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Steel Pipe

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The two most common types of pipes are welded pipe and seamless pipe. Both are available in carbon steel and stainless steel. Welded pipe is also called ERW (Electric Resistance Welded) pipe.

Seamless steel pipe Grades

Seamless steel pipes are perforated from whole round steel, and steel pipes without welds on the surface are called seamless steel pipes.

201 Seamless steel pipe

201 stainless steel pipe is prepared for the production process of round steel, acid and alkali resistant steel pipe.

The American Iron and Steel Institute uses three digit numbers to identify standard grades of malleable stainless steel. Among them:
(1) Austenitic stainless steel with 200 and 300 series of numbers marked;
② Ferrite and Martensite stainless steel with 400 series of numbers.
For example, some of the more common austenitic stainless steels are labeled 201, 304, 316 and 310, ferritic stainless steels are labeled 430 and 446, martensitic stainless steels are labeled 410, 420 and 440C, Duplex (austenitic ferritic) stainless steel, precipitate hardened stainless steel and high alloys with less than 50% iron content are usually patented or trademarked names.

201 stainless steel tube has: acid resistance, alkali resistance, high density without pinhole and other characteristics, is the production of all kinds of watchcase, watchband bottom cover quality materials. 201 stainless steel pipe can be used in decorative pipe, industrial pipe, some shallow tensile products.

304 Seamless steel pipe

304 seamless pipe has no sand holes, no sand holes, no black spots, no cracks, smooth weld. Bending, cutting, welding processing advantages, nickel content stable advantages.

304 seamless pipe is resistant to air, steam, water and other weak corrosive medium and acid, alkali, salt and other chemical corrosive medium corrosion steel pipe. Also known as stainless acid – resistant steel pipe.

The corrosion resistance of 304 seamless tube depends on the alloy elements contained in the steel. Chromium is the basic element to make stainless steel corrosion resistance. When the chromium content in steel reaches about 12%, chromium and oxygen in the corrosive medium react to form a very thin oxide film (self-passivation film) on the steel surface, which can prevent further corrosion of the steel matrix. In addition to chromium, stainless steel seamless tube commonly used alloy elements and nickel, molybdenum, titanium, niobium, copper, nitrogen, etc., to meet the requirements of various uses of stainless steel structure and performance.

304 seamless pipe is a hollow circular steel strip, widely used in petroleum, chemical, medical, food, light industry, mechanical instrument and other industrial pipeline and mechanical structure components. In addition, in the same bending, torsional strength, light weight, so it is also widely used in manufacturing machinery parts and engineering structures. Also commonly used for the production of conventional weapons, gun barrels, shells and so on.

The thicker the wall thickness of 304 seamless tube, it is more economical and practical, the thinner the wall thickness, its processing cost will rise greatly;

304 seamless tube process determines its limited performance, general seamless steel pipe precision is low: uneven wall thickness, low brightness inside the tube surface, the cost of size is high, and the inner surface and pitting, black spots are not easy to remove;

304 seamless tube detection and shaping must be offline processing. Therefore, it has its advantages in high pressure, high strength and material for mechanical structure.

904L Seamless steel pipe

904L stainless steel pipe (00Cr20Ni25Mo4.5Cu) is austenitic stainless steel with better corrosion resistance. Because 1.5% copper is added, it also has excellent corrosion resistance to reducing acids such as sulfuric acid and phosphoric acid. In addition, It has low carbon characteristics for welding applications.

