Project Description
Capsule-Profile Steel Tubes — Precision-Engineered Rounded Rectangular Cross-Section Hollow Sections
When performance demands more than a standard round or square tube can deliver, the capsule-shaped steel tube — defined by its distinctive rounded rectangular cross-section — offers a superior engineering solution. Characterized by two flat parallel sides seamlessly joined by fully radiused ends, this profile delivers a unique combination of structural rigidity, directional bending stiffness, aerodynamic efficiency, and ergonomic compatibility that conventional profiles simply cannot match. Whether referred to as a capsule-profile tube, a stadium-section tube, an oblong hollow section, or a rounded rectangular hollow section, the geometry itself is the product's most compelling advantage.
From the first glance, the capsule cross-section communicates precision. Its smooth, continuous curved ends eliminate sharp stress-concentration corners that plague traditional rectangular sections, while the flat lateral faces provide reliable mating surfaces for welding, clamping, and fastening. This is a tube engineered not only to bear load but to integrate seamlessly into modern assemblies across automotive, agricultural, and general mechanical engineering industries.
At Fushun Steel Tube, we manufacture capsule-profile steel tubes through cold-drawing and hot-rolling processes to tight dimensional tolerances. Available across a range of carbon steel grades from low-carbon forming steels (SAE 1010) through to heat-treatable medium and high-carbon grades (SAE 1045, SAE 1060), our capsule tubes deliver consistent wall thickness, excellent surface finish, and repeatable mechanical properties across every length. Custom dimensions, non-standard cross-section aspect ratios, and application-specific lengths are available through our flexible production program.
Contact our technical sales team to discuss your specific profile requirements and receive a detailed proposal tailored to your application.
Product Profile
Applications
Tube-Form Applications
Automotive Industry
- Chassis and subframe longitudinal and lateral structural members (SAE 1035, SAE 1045)
- Seat frame structures, seat back frames, and cross-members (SAE 1020, SAE 1035)
- Roll-over protection structures (ROPS) and side intrusion door beams (SAE 1045)
- Roof rails and body-in-white structural reinforcements for SUVs and commercial vehicles
- Suspension link arms and stabilizer bar sleeves
Agricultural Machinery
- Sprayer booms and header frames requiring controlled deflection over long unsupported spans
- Loader arms, lift linkages, and three-point hitch components (SAE 1045, SAE 1060, quenched and tempered)
- Tractor chassis rails and combine harvester frame structures
- Grain handling conveyor and elevator structural members
- Tillage equipment frames and soil-engaging tool mounting beams
Mechanical and General Engineering
- Robotic arm secondary links and end-effector mounting rails (SAE 1020, SAE 1035)
- Linear actuator housings and guide tube components
- Industrial conveyor frames, machine tool beds, and workstation structures
- Hydraulic cylinder guide tubes and precision linear slide components (SAE 1045, ground and polished)
- Cable management channels where flat tube faces serve as integrated guide surfaces
- Exercise equipment frames and gym machine structural members
- Architectural and furniture structural elements where the smooth profile provides an aesthetic advantage
Other Form Applications
- Round bar and forged components in corresponding steel grades for mating parts, end fittings, and weld-on brackets
- Flat bar and plate products in SAE 1020 through SAE 1060 for gusset plates and reinforcement members
Specifications and Standards
Capsule-profile steel tubes are manufactured under applicable international standards. The table below lists the key standards relevant to shaped, rectangular, and special-section structural and mechanical steel tubes.
