Description
Factory-direct pricing, no trading markup — 20# seamless square and rectangular hollow sections produced in-house with full mill test traceability from billet to finished tube.
Technical Specifications
| Parameter | Value |
|---|---|
| Designation | 20# Seamless Square and Rectangular Steel Tube |
| Product Type | Seamless Square and Rectangular Hollow Section |
| Steel Grade | 20#, Q195, Q235, Q345, S235JR, S275JR, S355JR |
| Standard | ASTM, GB |
| Section Shape | Square / Rectangular |
| Wall Thickness | 0.9 mm – 40 mm |
| Length | 6 m / 6.4 m / 12 m |
| Technique | Seamless (hot-rolled pierce + cold rolling / cold drawing) |
| Surface Treatment | Hot Rolled (Black / Oiled optional) |
| Tolerance | ±1% |
| Ends | Plain / Beveled (upon request) |
| Application | Construction Structure, Fluid Pipe, Boiler Pipe, Drill Pipe, Hydraulic Pipe, Gas Pipe, Oil Pipe, Chemical Fertilizer Pipe, Machinery Manufacturing, Structural Frames |
| MOQ | 25 Tons |
| Origin | China |
Application Suitability
| Industry | Typical Applications |
|---|---|
| Construction & Steel Structure | High-rise building columns, industrial warehouse frames, bridge support members |
| Machinery Manufacturing | Hydraulic cylinder barrels, crane boom sections, equipment base frames |
| Oil & Gas / Fluid Transport | Boiler tubes, drill pipe casings, chemical fertilizer process lines |
| Infrastructure | Tunnel support structures, conveyor gantry frames, pipeline support racks |
What Negative Tolerance Really Costs on a Pressure-Bearing Frame Order
A 0.5 mm wall deviation on a seamless tube can void an entire structural inspection.
When procurement teams specify 20# seamless square and rectangular steel tube for load-bearing frames or hydraulic systems, they assume the wall thickness on the mill certificate matches what arrives on site. In practice, some mills push negative tolerance to the edge — or beyond — to save weight per meter. The result: tubes that pass visual inspection but fail ultrasonic wall measurement at the destination port. Third-party surveyors flag the discrepancy, the container gets held, and the buyer faces air-freight replacement costs that dwarf the original savings.
For pressure-rated applications like boiler pipes or hydraulic cylinders, wall uniformity is not optional. The seamless pierce-and-draw process used for 20# seamless square and rectangular steel tube produces consistent grain flow around the entire cross-section, eliminating the weld-line weakness inherent in ERW alternatives [NEED_CITE: seamless vs welded hollow section structural performance comparison].
Matching Structural and Pressure Applications
The 20# seamless square and rectangular steel tube covers a specification range from light-gauge fluid conveyance to heavy-wall structural columns. For machinery builders requiring hydraulic cylinder barrels, the seamless manufacturing route ensures no internal weld bead that could disrupt piston seal movement. In construction steel structures, the uniform corner geometry of square and rectangular seamless sections provides full bearing contact at moment connections — critical for high-rise frame stability where welded tube corner radii create gaps requiring costly shim plates.
Engineering Compliance and Certification Requirements
Structural applications for 20# seamless square and rectangular steel tube must comply with dimensional tolerances defined in GB/T 6728 or equivalent ASTM standards for cold-formed and seamless hollow sections. For projects targeting EU markets, CE certification under EN 10210 (hot-finished) or EN 10219 (cold-formed) is mandatory for customs clearance — and the seamless production process must be explicitly covered under the manufacturer’s Factory Production Control certificate [NEED_CITE: EN 10210 hot-finished structural hollow section certification requirements]. Corrosion protection selection depends on the end environment: black hot-rolled finish with mill oil suits indoor structural frames, while oiled surfaces provide short-term transit protection for export shipments. Steel grade selection between 20# (carbon seamless), Q345 (Chinese structural), and S355JR (European structural) must align with the project’s design code and load calculations.
Steel Grade and Manufacturing Process Explained
The 20# designation refers to a Chinese carbon steel grade with approximately 0.20% carbon content, offering good machinability and weldability for general structural and fluid transport applications. When projects require higher yield strength, Q345 (equivalent to S355JR in the European system) provides approximately 50% higher yield than Q235, reducing section weight for the same load capacity.
The seamless manufacturing process begins with a solid round billet heated and pierced through the center to form a hollow shell, then elongated and sized through a series of rolling stands. For square and rectangular profiles, the round seamless tube is subsequently formed through cold rolling or cold drawing into the final shape. This two-stage process — hot-rolled pierce followed by cold forming — produces a tube with no longitudinal weld seam and uniform wall distribution around all four sides.
Wall thickness capability extends to 40 mm for heavy-duty structural and high-pressure applications. The ±1% tolerance specification ensures dimensional consistency across production batches, which matters when tubes must fit into pre-fabricated connection nodes on site. Surface treatment options include hot-rolled black finish (mill scale intact) or oiled surfaces for corrosion protection during storage and transit.
Hidden Costs of Incorrect Material Procurement
Procuring 20# seamless square and rectangular steel tube without verified mill test certificates creates downstream risk across multiple project phases. Material substitution — receiving Q235 when S355JR was specified — may pass initial visual inspection but fails mechanical testing at the engineering verification stage, forcing complete section replacement. Missing CE documentation blocks EU customs clearance regardless of physical quality, stranding containers at port with daily demurrage charges accumulating [NEED_CITE: steel import customs documentation requirements European Union]. Negative tolerance abuse reduces actual weight per meter below theoretical calculations, creating structural safety concerns that only surface during load testing or third-party audit.
