Difference between galvanized steel pipe and seamless steel pipe

What is a Galvanized Steel Pipe?

Galvanized steel pipe is a steel pipe that has been coated with zinc. This coating protects the steel from corrosion. It is most commonly used for outdoor construction like fences and handrails, or for some interior plumbing. It is also sometimes called galvanized iron pipe.

Galvanized steel can be made into a strong plumbing or tubing material — one that resists corrosion from exposure to water or the elements. It has been used used for water-supply pipes or as a strong tubing for outdoor applications.

It is most commonly used for outdoor construction like fences and handrails, or for some interior plumbing. It is also sometimes called galvanized iron pipe. Galvanized steel pipe has been coated with a layer of zinc. The zinc provides a barrier against corrosion so that the pipe may be exposed to the outdoor environmental elements. The protective barrier proves equally effective against damage from indoor humidity.

Galvanized steel pipe is covered with a zinc material to make the steel pipe more resistant to corrosion.

Galvanized steel hardness

Galvanized Steel are those steel that has been covered with a layer of zinc metal.

Galvanized steel in terms of hardness test is a Brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness, micro-hardness and high-temperature hardness, etc.,

which can be divided into a variety, most of the manufacturers or using a Buchner,Rockwell, Vickers hardness of these three methods.

Brinell hardness measurement principle is the test force F (N) with a certain size, the diameter D (mm) of hardened steel balls or carbide ball pressed into the surface of the metal under test, to maintain a predetermined time after the drop test force, the the indentation average diameter d (mm) measured with a reading microscope, and then the equation Brinell hardness HB value, or the value d from the prepared Brinell hardness table to detect HB Brinell hardness measurement method is suitable for cast iron, non-alloy, annealing and quenching and tempering steel, the determination should not be too hard, too small, too thin and the surface does not allow the larger indentation specimen or workpiece.

Rockwell hardness test when the sample is too small or Brinell hardness (HB) is greater than 450, to switch to a Rockwell hardness measurement. The test method is an apex angle of 120 degrees with a diamond cone or the diameter 1.59mm/3.18mm the ball, pressed into the surface of the material under a certain load, the hardness of the material by the indentation depth obtained.

The Vickers hardness means a standard of the hardness of the material. Vickers hardness there is a small negative Vickers hardness test load 1.961 <49.03N, it applies to a thinner workpiece, the tool surface or coating hardness measurement; micro-Vickers hardness test load <1.961N applicable to the metal foil, , of the ultra-thin surface layer hardness measurement.

History of Galvanized Steel Pipe

The process of galvanization was first discussed by scientists in the 1770s, nearly 60 years before it was finally introduced in the 1830s. French engineer Stanislaus Tranquille Modeste Sorel took out the first patent for the process in 1937, and began manufacturing it soon after. By the 1850s, Europe was producing galvanized steel out of manufacturing plants located around the continent. The United States followed shortly thereafter, opening its first plant in the 1870s.

To create galvanized steel pipe, steel materials are placed into a molten bath of zinc. This process is also called hot dip galvanization. The two metals are chemically bound to one another in this process, and will therefore never separate, resulting in a more resistant and longer lasting version of steel.

Uses Galvanized Steel Pipe

Galvanized Steel Pipe is used in a variety of settings. Until about 30 years ago, galvanized steel was utilized for water supply pipes in construction. It is used in outdoor applications wherever the strength of steel is desired, such as fence posts and rails, scaffolding and as protective railings.

Galvanized steel clamp connection technology applications

hot dip galvanized pipe - Difference between galvanized steel pipe and seamless steel pipe

Galvanized Steel are those steel that has been covered with a layer of zinc metal.

Galvanized steel pipe is protected by zinc, so it is not easy to rust, galvanized steel pipe is lighter than seamless steel pipe, if it is used in the balcony, the best light with galvanized steel pipe, because seamless steel pipe is heavy with thick wall thickness, and the cost of seamless steel pipe is higher than galvanized steel pipe, as well as galvanized steel is durable, useful life is much more than a seamless steel pipe. If the quality is excellent, using twenty years should not be an issue. Surface coated or hot dip galvanized welded steel pipe can enhance corrosion resistance and prolong life.

Pipe clamp - Difference between galvanized steel pipe and seamless steel pipe

Galvanized steel pipe with corrosion-resistant, not easy to pollution the transmission medium, which is widely used in domestic water supply systems, fire water systems, heating systems and gas delivery systems. In order to ensure the transmission medium process requirements and corrosion requirements, galvanized steel connection technology, the most widely used method is threaded connection. Clamp connection method for large diameter pipe connected to the system with easy maintenance construction, fast, able to meet higher working pressure requirements for piping systems, piping installation of high quality, low requirements of the construction team, the small number of requirements, equipment and simple, the disadvantage is the cost of using a clamp connection fittings slight increase.

