What is seamless steel pipe?

What is seamless steel pipe?

The seamless steel pipe is a steel pipe made of a single piece of metal with no joints on the surface, called a seamless steel pipe. According to the production method, the seamless pipe is divided into a hot rolled pipe, a cold rolled pipe, a cold drawn pipe, an extruded pipe, a top pipe, and the like. According to the shape of the section, the seamless steel tube is divided into two types: a circular shape and a special shape. The shaped tube has a plurality of complicated shapes such as a square shape, an elliptical shape, a triangular shape, a hexagonal shape, a melon shape, a star shape, and a winged tube. The maximum diameter is 650mm and the minimum diameter is 0.3mm. Depending on the application, there are thick-walled tubes and thin-walled tubes. Seamless steel pipes are mainly used as petroleum geological drilling pipes, cracking pipes for petrochemicals, boiler tubes, bearing tubes, and high-precision structural steel tubes for automobiles, tractors, and aviation.

Use of seamless steel pipe

Seamless steel tubes are used in a wide range of applications. 

  • 1. The general-purpose seamless steel pipe is rolled from ordinary carbon structural steel, low-alloy structural steel or alloy structural steel, and has the largest output, and is mainly used as a pipe or structural component for conveying fluid. .
  • 2. According to the use of three types of supply: a, according to chemical composition and mechanical properties; b, according to mechanical properties; c, according to water pressure test supply. Steel pipes supplied in categories a and b, if used to withstand liquid pressure, are also subjected to hydrostatic testing. 
  • 3. Special-purpose seamless pipes include boiler seamless pipes, chemical power, geological seamless steel pipes and petroleum seamless pipes.

Seamless steel tubes have hollow sections and are used in large quantities as pipelines for transporting fluids, such as pipelines for transporting petroleum, natural gas, gas, water and certain solid materials. Compared with solid steel such as round steel, the steel pipe has a lighter weight when it has the same bending and torsional strength, and is an economical section steel.
Widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipes, automotive drive shafts, bicycle frames and steel scaffolding used in construction, such as steel scaffolding, to make ring parts, improve material utilization, simplify manufacturing processes, save materials and processing In working hours, steel pipes have been widely used for manufacturing.

Seamless steel pipe quality requirements in production

1. Chemical composition
In order to improve the uniformity of chemical composition and the purity of steel, reduce the non-metallic inclusions of the tube and improve its distribution, often use the furnace refining equipment for the molten steel Refining, and even the use of electroslag furnace on the tube for remelting refining.
2. Dimensional accuracy and shape
The geometrical dimensions of the seamless steel pipe mainly include the outer diameter of the steel pipe, the wall thickness, the ellipticity, the length, the curvature, the cutting angle of the pipe end, the angle of the groove and the cross section of the blunt edge and the opposite.
3. The surface quality
The standard specifies the “smooth surface” requirements of seamless steel tubes. Common defects are: cracks, hairlines, inside the fold, outside the fold, rolling, within the straight, outside the straight, from the layer, scarring, pits, convex package, Ma Hang (Ma face), scratches (scratches) , Internal spiral, outer spiral, green line, concave, roll and so on. Which is broken, broken, broken, rolling, from the layer, scarring, pits, convex hull and other dangerous defects; steel plum, green line, abrasions, slightly inside and outside the straight, slightly inside and outside the spiral, Concave, roll for the general defects.
4. Physical and chemical properties
Including the mechanical properties at room temperature and mechanical properties at a certain temperature (thermal and low temperature performance) and corrosion resistance (such as oxidation, anti-acid, anti-acid and other properties) under normal circumstances depends on the chemical composition of steel, The organizational properties and the purity of the steel and the heat treatment of steel. In some cases, the rolling temperature and deformation of the steel pipe will also have an impact on the performance of the pipe.

Production process of seamless steel pipe

Main production process of hot-rolled seamless steel pipe (△ main inspection process):

Hot rolled seamless steel pipe deformed processes - What is seamless steel pipe?
Tube blank preparation and inspection △→Tube heating→Perforation→Rolling tube→Steel tube reheating→Fixed (reduced) diameter→heat treatment △→finished tube straightening→finishing→inspection △(non-destructive, physicochemical, Taiwan inspection)→Warehousing

Hot-rolled seamless steel pipe defects

Hot rolled seamless steel pipe - What is seamless steel pipe?

Hot-rolled seamless steel pipe production base deformation process can be summarized as three stages: perforation, extension and finishing.
a. Inner surface defects

  • 1. An inner flap: presenting a straight line, a spiral or a semi-helical sawtooth defect on the inner surface of the steel pipe.
  • 2. inside scarring: scars in the steel pipe inner surface, generally easily peel off. 
  • 3. Warping: a straight line or intermittent small nail-like tilt leather. Often seen in the capillary head, and easy to peel. 
  • 4. inside straights: a straight shape scratch with a certain width and depth. 
  • 5. inner edge: a straight shape protrusion with a certain width and depth. 
  • 6. inner drum kits: a super and regular protrusion and outer surface is not damaged. 
  • 7. Pull pits: a regular or non-regular pit and the outer surface without damage. 
  • 8. internal thread (this defect produced only at Accel units): spiral traces often seen in the thin-walled tube surface, and there are obvious rugged feelings.

