Seamless Carbon steel square tube 100x100x5mm ASTM A106 Grade B Hot Finished Pressure Tube

A seamless square hollow section is not welded at all: a round shell is pierced from a solid billet, cold drawn down to size over a mandrel and then shaped into a square profile, so there is no longitudinal weld anywhere in the perimeter. This 100 x 100 x 5 mm section is made that way from ASTM A106 Grade B shell, the same heat of steel used for seamless pressure pipe, which is why it can be hydro tested and used where a welded corner is not acceptable.

The reason buyers pay a premium for this route is fatigue and pressure. A welded corner in a hollow section is a geometric discontinuity with a heat affected zone, and under cyclic loading that corner is where a crack starts. In a seamless section the material is continuous around the perimeter, which is why you find it in hydraulic cylinder bodies, rotating machinery frames and pressure retaining components rather than in ordinary building frames.

• No Weld Seam Anywhere: Formed from a pierced and drawn shell, so the full perimeter is continuous material with no heat affected corner.
• A106 Grade B Chemistry: 0.30 percent maximum carbon, 0.29 to 1.06 percent manganese, suitable for elevated temperature service up to 400 degrees Celsius.
• Hydro Tested: Each lot is hydro tested to the pressure agreed at order, with test pressure and hold time recorded on the report.
• Fatigue Resistant Corners: Continuous material at the corner radius removes the stress concentration that limits welded hollow sections in cyclic service.
• Machinable and Boreable: Uniform wall and a clean inside surface allow boring, honing and internal welding without hitting a seam.
• Heavy Section Capacity: At 14.92 kg per metre the section has meaningful bending capacity for machine bases and structural columns.

Pressure and machinery applications dominate: hydraulic cylinder bodies, accumulator shells, heat exchanger frames, furnace and oven structural members, rotating drum frames, press columns and heavy machine bases. It is also used in structural columns where a welded corner would need additional fatigue assessment, and in high temperature frames where the A106 chemistry gives better creep behaviour than a plain structural grade. It is not the economical choice for ordinary building frames.

Seamless sections are heavier per length and are packed accordingly: bundles up to 2 tons, wooden dunnage between layers, three steel straps, waterproof paper and PVC sleeve, with ends protected by plastic caps. Pickled and oiled material is wrapped immediately after oiling to prevent condensation staining. Hydro test reports, mill test reports to EN 10204 3.1 and third party inspection documents are supplied per lot.

Ordering note: seamless square hollow section is made to order, not stocked, so lead time is 15 to 25 working days rather than the 7 to 15 of a welded section, and the minimum run is one heat. If the application does not genuinely require a seamless perimeter, a welded A500 section at roughly 60 percent of the cost will usually do the job.