Galvanized pipe for water - Difference between galvanized steel pipe and seamless steel pipe
Galvanized steel pipe for water belongs to the seam welded steel pipe.

Threaded connection clamp connection technology and process shortcomings compare

  • 1, during installation in pipe, a higher quality threaded threaded connection requirements, is more difficult threaded processing. After more than DN50 galvanized steel pipe specifications, especially for DN100, DN125, DN150 and other large-sized pipes, even to have the construction experience, high-level team of construction, installation and construction are more difficult, and this clamp connection method can overcome these difficult because only a pipe clamp connection butt, butt clamps, tighten the nut.
  • 2, threaded connections, requiring high pressure piping systems is difficult to meet the requirements. In practice, for the operating pressure exceeds 1MPa piping system, using threaded connection, it is difficult to ensure that no leakage, but with clamp connection method can meet the installation requirements are relatively higher operating pressure piping systems.
  • 3, threaded process connection pressure test of the entire system installed, or use, pipeline leak occurred after maintenance more difficult. Either a large area removal, replacement pipe fittings, pipes, or cut off the pipeline, with the welding tool repair. The former because a lot of demolished normal channels, thus greatly increasing the amount of maintenance work, while the latter uses a construction maintenance method specification is not allowed because of galvanized steel by welding, heat destroys the galvanized layer, so that the pipe joints at the long-term use may affect water quality, and even leaking, especially the fire sprinkler system. And for such shortcomings, clamp connection technology embodies a greater advantage. Such as certain pipe or a pipe leakage, simply connect the pipes, fittings at both ends of the clamp nut open, you can replace, very convenient, can greatly reduce installation engineering rework engineering, but also normal use can reduce the amount of maintenance work.
  • 4, threaded pipe connections requiring high quality, especially for higher working pressure fire pipeline system, does not allow the tube trachoma, burrs and other defects threaded tolerance with the bad, but in the actual installation works, often due to pipe fittings amount of maintenance and rework caused by unqualified installation is very large, such as the use of this clamp connection technology, the entire piping system can significantly improve the quality of the installation.
  • 5, install the necessary equipment and tools, threaded connection requires large-sized pipe wrench, chain wrench and twist wire machine, but you only need to pipe clamp connection technology equipment and general machining grooves end wrench to operate, relatively speaking , is much simpler.
  • 6, the construction team technical quality requirements, threaded connection when applied to large diameter, high pressure piping systems, high technical level of construction workers, construction experience demands to meet the higher number, but with clamp connection technology, for the number of technical quality requirements of the construction workers are much lower, requiring less fit.
  • 7, using a clamp connection pipe threaded connection time investment than the slightly more than the threaded connection clamp connection because in addition to the normal pipe clamps more than a cost, but reduces rework maintenance costs, so the total project cost to said little effect.
The common trouble in using

When used as water pipe, the zinc barrier coating tends to react to the minerals in the water, often causing plaque to build up inside of the pipe. This impedes the water flow and, in severe cases, may lead to burst pipes. Galvanized piping is connected with threaded fittings that may also introduce leaks into the plumbing if not properly fitted.

Types of galvanized

There are a number of methods of applying zinc coatings and each will determine the coating’s thickness and its ultimate durability in a specific environments The most commonly encountered types of zinc coatings are:

  • Zinc electroplating
  • Mechanical plating
  • Continuously galvanized sheet
  • Continuously galvanized wire
  • Galvanized steel pipe and steel tube
  • General or hot dip galvanizing
What is Hot-Dip Galvanizing?
Hot-dip galvanized (galvanizing), also known as hot-dip galvanized, it is an effective anti-corrosion of the metal, mainly used in various sectors of the metal structure facilities.

The rust steel immersed in liquid zinc melt around 500 ℃, steel members attached to the surface of the zinc layer, which play the purpose of anti-corrosion.

  • Difference between galvanized steel pipe and seamless steel pipe
  • Galvanized steel pipe process characteristics
  • Galvanized mild steel pipe
Hot-dip galvanizing process

RAW Material Pre Galvanized Steel Strip - Difference between galvanized steel pipe and seamless steel pipe

finished of Pickling – washing – plus help the bath – drying – hanging plating – cooling – Pharmaceutical – cleaning – polishing – completion of the hot-dip galvanizing, hot dip galvanized by the ancient method of hot-dipped development come since 1836, France had been used in industrial hot dip galvanized, has a history of 140 years. However, the hot-dip galvanizing industry the past three decades along with the rapid development and large-scale development of the cold-rolled steel strip.