The product has high strength, is not easy to rust, and has good heat insulation effect. It is suitable for new construction, reconstruction, and expansion projects that require waterproofing, heat insulation, heat preservation, leakage prevention, and water cooling. It has a wide range of application prospects. The easy-cut seamless pipe adopts a unique micro-hole design, which makes full use of the micro-hole space and flange, and at the same time, it is fastened by aluminum row bolts, which can obtain a close-fitting welding connection. It makes full use of the advantages of welding materials and is not compatible with vacuum cutting. Compared with the seam pipe, the cost is low, the economy is good, and the pressure resistance is strong
904L (N08904, 14539) super austenitic stainless steel contains 14.0-18.0% chromium, 24.0-26.0% nickel, and 4.5% molybdenum. 904L super austenitic stainless steel is a low-carbon, high-nickel, molybdenum austenitic stainless and acid-resistant steel. It is a proprietary material imported from France H·S. It has good activation-passivation conversion ability, excellent corrosion resistance, good corrosion resistance in non-oxidizing acids such as sulfuric acid, acetic acid, formic acid, and phosphoric acid, and good corrosion resistance in neutral chloride-containing media It has good pitting resistance and good resistance to crevice corrosion and stress corrosion. It is suitable for sulfuric acid of various concentrations below 70°C, and it is resistant to acetic acid of any concentration and temperature under normal pressure, and the corrosion resistance in the mixed acid of formic acid and acetic acid is also very good.

321 Seamless steel pipe

321 stainless steel is a material with excellent high temperature stress rupture (Stress Rupture) performance and high temperature creep resistance (Creep Resistance) stress mechanical properties are better than 304 stainless steel.

321 stainless steel pipes are delivered in a heat-treated state. In addition, there are also certain requirements for the microstructure, grain size, and decarburized layer of the finished steel pipe. Seamless steel pipes for geological drilling and oil drilling control; use drilling rigs to drill wells for the exploration of underground rock structure, groundwater, oil, natural gas and mineral resources.

Oil and natural gas exploitation is even more inseparable from well drilling. Seamless steel pipes for geological drilling and control are the main equipment for drilling, including core outer tubes, core inner tubes, casings, and drill pipes. Because the drilling pipe needs to be deep into the formation depth of several kilometers to work, 1cr5mo alloy pipe.1. 321 stainless steel pipe. Seamless steel pipe (GB14976-2002) is used to manufacture superheated steam pipes, boiling water pipes and locomotive boiler superheated steam pipes, large smoke pipes, small smoke pipes and arch brick pipes for various structures of low and medium pressure boilers. High-quality carbon structural steel hot-rolled and cold-drawn (rolled) seamless steel tubes.

  1. 321 stainless steel pipes: high-quality carbon structural steel, alloy structural steel and stainless heat-resistant steel seamless steel pipes mainly used to manufacture high-pressure and above steam boiler pipes. These boiler pipes are often under high temperature and high pressure. Work and pipes will also undergo oxidation and corrosion under the action of high-temperature flue gas and water vapor. Therefore, steel pipes are required to have high enduring strength, high oxidation resistance, and good organizational stability. Hydraulic prop pipes.

316L Seamless steel pipe

316L seamless steel pipe is a long steel with a hollow section and no joints on the periphery. Steel pipes have a hollow section and are used in large quantities as pipelines for conveying fluids, such as pipelines for conveying oil, natural gas, gas, water and certain solid materials. Compared with solid steel such as round steel, steel pipes are lighter in flexural and torsional strength when they are the same, and steel pipes have been widely used for manufacturing.

316L steel pipe is also indispensable for various conventional weapons. It is a kind of economical cross-section steel, which is widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipes, automobile transmission shafts, bicycle frames, and steel scaffolding used in construction. Making ring parts with steel pipes can improve material utilization, simplify the manufacturing process, save materials and processing man-hours, such as rolling bearing rings, jack sleeves, etc., less materials, *tubes, barrels, etc., must be made of steel pipes. Steel pipes can be divided into round pipes and special-shaped pipes according to their cross-sectional area shapes. Since the circle area is the largest under the condition of the same circumference, more fluid can be transported with a circular tube. In addition, when the ring section is subjected to internal or external radial pressure, the force is relatively uniform. Therefore, most steel pipes are round pipes.

