Seamless steel pipes / tubes

Seamless steel pipe is a tubular section or hollow cylinder, usually but not necessarily of circular cross-section, used mainly to convey substances which can flow — liquids and gases (fluids), slurries, powders and masses of small solids.

Steel Pipe & Tubing - All you need to know

Steel Pipe & Tubing seem similar at first blush and in fact they share many characteristics but they also have some important differences.


Steel Tubing is a hollow steel shape intended for structural purposes and made from carbon, stainless, or galvanized steel further divided as:

Mechanical Tubing is used in low stress applications such as fences, kitchens, restaurants, hospitals, solar panels and made with wall thicknesses up to 10 gauge.

Structural Tubing is for high stress structural application like bridges, buildings, roll cages, and underwater platforms with wall thickness from 3/16" and up. It is often referred to as Hollow Structural Sections or just the acronym HSS.

Pipe is a hollow structure that is intended to carry material such as liquids, gasses, or even solids. Its wall thickness is described by its Schedule and it is often broken down by type using the method of manufacturing it, either ERW or Seamless

How it's made:

Both Tubing and Pipe are manufactured by the first two methods below. The third is reserved for Tubing only.

Electric Resistance Welded, often abbreviated as ERW, is a process that uses specific machinery to shape the pipe and tubing. A continuous steel sheet is unwound from a coil and shaped using contoured rollers, forcing the edges together under pressure. These edges are then welded together by heating the material to over 2,000 degrees. After welding, the pipe or tubing is cut into the exact size needed.

Seamless Pipe (and tubing) is made by extruding a steel block or by drilling a solid steel bar. Next, the extrusion or the drilled steel bar is cold drawn through a dye to achieve the diameter and thickness needed. Because this process can cause mechanical hardening, sometimes the material is annealed and straightened as a final process. Seamless Pipe & Tubing is subdivided as:

Cold Drawn Seamless, or CDS, exhibits precise tolerances and a good surface finish.

Hot Finished Seamless, or HFS, has less critical tolerances and somewhat scaly finish and is not as strong as CDS.

For Drawn over Mandrel, or DOM tubing, the first stages of manufacturing are identical to ones used to make electric resistance welded tubing, but in the finishing stages the entire flash weld is taken out and the tube is cold drawn over a mandrel. A mandrel is a round object against which material can be forged or shaped. The cold drawn process provides the tube with better dimensional tolerances, improved surface finish and the strongest weld strength achievable.

Pipe Sizes:

Pipe Size is specified with two non-dimensional numbers:

  • Nominal Pipe Size (NPS) for diameter based on inches.
  • Schedule Number (SCH to specify the wall thickness of the Pipe.

Both the size and schedule are required to accurately specify a particular piece of pipe.

Nominal Pipe Size (NPS) is the current North American Set of standard sizes for pipes used for high and low pressures and temperatures. A further discussion of this is here.

Iron Pipe Size (IPS) was an earlier standard than NPS to designate the size. The size was the approximate inside diameter of the pipe in inches. Each pipe had one thickness, named (STD) Standard or (STD.WT.) Standard Weight. There were only 3 wall thicknesses at the time. In March 1927, the American Standards Association created a system that designated wall thickness based on smaller steps between sizes and introduced Nominal Pipe Size which replaced Iron Pipe Size.

Schedule Number for wall thickness ranges from SCH 5, 5S, 10, 10S, 20, 30, 40, 40S, 60, 80, 80S, 100, 120, 140, 160, STD, XS (Extra Strong) AND XXS (Double Extra Strong).

Pipe Grades:

A53 - ATSM A53 is a carbon steel alloy, used mostly for low pressure plumbing and comes in 3 types:

A53 Type F – Longitudinally furnace butt welded or continuous welded

A53 Type E – Longitudinally electric resistance welded (ERW)

A53 Type S - Seamless pipe

A106B – ASTM A 106 seamless pressure pipe, (ASME SA106 pipe) used in the construction of oil and gas refineries, power plants, and boilers.

A500B – Seamless carbon steel structural tubing in round, square and rectangular shapes. (HSS)

API 5L – Standards for pipe suitable for use in conveying gas, water, and oil in the natural gas and oil industries.

X52 – Welded pipe, widely used in petroleum and natural gas industries.

4130 – An alloy pipe often used int he Oil and Gas industries.

Other Pipe and Tubing Terms of Interest:

BPE – Black Plain End Pipe

BTC – Black Threaded & Coupled

GPE – Galvanized Plain End

GTC – Galvanized Threaded & Coupled

TOE – Threaded One End

Typical Pipe Coatings & Finishes:

Galvanized – Covered with a protective zinc coating on steel to prevent the material from rusting. The process can be hot-dip-galvanizing where the material is dipped in molten zinc or Electro-Galvanized where the steel sheet from which the pipe is made was galvanized during production by an electro-chemical reaction.