b. outer surface defects

  • 1. An outer fold: the outer surface of the pipe presents a layered folded spiral. 
  • 2. separation: presenting a spiral shape or blocky delamination and cracking. 
  • 3. external scarring: scars on the outer surface. 
  • 4. pock surface: steel surface showed uneven pits. 
  • 5. Line: a substantially symmetrical or asymmetrical linear rolling marks. 
  • 6. Hairline: a continuous or discontinuous hairy fine lines. 
  • 7. net cracks: scaly small cracks. 
  • 8. scratches: linear or spiral-shaped groove-like defects. 
  • 9. touch deflated: the outer surface of the steel pipe rendered in a convex outer concave phenomenon, and pipe wall thickness without injury. 
  • 10. bumps: collision irregular scars. 
  • 11. straightening recess: steel spiral concave outer surface. 
  • 12. rolled off: longitudinally local or long presentation in a convex outer concave folds, the outer surface into strips depression. 
  • 13. crack:opened the rupture surface phenomenon, much produced in the thin-walled tube.

Features of Hot-rolled Seamless Steel Pipe

With respect to hot-rolled seamless rolled seamless steel pipe is concerned, the cold-rolled seamless steel pipe is carried out at a temperature below the recrystallization rolling, but the hot-rolled seamless pipe is rolled in the recrystallization temperature or more carried out.


Ingot casting can destroy tissue, grain refinement of steel, and eliminate defects microstructure, so that the steel dense tissue, the mechanical properties are improved. This improvement mainly reflected in the rolling direction, so that the steel is no longer certain extent isotropic body; forming bubbles when pouring, cracks and loose, can also be welded together under high temperature and pressure.


  • 1. The hot-rolled steel pipe manufacturers after hot-rolled seamless steel inside the non-metallic inclusions (mainly sulphide and oxide, as well as silicate) is pressed into the sheet, stratification (mezzanine) phenomenon. Layered in the thickness direction so that the steel tension performance deteriorated significantly, and there may be an interlayer tear weld shrinkage. Weld shrinkage induced local strain reaches the yield point strain often several times larger than the load caused by the strain;
  • 2. Residual stresses caused by uneven cooling. The residual stress in the absence of external force internal self-equilibrium stress, hot-rolled steel has a variety of sections such residual stress, the greater the general steel cross-sectional dimension, the greater the residual stress. Although the residual stress is self-balanced, but still has some influence on the performance of the steel members under loads. Aspects such as deformation, stability, fatigue, etc. are likely to have an adverse effect.
  • 3. Hot-rolled steel products, poor control of the thickness and width edge in this regard. We are familiar with thermal expansion and contraction, since the beginning of the hot rolling out even the length, thickness are standard, and finally cooled or there will be some negative difference, this negative differential edge width wider, more obvious as the thickness performance. So for large steel, steel edge for width, thickness, length, angle, and no law requires too precise edges.

Heat treatment common quality defects of seamless steel pipe

Seamless steel pipe in the heat treatment, there is thermal stress and tissue stress, this internal stress can be superimposed or partially offset, is complex and varied, because it can with the heating temperature, heating speed, cooling, cooling speed, parts shape and size changes, so heat treatment deformation is inevitable. 
Seamless steel pipe in the heat treatment process of mechanical collision will also cause deformation of parts, but this deformation can be improved with the operation to reduce and avoid.
1. Surface decarburization
Seamless steel pipe in the heat treatment process, if it is heated in the oxidizing medium, the surface will be the oxidation of parts of the surface to reduce the quality of carbon, resulting in surface decarburization. The depth of the surface decarburization layer exceeds the final processing of the amount will make the parts scrapped. Determination of surface decarburization depth The metallographic method and microhardness method can be used in the metallographic examination. The surface layer of micro-hardness distribution curve measurement method shall prevail, to do arbitration criteria.
2. Soft points
Due to lack of heating, poor cooling, quenching improper operation and other reasons caused by seamless steel pipe surface hardness is not enough phenomenon known as quenching soft point. It can cause surface abrasion and fatigue strength as a result of surface decarburization.

Cold rolling (drawing) seamless steel pipe main production process:

