Seamless pipe

Seamless 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.

Seamless 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.

ASTM A179 tubes ASTM A179 tubes
Seamless Pipes

Common Types & Application Scope

Seamless pipes come in various types, each designed for specific applications and environments. Some of the common types of seamless pipes include:

What is a seamless pipe used for?

Seamless steel pipe is regularly used in the transportation of fluids such as water, natural gas, waste and air. It is also regularly required in many high-pressure, high-corrosive environments such as in the oil & gas, power generation and pharmaceutical industries. Some common uses of seamless pipes include:

What is a seamless pipe?

A seamless pipe is a pipe that has no seam or weld. They are made from solid steel billets that are heated and extruded to create a hollow pipe.

Quality problems of seamless steel pipes

There are two types of factors that affect the quality of seamless steel pipes: steel quality and rolling process factors.

Factors in the rolling process are discussed here. The main influencing factors are: temperature, process adjustment, tool quality, process cooling and lubrication, removal and control of sundries on the surface of rolled parts, etc.

1. Temperature

Temperature is the most important factor affecting the quality of seamless steel pipes. First of all, the uniformity of the heating temperature of the tube blank directly affects the wall thickness uniformity and inner surface quality of the perforated capillary, which in turn affects the wall thickness quality of the product. Secondly, the temperature and uniformity of the steel pipe during the rolling process (especially the final rolling temperature) are related to the mechanical properties, dimensional accuracy and surface quality of the delivered product in the hot-rolled state, especially when the steel billet or lamp tube is overheated or even When overburned, it will cause waste. Therefore, in the production process of hot-rolled seamless pipes, heating and controlling the deformation temperature in strict accordance with the process requirements are the first work that must be done.


2. Process adjustment

Process adjustment and work quality mainly affect the geometric shape and appearance quality of steel pipes.

For example, the adjustment of the piercing machine and the rolling mill affects the wall thickness accuracy of the product, and the adjustment of the sizing machine is related to the accuracy and straightness of the product's outer diameter. Moreover, process adjustment also affects whether the rolling process can be carried out normally.


3. Tool quality

The quality and stability of the cutting tool are directly related to the dimensional accuracy, surface quality and cutting tool consumption of the product can be effectively controlled; the quality of the mandrel surface treatment (chrome plating) first affects the inner surface of the seamless steel pipe, and secondly affects Mandrel consumption and production costs.


4. Process cooling and lubrication

The cooling quality of the piercing head and rolls not only affects their life, but also affects the quality control of the inner and outer surfaces of the finished product. The cooling and lubrication quality of the mandrel first affects the inner surface quality, wall thickness accuracy and mandrel consumption of the seamless steel pipe; it also affects the load during rolling.


5. Surface Purification

The removal and control of sundries on the surface of rolled parts refers to the timely and effective removal of iron sheets on the inner and outer surfaces of capillaries and waste pipes, and the control of reoxidation before rolling deformation. Nitrogen blowing in the inner hole of the capillary, borax spraying, pipe rolling and high-pressure water descaling at the entrance of fixed (reduced) diameter, effectively improving and enhancing the quality of the internal and external surfaces.


What is the minimum thickness of seamless pipe?

Thin wall pipe ovality rolled alloys

The outer diameter of hot-rolled seamless pipe is generally greater than 32mm, the wall thickness is 2.5-200mm, the outer diameter of cold-rolled seamless steel pipe can be 6mm, the wall thickness can be 0.25mm, the outer diameter of thin-walled pipe can be 5mm, and the wall thickness is less than 0.25mm, cold rolling

NPS/ DN/ OD Permissible Variations in Outside Diameter
Over Under
in. mm in. mm
NPS 1/8 to 1½, incl
DN 6 to 40
OD 10.3 to 48.3, mm
1/64 0.4 1/64 0.4
Over 1½ to 4, incl
DN 40 to 100
OD 48.3 to 114.3, mm
1/32 0.8 1/32 0.8
Over 4 to 8, incl
DN 100 to 200
OD 114.3 to 219.1, mm
1/16 1.6 1/32 0.8
Over 8 to 18, incl
DN 200 to 450
OD 219.1 to 457, mm
3/32 2.4 1/32 0.8
Over 18 to 26, incl
DN 450 to 650
OD 457 to 660, mm
1/8 3.2 1/32 0.8

According to the production method, seamless tubes are divided into hot - rolled tubes, cold - rolled tubes, cold - drawn tubes, extruded tubes, jacking tubes, etc. The maximum diameter is 650 mm and the minimum diameter is 0.3 mm. Depending on the application, there are thick - walled tubes and thin - walled tubes. Seamless steel tubes are mainly used as petroleum geological drilling tubes, cracking tubes for petrochemical industry, boiler tubes, bearing tubes and high - precision structural steel tubes for automobiles, tractors and aviation. In the plate, Q345B seamless steel pipe belongs to the low - alloy series.