| Standard | Title / Scope | Product Form | Grade Coverage |
|---|---|---|---|
| ASTM A500 | Cold-Formed Welded and Seamless Carbon Steel Structural Tubing in Rounds and Shapes | Seamless and welded structural hollow sections | Grades B, C |
| ASTM A513 | Electric-Resistance-Welded Carbon and Alloy Steel Mechanical Tubing | Welded mechanical tubing | Types 1–5 (1010–1060 range) |
| EN 10210-1 | Hot Finished Structural Hollow Sections of Non-Alloy and Fine Grain Steels | Hot-finished seamless and welded hollow sections | S235JRH, S275JRH, S355J2H |
| EN 10219-1 | Cold Formed Welded Structural Hollow Sections of Non-Alloy and Fine Grain Steels | Cold-formed welded hollow sections | S235JRH, S275J0H, S355J2H |
| EN 10305-1 | Steel Tubes for Precision Applications — Seamless Cold Drawn Tubes | Seamless cold-drawn precision tubes | E235, E355 |
| GB/T 3094 | Cold Drawn Shaped Steel Tubes | Cold-drawn special-section tubes (rectangular, obround, oval, capsule) | 10, 20, 35, 45 (equivalent to SAE 1010, 1020, 1035, 1045) |
| GB/T 6728 | Cold Formed Steel Hollow Sections for General Structure | Cold-formed welded hollow sections | Q235, Q345 |
| JIS G 3466 | Carbon Steel Square and Rectangular Tubes for General Structure | Welded square/rectangular tubes | STKR400, STKR490 |
Our capsule-profile tubes are supplied with full material traceability. For grades and dimensions not listed above, we can manufacture to customer-specified standards or proprietary specifications.
Available Sizes and Delivery
Size Range
| Product Form | OD / Major Axis Range | Wall Thickness Range | Length |
|---|---|---|---|
| Hot-Rolled Seamless Capsule Tubes | 30 mm – 200 mm | 2.5 mm – 15 mm | 6 m, 12 m standard; cut-to-length available |
| Cold-Drawn / Cold-Rolled Precision Capsule Tubes | 15 mm – 120 mm | 1.0 mm – 8 mm | 6 m standard; custom lengths on request |
Non-standard cross-section aspect ratios, custom radius specifications, and intermediate dimensions outside the ranges above can be produced through our custom manufacturing program with engineering review.
Delivery and Minimum Order Quantity
- Standard sizes in common grades (SAE 1020, SAE 1045): Ready stock available for selected dimensions; delivery approximately 7 working days.
- Custom dimensions or non-standard aspect ratios: MOQ 2–3 metric tons; lead time approximately 25–35 working days depending on tooling requirements.
- Special grades and small trial batches: We welcome small-volume trial orders to support your product development and qualification process.
- Large-volume project orders: Competitive pricing structures and negotiable lead times; contact us with your annual forecast for a tailored supply agreement.
Request a Quote for Capsule-Profile Steel Tubes — Tell us your dimensions, grade, and quantity, and we will respond with a detailed quotation within 24 hours.
Chemical Composition
The table below presents the chemical composition ranges (weight percent, ladle analysis) for each carbon steel grade available in capsule-profile tube form. Values are typical per relevant ASTM, SAE, EN, and GB standards.
| Grade | Equivalent Designations | C (%) | Mn (%) | Si (%) | P (max %) | S (max %) |
|---|---|---|---|---|---|---|
| ASTM A36 | S235JR, Q235B, SS400 | ≤ 0.26 | — | ≤ 0.40 | ≤ 0.040 | ≤ 0.050 |
| SAE 1010 | C10, 10# | 0.08 – 0.13 | 0.30 – 0.60 | 0.10 – 0.35 | ≤ 0.040 | ≤ 0.050 |
| SAE 1020 | C20, 20#, S20C | 0.18 – 0.23 | 0.30 – 0.60 | 0.15 – 0.35 | ≤ 0.040 | ≤ 0.050 |
| SAE 1035 | C35, 35#, S35C | 0.32 – 0.38 | 0.60 – 0.90 | 0.15 – 0.35 | ≤ 0.040 | ≤ 0.050 |
| SAE 1045 | C45, 45#, S45C | 0.43 – 0.50 | 0.60 – 0.90 | 0.15 – 0.35 | ≤ 0.040 | ≤ 0.050 |
| SAE 1060 | C60, 60#, S58C | 0.55 – 0.65 | 0.60 – 0.90 | 0.15 – 0.35 | ≤ 0.040 | ≤ 0.050 |
Note: For ASTM A36 supplied in tube form, manganese content varies with wall thickness per ASTM A36/A36M requirements. For SAE grades, small intentional additions of aluminum or silicon for deoxidation may be present. Actual heat analyses are provided on the mill test certificate for every shipment.
