It is a welded steel pipe used for conveying water, gas, air, oil, heating steam and other general lower pressure fluids and other purposes. The wall thickness of steel pipe is divided into ordinary steel pipe and thickened steel pipe. Pipe end form is divided into non – rebar steel tube (light tube) and with rebar steel tube. The welded steel pipe used for low pressure fluid transportation is mainly used as the original pipe of galvanized welded steel pipe used for low pressure fluid transportation.
  • 1. Galvanized welded steel pipe (GB/T3091) for low pressure fluid transportation, also known as galvanized electric welded steel pipe, commonly known as white pipe. It is a hot dip galvanized welded (furnace welding or electric welding) steel pipe used for conveying water, gas, air oil, heating steam, warm water and other general low pressure fluids or other purposes. The wall thickness of steel pipe is divided into ordinary galvanized steel pipe and thickened galvanized steel pipe. The end of the pipe is divided into galvanized steel pipe without thread and galvanized steel pipe with thread. Steel tube specifications are indicated by nominal diameter (mm), which is an approximation of the inner diameter. Traditionally, it is usually expressed in inches, such as 1/2, 3/4, 1, 2, etc.
  • Ordinary carbon steel wire bushing (YB/T5305) is used to protect the wire in industrial and civil buildings, installation machinery and equipment and other electrical installation projects.
  • 3. Straight seam electric welded steel pipe (GB/T13793) is a steel pipe with longitudinally parallel welds to the steel pipe. Used for general structure, usually divided into metric welded steel pipe, welded thin-wall pipe and so on.
  • 4. Spiral seam submerged arc welded steel pipe (SY/T5037-2000) for pressure fluid transportation is a spiral seam steel pipe used for pressure fluid transportation, which is made of hot rolled steel strip as tube blank, often formed at warm temperature and welded by double-sided submerged arc welding method. The steel pipe has strong bearing capacity and good welding performance. It is safe and reliable to use after all kinds of strict scientific inspection and testing. Large diameter steel pipe, high transmission efficiency, and can save the investment of pipeline laying. Mainly used for conveying oil and natural gas pipelines.
  • 5. Spiral seam high frequency welded steel pipe (SY/T5038) is a kind of spiral seam high frequency welded steel pipe used for pressure fluid transportation, which is made of hot rolled steel strip as tube blank, often warm spiral shaped and welded by high frequency lap welding method. The steel pipe has strong bearing capacity and good plasticity, which is convenient for welding and processing. After all kinds of strict and scientific inspection and testing, the use of safe and reliable, large diameter steel pipe, high transmission efficiency, and can save the investment of pipeline laying. It is mainly used for laying pipelines for conveying oil and natural gas.
  • 7. General low-pressure fluid transport spiral seam high-frequency welded steel pipe (SY/T5039) is a hot rolled steel strip as a tube billet, often warm spiral forming, high frequency lap welding welding method for general low-pressure fluid transport spiral seam high-frequency welded steel pipe.
  • 8. Spiral welded steel pipe for pile (SY/T5768) is made of hot rolled steel strip as tube blank, often warm spiral forming, double-sided submerged arc welding or high-frequency welding, used for civil construction structure, wharf, bridge and other foundation pile steel pipe.

Seamless steel pipe

Seamless steel pipe is a kind of long steel with hollow section and no joint around. Seamless steel pipe with hollow section, can be used for conveying fluid pipeline, such as conveying oil, natural gas, gas, water and some solid material pipeline. Compared with solid steel such as round steel, seamless steel tube has the same bending and torsional strength and lighter weight. It is a kind of economic cross-section steel, widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipe, automobile drive shaft, bicycle frame and steel scaffolding used in construction. Using seamless steel pipe to manufacture ring parts can improve material utilization rate, simplify manufacturing process, save material and processing time, such as rolling bearing ring, jack sleeve, etc., widely used steel pipe to manufacture. Steel pipe or all kinds of conventional weapons indispensable material, gun barrel, barrel and so on to make steel pipe. Steel pipe can be divided into round pipe and special-shaped pipe according to the shape of cross-sectional area. Since the area of a circle is maximum with equal perimeters, more fluid can be transported with a circular tube. In addition, the annular section under internal or external radial pressure, the force is more uniform, so the vast majority of steel tubes are round. However, round tube also has certain limitations, such as under the condition of plane bending, round tube is not as good as square, rectangular tube bending strength, some agricultural machinery framework, steel and wood furniture, such as commonly used square, rectangular tube. According to the different uses also need to have other section shape of special-shaped steel pipe.