Uncoated – Uncoated Pipe

Black Coated – Coated with a dark colored iron-oxide

Red Primed – Red Oxide Primed used as a base coat for ferrous metals, gives iron and steel surfaces a layer of protection

Seamless pipes Execution Standard

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


Seamless Carbon Steel for High Temperature Service


Seamless Cold-drawn Low-Carbon Steel Heat-Exchanger and Condenser Tubes


Seamless Carbon Steel Boiler Tubes for High Pressure


Seamless Ferritic and Austenitic Alloy Steel Boiler, Superheater and Heat-exchanger Tubes


Standard Specification for Seamless and Welded Steel Pipe for Low-Temperature Service and Other Applications.

DIN 1629

Seamless Circular Tubes of Non Alloys Steels with Special Quality Requirements, it's main grades are St 37.0, St44.0, St52.0.

EN 10305

Are very popular in hydraulic and pneumatic power system, low-voltage circuit, power steering, fuel circuit and such.

DIN 2391

DIN 2391 standard specifies the Seamless steel tubes used forMechanical and Automobile.


Seamless medium-carbon steel boiler and superheater tubes, including a minimum wall thickness of the security side.

Sunny Steel explains Seamless steel pipe

Seamless pipes are derived from solid steel that is in sheet or bar form and is formed into a solid round shape known as “billets” which are then heated and cast over a form such as a piercing rod to create a hollow tube or shell.

Material requirements

SMLS pipe is produced by heating a round billet of steel and then piercing it with a bullet-shaped piercer, over which the steel is stretched. This is followed by rolling and drawing to produce the desired dimensions. The final product is hydrostatically tested, inspected, coated if required, and stenciled with the specification. SMLS pipe is used in high-pressure, most critical locations and under most severe operating conditions. SMLS pipe is supplied according to ASTM Specifications A53, A106, A333, A312, A358, etc., and API 5L pipe

Sizes: 1/8″ (3.175 mm) nominal to 26″ (660.4 mm) OD. Less than 2 3/8″ (60.325 mm) OD is known as pressure tubing that has different dimensional standards (wall thickness and diameter). SMLS pipe, where available, is used in oil and gas production facilities both onshore and offshore (other than transmission lines) less than 26″ (660.4 mm) OD.

Offshore Overview

Mills produce two types of line pipe, seamless and welded

Seamless pipe is formed from a cylindrical bar of steel. The bar is heated to a high temperature and then a probe is inserted to create a hole through the cylinder. The cylinder is then transferred to rollers which size the cylinder to the specified diameter and wall thickness. A few mills can produce seamless pipe up to 24-in in diameter. For small diameter pipe, seamless pipe is common but unit costs are high and availability is usually limited. As pipe diameter increases, welded pipes are more economical.

In welded pipe, welding is used to close the seam after forming a steel plate or coil into a cylindrical shape. The mill uses ultrasonic and/or radiological inspection methods to ensure the quality of the weld seam and initiates pressure tests on each joint of pipe to levels that exceed the proposed operating pressure. Welded pipe is classified based on how it is formed and the type of welding technique used.

Submerged arc weld (SAW) pipe uses filler metal in welding, whereas electric resistance welded/electric fusion welding (ERW/EFW) are no-filler metal processes. SAW is further classified into longitudinal (or straight) welding (L-SAW) and S-SAW means spiral (or helical) weld tube. Normally, medium diameter straight L-SAW has a single seam, and large diameter L-SAW uses a double seam.

ERW pipe is manufactured using electric current to heat the steel to a point at which the edges melt together to form a bond. This manufacturing process was introduced in the 1920s and utilized low-frequency alternating current to heat the edges, but was found to be vulnerable to seam corrosion and inadequate bonding. Today, high-frequency alternating current is used, also known as contact welding. EFW pipe refers to a process that uses an electron beam to direct kinetic energy to melt the workpiece to form the weld.

PIPs are manufactured using two pipes separated by insulation and are used to maintain the temperature of the fluids to prevent the formation of hydrates, reduce wax deposition, or to reduce the pressure drop by reducing the viscosity of heavy crudes (Cochran, 2003).

Rigid flowlines are manufactured from carbon steel or a high-performance steel alloy, with additional coatings providing corrosion protection and insulation. Flexible flowlines have the same applications as rigid flowlines but are manufactured differently, using composite layers of steel wire and polymer sheathing that provide high flexibility (Box 1.3). A typical 8-in diameter flexible pipe, for example, can be safely bent to a radius of two meters or less. This flexibility is important for risers and flowlines laid on uneven seabeds and permits spooling on a reel or carousel in installation. The preference for using a rigid or flexible flowline is driven by design requirements, installation constraints, cost, schedule, and other factors.