Used in the manufacture of seamless steel pipes for pipes, containers, equipment, pipe fittings and mechanical structures
Construction: hall structure, sea trestle bridge, airport structure, shipyard, security door frame, garage door, reinforced steel door and window, interior partition wall, cable bridge structure and highway security guards, railings, decoration, residences, decorative pipes
Auto parts: automobile and bus manufacturing, transportation
Agriculture: agricultural equipment
Industry: machinery, solar mounts, offshore oilfields, mining equipment, electromechanical hardware, engineering, mining, heavy and resources, process engineering, material processing, mechanical parts
Transportation: pedestrian railings, guardrails, square structures, guide signs, road equipment, fences
Logistics storage: supermarket shelves, furniture, school appliances

2205 Seamless steel pipe

2205 duplex stainless steel pipe is defined as a stainless steel whose ferrite phase and austenite phases in its solid-quenched structure are half and half, referred to as 2205 stainless steel pipe, also called 2205 duplex steel pipe. The actual phase ratio is that ferrite accounts for 45~55%, and the corresponding austenite accounts for 55~45%. The excellent performance of 2205 duplex stainless steel is ensured by an appropriate ratio of two-phase structure.

2205 duplex stainless steel pipe has excellent mechanical properties, corrosion resistance, and good weldability, and has a wide range of uses in the oil and gas industry, marine engineering, chemical industry and other industries. The length of the oil and gas pipelines laid by duplex stainless steel in the oil and natural gas industry has exceeded 850Km, most of which are 2205 duplex stainless steel seamless steel pipes (some of them are S31803 duplex stainless steel pipes and 2507 duplex stainless steel pipes); West-East Gas Pipeline Due to the strong corrosiveness of the natural gas medium in the project, the high-pressure pipelines are all made of 2205 duplex stainless steel.

1）Used in the manufacture of seamless steel pipes for pipes, containers, equipment, pipe fittings and mechanical structures
2）Construction: hall structure, sea trestle bridge, airport structure, shipyard, security door frame, garage door, reinforced steel door and window, interior partition wall, cable bridge structure and highway security guards, railings, decoration, residences, decorative pipes
3）Auto parts: automobile and bus manufacturing, transportation
4）Agriculture: agricultural equipment
5）Industry: machinery, solar mounts, offshore oilfields, mining equipment, electromechanical hardware, engineering, mining, heavy and resources, process engineering, material processing, mechanical parts
6）Transportation: pedestrian railings, guardrails, square structures, guide signs, road equipment, fences Logistics storage: supermarket shelves, furniture, school appliances

Welded steel pipe Grades

Welded steel pipe is created using a flat steel plate or steel strip, and its manufacturing process results in a seam on its body.

Q355B Welded steel pipe

With the rapid development of high quality strip rolling production and the progress of welding and inspection technology, the quality of weld is constantly improving, the variety and specification of welded steel tube is increasing day by day, and it has replaced seamless steel tube in more and more fields.

The blank used for welding steel pipe is steel plate or strip steel, which is divided into furnace welding pipe, electric welding (resistance welding) pipe and automatic arc welding pipe because of the different welding process. Because of its different welding form is divided into straight seam welding pipe and spiral welding pipe two kinds. Because of its end shape is divided into circular welded pipe and shaped (square, flat, etc.) welded pipe.

Q235B Welded steel pipe

Q235 is a plain carbon structural steel that is used throughout China. It is also known as Q235A, Q235B, Q235C, and Q235D. Since it is mild steel, it is utilized in production without heat treatment. The Q designates the yield point, and the 235 indicates the yield strength. It has good plasticity and weldability.

Q235 Equivalent Materials

The Q235 steel can be substituted with equivalent materials that include A36 USA ASTM, Q235 China GB/T, and SS400 Vietnam/Japanese JIS.

Characteristics of Q235

As the thickness of the material increases, Q235’s yield value decreases. Due to its moderate carbon content, the performance is comprehensive and adequate. Q235 also matches well in strength, welding, and plasticity. Most often, it is rolled into a steel plate, rod, bar, or angle frame. It is most commonly used in the engineering and construction industries.

The Q235 steel material is in accordance with PRC standards. Carbon steel for special projects and purposes, like marine and bridge steel, typically uses carbon structural steel expression. However, the letter indicating intents and purposes is included at the end of steel grade.

While the Q235 grade steel plate has lower mechanical properties than the A36 materials, these materials can generally be substituted for one another, as long as there are no special requirements and needs involved. If only for the material’s mechanical properties, it is generally acknowledged that Q235 and A36 are similar to those of high-quality carbon structural steel.