With the discovery of the industrial, hot dip galvanized products have been applied to many areas, hot-dip galvanized advantage of the anti-corrosion service life for a long time, to adapt to the the antiseptic treatment method widely been very popular. Been widely used in power tower, communication tower, railway, road protection, light poles, marine components, construction steel structure components, substation ancillary facilities, light industry.


hot dip galvanized iron pieces cleaned, and then the solvent treatment, drying after immersion in liquid zinc, iron, and the reaction of molten zinc alloyed zinc layer, its processes: the skim – washing – pickling – the fluxing – drying – hot-dip galvanized – separation – cooling passivation.

Galvanizing alloy layer mainly depends on the thickness of the silicon content of the steel chemical composition, the rough degree of the size of the cross-sectional area of the steel surface of the steel, the temperature of the zinc pot, the zinc immersion time, the cooling speed, and the cold deformation.

Hot-galvanized advantages
  • low-cost processing: hot-dip galvanized anti-rust lower cost than the cost of other paint coating;
  • Durable: standard hot dip galvanized rust thickness can be kept for 50 years or more in the rural environment, without having to patch; standard hot dip galvanized rust layer can be maintained for 20 years in the urban areas or offshore area, without having to patch;
  • good reliability: galvanized layer with steel is metallurgically bonded to become a part of the surface of the steel, and therefore more reliable coating persistent;
  • the toughness of the coating: zinc coating to form a special metallurgical structure, this structure can withstand transportation and use of mechanical damage;
  • full protective: plated parts each part can be plated with zinc, even in the recesses, sharp corners and hiding places can be fully protected;
  • saving time and effort: the the galvanizing process faster than other coating construction method, and can avoid the the brushing time required on site after installation.

A hot-dip galvanized coating is relatively easier and cheaper to specify than an organic paint coating of equivalent corrosion protection performance. The British, European and International standard for hot-dip galvanizing is BS EN ISO 1461 which specifies a minimum coating thickness to be applied to steel in relation to the steels section thickness e.g. a steel fabrication with a section size thicker than 6 mm shall have a minimum galvanized coating thickness of 85 µm.

Galvanized steel pipe process characteristics

Zinc sulfate biggest advantage is the current efficiency of up to 100%, the deposition rate, which is the other galvanizing process unparalleled.

Galvanized steel pipe process characteristics:

Hot dip galvanized coating - Difference between galvanized steel pipe and seamless steel pipe

1 zinc sulfate optimization

As the crystalline coating is not detailed enough, dispersing ability and poor throwing power, and thus is only suitable for simple geometries such as pipe and wire plating. Sulfate galvanized iron alloy craft of traditional sulfate galvanizing process optimization, leaving only the main zinc sulfate salt, and the remaining components are discarded. In the process of forming a new recipe and adding the right amount of iron, so that the original single-plated zinc alloy metal plating layer is formed. Reorganization process, not only to carry forward the original process high current efficiency, fast deposition rate advantages, but also the dispersion ability and throwing ability has been greatly improved in the past can not be plated complex parts, simple and complex parts can now plated and protective properties increased by 3 to 5 times faster than a single metal. Practice has proved that for wire, pipe continuous plating, coating the grain is more refined than the original, more bright, fast deposition rate. Within 2 ~ 3 min coating thickness to meet the requirements. 

2 Zinc sulfate conversion

Sulfate zinc sulfate zinc alloy to retain only the primary zinc sulfate salt, the remaining components such as aluminum sulfate, alum (potassium aluminum sulfate), etc. can be processed in the bath, was added sodium hydroxide so as to precipitate an insoluble removal; organic additives, then add powdered activated carbon adsorption removed. Tests showed that aluminum sulfate and aluminum potassium sulfate is difficult to completely remove the one-time, affect the brightness of the coating, but not serious, may be accompanied by the consumption, the brightness can be restored at this time plating solution through the processing, according to new techniques additional ingredients required,to complete the conversion.

3 deposition rate, excellent protection performance

Sulfate galvanized iron alloy craft up to 100% current efficiency, fast deposition rate is unmatched in any galvanizing process, speed fine tube 8 ~ 12 m / min, the average coating thickness 2m/min, it is difficult to continuous galvanizing achieved. Bright coating delicate eye. According to national standards GB/T10125 “test in artificial atmospheres – Salt spray test” method of testing, 72 h, plating intact, unchanged; 96 h, coating the surface of a small amount of white rust.

4 unique clean production

Galvanized steel pipe with galvanized iron alloy sulfate process lies between the trough and the trough are perforated production straight out and no solution or overflow. Each step of the production process from the circulation system components, i.e. the alkali solution tank solution, plating solution, and the passivation fluid, light, not only by the outer loop back leakage or discharge system, located only 5 line cleaning tank, cyclic reuse periodic emissions, especially after the production process without passivation without cleaning the wastewater generated.