Flexible Pipeline Configuration

A flexible pipe is a configurable product made up of several independent layers tailored to each development (Fig. 1.21). Flexible pipes are used for risers, flowlines, and jumpers in offshore operations, but because the unit cost is much more expensive than a carbon steel pipe, its use is often limited to special applications and small quantities (Tuohy et al., 2001).

Flexible pipe is manufactured by wrapping several intertwining layers of stainless steel and special polymers. The helically wound steel wires give the pipe its high-pressure resistance and bending characteristics, and since the steel wires are not in direct contact with the conveyed fluid, they do not require the same corrosion resistance as steel pipe. Variation in the choice of materials, the number and order of layers, and manufacturing process depends on the conditions and operating environment.

The components of an unbonded flexible pipe are as follows:

Carcass. The carcass forms the innermost layer and is the conduit for fluid transport. It is commonly made of a stainless steel flat strip that is spirally wound and formed into an interlocking profile. The main function of the carcass is to prevent pipe collapse due to hydrostatic pressure in the annulus.

Internal polymer sheath. The internal polymer sheath provides a barrier to maintain the bore fluid integrity. Common materials used include Polyamide-11 (Rilsan), high-density polyethylene, cross-linked polyethylene, and PVDF.

Pressure armor. The pressure armor, as its name implies, is wound around the internal polymer sheath for protection and is made of interlocking wires or wire strips. Its role is to withstand the hoop stress in the pipe wall caused by the fluid pressure.

Tensile armor. The tensile armor layers are used to resist tensile loads, to support the weight of all the pipe layers, and to transfer the load through the end fitting to the structure. The tensile armor layers are cross-wound in pairs and in high tension applications, say in a deepwater riser, may require the use of four tensile armor layers.

External polymer sheath. The main function of the external sheath is as a barrier against seawater and is often made of the same materials as the internal polymer sheath. External sheaths also provide protection against clashing with other objects during installation.

Other layers. Antifriction and antiwear tape are wound around the armor layers to reduce friction and wear of the wire layers when they rub past each other as the pipe flexes from external loads. Antiwear tapes are used to ensure that the armor layers maintain their wound shape and prevent the wires from twisting out of their configuration, a phenomenon called birdcaging that is a result of hydrostatic pressure causing axial compression in the pipe. Additional layers of material with low thermal conductivity can be applied to obtain specific thermal insulation properties.


Seamless steel pipe for the use of engineering and construction is very widely, it is a hollow steel strip no seams, it is mainly used to transport liquids pipelines, different look and general steel,one of those heavy type steel, it has a strong resistance to corrosion, resistant to general corrosion.

  • high precision can do small batch production.
  • smaller diameter.
  • weldability strong, high compression capability.
  • steel pipe superior performance, relatively dense metal.
  • Steel Cross area is more complex.
  • high precision cold drawn products, good surface quality.
Some of the differences between Seamless steel pipes and welded tubes are:

A Seamless steel pipe 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 steel pipe offers a higher range of safety measures it is more expensive than a welded tube.
  • A Seamless steel pipe is relatively short in length, whereas welded tubes can be manufactured in long continuous lengths.
  • A Seamless steel pipe 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 steel pipe eliminates any such issues and thus offers high corrosion resistance.
Mechanical properties:

The mechanical properties of the seamless steel tube is a important indicator that ensure seamless pipe end-use properties (mechanical properties), which depends on the chemical composition and heat treatment of steel.

In steel standards, according to different requirements, it provide the tensile properties (tensile strength, yield strength or yield point elongation) and hardness.

① Tensile strength (σb)
During stretching, when pull off the bear most strongly (Fb), divided by the original cross-sectional area (So) from the stress (σ), known as the tensile strength (σb), units of N/mm2 (MPa). It said the maximum capacity resist destruction of metallic materials under tension.

② Yield point (σs)
Yield the phenomenon of metal materials, the sample does not increase during the tensile force (remains constant) and continue elongation stress is known as the yield point. If the force drop occurred, you should distinguish between upper and lower yield point. The yield point of the unit is in N/mm2 (MPa). On yield point (σsu):Sample to yield the maximum stress and force the first drop; lower yield point (σsl): yield minimum stress in the stage when excluding the initial transient effect.

③ Elongation (σ)
In the tensile test, the specimen fractured a percentage of the gauge to increase the length of the original gauge length, called elongation. Σ, said the unit is%.

(4) Cross-section contraction rate (ψ)
In the tensile test, the percentage of the specimen fractured its shrink the diameter at the cross-sectional area of the maximum reduction and the original cross-sectional area is known as section shrinkage. Ψ expressed in%.

⑤ Hardness testing
Metallic materials against hard objects indentation of the surface, known as hardness. accoring to the test method and scope of application, the hardness can be divided into brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness, hardness and high temperature hardness. Commonly used for pipe, Brinell, Rockwell, Vickers hardness of three kinds.

Recommended seamless pipes

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

Seamless pipe Specification, standard and identification

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