Uses of Q235

Not only does Q235 possess toughness, weldability, and excellent plasticity, it retains strength while offering outstanding cold-bending performance. It is perfect for welded structures, including factory buildings, steel bars, towers, boilers, bridges, containers, vehicles, and more. Q235 can also be used as mechanical parts, such as stands, stressed rods, nuts, connecting rods, brackets, and other components. Q235 and varying grades of steel plates can be cut to specification.

Q195 Welded steel pipe

With the rapid development of high quality strip rolling production and the progress of welding and inspection technology, the quality of weld is constantly improving, the variety and specification of welded steel tube is increasing day by day, and it has replaced seamless steel tube in more and more fields.

Q195 steel is a Chinese steel grade of carbon introductory steel,”q”represents yield quality,”195″signifies the yield quality is 195 mpa, and severity is 315 – 430 mpa, information is tried dependent on a 16 mm range steel bar. Q195 material consistence is7.85 g/ cm3, the physical properties and emulsion structure are commensurate to ASTM –gr.B (σs185),gr.C (σs205); chatter – st33, s185; jis – ss330 (σs205), sphc (σs205), sphd (σs205); bs – 040a10, s185 (σs185mpa). Q195 carbon supplementary steel is astronomically employed on the earth, on account of its brilliant incorporated donation in quality, versatility, and welding, and so forth. Q195 steel can be made into a large number of steel particulars, for illustration, steel line bar, aroused line, confining line, welded work, essence hedge, steel plates, steel tubes,as well as cylinders with a steel edge, and so forth.. Q195 material has high versatility, continuity, and weldability, great weight, and processability, still low quality. It has multitudinous applications, for illustration, the assembling of line poles, steel plates. Line poles can be cold brought into low carbon steel cables, at that point to make dark or aroused iron line, tie line, welded line work, line hedge, and some precipitously; cold and hot- moved steel wastes are generally employed in material boards, beautiful boards, speeding holders, iron cans, instrument cases, switch boxes, protective spreads, and so on. Different operations incorporate creation of steel pipes, steel points, stay jolts, heaps, material gobbets, bolts, tie poles, snares, sections, welded structures, and so forth.

The blank used for welding steel pipe is steel plate or strip steel, which is divided into furnace welding pipe, electric welding (resistance welding) pipe and automatic arc welding pipe because of the different welding process. Because of its different welding form is divided into straight seam welding pipe and spiral welding pipe two kinds. Because of its end shape is divided into circular welded pipe and shaped (square, flat, etc.) welded pipe.

Galvanized steel pipe Grades

Galvanized pipe, also known as galvanized steel pipe, divided into hot dip galvanized and electric galvanized two, hot dip galvanized galvanized layer thick, with uniform coating, strong adhesion, long service life and other advantages. Electric galvanized cost is low, the surface is not very smooth, its own corrosion resistance is much worse than hot dip galvanized pipe.

Q235A >> Q235B >> Q195 >> Q215B >> Q235C >> Q345A >> Q345C >> Q345D >> Q345B >> 20steel >>

Stainless steel pipe Grades

Stainless steel pipes are the most searched and most wanted pipes all around the world due to the qualities they exhibit. Stainless Steel pipes are the best and most reliable when working in any of the areas such as chemical industries, kitchen areas, hotter environments, water supply areas. It offers the best quality and the properties it exhibits makes it superior and best suited for many domains.

321 >> 316L >> 201 >> Q345E >> Q345D >> Q345C >> Q345B >> Q275B >> Q215B >> Q235B >> Q195 >> 304 >>

Steel Pipes: Everything You Need to Know

Steel pipes are hollow cylindrical tubes that have been utilized by mankind for thousands of years for different purposes. Pipes can be produced from almost every material, however, since the modern-day meaning of pipes requires more than only being hollow tubes that transport fluid, metals have become more popular in pipe production. As a metal alloy, steels offer a great variety of mechanical and chemical properties that can be utilized under even extreme applications, therefore today, steel pipes have been utilized in many different applications for transportation manufactural and structural purposes. Steel pipes may be produced with different grades of steel with different production methods which vary due to application requirements.