  • 1. Seamless steel pipe for structure (GB/T8162) is used for general structure and mechanical structure of seamless steel pipe.
  • 2. Seamless steel pipe for fluid transportation (GB/T12771) is used for conveying water, oil, gas and other fluids in general seamless steel pipe.
  • 3. Seamless steel pipe for low and medium pressure boiler (GB/T3087) is high quality carbon structural steel hot-rolled and cold-drawn (rolled) seamless steel pipe used for manufacturing all kinds of super-heated steam pipe, boiling water pipe of low and medium pressure boiler and super-heated steam pipe, big smoke pipe, small smoke pipe and arch brick pipe for locomotive boiler.
  • 4. Seamless steel tube for high pressure boiler (GB5310) is used for manufacturing high pressure and above pressure water tube boiler heating surface with high quality carbon steel, alloy steel and stainless heat resistant steel seamless steel tube.
  • 5. High pressure seamless steel pipe for chemical fertilizer equipment (GB6479) is suitable for the working temperature of -40~400℃, the working pressure of 10~30Ma chemical equipment and pipes of high quality carbon structural steel and alloy steel seamless steel pipe.
  • 6. Seamless steel tube for petroleum cracking (GB9948) is suitable for furnace tube, heat exchanger and pipeline seamless steel tube for petroleum refinery.
  • 7. Steel pipe for geological drilling (YB235) is used for core drilling by geological department, which can be divided into drill pipe, drill collar, core pipe, casing pipe and precipitation pipe according to its use.
  • 8. Seamless steel pipe for diamond core drilling (GB/T3423) is used for diamond core drilling drill pipe, core rod, casing seamless steel pipe.
  • 9. Oil drilling pipe (YB528) is a seamless steel pipe used for both ends of oil drilling thickening inside or outside. Steel pipe can be divided into two kinds: turning wire and non-turning wire. Turning wire pipe is connected with joint, and non-turning wire pipe is connected with tool joint by butt welding method.
  • 10. Shipboard carbon steel seamless steel pipe (GB5312) is a seamless carbon steel pipe used in the manufacture of class I pressure pipe system, class II pressure pipe system, boiler and superheater. The working temperature of seamless carbon steel pipe wall shall not exceed 450℃, and that of seamless alloy steel pipe wall shall exceed 450℃.
  • 11. Seamless steel pipe for automobile axle bushing pipe (GB3088) is a high quality carbon structural steel and alloy structural steel hot rolled seamless steel pipe for automobile axle bushing pipe and drive axle housing shaft pipe.
  • 12. High pressure tubing for diesel engine (GB3093) is a seamless cold drawn steel tube used in the manufacture of high pressure pipe for diesel engine injection system.
  • 13. Seamless steel tubes with precision inner diameter for hydraulic and pneumatic cylinders (GB8713) are cold-drawn or cold-rolled precision seamless steel tubes with precision inner diameter for the manufacture of hydraulic and pneumatic cylinders.
  • 14. Cold drawn or cold rolled precision seamless steel pipe (GB3639) is used for mechanical structure, hydraulic equipment with high dimensional accuracy and good surface finish.
  • 15. Stainless steel seamless steel pipe for structure (GB/T14975) is a hot-rolled (extruding, expanding) and cold-drawn (rolling) seamless steel pipe made of stainless steel, which is widely used in chemical, petroleum, textile, medical, food, machinery and other industries for corrosion resistant pipes and structural parts and parts.
  • 16. Seamless stainless steel tubes for fluid transportation (GB/T14976) are hot-rolled (extruded, expanded) and cold-drawn (rolled) seamless steel tubes made of stainless steel for fluid transportation.
  • 17. Special-shaped seamless steel pipe is the general term for seamless steel pipe with other cross section shapes except round pipe. According to the different shape and size of the steel pipe section, it can be divided into equal wall thickness special-shaped seamless steel pipe (code D), unequal wall thickness special-shaped seamless steel pipe (code BD), variable diameter special-shaped seamless steel pipe (code BJ). Special-shaped seamless steel tubes are widely used in various structural parts, tools and machinery parts. Compared with the round tube, shaped tube generally has a larger moment of inertia and section modulus, has a larger bending and torsion resistance, can greatly reduce the weight of the structure, save steel.