Cold drawn seamless steel tube process - What is seamless steel pipe?
Blank preparation → pickling lubrication → cold rolling (pull) → heat treatment → straightening → finishing → inspection
The production process of general seamless steel pipe can be divided into cold drawing and hot rolling. The production process of cold rolled seamless steel pipe is generally more complicated than hot rolling. The pipe blank must first be rolled in three rolls. The sizing test, if the surface does not respond to the crack, the round tube is cut by a cutter and cut into a blank having a length of about one meter. Then enter the annealing process, the acidification should be acid-washed with acid liquid. When pickling, pay attention to whether there is a large amount of foaming on the surface. If there is a large amount of foaming, the quality of the steel pipe will not reach the corresponding standard. The appearance of cold-rolled seamless steel pipe is shorter than that of hot-rolled seamless steel pipe. The wall thickness of cold-rolled seamless steel pipe is generally smaller than that of hot-rolled seamless steel pipe, but the surface looks brighter than thick-walled seamless steel pipe, and the surface is not too More rough, not too many burrs in the caliber.
The delivery status of the hot-rolled seamless steel pipe is generally delivered after the heat treatment in the hot rolled state. After the quality inspection, the hot-rolled seamless steel pipe is subjected to strict manual selection by the staff. After the quality inspection, the surface is oiled, followed by multiple cold drawing experiments, and the perforation experiment is performed after the hot rolling process. If the perforation is too large, straightening correction is required. After straightening, the conveyor is sent to the flaw detector for flaw detection experiments. Finally, the label is placed, the specifications are arranged, and then placed in the warehouse.
Round tube billet → heating → perforation → three-roll cross-rolling, continuous rolling or extrusion → pipe removal → sizing (or reducing diameter) → cooling → straightening → hydraulic test (or flaw detection) → marking → storage seamless steel pipe The steel tube or the solid tube blank is made into a capillary tube by perforation, and then is formed by hot rolling, cold rolling or cold drawing. The specifications of the seamless steel pipe are expressed by the outer diameter * wall thickness in millimeters.
The outer diameter of hot-rolled seamless pipe is generally larger than 32mm, the wall thickness is 2.5-200mm, the outer diameter of cold-rolled seamless steel pipe can reach 6mm, the wall thickness can be 0.25mm, the outer diameter of thin-walled pipe can reach 5mm, the wall thickness is less than 0.25mm, cold Rolling is more accurate than hot rolling.
Generally, the seamless steel pipe is formed by hot-rolled or cold-rolled low-alloy structural steels such as 10, 20, 30, 35, 45, etc., such as 16Mn and 5MnV, or 40Cr, 30CrMnSi, 45Mn2, 40MnB, and the like. Seamless pipes made of low carbon steel such as 10 and 20 are mainly used for fluid conveying pipes. 45, 40Cr and other medium carbon steel seamless pipes are used to make mechanical parts, such as the force parts of automobiles and tractors. Generally, seamless steel pipes are required to ensure strength and flattening test. The hot rolled steel pipe is delivered in a hot rolled state or a heat treated state; the cold rolling is delivered in a heat treated state.
Hot rolling, as the name suggests, has a high temperature of the rolled piece, so the deformation resistance is small and a large amount of deformation can be achieved. Taking the rolling of the steel sheet as an example, the thickness of the continuous casting blank is generally about 230 mm, and after rough rolling and finish rolling, the final thickness is 1 to 20 mm. At the same time, due to the small width-to-thickness ratio of the steel plate, the dimensional accuracy requirement is relatively low, and the shape problem is not easy to occur, and the convexity is mainly controlled. For the organization, it is generally achieved by controlled rolling and controlled cooling, that is, controlling the rolling temperature and finishing temperature of the finishing rolling. Round billet → heating → perforation → heading → annealing → pickling → oiling (copper plating) → Multi-pass cold drawing (cold rolling) → blank tube → heat treatment → straightening → hydraulic pressure test (inspection) → marking → storage.

General process of cold drawing

A considerable proportion of the seamless tubes and pipes manufactured through the cold roll piercing technology undergo subsequent cold forming.
The principal reasons behind cold drawing are:

Cold drawn seamless steel tube process

seamless process colddraw - What is seamless steel pipe?

Cold drawn steel tube is with hot-rolled steel coil as raw material, and tandem cold rolling pickled to remove oxide scale, its finished rolling hard roll, rolling hard volumes due to the continuous cold deformation caused by cold hardening strength, hardness increased indicators declined tough plastic, stamping performance will deteriorate, which can only be used for simple deformation of the parts.

Cold formed steel
Cold-formed steel refers to the use plates or strip bent in a cold state of the various cross-sectional shape of the finished steel. Cold-formed steel is an economical lightweight thin-walled steel cross-section, also called cold-formed steel profiles. Bending section steel is the main material of light steel structure. It has a hot rolling can produce all kinds of thin, reasonable shape and complex cross section.
Hot forging and cold forging
Hot forging means forging blank metal above the recrystallization temperature carried out.
Cold forming performance
Cold forming is not performed in the case of heating the material for punching, bending, stretching and other processing methods. Cold forming processes are cold heading, cold rolled, forging and so on.
The advantages of cold-rolled tube
Cold-rolled tube refers to steel product that is through cold drawing, cold-formed, cold drawn, cold plate or strip processed at room temperature.
Annealing and quenching of cold drawn steel
The annealing of cold drawn steel is commonly used in the production of preliminary heat treatment process. The annealing of cold drawn steel is commonly used in the production of preliminary heat treatment process.
Application of ASTM A179 Cold Drawn Seamless Tubes
ASTM A179 cold drawn seamless carbon steel pipe is mainly used in various sectors of the metal structure facilities, mainly after the rust of steel pieces immersed in 440 – 460 ℃ melting zinc solution, so that the steel surface attached to the zinc layer, which play a preservative purpose.
Weld cold crack
Welded joints cooled to a lower temperature ( for steel, in the martensitic transformation start temperature Ms less ) generated by the weld cracking.