What is a Pipe?

Steel pipes are long and hollow tubes that are used for many different applications in a variety of places. Its versatility makes pipes the most often used product that is produced by the steel industry. They are commonly used to convey fluid substances that can flow, and small solid particles. Due to their high strength, they can also be utilized in underground transportation of water and gas through cities, or in construction for purposes like heating, plumping, etc. People have been utilizing and producing pipes for different purposes for thousands of years. Archeological evidence verifies that even in 2000 BC ancient agriculturists or Chinese people have utilized pipes made from different materials like wood or bamboo, for water transportation. Since the 1800s, great strides have been accomplished in the technology of steel pipes, including improving manufacturing methods, developing applications for their use, and establishment of regulations and standards that govern their certification.

How is Pipe Used?

Pipes are utilized in structures, transportation, and manufacturing. Different materials, design characteristics, and production methods for steel pipes have been developing and varying accordingly to the application.

Structural use is commonly building and construction in which the building material is commonly referred to as steel tubes. Steel tubes are used to provide additional strength and stability for especially high buildings or constructions. Two types of steel pipes are utilized in structural usage as end-bearing piles and friction piles that both have the aim of transferring the load of the building. In those applications, steel pipes are driven deep into the earth before the foundation is laid, which constitutes great support to the building especially when the ground is not secure. Another structural application of steel pipes is scaffolding poles which allow construction workers to access all areas of the building that are out of reach. They are made by linking steel tubes into each other as a cage that surrounds the building.

Steel pipes are being utilized for many different purposes in manufacturing use. Guard rails are one of the most common usages to provide a safety feature for stairs and balconies, or, in street, for cyclists and pedestrians. Steel pipes can also be utilized as security bollards which are used to cordon off an area from vehicle traffic to protect people, buildings, or infrastructures. Also, steel pipes constitute an option for outdoor site furnishings. Many commercial bike racks are formed by bending steel tubes. High toughness and strength of steel make it secure against thieves.

The most common usage of steel pipes is the transportation of products since the characteristics of the raw material is very suitable for long-term installations. As it has mentioned before, different applications require different properties, as for low-pressure applications it is not expected for a steel pipe to exhibit ultra-high-strength since it does not expose to significant loading. More specialized applications to be used in the oil and gas industry may require more stringent specifications due to the hazardous nature of the product and the possibility of increasing pressure. These requirements bring a higher cost and quality control becomes more critical.

Design Parameters

There are two types of pipes as seamless and welded seam, and both have different uses. Seamless pipes are generally thinner and lighter, thus they are most widely used in bicycle production and fluid transportation. Seamed pipes are more heavy and rigid to obtain better consistency and durability. Pipes that are used for gas transportation, electrical conduit, and plumbing are generally seamed. During production, several parameters should be controlled to maintain the required properties for the application. As an example, the diameter of a pipe is designed directly related to how it will be used. While pipes with a smaller diameter may be used for hypodermic needles, large diameter pipes may be used for transport through cities. Wall thickness is also an important parameter to control since it directly affects the pipe’s strength and flexibility. Length, coating, and end finish are also other controllable parameters that are all related to each other as will be explained later. 

Steel Types Used in Pipes

Carbon steels represent approximately 90% of total steel pipe production. They are consist of relatively lower amount of alloying elements and are generally perform weak as used alone. Since their mechanical properties and machinability are sufficient they may cost a little less and they may be preferred more for especially low-stress applications. Lack of alloying elements lowers the suitability of carbon steels for high-pressure applications and extreme conditions, so they become less durable under high loadings. The main reason to prefer carbon steels for pipes may be their advanced ductility and non-bending nature under loading. They are generally used in the automotive and marine industry, and oil and gas transportation. A500, A53, A106, A252 are carbon steel grades that can either be used as seamed or seamless.

The presence of alloying elements improves the mechanical properties of steel, thus pipes become more resistant to high-stress applications and high pressures. The most general alloying elements are nickel, chromium, manganese, copper, etc. which are present in the composition between 1-50 weight percent. Different amounts of different alloying elements contribute mechanical and chemical properties f the product in varying manners, therefore the chemical composition of steels is also modified accordingly to requirements of applications. Alloyed steel pipes are generally used under high loadings with unstable conditions as in the oil and gas industry, refineries, petro-chemistry and chemistry factories.