Where to buy steel pipe

Obviously, the intended use (e.g., petrochemical oil and gas pipelines versus water plant transmission lines) determines which pipe to purchase and where to obtain it. However, this is also where steel pipe manufacturers consider other factors in their steel pipe production parameters, including
Environmental conditions, including humidity, heat, acidity, pressure – all of which can affect the performance of the steel pipe.
1. Chemical composition of steel pipe: The chemical composition of steel pipe is one of the most important factors affecting the performance of seamless steel pipe, and is the main basis for developing the parameters of the pipe rolling process and the parameters of the steel pipe heat treatment process.

  • a. Alloying elements: intentionally added, according to the use;
  • b. Residual elements: steelmaking brought in, appropriate control;
  • c. Harmful elements: strictly controlled (As, Sn, Sb, Bi, Pb), gas (N, H, O).

Off-furnace refining or electroslag remelting: improve the homogeneity of the chemical composition of the steel and the purity of the steel, reduce the non-metallic inclusions in the pipe billet and improve its distribution pattern.
2. Geometric accuracy and shape of steel pipe
a. Outer diameter accuracy of steel pipe: depends on the method of fixing (reducing) diameter, equipment operation, process system, etc.
Allowable deviation of outer diameter: δ = (D – Di) / Di × 100%
In the formula.

  • D: maximum or minimum outside diameter mm;
  • Di: nominal outside diameter mm.

b. Steel pipe wall thickness accuracy: with the heating quality of the billet, the process design parameters and adjustment parameters of the deformation process, the quality of the tool and its lubrication quality, etc.
Wall thickness allowable deviation: ρ = (S – Si) / Si × 100%
In the formula.

  • S: the maximum or minimum wall thickness in the cross-section;
  • Si: nominal wall thickness mm.

c. The ellipticity of the steel pipe: the extent of the steel pipe is not round.
d. Length of steel pipe: normal length, fixed (times) the length, length allowable deviation
e. Steel pipe curvature: the curvature of the steel pipe: the curvature of each meter of steel pipe length, the curvature of the full length of the steel pipe
f. Steel pipe end tangency: steel pipe end and the degree of inclination of the steel pipe cross-section
g. Steel pipe end bevel angle and blunt edge
3. Surface quality of steel pipe: surface finish requirements

  • a. Dangerous defects: cracks, internal folding, external folding, rolling breakage, delamination, scarring, pulling concave, convex package, etc.
  • b. General defects: pockmarks, green lines, scratches, bruises, minor internal and external straight path, roll marks, etc.


  • ① Brought about by surface defects or internal defects of pipe billets.
  • ② Produced during the production process, such as incorrect design of rolling process parameters, mold surface is not smooth, poor lubrication conditions, hole design and adjustment is not reasonable.
  • ③ Pipe billet (steel pipe) in the heating and rolling, heat treatment and straightening process, if the heating temperature control is improper, uneven deformation, heating and cooling rate is not reasonable or straightening deformation is too large and excessive residual stress, then it may also lead to surface cracks in the steel pipe.

4. The physical and chemical properties of steel pipe: room temperature mechanical properties, high temperature mechanical properties, low temperature properties, corrosion resistance. The physical and chemical properties of the steel pipe depends mainly on the chemical composition of the steel, the organizational structure and purity of the steel and the steel heat treatment.
5. Process performance of steel pipe: flattening, flaring, crimping, bending, welding, etc.
6. Steel pipe metallographic organization: low times the organization (macro), high times the organization (micro) M, B, P, F, A, S.
7. Special requirements of steel pipe: contract annexes, technical agreements.
Last, but not least, the price of steel pipe plays a very important role when purchasing steel pipe. However, when you start buying steel pipes, do not make pricing the main deciding factor. The prices listed above may not quite match the other specifications.
Choose your steel pipe supplier carefully. Purchasing inventory from relatively unknown suppliers may harm your project. Yaang, as a steel pipe manufacturer, specializes in manufacturing and supplying steel pipes: thin wall/thick wall seamless pipes, thin wall/thick wall welded pipes, precision seamless pipes, small diameter seamless pipes, offering a wide range of specifications and materials, with a large inventory and experience in customizing services according to customer requirements.

Source: China Steel Pipes Manufacturer – Yaang Pipe Industry Co., Limited (www.metallicsteel.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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