5 Particularity of electroplating equipment

Electroplated galvanized steel pipe with wire plating, as are all continuous plating, but different plating equipment. Wire with its characteristic elongated strip designed plating tank, the tank is long and wide but shallow. Electroplating wire from the hole piercing, showing a shape in the liquid started to keep distance from each other. Unlike wire and galvanized steel pipe but has its unique slot equipment is more complex.

The tank by the upper and lower parts, the upper part of the plating tank, the lower part of the storage solution circulation tank, the narrow width forming a shape similar to the trapezoidal grooves in the plating bath has a channel running plated galvanized steel pipe, There are two holes in the bottom of the storage tank is connected to the lower, and the formation of the bath round robin system and sump pump. Therefore, galvanized steel pipe with wire plating as plating are dynamic in nature, with the difference between the wire plating, plating bath galvanized steel pipe is dynamic nature.

What is a seamless steel pipe?

Seamless steel pipe is a kind of hollow cross-section, there is no seam around the long steel. Seamless steel pipe with hollow cross-section, a large number of pipes used to transport fluid, such as the transportation of oil, natural gas, gas, water and certain solid materials such as pipes. Seamless steel and round steel and other solid steel, the same bending strength in the bending, the lighter weight, is an economic section of steel, is widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipe, car drive shaft , Bicycle frames and steel scaffolds used in construction. Seamless steel pipe manufacturing ring parts, can improve material utilization, simplify the manufacturing process, save materials and processing time, such as rolling bearing rings, jackets, etc., has been widely used to manufacture seamless steel pipe. 
Seamless steel pipe or a variety of conventional weapons indispensable materials, barrel, barrel, etc. to be seamless steel pipe to manufacture. Seamless steel pipe according to the different cross-sectional shape can be divided into round tube and shaped tube. Because the circle area is the largest under circum- stances of equal length, more fluid can be delivered with a circular tube. In addition, the circular cross-section to withstand internal or external radial pressure, the force is more uniform, so the vast majority of seamless steel pipe is a round tube. However, the tube also has some limitations, such as bending in the plane by the conditions, the tube is not as square, rectangular tube bending strength, a number of farm machinery with skeleton, Gangmu furniture on the common side, rectangular tube.
According to different uses need to have other cross-section shape of the shaped seamless steel pipe.

  • 1. Structure seamless steel pipe (GB / T8162-1999) is used for general structure and mechanical structure seamless steel pipe.
  • 2. seamless steel pipe for fluid transport (GB / T8163-1999) is used to transport water, oil, gas and other fluids in general seamless steel pipe.
  • 3. Low and medium-pressure boiler seamless steel pipe (GB3087-1999) is used to manufacture a variety of low and medium pressure boiler superheated steam pipe, boiling water pipes and locomotive boiler superheated steam pipe, smoke pipe, small pipe and Arch brick with high-quality carbon structural steel hot-rolled and cold drawn (rolling) seamless steel pipe.
  • 4. High-pressure boiler seamless steel pipe (GB5310-1995) is used to manufacture high pressure and above pressure water pipe boiler heating surface with high-quality carbon steel, alloy steel and stainless steel seamless steel pipe.
  • 5. High-pressure seamless steel pipe for fertilizer equipment (GB6479-86) is applicable to the working temperature of -40 ~ 400 ℃, working pressure of 10 ~ 30Ma chemical equipment and piping high-quality carbon structural steel and alloy steel seamless steel pipe. 
  • 6. seamless steel pipe for oil cracking (GB9948-88) is applicable to the oil refinery furnace tubes, heat exchangers and seamless pipe. 
  • 7. Seamless steel pipe for geological drilling (YB235-70) is a seamless steel pipe used for core drilling in the geological department. It can be divided into drill pipe, drill collar, core pipe, casing and sediment pipe etc. 
  • 8. seamless steel pipe for diamond core drilling (GB3423-82) is used for diamond core drilling of the drill pipe, core rod, casing seamless steel pipe. 
  • 9. Oil drilling pipe (YB528-65) is used for oil drilling both ends of the thickening or thickening of seamless steel pipe. Seamless tube sub-car wire and not car wire two, car thread tube connection with the joint, not the wire with the butt welding method and tool joints. 
  • 10. Seamless carbon steel pipe (GB5213-85) is the manufacture of ships Class I pressure pipe, Ⅱ pressure pipe, boiler and superheater with seamless carbon steel pipe. Seamless carbon steel pipe wall temperature does not exceed 450 ℃, seamless steel pipe operating temperature of more than 450 ℃. 
  • 11. seamless Steel Tube for Automotive Axle Bushings (GB3088-82) is a hot-rolled seamless steel tube with high quality carbon structural steel and alloy structural steel for automobile shaft axle casing and axle axle housing axle tube. 
  • 12. Diesel engine with high-pressure tubing (GB3093-86) is the manufacture of diesel injection system for high-pressure cold drawn seamless steel pipe. 
  • 13. Hydraulic and pneumatic cylinder with precision seamless steel pipe diameter (GB8713-88) is the manufacture of hydraulic and pneumatic cylinder with precision diameter diameter cold-drawn or cold-rolled precision seamless steel pipe. 
  • 14. Cold-drawn or cold-rolled precision seamless steel pipe (GB3639-83) is used for mechanical structure, hydraulic equipment, high dimensional accuracy and good surface finish cold drawn or cold-rolled precision seamless steel pipe. Precision seamless steel pipe manufacturing machinery or hydraulic equipment, can greatly save machining time, improve material utilization, while helping to improve product quality. 
  • 15. Structure stainless steel seamless pipe (GB / T14975-1994) is widely used in chemical, petroleum, textile, medical, food, machinery and other industries corrosion-resistant pipes and structural parts and parts made of stainless steel heat Rolling (extrusion, expansion) and cold drawing (rolling) seamless steel pipe. 
  • 16. seamless steel pipe for fluid transportation (GB / T14976-1994) is a hot-rolled (extruded, expanded) and cold drawn seamless steel pipe made of stainless steel for conveying fluids. 
  • 17. Shaped seamless Steel Tube is a general term for seamless steel tubes other than round tubes.