Stainless steel can also be included in the alloyed steel family. The main alloying element in stainless steel is chromium whose fraction varies between 10-20 weight percent. The main purpose of chromium addition is to make steel gain stainless properties by preventing corrosion. Stainless steel pipes are generally utilized under extreme conditions where corrosion resistance and high strength are vital, as in the marine industry, water purification, medicine and, oil and gas industry. 304/304L and 316/316L are stainless steel grades that can be used in pipe production. While 304 grade has great corrosion resistance and strength; due to low carbon content, 316 series exhibit lower strength and can be welded.

Galvanized pipes are steel pipes that are treated with a zinc coating to prevent corrosion. Zinc coating keeps corrosive substances from corroding the pipe.  It was once the most common type of pipe for water supply lines, but because of labor and time that goes into cutting, threading, and installing galvanized pipe, it no longer used much, except for limited use in repairs. These types of pipes are prepared from 12 mm (0.5 inches) to 15 cm (6 inches) in diameter. They are available in 6 meters (20 feet) length. However, galvanized pipe for water distribution is still seen in larger commercial applications. One important disadvantage of galvanized pipes is their 40-50 years of lifetime. Despite that zinc coating covers the surface and avoids external substances to react with steel and corrode it, if the transported substances are corrosive pipe may start corroding from inside. Therefore, it is crucial to control and upgrade galvanized steel pipes in certain periods.

Pipe Types

Pipes are classified into two groups as seamless pipes and seamed pipes accordingly to the manufacturing methods. Seamless pipes are formed at one stage during rolling, however seamed pipes require a welding process after rolling. It is possible to classify seamed pipes into two due to the seam geometry as spiral welding and straight welding. Although there is a debate about whether seamless is better than seamed steel pipes, both seamless and welded pipe manufacturers can produce steel pipes providing high quality, reliability, and corrosion resistance. The main focus should be the specifications of the application and cost aspects while determining pipe type.

Seamless pipes are generally made in complex steps starting from drilling hollows from billets, by cold drawing and cold rolling processes. To control outside diameter and wall thickness, seamless type dimension is difficult to control compared to the welded tube, cold work improves the mechanical properties and tolerances. The most significant advantage of seamless pipes is that they can be produced in heavy and thick wall thicknesses. Due to their having no weld seam, makes they to be considered as exhibiting better mechanical properties and corrosion resistance than seamed pipes. Also, a better ovality or roundness is expected from seamless pipes. They are generally preferred to be used under extreme environmental conditions as high loading, high pressure, and high corrosivity.

The welded steel pipe is formed by welding a steel plate rolled into a tubular shape by a seam or a spiral seam. Depending on the outer dimension, wall thickness, and application, there are different ways of manufacturing welded pipes. Each method initiates with steel hot billet or flat strips and then made into a pipe by stretching the hot steel billet and forcing the edges together and sealing them with a weld. Seamed pipes offer tighter tolerances but thinner wall thickness rather than seamless pipes. Shorter lead time and lower cost may also be reasons why seamed pipes can be preferred over seamless pipes. However, since weld seam may constitute sensitive areas that may be suitable for any crack to propagate and lead to fracture of the pipe, surface finishing of outside and inside of the pipe should be controlled during production.

Pipe Manufacturing

In both the manufacturing methods, raw steel is first cast into a more workable starting form (hot billet or flat strip). It is then made into a pipe by stretching the hot steel billet out into a seamless pipe or forcing the edges of the flat steel strip together and sealing them with a weld.

