Description
Factory-direct seamless tubes, no broker markup — Every 20# seamless square and rectangular steel tube is pierced from solid billet and rolled in-house, so you pay mill price without trading company layers.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | 20# Seamless Square and Rectangular Steel Tube |
| Product Type | Seamless Square and Rectangular Steel Tube |
| Steel Grade | Q195, Q235, Q345, 10#, 20#, 45#, S235JR, S275JR, S355JR, SS400 |
| Standard | GB, ASTM |
| Section Shape | Square / Rectangular |
| Wall Thickness | 0.9 mm |
| Length | 6 m / 6.4 m / 12 m |
| Technique | Seamless (hot-rolled pierce + cold rolling/cold drawing) |
| Surface Treatment | Hot Rolled |
| Tolerance | ±1% |
| Ends | Plain (default) |
| Processing Service | Welding, Punching, Cutting, Bending, Decoiling |
| Oiled or Non-oiled | Non-oiled |
| Invoicing | By Theoretical Weight |
| Application | Construction Structure, Fluid Pipe, Boiler Pipe, Drill Pipe, Hydraulic Pipe, Gas Pipe, Oil Pipe, Chemical Fertilizer Pipe, Structure Pipe |
| MOQ | 25 Tons |
| Origin | China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Construction & Steel Structures | High-rise building frames, bridge trusses, industrial warehouse columns |
| Energy & Petrochemical | Oil and gas transmission pipelines, boiler tubes, chemical fertilizer process pipes |
| Machinery & Hydraulic Systems | Hydraulic cylinder barrels, drill pipe casings, equipment support frames |
| Infrastructure & EPC Projects | Conveyor structures, solar mounting frames, utility pole bases |
What Negative Tolerance Really Costs on a 20# Seamless Square Rectangular Steel Tube Order
A tube that measures under-spec at the weld-free wall will fail load calculation before it ever reaches the site.
I once watched a container of 20# seamless rectangular tubes get held at Santos port because the wall thickness had been pushed past the ASTM A500 minimum during cold drawing. The SGS inspector pulled random pieces, measured them, and the entire lot was flagged. The client’s structural frame design relied on that minimum wall — when the actual thickness fell short, the engineer had to redesign connections, delay erection, and absorb demurrage. That kind of cost does not show up on a proforma invoice. It shows up months later, in rework and schedule slippage. [NEED_CITE: ASTM A500 dimensional tolerance requirements for cold-formed seamless structural tubing]
How Seamless Piercing Matches Structural and Pressure Applications
The 20# seamless square and rectangular steel tube starts as a solid round billet that is heated, pierced through the center, then shaped through hot rolling and cold drawing into square or rectangular profile. Because there is no weld seam, the wall thickness remains uniform around all four sides and both corners — which matters when the tube carries internal pressure in hydraulic lines or bears compressive load in a building column. The GB ASTM 20# seamless square rectangular steel tube supplier process ensures that grain structure flows continuously around the cross-section, giving consistent mechanical behavior under load. For EPC contractors procuring structural members and process piping from a single source, this eliminates the risk of mixing welded and seamless tubes on the same project.
Engineering Compliance Across GB, ASTM, and EN Frameworks
When a 20# seamless square rectangular steel tube is specified for a structural frame in the EU, the engineer will reference EN 1993 and expect compliance with EN 10210 for hot-finished seamless hollow sections. For North American projects, ASTM A500 Grade B or C governs the same application. The 20# carbon steel grade under GB/T 8162 roughly corresponds to S235JR under EN 10025 and falls within the mechanical property range of ASTM A500 Grade B. [NEED_CITE: steel grade equivalence mapping between GB 20# and EN ASTM systems] Hot-rolled surface condition means the tube arrives with mill scale intact — suitable for structures that will be blast-cleaned and painted on site, or for internal applications where surface finish is not critical. For projects requiring CE marking, the manufacturer must hold EN 10210 Factory Production Control certification, and the mill test certificate must trace each piece back to its heat number.
Why the Seamless Process and 20# Grade Matter Together
The 20# carbon steel grade sits in the low-carbon structural range — it offers adequate strength for frames, supports, and low-pressure piping while remaining weldable without preheat in most thickness ranges. When formed into seamless square and rectangular profiles, the absence of a longitudinal weld seam means there is no heat-affected zone to create a weak line under bending or torsion. The cold drawing step after hot rolling brings the dimensional tolerance down to ±1%, which is tighter than what typical ERW processes achieve on square sections. [NEED_CITE: cold drawing dimensional accuracy advantages for seamless structural hollow sections] For hydraulic and boiler applications, this uniformity directly affects pressure containment. For structural applications, it means the theoretical weight used for invoicing closely matches the actual weight on site — no surprise shortfalls when the project is counted by the ton.
The Hidden Price of Unverified Seamless Tubes
Ordering a GB ASTM 20# seamless square rectangular steel tube without requiring an original mill test certificate means you cannot confirm the chemical composition matches 20# requirements — specifically the carbon, manganese, and silicon ranges that determine weldability and strength. If the supplier substitutes a lower grade or ships ERW tubes labeled as seamless, the weld seam will become visible under bending or ultrasonic inspection. Missing CE documentation for EU-bound shipments leads to customs holds. [NEED_CITE: EN 10204 inspection document types for steel hollow sections] The cost of replacing tubes after they arrive on site — including crane time, labor, and project delay — far exceeds the price difference between a verified and unverified source.
