Seamless pipe is made by piercing a solid round billet and rolling it out into a hollow, so it has no weld seam along its length. That makes it the first choice for high pressure, high temperature and critical service: oil and gas wells, process piping, boilers and hydraulic systems.
A seamless tube starts as a solid round billet. It is heated to about 1,250 °C and pierced in a rotary piercing mill, where barrel-shaped rolls spin the billet over a pointed plug and open a hole through its centre. The thick hollow shell is then elongated over a mandrel — in a continuous mandrel mill, a plug mill or a pilger mill — and sized or stretch-reduced to the final outside diameter and wall. Larger sizes are made by rotary expansion; smaller, precise tubes are cold drawn or cold pilgered from hot-finished tube.
With no weld, the pipe has the same properties all round its circumference, which is why codes and owners specify seamless for the most demanding service: high-pressure and high-temperature process lines (ASTM A106 Grade B is the workhorse of refinery and plant piping), boiler and superheater tubes, sour-service and offshore line pipe, and casing and tubing for oil and gas wells. The trade-offs are cost and size: seamless is dearer than welded pipe, its wall thickness varies more around the circumference, and above about NPS 24 large-diameter pipe is almost always welded.
Dimensions follow ASME B36.10M in American practice — nominal pipe size and schedule, as in the pipe schedule table — and EN 10220 in European practice, where pipe is ordered by outside diameter × wall in millimetres. Oil country tubular goods (OCTG) — casing, tubing and drill pipe — are made to API 5CT and API 5DP, with threaded and coupled ends and premium connections.
The GCC is one of the world's largest markets for seamless pipe, driven by drilling and the oil, gas and petrochemical industries of Saudi Arabia, the UAE, Kuwait, Qatar and Oman. National oil companies such as Saudi Aramco, ADNOC and KOC buy OCTG and line pipe on long-term contracts and qualify each mill, and in-country value programmes have brought OCTG threading, heat-treatment and pipe-making plants to the region. Process and structural seamless pipe is imported in large volumes from China, India, Japan, Europe and Russia and held by regional stockists.
Seamless pipe is ordered by size (NPS and schedule, or OD × wall), standard and grade, ends, length and finish. Hot-finished pipe covers most sizes; cold-drawn tube is used for small, thin-walled and precision tubes such as heat-exchanger, hydraulic and mechanical tubing.
Full dimensions: Pipe sizes and schedules (ASME B36.10M)
| Region | Standard | What it covers |
|---|---|---|
| USA | ASME B36.10M ASME |
Welded and seamless wrought steel pipe — sizes, schedules and masses |
| USA | ASTM A106/A106M ASTM |
Seamless carbon steel pipe for high-temperature service — Grades A, B and C |
| USA | ASTM A53/A53M ASTM |
Pipe, steel, black and hot-dipped zinc-coated, welded and seamless (Type S is seamless) |
| USA | ASTM A333/A333M ASTM |
Seamless and welded steel pipe for low-temperature service |
| USA | ASTM A179 / A192 / A210 ASTM |
Seamless cold-drawn heat-exchanger tubes; boiler tubes for high-pressure service; medium-carbon boiler and superheater tubes |
| USA | ASTM A519/A519M ASTM |
Seamless carbon and alloy steel mechanical tubing |
| USA | API Spec 5L API |
Line pipe, seamless and welded, PSL1 and PSL2 (equivalent to ISO 3183) |
| USA | API Spec 5CT API |
Casing and tubing for oil and gas wells (equivalent to ISO 11960) |
| Europe | EN 10216-1 to -5 CEN-CENELEC |
Seamless steel tubes for pressure purposes — room temperature, elevated temperature (P235GH, P265GH, 16Mo3…), fine-grain, low-temperature and stainless |
| Europe | EN 10220 CEN-CENELEC |
Seamless and welded steel tubes — dimensions and masses per unit length |
| Europe | EN 10297-1 CEN-CENELEC |
Seamless circular steel tubes for mechanical and general engineering purposes (E235, E355…) |
| Europe | EN 10305-1 CEN-CENELEC |
Steel tubes for precision applications — seamless cold drawn tubes |
| Europe | EN 10210 CEN-CENELEC |
Hot-finished structural hollow sections, including seamless circular sections |
| Germany | DIN 2448 DIN replaced by EN 10220 |
Seamless steel tubes — dimensions and masses |
| Germany | DIN 1629 DIN replaced by EN 10216-1 |
Seamless circular unalloyed steel tubes subject to special requirements (St 37.0, St 52.0) |
| Germany | DIN 17175 DIN replaced by EN 10216-2 |
Seamless tubes of heat-resistant steels (St 35.8, St 45.8) |
| UK | BS 3601 / BS 3602 BSI replaced by EN 10216 / EN 10217 |
Carbon steel pipes and tubes for pressure purposes — room and elevated temperatures |
| Japan | JIS G3454 / G3455 / G3456 JSA |
Carbon steel pipes for pressure service (STPG), high-pressure service (STS) and high-temperature service (STPT) |
| Japan | JIS G3461 JSA |
Carbon steel boiler and heat exchanger tubes (STB) |
| China | GB/T 8163 SAC |
Seamless steel tubes for liquid service (10, 20, Q345) |
| China | GB/T 8162 SAC |
Seamless steel tubes for structural purposes |
| China | GB/T 5310 SAC |
Seamless steel tubes and pipes for high-pressure boilers |
| Russia / CIS | GOST 8732 | Hot-deformed seamless steel pipes — dimensions (technical requirements in GOST 8731) |
Grade equivalents and the standards bodies: Steel grades & standards
Stockist - Distributor · Fabrication · Contractors · Shanghai
Steel Mills - Agents & Traders · Tube Manufacturer · Stockist - Distributor · Dubai
Stockist - Distributor · Fabrication · Contractors · Shanghai
Steel Mills - Agents & Traders · Tube Manufacturer · Stockist - Distributor · Dubai
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