Mandrel Mill Process

In the Mandrel Mill Process, a solid round steel billet is used. The billet is charged into a rotary hearth furnace. After the billet is discharged from the rotary hearth furnace, a small hole is punched into its end. This indentation acts as a starting point to aid in the rotary piercing. Rotary piercing is a very fast and dynamic rolling process that cross rolls the preheated billet between two barrel-shaped rolls at a high speed. The design of the piercer rolls causes the metal to flow along with the roll and over a piercer point as it exits the process. The piercer point is a high-temperature, water-cooled alloy tool designed to allow the metal to flow over it as a pipe shell forms from the rotary process. Once the pierced pipe shell is produced, it is immediately transferred to the floating mandrel mill. The floating Mandel mill comprises eight rolling stands using 16 rolls and a set of mandrel bars. These bars are inserted into the pierced pipe shell and then conveyed into the mandrel mill, and rolled into a pipe shell. Then the mandrel mill is re-heated in order to complete the final rolling stage and to gain final dimensions. While the mill is leaving the furnace, the iron-oxide scale is removed from the surface via high-pressure water descale. The pipe shell is further reduced to specified dimensions by the stretch mill.

Mannesmann Plug Mill Process

Mannesmann plug mill process differs from mandrel milling with a great difference of rolling plug usage instead of a mandrel mill. In the Mannesmann process, a pair of conical rolls are arranged on top of each other and operate in the opposite direction to material flow. A hollow pipe shell having thick walls is guided towards the plug mill rolls.  As soon as it is gripped by the tapered portion of the work pass, a small material wave is sheared off the hollow pipe shell. This wave is forged to the desired wall thickness on the mandrel by the smoothing portion of the work pass, with the hollow pipe shell plus mandrel moving backward in the same direction as the rolls are rotating until they reach the idler pass of the rolls and are released. As the hollow pipe shell is rotated it is once again pushed forward between the rolls, and a new rolling cycle begins.

Extrusion

Extrusion is a metal forming process in which a workpiece is forced into a die of the smaller cross-section. The length of the extruded part will vary, dependent upon the amount of material in the workpiece and the profile extruded. Numerous cross-sections are manufactured by this method. Steel pipes can be directly produced by extrusion with the usage of a mandrel attached to the dummy block. A hole is created through the workpiece parallel to the axis over which the ram applies the force to form the extrusion. When the operation begins, the ram is forced forward. The extruded metal flows between the mandrel and the die surfaces, forming the part. The interior profile of the metal extrusion is formed by the mandrel, while the exterior profile is formed by the extruding die.

Seamed pipes are manufactured from plate or continuous coil or strips. To manufacture a seamed pipe, the first plate or coil is rolled in the circular section with the help of a plate bending machine or by a roller in the case of a continuous process. When the circular section is rolled from the plate, the pipe can be welded with or without filler material. There are different welding methods used to weld the pipe.

Electric Resistance Welding Process (ERW)

In the electric resistance welding process, the pipe is produced by cold-forming a flat sheet of steel into ay cylindrical geometry. Then the current is passed through the edges of the steel cylinder to heat up the steel and form a bond between the edges at a point that they are forced to meet. During ERW processes filler materials may also be utilized. There are two types of electric resistance welding as high-frequency welding and rotary contact wheel welding.

The requirement for high-frequency welding has arisen from the tendency of low-frequency welding products to undergo selective seam corrosion, hook cracks, and inadequate bonding of seams. So, low-frequency ERW is no longer used to manufacture pipes. The high-frequency ERW process is still being used in pipe manufacturing. There are two types of high-frequency ERW processes. High-frequency induction welding and high-frequency contact welding are types of high-frequency welding. In high-frequency induction welding, the weld current is transmitted to the material through a coil. The coil does not contact the pipe. The electrical current is induced into the pipe material through magnetic fields that surround the pipe. In high-frequency contact welding, the current is transmitted to the material through contacts that ride on the strip. The welding power is applied directly to the pipe, which makes this process more effective. This method is generally preferred for large diameter and high wall thickness pipe production.

Another type of electric resistance welding is the rotary contact wheel welding process. During this process, electrical current is transmitted through a contact wheel at the weld point. The contact wheel also applies the pressure necessary for welding. Rotary contact welding is generally utilized for applications that cannot accommodate an impeder inside the pipe.