Manufacturing Process
Steelmaking Routes
At Fushun Steel Tube, we offer multiple steelmaking routes to match the cleanliness, homogeneity, and property requirements of each application:
- Standard route
- Electric Arc Furnace (EAF) + Ladle Furnace (LF) refining + Vacuum Degassing (VD). This route produces clean, fully killed steel suitable for the majority of structural and mechanical tubing applications across all grades.
- Elevated cleanliness route
- EAF + LF + VD + Electroslag Remelting (ESR) or Protective Atmosphere ESR (PESR). Recommended for SAE 1045 and SAE 1060 components subject to high cyclic or dynamic loading, where improved micro-cleanliness directly extends fatigue life.
- Highest-purity route
- Vacuum Induction Melting (VIM) + Vacuum Arc Remelting (VAR). Available for critical applications demanding the lowest possible inclusion content and highest mechanical property consistency.
Tube-Making Processes
- Hot-Rolled Seamless
- Billet heating → Piercing → Pilger or continuous rolling → Sizing → Controlled cooling → Heat treatment (normalizing or annealing) → Straightening → NDT inspection → Final inspection.
- Cold-Drawn / Cold-Rolled
- Hot-rolled hollow shell → Annealing → Surface conditioning (pickling, phosphating) → Cold drawing or cold rolling → Intermediate annealing (as needed) → Final heat treatment → Straightening → Precision cutting → Final inspection.
- Honed Tubes
- (where internal surface finish is critical): Cold-drawn tube → Stress-relief annealing → Honing to specified Ra → Cleaning → Preservation → Final inspection.
We encourage customers to discuss their specific performance requirements with our engineering team so that the optimal steelmaking and tube-making route can be matched to the intended application.
Mechanical Properties
Mechanical properties for each grade under typical delivery conditions. Values represent minimum requirements unless a range is specified. Actual properties are documented on the EN 10204 3.1 inspection certificate supplied with each shipment.
| Grade | Delivery Condition | Tensile Strength (MPa) | Yield Strength (MPa, min) | Elongation (%, min) | Hardness (HBW) |
|---|---|---|---|---|---|
| ASTM A36 | Hot-rolled | 400 – 550 | 250 | 20 | ≤ 160 |
| SAE 1010 | Cold-drawn / Normalized | ≥ 325 | 180 | 28 | ≤ 143 |
| SAE 1020 | Cold-drawn / Normalized | ≥ 395 | 295 | 25 | ≤ 156 |
| SAE 1035 | Normalized | ≥ 585 | 370 | 20 | ≤ 183 |
| SAE 1035 | Quenched + Tempered | ≥ 650 | 450 | 15 | 185 – 235 |
| SAE 1045 | Normalized | ≥ 625 | 410 | 16 | ≤ 207 |
| SAE 1045 | Quenched + Tempered | 700 – 850 | 500 | 14 | 201 – 269 |
| SAE 1060 | Normalized | ≥ 660 | 420 | 12 | ≤ 229 |
| SAE 1060 | Quenched + Tempered | 800 – 950 | 550 | 10 | 229 – 285 |
Notes: Mechanical properties are based on longitudinal test specimens. Elongation values are for gauge length 5.65√S₀ (proportional test piece). For tubes with wall thickness below 5 mm, elongation requirements may be adjusted per applicable standards. Quenched and tempered properties for SAE 1045 and SAE 1060 assume appropriate austenitizing, quenching, and tempering practice and are dependent on section thickness.
