Manufacturing Process

Petrosadid: Manufacturing Process

Steel pipe can be broadly categorized according to manufacturing method as seamless pipe made by hot rolling or hot extrusion, and welded pipe and butt-welded pipe made by bending and welding sheets or plates.

When seamless pipe is made by rolling, the rolling method involves piercing the material while it is being rolled, and is suitable for mass production. The figure shows the manufacturing process used in the Mannesmann plug mill, which is a typical rolling process. The Mannesmann-type piercer reduces the material by rolls that are inclined obliquely to each other. When the round billet is rotated while being compressed in the diametric direction, the central part of the billet becomes loose, which makes it easy to pierce a hole through the center. This is called the Mannesmann effect. The pierced portion is expanded by the elongator, and the wall thickness is then thinned and elongated by the plug mill. The internal and external surfaces are smoothed by the reeler, and the final dimensional adjustments are made by the sizer.

The hot-extrusion method involves working in the compressive-stress field. Therefore, it is characteristic of this method that high-alloy steel pipe of low deformability can be produced, as well as heavy-wall and large-diameter pipes.

Seamless pipe has outstanding homogeneity in the circumferential direction and is thus highly resistant to internal pressure and torsion. Taking advantage of this feature, seamless pipe is widely used for drilling and pumping petroleum and natural gas.

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Welded pipe is divided into electric-resistance welded (denoted ERW hereinafter) pipe, spiral pipe, and UO pipe according to the forming and welding method. ERW pipe and butt-welded pipe are produced by continuously forming a hot-rolled coil into a tubular shape by forming mills. ERW pipe is produced by cold forming, and the seam is welded by electric-resistance welding. This type of steel pipe is used in large quantities as line pipe for transporting petroleum and gas. Butt-welded pipe is produced by hot forming after the whole material has been heated, and seams are then butt welded. This type of pipe is hot-dip galvanized and used for carrying water and gas.

The outer diameter of ERW pipe and butt-welded pipe is determined by the width of the material coil. However, as shown in the figure, spiral pipe is made by forming the coil into a spiral shape, which makes it possible to obtain a large outer diameter regardless of the width of the material. UO pipe is usually large in diameter and produced one piece at a time by forming plates. The plate is first pressed into a U shape by the U-press, and then into an O shape by the O-press.

Because relatively thick material is used for making spiral and UO pipes, submerged arc welding is used for joining. The principal application of spiral pipe is pipe piles. UO pipe, as mentioned above, is mainly used as line pipe for transporting petroleum and natural gas in large quantity over long distances.

Seamless Pipes

Seamless pipe is Strongest amongst all pipes type as it has a Homogeneous structure throughout pipe length.

Seamless pipes are manufactured in a verity of size and schedule. However, there is a Restriction on the manufacturing of large diameter pipe. Seamless pipes are widely used in the manufacturing of pipe fittings such as bends, elbows, and tees.

Various Manufacturing process are explained in detail;

• Mandrel Mill Process

• Mannesmann Plug Mill Pipe

• Forged Seamless Pipe

• Extrusion Processes

Petrosadid: Manufacturing Process

The seamless pipes manufacturing process involves the following steps:

• Transformation of raw materials into steel bars (Electric arc furnace, ladle furnace, vacuum degassing and continuous casting processes)

• Transformation of steel bars into mother pipe, which is manufactured in different types of rolling mills

Each product is manufactured in accordance with customer specifications, including heat treatment for more demanding applications. The pipes are threaded and undergo non-destructive testing before delivery to the customer.

We can also offer cold-drawing for pipes with the diameter and wall thickness required for use in boilers, superheaters, condensers, heat exchangers, automobile production and several other industrial applications.

Seamless Pipes Manufacturing

In Mandrel Mill pipe manufacturing process, steel billet is heated to high temperature in the rotary furnace. A cylindrical hollow, which is also known as mother hollow, is produced with the help of a rotary piercer and set of roller arrangement that keeps the piercer at the center of the billet. Outside diameter of piercer is approximately that of the inside diameter of the finished pipe. With the help, secondary roller arrangement outside diameter and thickness are achieved.

Petrosadid: Manufacturing Process

In the Plug Mill Process, a solid round (billet) is used. It is uniformly heated in the rotary hearth heating furnace and then pierced by a Mannesmann piercer. The pierced billet or hollow shell is roll reduced in outside diameter and wall thickness. The rolled pipe simultaneously burnished inside and outside by a reeling machine. The reeled pipe is then sized by a sizing mill to the specified dimensions. From this step the pipe goes through the straightener. This process completes the hot working of the pipe. The pipe (referred to as a mother pipe) after finishing and inspection, becomes a finished product.