Seamless steel pipe according to the different shape and size can be divided into different thickness seamless steel pipe (code-D), ranging from different thickness seamless steel pipe (code-named BD), variable diameter seamless Seam steel pipe (code-named BJ). Shaped seamless steel pipe is widely used in a variety of structural parts, tools and mechanical parts. Compared with the tube, shaped pipe generally have a larger moment of inertia and section modulus, a greater bending and torsion resistance, can greatly reduce the weight of the structure, saving steel.

Hot-rolled seamless steel pipe

Hot rolled seamless steel pipe - Difference between galvanized steel pipe and 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.

Hot-rolled seamless steel pipe: hot rolled is relative to the cold-rolled, cold rolling is below the recrystallization temperature of the rolling, and hot rolled is carried out at above the recrystallization temperature of the rolling.


hot rollded seamless steel pipe can damage the cast microstructure of the steel ingot, refinement of the crystal grains of the steel, and eliminate the defects of the microstructure, so that the the steel organization compacting, improve the mechanical properties. This improvement is reflected in the rolling direction, so that the steel is no longer to a certain extent isotropic; pouring the formation of bubbles, cracks, and osteoporosis, under high temperature and pressure can also be welded together.


1 After the hot rolling, the nonmetallic inclusions in the interior of a steel (mainly sulfides and oxides, as well as the silicate) was pressed into a sheet, stratified (laminated) phenomenon appears. The layering of the steel in the thickness direction by the pull performance deteriorated significantly, and may appear in the weld shrinkage interlayer tear. Weld shrinkage induced local strain often reach several times the yield point strain, the strain is much greater than the load caused;

2 Residual stress caused by uneven cooling. The residual stress is the stress of internal self-phase equilibrium in the absence of external force, the hot-rolled steel of various cross-sectional has a residual stress such Usually steel sectional dimension is the greater, the greater the residual stresses. Residual stress is self-phase equilibrium, but the steel members in the performance external force or have a certain influence. Such as deformation, stability, anti-fatigue may adversely.

3 Hot-rolled steel products, poor control of thickness and edge width. We are familiar with the thermal expansion and contraction, even if the beginning of the hot-rolled out are standard length, thickness, or there will be some negative final after cooling, this negative differential edge width wider the increasing thickness of the performance of the more obvious.

So for large steel for steel edge width, thickness, length, angle, and sideline no law requires too precise.

How to make hot rolled pipe ?

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

Rolling seamless tube of raw materials is a round tube, tube embryos go through a cutting machine to cut the growth of the degree approximately 1 meter, and sent by conveyor belt furnace heating.

Hot rolled (extrusion seamless steel pipe):

round tube → heating → perforation → → three-roll rolling, rolling or extrusion → detached → sizing (or reducing) → cooling → straightening hydraulic test (orflaw) → tag → storage.

Billet is fed into the heating furnace, the temperature is about 1200 degrees Celsius. Fuel for a hydrogen or acetylene. The furnace temperature control is critical to wear air tube round, after the release of pressure puncher. which are generally more common puncher tapered roller punch this punch, high production efficiency, product quality, perforated expanding volume, wearing a variety of steels. After perforation, round tube has been three-roll cross rolling, rolling or extrusion.