Heat Treatment of Cold Drawn Seamless Steel Pipe

Cold drawn seamless tube is used for high dimensional accuracy mechanical structure, hydraulic equipment and good surface finish cold drawn or cold rolled precision seamless steel tubes. High-precision drawing denotes the outer diameter size precision (tolerance) strict and external surface finish, roundness, straightness good thickness uniformity. 

Heat treatment of cold drawn seamless steel pipe:

  • (1). Cold drawn steel annealing: refers to the metal material is heated to the appropriate temperature, to maintain a certain time, and then slowly cooled heat treatment process. Common annealing process are: recrystallization annealing, stress relieving, ball annealing, fully annealed and so on. The purpose of annealing: mainly to reduce the hardness of the metal material, to improve the plasticity, or cutting processing to Liqie pressure processing, reduce the residual stress and improve the uniformity of microstructure and composition, heat treatment, after possible or tissue preparation. 
  • (2). Cold drawn steel normalizing: refers to the heating of steel or steel to Ac3 or Acm (the critical temperature of steel) over 30 ~ 50 ℃, after an appropriate time to keep cool in still air in the heat treatment process . The purpose of normalizing: mainly to improve the mechanical properties of low carbon steel to improve machinability, grain refinement, elimination of tissue defects, prepare for the heat treatment, after tissue preparation. 
  • (3). Cold drawn steel hardening: refers to the heated steel Ac3 or Ac1 (lower critical temperature of steel) above a certain temperature for a certain time, then the appropriate cooling rate to obtain martensite (or shellfish Heat Treatment’s body) tissue. Common salt bath quenching process has hardened, martensitic quenching, Austempering, surface hardening and partial quenching. Quenching purpose: to make the steel needed to obtain martensite improve workpiece hardness, strength and wear resistance, heat treatment, after prepare for the organization and preparation. 
  • (4). Cold drawn steel tempered: that after hardened steel, and then heated to a temperature below Ac1, holding a certain time, and then cooled to room temperature, the heat treatment process. Common tempering process are: tempering, tempering, tempering and multiple tempering. The purpose of tempering: mainly steel eliminate stress produced during quenching, the steel having high hardness and wear resistance, but also has the required plasticity and toughness. 
  • (5). Cold drawn steel quenched: refers to the quenching and tempering of steel or composite steel heat treatment process. Used in quenching said steel quenched and tempered steel. It generally refers to the carbon structure of carbon steel and alloy steel. 
  • (6). Cold drawn steel chemical treatment: refers to the metal or alloy workpieces placed in a constant temperature of the active medium heat, so that one or several elements into its surface to change its chemical composition, microstructure and properties of the heat treatment process. Common chemical heat treatment process are: carburizing, nitriding, carbonitriding, aluminized boron penetration. The purpose of chemical treatment: The main is to improve the steel surface hardness, wear resistance, corrosion resistance, fatigue strength and oxidation resistance. 
  • (7). Cold drawn steel solution treatment: that the alloy is heated to a high temperature single-phase region to maintain a constant temperature, so that the excess phase fully dissolved into the solid solution after rapid cooling, in order to get over the supersaturated solid solution heat treatment process. The purpose of solution treatment: mainly to improve the ductility and toughness of steel and alloys, to prepare for the precipitation hardening treatment and so on.

Difference between hot rolled and cold formed steel

There are several major differences between hot rolled steel and cold rolled steel, all relating to the ways these metals are processed at the mill.

Hot rolled steel

Hot rolled seamless steel pipe - What is seamless steel pipe?

Hot-rolled is with continuous casting slab or blooming slab as raw material, after reheating furnace heating, high pressure water descaling into roughing mill, roughing material by the cutting head, tail, and then enter the finishing mill, the implementation of a computer-controlled rolling made the final rolling after coiling after the laminar cooling (computer-controlled cooling rate) and the coiler, straight hair volume. Straight hair the volume of the head, the tail is often poor, was a tongue-and fishtail, thickness, width, precision the edge often there is a wave-shaped, folding, pyramid defects. Coil weight heavier coil diameter of 760mm. (Normal pipe industry prefer to use.) Straight hair volume by the cutting head, tail cutting, trimming, and multi-pass straightening flat finishing line treatment, a cutting board or heavy volume, that is, to become: hot-rolled steel plate, flat hot-rolled steel coils, slitting with other products. Serve hot finishing volume descaled, pickled and oiled hot-rolled pickled coils.

Cold formed steel

ASTM A179 cold drawn steel tube - What is seamless steel pipe?

Cold formed is as raw material, after oxide removal by pickling tandem cold formed finished rolling hard roll, work hardening due to the volume of the rolling hard due to the continuous cold deformation strength, hardness rise, tough Plastic indicators declined, stamping performance will deteriorate, and can only be used for simple deformation of the parts. Rolling hard roll can be used as the raw material of the hot-dip galvanizing plant, hot dip galvanizing line set annealing line. Rolling hard roll weight is generally 6 to 13.5 tons, the coil diameter of 610mm. The general cold strip mills, volume should go through continuous annealing (CAPL unit) to eliminate cold hardening and rolling stress, or batch annealing reach the mechanical properties of the corresponding standard specifies. The cold-formed steel sheet surface quality, appearance, dimensional accuracy superior to the hot-rolled sheet, and right rolling thin product thickness to about 0.18mm. 