Among the low - alloy materials, this kind of material is the most common. The outside diameter of hot - rolled seamless pipe is usually more than 32mm, the wall thickness is 2.5 - 200mm, the outside diameter of cold - rolled seamless steel pipe can be 6mm, the wall thickness can be 0.25mm, the outside diameter of thin - walled pipe can be 5mm, and the wall thickness is less than 0.25mm, cold rolling has higher dimensional accuracy than hot rolling.

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.

Definitions

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).


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

How to distinguish pipe material

Seamless Steel Pipe Explained

Seamless pipes are manufactured from solid steel billets that are heated and pierced to form a hollow tube. They are widely used in high-pressure and critical applications due to their superior strength and reliability.

Manufacturing Process

The production starts with heating a round steel billet and piercing it with a bullet-shaped mandrel. The tube is then rolled and drawn to achieve the required dimensions. Final steps include hydrostatic testing, inspection, and coating when required.

Seamless steel pipes are supplied according to standards such as ASTM A53, A106, A333, A312, A358 and API 5L. Sizes range from 1/8" (3.175 mm) to 26" (660.4 mm) OD.

Offshore & Pipeline Applications

Steel pipe types

Mills produce two main types of line pipe: seamless and welded.

Seamless pipe is formed from a heated cylindrical bar pierced by a mandrel, then rolled to the desired size.

Welded Pipe Types

  • SAW (Submerged Arc Welded) – Longitudinal (L-SAW) or Spiral (S-SAW)
  • ERW/EFW (Electric Resistance/Fusion Welded) – High-frequency welding

Flexible Pipelines

Flexible pipes consist of multiple layers (carcass, polymer sheaths, pressure armor, tensile armor, etc.) and are used for risers and flowlines where high flexibility is required.

Key Characteristics of Seamless Steel Pipes

  • High precision, suitable for small batch production
  • Excellent corrosion resistance
  • Strong weldability and high pressure capability
  • Superior mechanical properties and dense metal structure
  • Complex cross-section capability
  • Excellent surface quality (especially cold drawn)

Seamless vs Welded Pipes

  • Seamless pipes offer higher safety and are preferred in critical applications
  • Seamless pipes are generally more expensive but have better corrosion resistance
  • Welded pipes can be produced in longer continuous lengths
  • The weld area in welded pipes is more susceptible to corrosion

Mechanical Properties

Mechanical properties (tensile strength, yield strength, elongation, etc.) are key indicators for the end-use performance of seamless pipes. These properties depend on chemical composition and heat treatment.

Tensile Strength (σb) – Maximum stress the material can withstand while being stretched.
Yield Strength (σs) – Stress at which permanent deformation begins.
Elongation (δ) – Measure of ductility (percentage increase in length).
Hardness – Resistance to indentation (Brinell, Rockwell, Vickers commonly used for pipes).

Cold drawn tube

Cold drawn seamless tubing possesses a high strength-to-weight ratio and can be processed to provide a combination of desired characteristics. Cold drawn seamless mechanical tubing is used in a variety of uses, particularly when heavy wall thicknesses, specific steel alloys or both are required.

Small diameter cut to length tubes
Small Diameter Cut-to-Length Tubes

Customization

Steel Grade & Mechanical Properties Customization

We offer full customization for both seamless steel tubes and rebar couplers, including steel grade, dimensions, mechanical properties, and surface quality. Available steel grades comply with international standards such as ASTM A519, ASTM A106, ASTM A500, ASME SA500, DIN2391, DIN1629, EN10305-1, DIN17121, EN10297-1, JIS G3441, JIS G3444, and JIS G3445.

Mechanical Testing

Mechanical property test of Ø36 rebar coupler (maximum tensile force exceeding 850 kN).

Small Batch Orders

We accommodate small batch production with full customization requirements.

Precision Machining

Cutting, chamfering, tapping, and laser marking services.

Comprehensive Solutions

Tailored solutions designed to meet your exact product requirements while improving quality and reducing overall production costs.

Shape & Thickness Customization

Thick-walled and special-shaped seamless steel tubes are our core strength and can be fully customized to customer specifications.

Alloy Steel

Advanced alloy steel tubes produced with fully automated heat treatment equipment (±2°C precision), delivering stable and consistent performance.

Cutting steel tube

Seamless Tube Processing

With years of expertise, we provide a wide range of steel tube processing services. From basic sawing and machining to complex bending and upsetting operations, we support you at every stage of your project.

Our capabilities include eccentricity reduction and concentricity improvement through turning and grinding. We specialize in creating complex geometries using rotary swaging and axial forming, and offer property modifications through partial heat treatment to meet your exact requirements.

Our Processing Capabilities

Variable wall thicknesses
Drilling / Stamping / Lasering
Peeling / Roller Burnishing
Cold Forming
Cutting
Beveling
Deburring
Thread Rolling / Threading
Partial Hardening
Turning / Milling / Grinding
Reducing / Expanding
Swing

Related GB5310 steel pipes

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