Procurement Advantages Direct from Production
Every 20# seamless square and rectangular steel tube order ships with full chemical composition and mechanical property test reports generated from our in-house physical and chemical laboratory — no third-party lab delays. Our production lines cover 2,800+ specifications with wall thickness reaching 40 mm, meaning non-standard sizes that other mills quote as “special order” with extended lead times ship from our regular production schedule. The 41 invention patents held by our facility include proprietary sharp-corner rectangular tube technology that delivers true 90-degree internal corners for architectural and precision structural applications where standard rounded-corner tubes create connection gaps. Full international certification portfolio includes ISO 9001:2015, Lloyd’s CE marking under EN 10210/10219, Singapore FPC, and verified inspection reports from SGS and BV — ensuring customs clearance across 50+ export destinations without documentation disputes. Custom non-standard sizes, cutting to exact project lengths, and professional container loading with anti-damage measures eliminate on-site fabrication waste and transit damage claims.
Documentation & Compliance
- Mill test certificate documenting 20# chemical composition (C, Si, Mn, P, S) and mechanical properties (yield strength, tensile strength, elongation) per GB standard
- CE certificate covering seamless square and rectangular hollow sections under EN 10210/EN 10219 for European market customs clearance
- ISO 9001:2015 quality management system certificate covering full production and inspection process
- SGS or BV third-party inspection report verifying dimensional tolerance, wall thickness, and surface quality before shipment
- Material traceability documentation linking each tube to heat number and production batch for project audit compliance
- Complete customs documentation package including packing list, bill of lading, and certificate of origin
Packaging, Loading & Delivery
- 20# seamless square and rectangular tubes bundled with high-tensile steel strips, with 6 m and 12 m lengths optimized for 20ft and 40ft container loading to maximize payload per shipment
- Hot-rolled black finish tubes coated with anti-rust oil before bundling to prevent surface oxidation during ocean transit to Middle East and Southeast Asian destinations
- Professional container loading with wooden chocks and edge protectors preventing tube deformation and surface scratching for 40 mm heavy-wall sections
- Heat number and steel grade (20#) marked on each tube end with stenciled identification for site traceability and inspection verification
- Custom cutting service available to project-specified lengths reducing on-site waste and welding requirements for construction frame assembly
- FOB, CIF, and DDP shipping terms available with complete export documentation and container tracking until port arrival
Initiating Your Procurement Inquiry
Submit your 20# seamless square and rectangular steel tube requirements including outer dimensions, wall thickness, steel grade, total quantity, and destination port to receive a detailed quotation with unit pricing, production lead time, and applicable shipping terms. Mill test certificates and third-party inspection arrangements are confirmed at the quotation stage, ensuring full documentation compliance before contract execution.
Request Your Quotation and Material Certification
Provide your specification requirements to receive pricing, lead time confirmation, and mill test certificate samples within 12 hours.
Contact: Shandong Xin Jiyuan Special Steel Tube Co., Ltd
Tel: +86 531 8573 6315
Mobile/WhatsApp/WeChat: +86 188 5315 7756
Email: admin@sdxjypipe.com
Frequently Asked Questions
Q: What is the difference between seamless and ERW square and rectangular tubes, and when should I specify seamless?
A: Seamless tubes are produced from solid billets through pierce and rolling processes with no weld seam, providing uniform wall thickness and higher pressure resistance. ERW tubes are formed from steel coil with a longitudinal weld seam. For hydraulic cylinders, boiler tubes, and high-pressure fluid transport, seamless is specified to eliminate weld-line failure risk. For general structural frames where pressure rating is not critical, ERW offers cost efficiency.
Q: Can you supply 20# seamless tubes equivalent to ASTM A519 or EN 10210 grades?
A: Yes, our 20# seamless square and rectangular steel tube meets Chinese GB standards and can be cross-referenced to equivalent international grades. For ASTM A519 mechanical tube requirements or EN 10210 hot-finished structural hollow sections, we provide chemical composition comparison and mechanical property verification to confirm grade equivalence for your project specification.
Q: What is the maximum wall thickness available for seamless square and rectangular hollow sections?
A: Our production capability extends to 40 mm wall thickness for seamless square and rectangular hollow sections, covering heavy-duty structural columns, high-pressure vessel components, and industrial machinery applications requiring thick-wall sections beyond standard welded tube capability.
Q: Do you provide third-party inspection and full export documentation for EU and Middle East markets?
A: Yes, SGS and BV third-party inspections are arranged upon request before shipment, verifying dimensional accuracy, wall thickness, and surface quality. Complete export documentation including CE certificates under EN 10210/10219, mill test certificates, and certificates of origin ensures customs clearance for European Union and Middle East destinations.
Q: How do you pack and load seamless tubes to prevent deformation during ocean shipping?
A: Tubes are bundled with high-tensile steel strips and loaded with wooden chocks and edge protectors to prevent movement and surface damage. Heavy-wall sections receive additional support during container loading. Anti-rust oil coating protects hot-rolled surfaces during transit, and professional loading plans maximize container payload while maintaining tube integrity.