Difference between hot-rolled and cold-formed:

  • 1. Cold formed steel to allow cross-section a local buckling, which can make full use of the rod buckling bearing capacity;-section hot rolled steel does not allow local buckling occurs.
  • 2. The residual stress of the hot-rolled steel and cold-formed steel produced by different reasons, so the distribution of the cross section is also very different. The residual stress distribution in the cross section of cold-formed steel bending, residual stress distribution in the hot rolling steel or welded steel cross-section is a film type.
  • 3. Free torsional stiffness of hot-rolled steel, cold-formed steel, the torsional properties of hot-rolled steel is better than cold-formed steel.

Notes of seamless steel pipe manufacturing process

There are many types of defects that may occur in the manufacturing process of seamless steel pipe. Depending on the production process, the types of defects also show differences. It is precisely because of these potential defects that the pipeline is greatly reduced in strength and premature failure during use, and even causes unpredictable losses. Therefore, taking effective measures to monitor defects in the production process in real time and identify the types of defects has far-reaching significance for improving product quality, improving processes, and rationally utilizing resources.
For a very large number of seamless steel pipe production lines, relying on manual intervention to identify the type of defects is obviously not in line with the requirements of modern mass production. In order to realize online automatic detection of defect type identification, many artificial intelligence algorithms show strong vitality in today’s manufacturing informationization, such as genetic algorithm, expert system, empirical heuristic algorithm, signal processing and pattern recognition, adaptive learning, artificial neural network. Network, etc. Artificial neural networks have once been highly anticipated. However, artificial neural networks have the disadvantages of large number of training samples required, easy to fall into local minimum points, slow convergence rate, and poor generalization ability in small samples, which makes it difficult to obtain a large number of samples (such as for power station boilers, Nuclear reactor containers, aero engine rotors, ship turbochargers and other products are unpredictable. As an intelligent optimization algorithm, Particle Swarm Optimization (PSO) has the characteristics of global optimization.
Clustering analysis using particle swarm optimization to identify the type of seamless steel tube defects must first extract the characteristic parameters of the defect. The information that can be obtained by ultrasonic non-destructive testing technology can only be echo signals, and the echo signals are often rich. Information. Therefore, based on the defect echo signal, feature extraction can be performed.

Mechanical properties of seamless steel tubes

The mechanical properties of steel are important indicators to ensure the ultimate performance of steel (mechanical properties), which depends on the chemical composition of the steel and the heat treatment system. In the steel pipe standard, tensile properties (tensile strength, yield strength or yield point, elongation), hardness and toughness indexes, and high and low temperature properties required by users are specified according to different use requirements.
1. Tensile strength (σb)
The maximum force (Fb) that the specimen is subjected to during the drawing process, divided by the original cross-sectional area (So) of the specimen, is called the tensile strength (σb). The unit is N/mm2 (MPa). It represents the maximum ability of a metal material to resist damage under tensile forces.
2. Yield point (σs)
The metal material with yielding phenomenon, the force of the sample does not increase (maintains constant) during the stretching process, and the stress at the time of elongation can be continued, which is called the yield point. If the force drops, the upper and lower yield points should be distinguished. The unit of yield point is N/mm2 (MPa).
Upper yield point (σsu): The maximum stress before the specimen yields and the force first drops; Lower yield point (σsl): The minimum stress in the yielding phase when the initial transient effect is not counted.
The calculation formula for the yield point is:
Where: Fs–the yield force (constant) during the tensile process of the specimen, N (Newton) So–the original cross-sectional area of the specimen, mm2.
3. Elongation after break (σ)
In the tensile test, the percentage of the increase in the gauge length and the length of the original gauge length after the sample is broken is called the elongation. Expressed in σ, the unit is %. The calculation formula is: σ=(Lh-Lo)/L0*100%
Where: Lh–the gauge length after the sample is broken, mm; L0–the original gauge length of the sample, mm.
4. Section shrinkage rate (ψ)
In the tensile test, the percentage of the maximum reduction in the cross-sectional area of the reduced diameter after the sample is broken and the original cross-sectional area is called the reduction ratio of the section. Expressed in ψ, the unit is %. Calculated as follows:
Where: S0–the original cross-sectional area of the sample, mm2; S1–the minimum cross-sectional area at the reduced diameter after the sample is broken, mm2.
5. Hardness index
The ability of a metal material to resist the indentation of a hard object is called hardness. According to the test method and the scope of application, the hardness can be divided into Brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness, microhardness and high temperature hardness. Commonly used for pipes are Brinell, Rockwell and Vickers hardness.
A. Brinell hardness (HB)
Press the steel ball or carbide ball of a certain diameter into the surface of the sample with the specified test force (F). After the specified holding time, remove the test force and measure the indentation diameter (L) on the surface of the sample. The Brinell hardness value is the quotient obtained by dividing the test force by the spherical surface area of the indentation. It is expressed by HBS (steel ball) and the unit is N/mm2 (MPa).
Its calculation formula is:
Where: F – the test force pressed into the surface of the metal sample, N; D – the diameter of the test steel ball, mm; d – the average diameter of the indentation, mm.
Determination of Brinell hardness is more accurate and reliable, but generally HBS is only suitable for metal materials below 450N/mm2 (MPa), not suitable for harder steel or thinner plates. Among the steel pipe standards, Brinell hardness is the most widely used, and the hardness of the material is often expressed by the indentation diameter d, which is both intuitive and convenient.
Example: 120HBS10/1000/30: indicates that the Brinell hardness value measured by holding a 10mm diameter steel ball under the test force of 1000Kgf (9.807KN) for 30s (seconds) is 120N/mm2 (MPa).

