What is seamless pipe ?

Seamless steel pipes are perforated from whole round steel, and steel pipes without welds on the surface are called seamless steel pipes. According to the production method, seamless steel pipes can be divided into hot-rolled seamless steel pipes, cold-rolled seamless steel pipes, cold-drawn seamless steel pipes, extruded seamless steel pipes, and top pipes. According to the cross-sectional shape, seamless steel pipes are divided into two types: round and special-shaped. Special-shaped pipes include square, oval, triangular, hexagonal, melon seed, star, and finned pipes. The maximum diameter is 900mm and the minimum diameter is 4mm. According to different purposes, there are thick-walled seamless steel pipes and thin-walled seamless steel pipes. Seamless steel pipes are mainly used as petroleum geological drilling pipes, cracking pipes for petrochemical industry, boiler pipes, bearing pipes, and high-precision structural steel pipes for automobiles, tractors, and aviation.

Seamless steel pipes are widely used.

  1. General-purpose seamless steel pipes are rolled by ordinary carbon structural steel, low-alloy structural steel or alloy structural steel, with the largest output, and are mainly used as pipelines or structural parts for conveying fluids.
  2. According to different purposes, it can be supplied in three categories:
    a. Supply according to chemical composition and mechanical properties;
    b. According to mechanical performance;
    c. According to the water pressure test supply. Steel pipes supplied according to categories a and b. if used to withstand liquid pressure, shall also be subjected to a hydraulic test.
  3. Special-purpose seamless pipes include seamless pipes for boilers, chemical and electric power, seamless steel pipes for geology, and seamless pipes for petroleum.

Seamless steel pipes have a hollow section and are used in large quantities as pipelines for transporting fluids, such as pipelines for transporting oil, natural gas, gas, water and certain solid materials. Compared with solid steel such as round steel, steel pipe is lighter in flexural and torsional strength and is an economical section steel. Widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipes, automobile transmission shafts, bicycle frames, and steel scaffolding used in construction. Steel pipes are used to make ring parts, which can improve material utilization, simplify manufacturing procedures, and save materials and processing. Working hours.

There are two main production processes for seamless steel pipes (cold rolling and hot rolling):
①Main production process of hot-rolled seamless steel pipe (△main inspection process):
Tube billet preparation and inspection△→tube billet heating→perforation→tube rolling→pipe reheating→fixed (reduced) diameter→heat treatment△→finished tube straightening→finishing→inspection△(non-destructive, physical and chemical, bench inspection)→in storage

②Main production process of cold-rolled seamless steel pipe:
Blank preparation → pickling and lubrication → cold rolling (drawing) → heat treatment → straightening → finishing → inspection → storage

Seamless pipe specification, dimensions, and sizes

seamless pipe specification 1

How is a seamless pipe made?

A single solid piece of the desired material is used to make the seamless pipes. There are two ways of making them; one is a cold drawing, and the other is a hot drawing. The Cold drawn seamless pipe is pulled or extruded from a single metallic billet without the need for heating. The piece of metal is extruded to form the pipe. The hot drawing involves heating the metal to ambient temperatures and then drawing it to the desired shape.

What are the seam and seamless pipe differences?

Cold rolled seamless steel pipe and hot-rolled ones have no seams because they are not welded to make the pipe. The welded pipes are made from a single piece of metallic sheet and rolled to make the ends of the plate touch each other. Then the ends are welded together. So the welded line is always present in the welded pipe. This is called the seam; the seamless pipes don’t look polished because of the extrusion process. The welded pipes have a surface polished up to make sure that the seam does not block the fluid flow. The nominal sizes of the seamless pipes are restricted to a maximum of 24 inches. The welded pipes can have any diameter. The seamless pipes have a higher production cost and higher processing time compared to the welded pipes.

What is seamless pipe used for?