After extrusion off pipe sizing. Sizing mill by the high-speed rotation of the cone drill into the Billet punch to form a steel pipe. The steel pipe inner diameter is determined by the length of the outer diameter of the sizing mill drill. After sizing, the steel pipe to enter the cooling tower by the water spray cooling, the steel pipe after cooling, it is necessary to be straightening. Sent by conveyor pipe by straightening the metal detection machine (or hydrostatic test) to conduct an internal flaw. Steel pipe internal issues such as cracks, bubbles will be detected.

Steel pipe quality inspection but also through a rigorous manual selection. Steel pipe of Quality Supervision, Inspection, use spray paint on the number, size, production batch. By a cable car hanging into the warehouse.

Seamless steel pipe pressure

Composed piece of seamless steel pipes are generally standard, so the pressure piping components are primarily designed selection, pipeline pressure levels to determine their standard of its standard level is determined.

Pipe pressure rating: usually determined by a common pipe fittings standard nominal pressure rating and wall thickness of the pipe pressure rating that can reflects the parameters characteristic called pipe pressure rating. The customary to simplify the description, often to the pipe fittings nominal level called pipeline pressure rating. Pressure levels to determine the basis for the design pressure of the pipeline, but also the core design. It is the pressure piping, pressure piping design stress check preconditions pressure pipeline is an important factor in investment in infrastructure and pipeline reliability impact.

Different materials, the mechanical properties are different, the temperatures are in the standard – the corresponding value on the pressure gauge is not the same. Therefore, before determining nominal pipe material pipeline should first determine its components. It is determined by the choice of material design temperature, design and operation of the pressure medium. With forging material, while valve multi-cast material. No matter what material standard used, they should be the same level of material that has the same operating conditions, such as strength and adaptability; note pipe, plate, bar, cast material compatibility.

Allowable stress of the material refers to the material strength index value divided by the appropriate factor of safety obtained. Mechanical performance materials are yield limit, ultimate strength, creep limit, fatigue limit, these indicators reflect different states were failures limit. To ensure reliable operation of the pipe strength, the pipe element is often restricted to a value of stress at each intensity index, the value is the allowable stress. When the pipe element stress exceeds the allowable stress values, it believes its strength can not be guaranteed. So, to say, material allowable stress level is to determine the basic parameters of the pipe wall thickness.

Stress relief annealing of seamless steel pipe

Stress relief annealing of seamless steel pipe: annealed to remove stress and residual stress in the casting of memory due to plastic deformation processing, welding, etc. caused by the conduct referred to as stress relief annealing.
Cold drawn seamless steel pipe deformation (stress relief annealing phase transition does not occur), can not reach the surface finish and dimensional accuracy requirements, they can not achieve strength index components; deformation is too large, seamless steel ductility, toughness reduce excessive Moreover, elongated grains excessively pulled, the formation of fibrous tissue, metals having a significant anisotropy. Cold drawn seamless steel tube axially parallel to the elongated direction of the grain, increased strength; cold drawn seamless steel pipe radially, perpendicular to the elongated direction of the grain, but lower strength, maximum stress and the hydraulic cylinder being present in the radial direction of seamless steel tubes on, so much to give full play to the deformation properties of cold drawn tubes unfavorable. For the fibrous tissue that appears in the steel and dislocations, vacancies and other crystal defects are generally taken annealing or normalizing heat treatment methods to eliminate them. The purpose is to refine the grain annealing, eliminating tissue defects, reduced hardness, improved ductility, but also facilitate cold. 
Process of stress relief annealing: the workpiece was slowly heated to Ac 1 or less 100 ~ 200 ℃ (500 ~ 600 ℃) holding a certain time (1 ~ 3h) followed by slow furnace cooling to 200 ℃, baked and then cooled. Steel is generally 500 ~ 600 ℃,Iron is generally 500 ~ 550 ℃ likely to cause pearlite graphitization than 550. Weldment generally 500 ~ 600 ℃. 
Scope: the elimination of casting, forging, welding parts, cold stamping and machining the workpiece residual stress in order to stabilize the size of steel, reducing distortion and prevent cracking. 
Purpose: cold drawn seamless steel pipe were needed after stress relief annealing, to eliminate the residual stress of the material, improve the organization of materials, improved plastic material, so as to achieve the purpose of preventing seamless steel pipe fracture failure occurs.

Wall thickness tolerance of seamless steel pipe

We can makes and markets cold-drawn and hot rolled seamless steel pipes and cold-drawn special-section seamless steel pipes which are widely applied in the industries of petrochemical, boiler, automobile, mechanica…

Seamless steel pipes are extensively applied for the nuclear device, gas, petrochemical, ship building and boiler industries. seamless steel pipes dominates 65% of market share in Chinese boiler industry.