Petrosadid: Manufacturing Process

In a Forging pipe manufacturing process, a heated billet is placed in forging die that has a diameter slightly larger than the finished pipe. A hydraulic press of forging hammer with matching inside diameter is used to create cylindrical forging. Once this forging is done pipe is machined to achieve final dimension. Forging pipe manufacturing process is used to manufacture large diameter seamless pipe that cannot be manufactured using traditional methods. Forged pipes are normally used for the steam header.

Petrosadid: Manufacturing Process

In an extrusion pipe manufacturing a heated billet is placed inside the die. A hydraulic ram pushes the billet against the piercing mandrel, material flows from the cylindrical cavity between die and mandrel. This action produces the pipe from the billet. Sometimes pipe manufactured produce pipe with a high thickness which is known as mother hollow. Many secondary pipes manufactured used this mother hollow to produce pipe with different dimensions.

Petrosadid: Manufacturing Process

Welded Pipes

Welded Pipes are manufactured from Plate or continues Coil or strips. To manufacture welded pipe, first plate or coil is rolled in the circular section with the help of plate bending machine or by a roller in the case of continues process. Once the circular section is rolled from the plate, the pipe can be welded with or without filler material. Welded pipe can be manufactured in large size without any upper restriction. Welded pipe with filler material can be used in the manufacturing of long radius bends and elbow. Welded pipes are cheaper with compared to the seamless pipe and also Weak due to the weld

There are different welding methods used to weld the pipe.

• ERW- Electric Resistance Welding

• EFW- Electric Fusion Welding

• HFW- High-frequency welding

• SAW- Submerged Arc Welding (Long seam & Spiral Seam)

Less thickness pipe, mainly ERW / EFW or HFW welded pipe are formed by continues rolling method. In this method, a flat metal strip from the strip coil is feed into the series of roller assembled in line. These rollers gradually form the strip in the circular section. At the end of rolling assembly, this pipe is continuously welded by welding machine.

ERW/EFW and HFW are welding methods in which pipe is welded without adding filler material. However, EFW welding method can be used with filler material also.

Petrosadid: Manufacturing Process

Welded Pipes Manufacturing Process

In ERW welding, two electrodes, usually made from copper, are used to apply pressure and current. The electrodes are disc shaped and rotate as the material passes between them. This allows the electrodes to stay in constant contact with the material to make long continuous welds.

A welding transformer supplies low voltage, high current AC power. The joint of the pipe has high electrical resistance relative to the rest of the circuit and is heated to its melting point by the current. The semi-molten surfaces are pressed together with a force that creates a fusion bond, resulting in a uniformly welded structure.

Petrosadid: Manufacturing Process

EFW steel pipe is formed by rolling plate and welding the seam. The weld flash can be removed from the outside or inside surfaces using a scarfing blade. The weld zone can also be heat treated to make the seam less visible. Welded pipe often has tighter dimensional tolerances than seamless, and can be cheaper if manufactured in the same quantities. It is mainly used for welding dissimilar steel welding sheet or which high power density, metal weldment can rapidly heated to high temperatures, which can melt any refractory metals and alloys. Deep penetration welding fast, heat-affected zone is extremely small, so small performance impact on the joints, the joint almost no distortion. But it has a requirement on a special welding room because welding using X-rays.

Petrosadid: Manufacturing Process

High frequency welding (HFW) steel pipe is that ERW pipe produced with a welding current frequency equal to or greater than 70 kHZ. Through high-frequency current welding resistance, the heat generated in the contact objects, so the objected surface are heated to the plastic state, then with or without forging to achieve a combination of steels. HFW is a solid resistance heat energy. The high frequency current pass through the metal conductor, will produce two peculiar effects, skin effect and proximity effect. And HFW process is to use the skin effect to concentrate on steel object surface, use proximity effects to control the position and the power of the high-frequency electric current flow path. Since the speed is very high, the contacted plate edge could be heated and melted in short time, then extruded through docking process.

In the welding process, HFW steel pipes do not need to add filling meta. So it has fast welding speed and high efficiency in production. HFW pipe is widely used in the fields of oil and gas transportation, oil well pipeline, building structure and various kinds of mechanical pipe. However, HFW steel pipe quality is affected by many factors, such as raw material and process. And the production quality control become difficult. So the yield and welding process still need to be improved continuously.

Petrosadid: Manufacturing Process

LSAW Pipe (Longitudinal Submerged Arc-Welding Pipe), is taking the steel plate as raw material, mold it by the molding machine, then do double-sided submerged arc welding. Through this process the LSAW steel pipe will get excellent ductility, weld toughness, uniformity, plasticity and great sealing.