Production Equipment of Seamless Steel Pipe:

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Piercing Mill
That of conical-roler features as quick-roling and uniform tubularbile thickness,easily adjustable available for feeding angle and toe angle, roller-saving available,PLC control system, outstanding domes-tically by itssuper precosion and high automatization.
Slight-stretch Reducing Mill
Respective-power-transmission of three rollers, fiexible adjustment, char-actenize as high-precised of outerdiameter and superior surface finishing.
Rotating Heat Furnace
Single or dual-feeding available, fueled by LEG, automated furance-temperature, furnace-pressure and furnace flow, domestical-topping controlling performance.
Cooling Bed
Stepwise cooling bed, lifted by motor-transmitted, hydraulical-controlled translating, cooling sectioned as 27*28m, dual-feeding available.
Hot Rolling Mill
Conical roller, big disk, fiexible adjustment, hydraulic-controlled lock system and balance system, easy andreliable operation, max pierced billet out diameters 300mm, max length is 14m, designed by “DEYANG ERZHONG”, and manufactured by “Angang Group machine manufacturing company”; ranking top class for its design, manufactur and control.
Tube Cutter
High-perfermance tube cutter supplied by Yingcheng Huaxing Tool Machine Limited Company, sysfeaturs as high-speed and well-finished cut.


seamless process Acid Cleaning Workshop - What is seamless steel pipe?
Acid cleaning workshop
seamless process Cold Drawn Workshop - What is seamless steel pipe?
Cold Drawn Workshop
seamless process ECT 620 Eddy Currentautomatic Test System - What is seamless steel pipe?
ECT-620 Eddy Test System
seamless process Feeding intake - What is seamless steel pipe?
Feeding intake
seamless process Heat Treatment Workshop - What is seamless steel pipe?
Heat Treatment Workshop
seamless process Ingot heating - What is seamless steel pipe?
Ingot heating
seamless process cutting - What is seamless steel pipe?
Pipe cutting
seamless process Beveld cut - What is seamless steel pipe?
Pipeline Beveled Ends
seamless process packing - What is seamless steel pipe?
Well packing


seamless process Ultrasonic inspection of seamless pipes - What is seamless steel pipe?
Ultrasonic inspection
seamless process ultrasonic test on astm a335 p22 pipe - What is seamless steel pipe?
Ultrasonic test on A335 pipe
seamless process Non destructive testing of seamless steel pipe - What is seamless steel pipe?
Non destructive testing

Seamless steel pipe quality testing is a very important step, and for its detection method is also very particular to now all three – ultrasonic testing, Eddy current testing, magnetic flux leakage testing, specific circumstances.

Characteristics of seamless pipe

Seamless tube process performance test: flattening test, tensile test, impact test, flaring test, hardness test, metallographic test, bending test, nondestructive testing (including eddy current X-ray and ultrasonic testing). 
Seamless pipe chemical analysis: the chemical composition of the material for chemical analysis, chemical composition to meet the standard requirements. 
Seamless pipe pressure and hydrostatic test is for pressure tube by into the hydrostatic test, which do not maintain the prescribed pressure value not less than 5 seconds, not to disclose, the regular supply hydraulic pressure test is 2.45MPa pressure The pressure test is P = 0.5MPAa. 
The corrosion test: industrial corrosion-resistant steel pipe according to standard regulations or agreement between the corrosion of steel pipe corrosion resistance test, no intergranular corrosion. 

Characteristics of seamless pipe

  • the outer diameter is smaller.
  • High precision can do small quantities of raw.
  • cold drawn steel pipe with high precision and good surface quality.
  • steel pipe cross area is more complex.
  • steel pipe superior performance, relatively dense metal.

The crack factor on the surface of seamless steel tube

The cleanliness and smoothness of the seamless steel tube is a requirement for the choice of seamless steel tube. Now everyone will look at it when they buy it, which is the key to whether customers can buy it successfully. So what are the factors that lead to this? The seamless steel tube manufacturers below will tell you in detail.
First, the raw material factors. The poor quality of the tube blank will appear inside and outside the skin, crusting, cracks, etc.;
Second, the temperature factor. The first important process of seamless steel tube production is heating, poor heating (uneven, insufficient temperature, etc.) will cause internal skin, etc.;
Third, equipment factors. From the beginning of the furnace, each equipment component will affect the final quality of the pipe. For example, if the equipment parts are scratched, it will cause the outer skin and pits; if the punching machine is not smooth, the head of the tube blank will be bitten by water and it will be difficult to bite or the inside of the head will be warped;
Fourth, the process problems. Process problems are also quite complex, there are adjustment problems, problems with equipment failure, and the quality of the pipe produced after the wear of process parts (heads, guides, rolls, etc.). The problems caused are all-encompassing.