Types Sizes allowed tolerance
Ordinary steel pipe Senior steel pipe
Hot rolled Out diameter <50 ± 0.50 mm ± 0.40 mm
≥50 ± 1 % ± 0.75 %
Wall thickness <4 ± 12.5 % ± 10 %
4-20 +15%
± 10 %
≥20 ± 12.5 % ± 10 %
Cold drawn Out diameter 6-10 ± 0.20 mm  ± 0.10 mm
>10-30 ± 0.40 mm ± 0.20 mm 
>30-50 ± 0.45 mm ± 0.25 mm 
>50 ± 1 % ± 0.5 %
Wall thickness ≤1 ± 0.15 mm ± 0.12 mm
1-3 + 15 %
– 10 % 
± 10 %
>3 + 12.5
– 10 %
± 10 %

Marine Seamless Steel Pipe

Marine Seamless Steel Pipe is very common in marine engineering.

Two systems of ship and marine engineering demand roughly in three types of steel pipe:

  • steel pipe in the conventional system
  • constructed with steel pipes
  • special purpose steel pipes
pipe oil 1 - Difference between galvanized steel pipe and seamless steel pipe

steel pipe in the conventional system.

Different ship and marine engineering, both conventional systems have a dedicated system.

Ship service life of 20 years. Many of the conventional system, bilge water, ballast, dewater sewage, air, measurement, injection, domestic water, fire, cargo oil stripping, breathable, inert gas, heating, washing, foam extinguishing sprinkler, vapor, liquid level telemetry, valve remote control systems, special ships also include a dedicated system for the transportation of liquefied petroleum gas (LPG), liquefied natural gas (LNG). Marine engineering service life of up to 30 years, or even longer. Marine engineering in addition to the conventional system, special drilling equipment systems, crude oil / LPG / LNG processing workflow system, special mooring system, flare system, and so on. It has been statistics, ship pipe annual consumption of 450 million tons, about 440,000, its standards are GB, YB, CB, 70% of the steel pipe connection. Only a 30-ton very large crude oil pipes for the amount of up to tens of kilometers, only steel pipe usage (including), there are about 1,500 tons, of course, the amount of 40,000 tons relative to the hull structure or limited. In addition, taking into account the same ship, to the construction of ships, as well as many other ships, so the cumulative dosage is also a lot of. And a 300,000 tons-class number of large FPSO pipe over 30,000, more than 90 km in length, which is the same tonnage level 2 to 3 times. Therefore, the shipbuilding industry has become a big user of steel pipe market.

Steel pipe in construct
Steel tube marine engineering applications, in addition to the above conventional system with a dedicated system, many constructed a large number of steel pipes, such as jacket, underwater steel piles, Casing, mooring bracket, helicopter platform, torch tower. Type of steel pipe, material specifications, with the same diameter, reducers, different wall thickness, as well as a large number of Y, K, T-managed nodes. Such as jacket, steel piles, wellhead impermeable sleeve, mostly large diameter steel pipe sizes, are generally made of rolled steel. Their material for E36-Z35, D36-Z35, E36, D36. Such steel pipe standards have not with YB, CB, and mainly is GB712-2000. The production of steel pipe structure steel pipe manufacturing practice SY/T10002-2000 developed by China’s Petroleum Industry Standards and Technology Commission (CPSC). Since China does not have the specialized enterprises, are usually the purchase of steel plate from construction units, self-molding process.

Steel pipe for special purpose
Special purpose steel special steel pipe used in the specific working environment and the working medium. Undersea pipeline is typical specialty steel pipe, the demand for larger, high strength, small tolerances, good corrosion resistance. Currently, the pipeline production is only in its infancy, because the welding materials, corrosion resistance or less Specifications (diameter and wall thickness), expensive, etc. China’s offshore crude oil need insulation transport. The past, using the double pipe insulation structure, safe and reliable. But as a protective pipe steel pipe is very economical, and offshore pipe laying ago, have to carry out internal and external pipe welding, greatly reducing the efficiency of the pipe laying, to cause installation costs increase exponentially. Into the 21st century, it has launched a concrete counterweight steel pipe.

Its structure is (from inside to outside):
anti-corrosion layer of steel, epoxy powder (FBE), polyurethane insulation, polyethylene (PE) jacket tube, reinforced concrete counterweight layer (the internal configuration of the steel mesh). This type of special steel, China has imported from abroad, such as the Bohai Penglai 19-3 oil field, a project using Malaysian BREDEROPRICE company products. China after research and testing, and in 2002 built in Tanggu, China‘s first concrete with heavy steel pipe production line, has thousands of kilometers of pipelines for offshore oilfield products. It is reported that, using this steel per kilometer subsea pipeline to reduce the cost of 50 million to 100 million, and greatly reduce the cost of offshore oilfield development, so that a number of marginal oil fields to be cost-effective to develop.