Heat Treatment
Capsule-profile tubes can be supplied in a range of heat treatment conditions to meet specific mechanical property, machinability, or forming requirements. The table below summarizes the applicable processes and typical parameters.
| Grade | Process | Temperature Range (°C) | Cooling Method | Typical Application Purpose |
|---|---|---|---|---|
| SAE 1010 | Annealing | 850 – 900 | Furnace cool | Maximum softness for severe cold forming |
| SAE 1010 | Normalizing | 900 – 930 | Air cool | Refine grain structure after hot working |
| SAE 1020 | Normalizing | 890 – 930 | Air cool | Uniform structure for general mechanical use |
| SAE 1020 | Annealing | 850 – 890 | Furnace cool | Improve machinability and cold formability |
| SAE 1035 | Normalizing | 850 – 880 | Air cool | Standard delivery condition for structural use |
| SAE 1035 | Quenching + Tempering | Quench 840 – 870; Temper 550 – 650 | Water or oil quench; air cool from temper | Balanced strength and toughness |
| SAE 1045 | Normalizing | 840 – 870 | Air cool | Uniform fine pearlitic structure |
| SAE 1045 | Quenching + Tempering | Quench 820 – 850; Temper 550 – 650 | Water or oil quench; air cool from temper | High strength with good toughness |
| SAE 1060 | Normalizing | 820 – 850 | Air cool | Prepare structure prior to hardening |
| SAE 1060 | Quenching + Tempering | Quench 800 – 830; Temper 550 – 650 | Oil quench preferred; air cool from temper | Maximum strength and wear resistance |
Special considerations for capsule-profile tubes: The asymmetric wall thickness distribution inherent to the rounded rectangular cross-section demands careful control of heating rates and quench severity to minimize distortion and residual stress. For quenched and tempered SAE 1045 and SAE 1060 tubes, we apply controlled-atmosphere or protective-atmosphere heat treatment to prevent decarburization of the surface layer. Stress-relief annealing at 500–600 °C is available for cold-drawn tubes where dimensional stability after machining is critical.
Our metallurgical team works with customers to define the optimal heat treatment condition for each application. Specify your target hardness range or mechanical property requirements, and we will recommend — and validate — the appropriate cycle.
Surface Finish and Tolerances
Capsule-profile tubes are available in a range of surface finishes and dimensional tolerance grades, selected according to the demands of the application.
Hot-Rolled Finish
- As-rolled (black) surface suitable for applications where the tube will be machined or where surface appearance is not critical.
- Pickled and oiled finish removes mill scale, providing a clean surface ready for welding or painting.
- OD tolerance: ±0.75% of nominal, with a minimum of ±0.3 mm.
- Wall thickness tolerance: ±10% standard; ±7.5% on request.
Cold-Drawn / Cold-Rolled Bright Finish
- Bright, smooth surface achieved through cold drawing or cold pilgering.
- OD tolerance: ±0.10 mm for diameters up to 50 mm; ±0.15 mm for 50–120 mm.
- Wall thickness tolerance: ±5% for wall thicknesses ≥ 2 mm.
- Surface roughness: Ra ≤ 3.2 μm achievable as standard; Ra ≤ 1.6 μm available with additional processing.
Honed / Bored Internal Surface
- Internal honing achieves surface roughness Ra 0.2–0.4 μm for hydraulic cylinder and precision sliding applications.
- Internal diameter tolerance: H8 or H9 as standard; H7 available on request.
External Machined Surface
- Turned (peeled) surface for improved roundness and surface quality on hot-rolled stock.
- Ground external surface achieving Ra ≤ 0.8 μm and dimensional tolerance within 0.05 mm for precision guide and bearing applications.
Custom surface treatments — including phosphating, zinc plating, and protective coatings — are available on request.
Quality Assurance and Testing
Every capsule-profile tube shipped by Fushun Steel Tube undergoes a rigorous, multi-stage quality control program that covers the entire production chain from incoming raw material to final dispatch.
Raw Material Inspection
- Full chemical composition analysis by optical emission spectrometer (OES) on every heat of steel.
- Verification of heat identity and traceability documentation before material is released to production.
In-Process Inspection
- Online wall thickness measurement and outer dimension monitoring during hot rolling and cold drawing.
- Surface quality inspection at intermediate stages to detect and isolate defects early.
Finished Product Testing
- Non-destructive testing: Ultrasonic testing (UT) per ASTM E213 or ISO 10893-10; eddy current testing (ET) for cold-drawn tubes; magnetic particle inspection (MT) for surface and near-surface discontinuities on quenched and tempered grades.
- Hydrostatic pressure testing on every tube, or on a statistical sampling basis per applicable standards.