Seamless pipes have applications for high pressure, high temperature, and thicker walls. The applications include hydraulics, industrial boilers, and chemical gas processing industries. The pipes can also be coated through different coating materials and methods such as the Seamless gi pipe so as to bring more corrosion resistance. Since the absence of the seam, the seamless pipes are less corrosive compared to the welded pipes. So the applications include oil and gas industries, both offshore and onshore.

Applications for Seamless Steel Pipe

Seamless steel pipe is versatile and can be used for several different purposes. Below are a few of its most common applications.


When used as bearing piles, seamless steel pipe is an incredibly effective means of carrying as well as supporting loads from heavy structures. Seamless steel pipe can be filled with concrete to enhance its strength when used as bearing piles.


During the construction of drilled shafts, either permanent or temporary pipe casing is needed, which is where seamless steel pipe can come in handy. Seamless steel pipe is able to support the hole during construction while concrete and cage are applied.


Seamless steel pipe can be used to create combi walls, which are retaining wall structures. Seamless steel pipe is used as the king pile in combi wall construction in conjunction with steel sheet piles. The pipe supports most of the load while sheet pile assists in transferring the load to both the soil and the king pile. Combi wall design eliminates transfer of shear forces across the interlock of the system.


When used for structural sections, seamless steel pipe is a great choice because it offers an equal amount of bending strength in all directions, which makes it resistant to buckling. Its resistance to buckling enables it to handle significantly heavier loads for exceptional lengths. The employment of seamless steel pipe as structural sections is particularly useful for big, open structures as well as cofferdams.


Jacked and bored seamless steel pipe is an excellent choice in aiding in the installation of underground utilities. When used in this manner, a section of steel pipe is typically driven with the use of hydraulic jacks in between excavations. Then, a subsequent section of pipe is spliced to attach to the first section, and the pipe is subjected to cleaning out to make space for safe and efficient utility installation. When used for underground utilities in this way, disruption to nearby areas, specifically roads and businesses, is minimized.

These are just some of the main applications in which seamless steel pipe can be useful. Overall, seamless steel pipe is a practical option where versatility, durability, and strength are required, particularly when heavy loads are involved.

What Does Seamless Tube Mean?

A seamless tube is a tube that does not have any welding seam. The seamless tube will ideally be a solid metal tube with each end connected to another tube without having any welding joint. These tubes have threads either at one end or at both ends and can be threaded to the end of another hollow tube or pipe.

The presence of any seam on a welded tube acts as a weak point, however if the tube is seamless, it tends to be solid and overcome various industrial forces and pressures while in operation.

A seamless tube may also be known as a seamless pipe.

A seamless tube can be made from any of several alloys and metals such as carbon steel, stainless steel, molybdenum or tungsten. Seamless tubes are used in those industrial applications that mandate the highest safety requirements. In order to produce a seamless tube, a solid block is penetrated by a piercing plug before the tube is drawn to its desired size.

Some of the differences between seamless tubes and welded tubes are:

  • A seamless tube is extruded and drawn from a billet whereas a welded tube is produced from a strip that is roll formed and welded to produce a tube.
  • Since a seamless tube offers a higher range of safety measures it is more expensive than a welded tube.
  • A seamless tube is relatively short in length, whereas welded tubes can be manufactured in long continuous lengths.
  • A seamless tube generally doesn’t show any sign of corrosion until and unless it is subjected to a highly corrosive environment, whereas the weld area in the welded tube is much more prone to corrosion attacks.

A welded area is considered to be inhomogeneous, thus it exhibits a different malleability and less corrosion resistance as well as greater dimensional variation. A seamless tube eliminates any such issues and thus offers high corrosion resistance.

What is the difference betweenEN 10305-1 E235 Seamless Precision SteelPipe and Ordinary Seamless Pipe?

Many netizens have some doubts about the question of “the difference between EN 10305-1 E235 seamless precision steel pipe and ordinary seamless pipes”. I searched the internet and found that most of the answers were unanswered or messy, which disturbed the audiovisual, so I will explain this topic in detail.

Precision seamless tubes are a kind of seamless tubes, which complement each other with ordinary seamless tubes and play an important role in modern industry together. This paper mainly describes the difference between the two in six respects.