Seamless steel pipe piercing

Hot Piercing Workshop2 - Difference between galvanized steel pipe and seamless steel pipe
Seamless steel pipe piercing

The seamless steel pipe process is much different from any other manufacturing process because it has no welds or seams. The pipe starts as a solid steel billet, and is then heated and placed over a piercing point which creates a steel shell. The process is finished further once the initial shell is created, and is then molded into the desired diameter and wall thickness. The pipe created from this process is made in a heated application, so the pipe should be fully normalized and have a consistent cellular pattern throughout the entire circumference of the material.

Seamless steel pipe piercing - Difference between galvanized steel pipe and seamless steel pipe

Piercing is the first step of hot-rolled seamless steel pipe deformation, and its role is to solid hollow tube billet dressed as capillary.

Due to wear a capillary surface defects or eccentric (uneven thickness) is difficult to eliminate or reduce the deformation process, therefore, the quality of perforated capillary has a very important impact on the quality of hot-rolled seamless steel pipe. Way pressure tube perforation punching, pushing rotary piercing and piercing. Thick-walled seamless steel mainly used in petroleum geology drilling pipe, petrochemical used in cracking tubes, boiler tubes, pipes and automotive bearings, tractors, aviation and other precision tube structure, its manufacturing process:

hot rolled seamless steel tube round → heating → three perforated roll rolling, rolling or extrusion → detached → sizing (or reducing) cooling → straightening → hydrostatic test (or testing) logo → storage.

Hot-rolled seamless steel ingot casting can destroy tissue, grain refinement of steel and eliminate defects microstructure, so that the steel dense tissue mechanical properties are improved. This improvement is mainly reflected in the direction along the rolling direction to a certain extent in the steel is no longer isotropic; pouring formed bubbles, cracks and loose, can be welded at a high temperature and pressure.

After hot-rolled seamless steel tube round baked to go through the pressure puncher piercing. Generally more common punch is tapered roller punching machine, punching machine such high production efficiency, product quality, perforated expanding capacity, can be worn a variety of steel. After perforation, round tube has been three-roll rolling, rolling or extrusion. To squeeze off the pipe after sizing. Sizing mill into high-speed rotating cone drill through perforated steel embryo formed steel. Pipe inside diameter is determined by the outside diameter sizing mill drill length.

After sizing the pipe into the cooling tower through spray cooling pipe after cooling, it is necessary to be straightened. After straightening the steel conveyor belt to the metal detection machine (or pressure test) for internal testing. If the internal pipe cracks, bubbles and other issues, will be detected. After the selection of steel but also through strict quality control manual. After the steel quality, spray paint on number, size, batch number and so on. By a crane into the warehouse.

Difference between galvanized steel pipe and seamless steel pipe

Galvanized steel pipe is protected by zinc, so it is not easy to rust, galvanized steel pipe is lighter than seamless steel pipe, if it is used in the balcony, the best light with galvanized steel pipe, because seamless steel pipe is heavy with thick wall thickness, and the cost of seamless steel pipe is higher than galvanized steel pipe, as well as galvanized steel is durable, useful life is much more than a seamless steel pipe. If the quality is excellent, using twenty years should not be an issue.

Surface coated or hot dip galvanized welded steel pipe can enhance corrosion resistance and prolong life.

Manufacturing process difference: galvanized steel refer to a galvanized surface, there may be welded pipe, it could be seamless, seamless steel pipe manufacturing process means welded and seamless points.

Seamless steel pipes are extensively applied for the nuclear device, gas, petrochemical, ship building and boiler industries. seamless steel pipes dominates 65% of market share in Chinese boiler industry.

Uses difference:

Seamless steel pipe is very widely used, except for water, gas, oil, general low pressure fluid line pipe, also used as heating oil oil industry in particular, marine oil field oil well pipes, pipelines, chemical coking equipment, a condensate cooler, coal distillation of wash oil exchange Used pipe, and trestle piles, mine tunnel support frame with a pipe. Galvanized steel pipe generally is utilized to make make fences, fence, fence, balcony guardrail. Commonly used in municipal projects, roads, factories, schools, development zones, gardens, squares, residential and other places.

Source: Network Arrangement – China Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.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.)

If you want to have more information about the article or you want to share your opinion with us, contact us at [email protected]

Please notice that you might be interested in the other technical articles we’ve published:

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  • Engineering Specification for Pressure Test of Piping System

  • How To Distinguish Inferior Steel Pipe

  • How to get high quality steel pipes

  • Manufacturing process of cold rolled steel pipe

  • How to get high quality boiler tubes

  • How to get high quality flanges

  • How to get high quality alloy steel pipes

  • How to get high quality pipe fittings

  • How to get high quality heat exchanger tubes

  • The difference between steel tubes and steel pipes



  • https://www.galvanizing.org.uk/hot-dip-galvanizing/history-of-galvanizing/
  • https://www.yaang.com
  • https://www.steeljrv.com

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