- Mechanical testing: Room-temperature tensile testing, Charpy V-notch impact testing (where specified), and hardness testing (Brinell or Rockwell).
- Dimensional inspection: OD, wall thickness, straightness, length, and cross-section profile geometry verified against order specifications.
- Metallographic examination: Microstructure evaluation to confirm heat treatment response and grain size control.
Certification and Third-Party Inspection
- EN 10204 Type 3.1 inspection certificate issued as standard with every shipment, documenting chemical composition, mechanical properties, NDT results, and dimensional conformance.
- EN 10204 Type 3.2 certificate available on request through independent inspection agencies.
- Third-party inspection by SGS, TÜV, Bureau Veritas, or customer-nominated inspectors welcomed and routinely accommodated.
- Fushun Steel Tube is ISO 9001:2015 certified, with an internal quality management system that governs every aspect of production and delivery.
Request a sample or technical datasheet for the grade and profile you need — we are happy to provide detailed test data and metallurgical documentation.
Packing and Shipping
Hot-Rolled Tubes
- Anti-rust protective oil applied to external surfaces.
- Secured in compact bundles with steel strapping.
- End protection with plastic caps or wrapping on tube ends to prevent handling damage.
Cold-Drawn Precision and Honed Tubes
- Individual polyethylene end caps on every tube to protect internal surfaces from contamination and mechanical damage.
- VCI (Volatile Corrosion Inhibitor) paper or VCI film wrapping on each tube or bundle.
- Packed in sturdy wooden cases or welded steel frame crates with internal spacing and cushioning to prevent tube-to-tube contact during transit.
Logistics
- Sea freight (FCL and LCL), air freight, and land transportation all available.
- Standard packing marks applied; custom shipping marks, barcodes, and labeling per customer specifications accommodated at no additional charge for standard requirements.
Frequently Asked Questions
Can you produce capsule-profile tubes in non-standard cross-section dimensions?
Yes. Our cold-drawing and cold-rolling processes allow us to produce custom cross-section aspect ratios, radii, and dimensions outside our published standard range. We review each custom profile request with our engineering team and typically provide a feasibility assessment and quotation within 2–3 working days. The minimum order quantity for custom profiles is generally 2–3 metric tons depending on tooling complexity.
What is the hardest condition you can supply SAE 1045 and SAE 1060 capsule tubes in?
SAE 1045 can be supplied in the quenched and tempered condition at hardness levels up to approximately 269 HBW (28 HRC), delivering tensile strengths in the 700–850 MPa range. SAE 1060 quenched and tempered can reach approximately 285 HBW (30 HRC) with tensile strength exceeding 800 MPa. Higher hardness levels up to 55–58 HRC are achievable through induction hardening of selected surfaces, which we can arrange for components requiring localized wear resistance. Please discuss your specific hardness and strength targets with our technical team.
What are your typical lead times for standard and custom capsule-profile tubes?
Standard sizes in SAE 1020 and SAE 1045 with common dimensions are often available from our ready stock and can ship within approximately 7 working days. Custom dimensions, non-standard grades, or profiles requiring new tooling typically ship within 25–35 working days from order confirmation. Large project volumes can be delivered against a phased schedule negotiated at the time of order placement.
Do you provide material certificates and can you arrange third-party inspection?
Yes. Every shipment is accompanied by an EN 10204 Type 3.1 inspection certificate documenting the chemical composition, mechanical test results, NDT outcomes, and dimensional verification for your specific order. For projects requiring EN 10204 Type 3.2 certification with independent witness testing, we routinely coordinate with SGS, TÜV, Bureau Veritas, or your nominated inspection agency. All testing and documentation is managed within our ISO 9001-certified quality management system.
Can you produce small quantities for prototyping and product development?
Absolutely. We understand that new product development programs often begin with small trial quantities. We accept small-batch orders for prototype builds and pre-production validation, even for custom profiles. Our engineering team can work with you on material selection, heat treatment condition, and tolerance requirements to ensure that your prototypes are representative of series production quality.
Request a Quote for Capsule-Profile Steel Tubes — Contact our technical sales team to discuss your specific profile requirements and receive a detailed proposal tailored to your application.