  1. Appearance

I think most people are no strangers to ordinary seamless pipes, which are round in shape and covered with a layer of red rust. Ordinary seamless pipes are made of carbon steel. Over time, iron oxide will form on the surface. As shown. In fact, the surface of the seamless tube that has just been made is not of this color, but of a cyan color, as shown in the figure. The use ofEN 10305-1 E235 seamless precision steel pipeis less than that of ordinary seamless pipes, so not everyone has seen this kind of pipe. Precision seamless pipes are usually produced by a cold rolling process. The metal is extruded and becomes dense. So the outer surface becomes very bright. Since mechanical oil is needed to cool in the production process, there is usually a thin layer of oil on the outer surface of the precision seamless pipe. This layer of oil film can play a certain role in preventing oxidation.

EN 10305-1 E235 seamless precision steel pipe: the outer surface is relatively bright.

Common seamless pipe: Seamless pipe that has been laid for a period of time has a thin layer of rust on the outer surface.

The newly produced precision steel pipe: the outer surface is cyan.

  1. Dimensional accuracy

You can see the difference in dimensional accuracy between the two by name, but this is perceptual, and I can tell you the difference with specific numbers. The dimensional error accuracy of precision steel pipes is measured in units of {{0}}.01 mm, while the dimensional error accuracy of ordinary seamless pipes is measured in units of 0.1 mm, which are not in the same order of magnitude. The size error of ordinary seamless tubes is much larger. For example, ordinary seamless pipes with an outer diameter of 219 mm have 2 percent of the outer diameter according to the national standard GB/T8162-2008, i.e. 4 mm. The actual measurement is 221 mm, which meets the standard. , that is, the error is 2 mm. The error of ordinary precision steel pipe is much less. The precision steel pipe with a specification of 80mm is 0.3mm according to the national standard GB/T3639-2008, and the actual measurement is also 79.9-80.13. The measuring tool for ordinary precision seamless tubes is a calibrator, and the measuring tool for precision seamless tubes is an outer micrometer.

Measuring tool for precision tubes: outer micrometer

  1. Specifications

The specifications for ordinary seamless tubes are stipulated in national standard GB/T17395-2008. According to the regulations of national standards, the steel pipe factory produces pipes of any specification, and non-standard pipes are basically not available. The specifications of the precision seamless pipe are customized according to the needs of customers. For example, pipe with an outer diameter of 89mm, the national standard of ordinary seamless pipe is 76, 77 and 80. You can’t buy an ordinary 78 seamless pipe. UnlikeEN 10305-1 E235 seamless precision steel tube, if you need 78mm, it can produce 78mm.

  1. Mechanical properties

Due to the different production processes, the two also have differences in mechanical properties. The production of ordinary seamless pipes is mainly carried out by cold drawing and hot rolling, and the production of precision pipes is mainly carried out by the cold rolling process. In the production process of the cold drawing process, multiple annealing is required, and the mechanical stress of the seamless pipe is small. Most cold-rolled pipes are formed all at once, with great mechanical stresses and little plasticity. Of course, this can also be improved by annealing.

  1. Production process

The raw materials for the testing production of precision seamless pipes and ordinary seamless pipes are round steel. The round steel is sawn and drilled to form a capillary tube, and the newly produced capillary tube is subjected to a hot-rolled sizing unit to form a hot-rolled tube, and the hot-rolled tube and the capillary tube have the same diameter or reduced diameter. . After the capillary tube cools, it undergoes multiple steps of cold drawing and annealing to form a cold-drawn tube. The outer diameter of the cold-drawn tube is usually much smaller than that of the capillary tube. After cooling the capillary tube, it is placed directly into the cold rolling mill and laminated once to form the precision tube of the required specification.

  1. Price

Usually, due to the simpler production process, higher production and lower price of hot-rolled pipes. The cold-drawn pipe production process is complicated, but the production is high, so the price is low. Finished laminated pipe products have high dimensional accuracy and low performance, so the price is higher.