Seamless steel pipe effect

The reasons for the wide effect of seamless steel tubes include the following: Seamless steel tubes can be combined with other materials for production, and the production volume is very large. It can be used for the transportation of substances and speed up the circulation of substances, such as pipeline transportation. 
Because it is stronger than ordinary steel pipes, it can also be used to measure the external pressure of the liquid. It is a very good pressure measurement tool. Not only can be used to measure the water pressure of ordinary water, but also to supply energy for some mechanical products.

  • 1. Structural seamless steel tube. Mainly used for general structure and mechanical structure.
  • 2. Seamless steel tube for conveying fluid. It is mainly used for conveying fluid pipelines in engineering and large-scale equipment.
  • 3. Seamless steel tubes for low and medium pressure boilers. Mainly used for industrial boilers and domestic boilers to transport low and medium pressure fluids.
  • 4. Seamless steel tubes for high pressure boilers. Mainly used in power station and nuclear power plant boilers on high temperature, high pressure conveying fluid headers and pipes.
  • 5. Marine carbon steel and carbon-manganese steel seamless tubes. Mainly used for ship boiler and superheater I, II pressure tube.
  • 6. Seamless steel tube for high-pressure fertilizer equipment. It is mainly used for conveying high-temperature and high-pressure fluid pipes on chemical fertilizer equipment.
  • 7. Seamless steel tube for oil cracking. It is mainly used in boilers, heat exchangers and pipelines for transporting fluids in petroleum smelters.
  • 8. Seamless steel tubes for gas cylinders. Mainly used for the production of various gas, hydraulic cylinders.
  • In addition, there are seamless steel tubes for hydraulic pillars, high-pressure seamless steel tubes for diesel engines, precision seamless steel tubes for cold drawing or cold rolling, and special-shaped inner diameters for cold drawn seamless steel tubes, hydraulic and pneumatic cylinders. 

Cutting method of seamless steel pipe

The main methods of cutting the seamless steel pipe are cutting machine cutting, machine cutting, flame cutting, sawing, and the like. The characteristics of the pipe cutting equipment are as follows.
(1) Pipe cutting machine
The pipe cutting machine is simple in equipment, low in investment, and widely used, and some also have the function of the inverted groove and the automatic loading and unloading material and the collecting device. The pipe cutting machine is a commonly used equipment for seamless thick-walled steel pipe finishing production lines.
(2) Pipe saw
It can be divided into tube saws, band saws and circular saws and other forms. The pipe saw can cut a number of seamless thick-walled steel pipes in a row, which has high production efficiency, but the equipment structure is complex and the investment is high; the band saw and the circular saw have lower production efficiency and less investment. Circular saws are suitable for cutting seamless thick-walled steel pipes with small outer diameters, while band saws are used to cut seamless thick-walled steel pipes with large outer diameters.
(3) Flame cut
The flame cutting includes oxygen cutting, hydrogen-oxygen cutting, plasma cutting, etc., and the cutting method is suitable for cutting thick-walled steel pipes with extremely large pipe diameter and thick wall. When plasma cutting, the cutting speed is faster. Due to the high temperature at the time of flame cutting, there is a heat affected zone near the slit and the port surface is not smooth.
(4) Machine cutting
This cutting is inefficient and is generally used for sampling and sample preparation.

How to packing the steel pipes

There are probably hundreds of different methods for packing a pipe, and most of them have merit, but there are two principles that are vital for any method to work prevent rusting and Sea transportation security.

steel strips bunding for fixed pipes - What is seamless steel pipe?

  • Plastic caps plugged at the two sides of pipe ends
  • Should be avoided by the steel strapping and transport damage
  • Bundled signs should be uniform and consistent
  • The same bundle(batch) of steel pipe should be came from the same furnace.
  • The steel pipe has the same furnace number, the same steel grade, the same specifications.

Our packing can meet any needs of the customers.

bundle packing seamless pipe - What is seamless steel pipe?
Bundle packing
naked packing seamless pipe - What is seamless steel pipe?
Naked packing
crate packing seamless pipe - What is seamless steel pipe?
Crate packing ASTM A213 T5b
protect by wood at both ends - What is seamless steel pipe?
Protect by wood at both ends
packing u bend tubes - What is seamless steel pipe?
Packing the U-bend tubes
packing oil pipes - What is seamless steel pipe?
Protect by the pipe-caps