Petrosadid: Manufacturing Process

SSAW Pipe (Spiral Submerged Arc-Welding Pipe), also called HSAW pipe, welding line shape like a helix. It is using the same welding technology of Submerged Arc-Welding with LSAW pipe. Differently SSAW pipe is spiral welded where the LSAW is longitudinally welded. 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.

Petrosadid: Manufacturing Process
Petrosadid: Manufacturing Process

Heat Treatment Method of Carbon and Alloy Steel Pipe

Heat treatment methods for carbon and alloy steel pipe include 4 mainly types:

Normalizing, Annealing, Quenching and Tempering.

It will improve steel material mechanical properties, uniform chemical composition, and machinability.

Heat treatment for steel metal materials can be divided into integral heat treatment, surface heat treatment and chemical heat treatment. Steel pipe generally adopts the integral heat treatment.

The performance of steel material mainly refers on mechanical properties, physical properties, and process performance. Heat treatment will bring different metallurgical structure and corresponding performance for the steel pipe, so could be better applied in different industrial or the oil and gas services.

There are two methods to improve the properties of steel material. One method is to adjust the chemical composition, named alloying method. The other method is heat treatment. In the field of modern industrial technology, heat treatment improve steel pipe performance at dominate position.

Heat treatment purposes

1. Heating.

The steel material could be heated below the critical point or above critical point. The former heating way can stabilize structure and eliminated the residual stress. The latter way can make material austenitizing.

Austenitizing is to heat steel metal over its critical temperature long time enough, so it could be transformed. If a quenching followed after Austeniting, then the material will be harden. Quenching will take fast enough to transform austenite into martensite. Once reached austenitizing temperature, suitable microstructure and full hardness, the steel pipe material will be attained in further heat treatment processes.

2. Heat preservation.

The purpose of heat preservation is to uniform the heating temperature of steel material, then it will get a reasonable heating organization.

3. Cooling

The cooling process is the key process in heat treatment, it determines mechanical properties of steel pipe after cooling process.

Four main heat treatment methods in carbon and alloy steel pipe industry

The heat treatment processes for steel pipe includes normalizing, annealing, tempering, quenching and other process.


Heating the steel pipe above the critical temperature, and cooled in the air.

Through normalizing, the steel material stress could be relieved, improves ductility and toughness for the cold working process. Normalizing usually applied for the carbon and low alloy steel pipe material. It will produce different metal structure, pearlite, bainite, some martensite. Which brings harder and stronger steel material, and less ductility than full annealing material.


Heating the material to above its critical temperature long enough until microstructure transform to austenite. Then slow cooled in the furnace, get maximum transformation of ferrite and pearlite.

Annealing will eliminate defects, uniform the chemical composition and fine grains. This process usually applied for the high carbon, low alloy and alloy steel pipe need to reduce their hardness and strength, refine the crystal structure, improve the plasticity, ductility, toughness and machinablity.


Heating the steel pipe material to critical temperature until microstructure transformation is done, cooling it in a rapid rate.

Quenching purpose is to produce the thermal stress and tissue stress. It can eliminate and improve through the tempering. The combination of quenching and tempering can make the comprehensive performance improved.


Heating the steel material to a precise temperature below the critical point, and often done in the air, vacuum or the inert atmospheres. There are low temperature tempering 205 to 595°F (400 to 1105°F), medium temperature and high temperature tempering (to 700℃ 1300°F).

The purpose of tempering is to increase the toughness of steel and alloy steel pipe. Before tempering, these steel is very hard but too brittle for the most application. After process can improve the plasticity and toughness of steel pipe, reduce or eliminate the residual stress and stabilize the steel pipe’s size. Brings good comprehensive mechanical properties, so that it does not change in service.

Solution treatment for alloy-based steel pipe material

Heating an alloy to a proper temperature, preserve it at this temperature long enough to cause or more constituents to change into a solid solution, then cooling it at rapid rate to hold these constituents in solution.

There are several of cast and wrought nickel-based alloys that can achieve different required performances through solution treatment or by precipitation age hardening. Characteristics as room temperature and elevated temperature mechanical strength, corrosion resistance and oxidation resistance will be significantly enhanced by this heat treatment. Many nickel-based alloys develop their desired properties solely through the solution treatment, like Hastelloy and nickel alloy steel pipe.

During solution treatment, the carbide and various alloying elements are dissolved uniformly in the austenite. Cooling rapidly will make carbon and alloy elements too late to precipitate, and obtain the heat treatment process of single austenite tissue. The solution treatment can uniform internal structure and chemical compostion. It can also restore the corrosion resistance for Hastelloy and nickel alloy steel pipe.

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