Electric Fusion Welding Process (EFW)

The electric fusion welding process refers to an electron beam welding of a steel plate by the use of the high-speed movement of the electron beam. High impact kinetic energy of the electron beam is converted into heat to heat the workpiece so that the weld seam is produced.  The welding zone can also be heat treatment so that the weld is not visible. Welded tubes generally have tighter dimensional tolerances than seamless tubes, and if made in the same amount, the cost is lower. Mainly used for dissimilar steel welding sheet or high power density welding, metal welding parts can be quickly heated to high temperatures, melting any refractory metals and alloys.

Submerged Arc Welding Process (SAW)

Submerged arc welding involves arc formation between a wire electrode and the workpiece. A flux is used to generate protective gases and slag. As the arc moves along the joint line, excess flux is removed via a hopper. As the arc is completely covered by the flux layer, it is not normally visible during welding, and heat loss is also extremely low. There are two types of submerged arc welding processes as longitudinal submerged arc welding and spiral submerged arc welding processes.

In longitudinal submerged arc welding, longitudinal edges of steel plates are first beveled by milling to form a U shape. Edges of the U shaped-plates are then welded. Pipes manufactured by this process are subjected to expanding operation in order to relieve internal stresses and obtain a perfect dimensional tolerance.

In spiral submerged arc welding, weld seams are like a helix around the pipe. In both of the longitudinal and spiral welding methods the same technology is utilized, the only difference is the spiral shape of seams in spiral welding. The manufacturing process is rolling the steel strip, to make the rolling direction have an angle with the direction of the pipe center, forming and welding, so the welding seam is in a spiral line. The major disadvantage of this process is bad physical dimension of pipes and higher seam length which can easily lead into a defect or crack formation.

Quality Control

A variety of measures are taken to ensure that the finished steel pipe meets specifications. For example, x-ray gauges are used to regulate the thickness of the steel. The gauges work by utilizing two x rays. One ray is directed at a steel of known thickness. The other is directed at the passing steel on the production line. If there is any variance between the two rays, the gauge will automatically trigger a resizing of the rollers to compensate. Pipes are also inspected for defects at the end of the process. One method of testing a pipe is by using a special machine. This machine fills the pipe with water and then increases the pressure to see if it holds. Defective pipes are returned for scrap.

Specifications

There can be confusion about the way these materials are specified, and what the means to the exact characteristics of the pipe. The American Society for Testing and Materials (ASTM) along with The American Society of Mechanical Engineers (ASME) and the American Petroleum Institute (API) are the most referenced organizations for piping specifications in North America.

Pipe size is quoted as a “Nominal Pipe Size” or NPS. The origin of the NPS numbers for smaller pipes (< NPS 12) is different to the origin for larger diameter pipes. However, all pipes of a specific NPS number have the same external or outer diameter (OD). The internal diameter will vary depending on the wall thickness of the metal. The reason for this is so that the same structural supports can be used for all piping of a specific NPS number regardless of the wall thickness.

Steel pipe schedules are used to describe the wall thickness for pipes. Since it is a significant parameter that affects the strength of the pipe directly, it should be controlled properly. A pipe schedule is a dimensionless number and is calculated based on the design formula for wall thickness, given the design pressure and allowable stress. As the schedule number increases, the wall thickness of the pipe increases. The schedule number of a pipe therefore defines the internal diameter, as the OD is fixed by the NPS number.

Pipe weight can be calculated by depending on NPS, which defies outer diameter, and the schedule which defines wall thickness of pipes. The formula uses the theoretical weight of steel of 40.8 pounds per square foot per 1 inch of thickness to determine the constant. Pipe weight is represented by the following formula where t is thickness, OD is outer diameter and W is pipe weight: W = 10.69 x t (OD – t)

Standards

Manufacturing standards for pipes commonly require a test of chemical composition and a series of mechanical strength tests for each heat of pipe. A heat of pipe is all forged from the same cast ingot, and therefore had the same chemical composition. Mechanical tests may be associated to a lot of pipe, which would be all from the same heat and have been through the same heat treatment processes. Material with these associated test reports is called traceable. For critical applications, third party verification of these tests may be required; in this case an independent lab will produce a certified material test report, and the material will be called certified.

Some widely used pipe standards or piping classes are as following:

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