Flattening test of seamless steel pipes

Seamless steel pipes are more tedious and more rigorous in the production process. Seamless steel pipes is a relatively important type of steel pipe. It is necessary to carry out repeated experiments in production, but also to carry out development and production, so that the performance and use of the pipe meet the usage habits of seamless steel pipes and maximize its use of its various applications make use of engineering and machining. Seamless steel pipes during the development and production is to conduct some tests, here is mainly to explain the flattening test, is the seamless steel pipe plant physics and chemistry studio when the seamless steel pipe research a more important test. What are the common methods and steps for conducting tests?
Flattening test is to test the ultimate plastic deformation ability of seamless steel pipes under the given conditions and crush deformation without crack defects. The principle is to apply the length of the seamless steel pipe to the specified length of the end of the sample or seamless steel pipes. The force is pressed until the distance between the two platens under the action of force reaches the value specified by the relevant product standard.
First, flattening sample
1. The sample is cut from any part of the seamless steel pipe that has passed the visual inspection. The sample shall be the full-loaded pipe section of the pipe product.
2, The length of the sample should not be less than 10mm, but not more than 100mm. The edge of the specimen is allowed to be rounded or chamfered with yttrium or other methods. Note: If the test results meet the test requirements, you can not round or chamfer the edge of the sample.
3. If the test is to be carried out on the pipe end of a full-length pipe, cut perpendicular to the longitudinal axis of the pipe at the length of the sample from the end face of the pipe. The cutting depth shall be at least 80% of the outside diameter.
Second, test equipment
The test can be performed on a universal testing machine or a pressure testing machine. The test machine shall be equipped with two parallel upper and lower platens. 
The width of the parallel platen shall exceed the width of the flattened sample, ie at least 1.6D. The length of the platen is not less than the length of the sample. 
The tester has the ability to flatten the sample to the specified platen distance. The platen should have sufficient rigidity. And can control the speed range required by the test.

Seamless Steel Pipe VS Welded Steel Pipe

The main difference between seamless steel pipe and welded steel pipe are molding process. General welded steel pipes such as water pipes, is generally flat plate by bending and welded together after that you can find a seam in the above; coarse diameter is usually spiral weld. The molten steel seamless pipe is generally through an annular slit molten state and then by stretching out the backlog of processing molding process, so there is no seam. In performance, especially compared to welded steel has greatly improved the bearing capacity, it is often being used for high-voltage equipment. Hydraulic equipment such as piping connections. 

Welded steel pipe 

weld area is its weak link, weld quality is also a major factor in its overall performance impact. Welded steel pipe lived in the north generally have had water pipes or heating pipes burst in the winter cold experience explosive place are generally weld.
Seamless steel pipe is piercing round holes to produce steel. Weld steel pipe is rolled into a bucket and then weld. According to their method of manufacturing seamless steel pipe and welded steel pipe in two. Seamless steel pipe with high-quality carbon steel or alloy steel, hot-rolled, cold-rolled (pull) of the points. 
Welded steel is rolled into a tube-shaped plate with the seam or spiral seam welded, in the manufacturing method, is divided into low pressure fluid welded pipe, spiral welded steel pipe, directly welded steel pipe, welded pipe. Seamless steel pipe can be used for a variety of liquids, gas pipelines. Welded pipes can be used for water pipes, gas pipes, heating pipes. Seamless steel tubes are used in important applications, uniform, high pressure tolerance, such as the barrel, the barrel and so on. Generally with high-quality steel, alloy steel and even. Weld steel are used in general purpose compression generally well tolerated, such as water pipes, gas pipes, etc., with ordinary steel.

Different Mechanical Properties of Seamless Steel Pipe

Seamless steel pipe according to different cross-sectional shapes can be divided into tube and shaped tubes. Because in the perimeter of equal conditions, the largest area of a circle with a circular tube can carry more fluid. In addition, the circular cross section to withstand internal or external radial pressure, the force is uniform. Thus, the vast majority of pipe is pipe. However, the tube also has some limitations. Under conditions such as by plane bending, tube as good as square, a large seamless steel pipe bending strength, the skeleton of some farm machinery, steel and wood furniture on the popular square, rectangular tube. Different seamless steel pipe according to mechanical properties.
Seamless hot-rolled coil as raw materials for cold rolling after pickling descaling, the finished product is rolling hard volumes, due to continuous cold work hardening caused by deformation of the strength of the rolling hard volumes, and increased hardness, toughness plastic index decreases. Accordingly stamping performance will deteriorate and can only be used for simple modification parts. Rolling hard volumes can be used as raw material for hot-dip galvanizing plant, because hot dip galvanizing line is provided with annealing line. Rolling hard volumes generally weighs 6 to 13.5 tons, coil inner diameter of 610mm. Usually cold rolling plate, coil should be evaluated by continuous annealing (CAPL unit) or batch annealing and rolling to eliminate work hardening stress, achieve appropriate standards for mechanical performance indicators.

Difference between Galvanized Steel Pipe and Seamless Steel Tube

Differences in manufacturing process:

Galvanized steel pipe and seamless steel pipe is two kinds of steel pipe, galvanized steel pipe surface is galvanized, there may be welded pipe, it may be seamless pipe, seamless steel pipe refers to the manufacturing process, Seamlessly Galvanized pipe corrosion-resistant, seamless steel pipe can withstand higher pressure. 
Galvanized steel pipe due to the protection of zinc, not easy to rust, galvanized steel pipe than the seamless steel pipe, if it is used for the balcony, it is best to use galvanized light pipe, seamless steel pipe is not suitable for use on the balcony, due to the seamless steel pipe wall thickness, natural weight on the heavy, and the cost of seamless steel pipe than the cost of galvanized steel pipe is high, there are galvanized steel pipe is very durable, the service life is far more than seamless steel pipe. If the quality is excellent, the use of more than 20 years should not be a problem, of course, welding and paint should do a good job, will not affect the use of galvanized steel pipe life.

Source: China Seamless Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.pipelinedubai.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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