Procurement Confidence Backed by In-House Verification
Every GB ASTM 20# seamless square rectangular steel tube produced here passes through an in-house physical and chemical laboratory before loading. The lab tests each heat for composition and mechanical properties, and the results go directly onto the mill test certificate — not copied from a template. With 2,800+ specifications in the product range covering square, rectangular, and round profiles in wall thicknesses up to 40 mm, non-standard sizes can be produced without forcing the buyer to accept oversized stock. The sharp-corner rectangular tube technology — covered under proprietary patents — delivers tight external corner radii that fit flush against connecting plates, reducing welding gaps and improving joint appearance. All products carry CE EN 10210/10219, ISO 9001:2015, and are verifiable through SGS or BV third-party inspection at the port of loading.
Documentation & Compliance
- Mill test certificate documenting 20# chemical composition (C, Mn, Si, S, P) and tensile properties per GB/T 8162, with heat number traceability
- CE certificate covering EN 10210 hot-finished seamless hollow sections for EU market customs clearance
- ISO 9001:2015 quality management system certificate confirming controlled production and inspection processes
- SGS or BV third-party inspection report verifying wall thickness, dimensions, and surface condition before shipment
- Material traceability sheet linking each bundle to its heat number, production date, and test results
- Full customs document package including packing list, bill of lading, and certificate of origin for the destination country
Packaging, Loading & Delivery
- Hot-rolled 20# seamless square and rectangular tubes bundled with steel strips and padded at contact points to prevent surface scratches on the mill scale finish
- 6 m, 6.4 m, and 12 m lengths loaded into 20ft or 40ft containers using optimized stacking plans that maximize weight per shipment while staying under port crane limits
- Plain-end tubes capped at both ends to prevent debris entry during ocean transit, with bundle tags showing steel grade, heat number, size, and length
- Cutting-to-length service available before shipment for projects requiring specific piece lengths beyond standard 6 m or 12 m
- FOB, CIF, and DDP shipping terms available to ports across 50+ countries, with professional loading supervision and real-time container tracking
- Non-oiled surface condition means no residue to clean before painting or welding on site
Getting Your Quote and Mill Test Certificate Started
Send your specification list — including section shape, outer dimensions, wall thickness, length, steel grade, quantity, and destination port — and receive a detailed quotation within 12 hours. The quote includes unit price, total cost, production lead time, payment terms, and a sample mill test certificate showing the exact chemical and mechanical values for your specified grade. For non-standard sizes outside the 2,800+ catalog range, the engineering team will confirm feasibility and tooling requirements before you commit.
Frequently Asked Questions
Q: How does 20# steel grade under GB compare to S235JR or ASTM A500?
A: The 20# carbon steel grade under GB/T 8162 has similar carbon and manganese content to S235JR under EN 10025 and falls within the mechanical property range of ASTM A500 Grade B. For exact equivalence on a specific project, the mill test certificate provides the actual chemical composition and tensile test results so your engineer can verify compliance with the governing standard.
Q: Can I request third-party inspection before the GB ASTM 20# seamless square rectangular steel tube ships?
A: Yes. SGS and BV inspection can be arranged at the mill or at the port of loading. The inspector verifies dimensions, wall thickness, surface condition, and reviews the mill test certificate against the purchase order. The inspection report is issued independently and provided to you before the container is sealed.
Q: What is the MOQ for custom non-standard sizes outside the regular catalog?
A: The standard MOQ is 25 Tons. For non-standard dimensions requiring dedicated cold-drawing dies or special piercing setups, the minimum quantity depends on the specific size and production run efficiency. The engineering team will confirm the exact MOQ after reviewing your drawing or specification.
Q: How are the tubes invoiced — by actual weight or theoretical weight?
A: The 20# seamless square and rectangular steel tubes are invoiced by theoretical weight calculated from the specified outer dimensions, wall thickness, and length using the standard steel density formula. The ±1% dimensional tolerance ensures the theoretical weight closely matches the actual weight of each bundle.
Q: What surface treatment options are available if I need corrosion protection?
A: The standard supply condition is hot-rolled with mill scale. For projects requiring corrosion protection, the tubes can be supplied with galvanized coating, 3PE coating, or painted finish based on your specification. The processing service also includes welding, punching, cutting, and bending if fabrication is needed before shipment.
Get Your GB ASTM 20# Seamless Square Rectangular Steel Tube Quote with Full Mill Test Certificate
Submit your specifications — section shape, dimensions, wall thickness, steel grade, quantity, and destination — to receive pricing and a sample test certificate within 12 hours.
Shandong Xin Jiyuan Special Steel Tube Co., Ltd
Website: www.sdxjysteel.com
Tel: +86 531 8573 6315
Mobile/WhatsApp/WeChat: +86 188 5315 7756
Email: admin@sdxjysteel.com
Address: No.11889, Jingshi West Road, Lulian Group, Jinan City, Shandong Province, China
