Stainless Steel Coil Tube (Coiltube) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a continuous-length tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Product No. 1623). Unlike standard straight-length piping, coil tubes are supplied in continuous helical coils, enabling seamless downstream processing, roll-forming, and automated fabrication without the introduction of additional weld seams. This product is particularly suited for applications demanding high structural integrity, corrosion resistance, and dimensional precision — including heavy-duty trailer chassis systems, industrial mixing equipment, and structural piping assemblies.
The coil tube design eliminates the need for butt-welding of individual pipe sections, thereby reducing stress concentration points and enhancing overall mechanical reliability. This is a critical advantage in applications such as the chassis pipe joints of heavy-load trailers (e.g., 63-ton granular material mixing machine trailers), where weld joint strength and fatigue resistance are paramount.
2. Material & Properties
2.1 Base Material
Coil tubes are manufactured from austenitic stainless steel grades conforming to international standards, with the most commonly specified grades being:
- ASTM A269 / A270 — Seamless and welded austenitic stainless steel tubing
- EN 10216-5 — European specification for seamless and welded stainless steel tubes
- JIS G3459 / G3460 — Japanese Industrial Standard for stainless steel tubes
- GB/T 12771 / GB/T 13296 — Chinese national standards for stainless steel tubes
2.2 Mechanical Properties
| Property | Grade 304 (06Cr19Ni10) | Grade 316 (06Cr17Ni12Mo2) | Grade 321 (06Cr18Ni11Ti) |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 515 | ≥ 520 |
| Yield Strength (MPa) | ≥ 205 | ≥ 205 | ≥ 205 |
| Elongation (% at fracture) | ≥ 40 | ≥ 40 | ≥ 40 |
| Hardness (HBW) | ≤ 187 | ≤ 187 | ≤ 187 |
| Density (g/cm³) | 7.93 | 8.00 | 7.93 |
| Operating Temperature Range (°C) | −196 to +870 | −196 to +870 | −196 to +900 |
| Corrosion Resistance (pH range) | 1–14 (non-oxidizing) | 1–14 (chloride-resistant) | 1–14 (stabilized) |
2.3 Key Alloying Elements
- Chromium (Cr): 18–20% — provides passive oxide layer for corrosion resistance
- Nickel (Ni): 8–12% — stabilizes austenitic microstructure, enhances ductility
- Molybdenum (Mo): 2–3% (Grade 316) — improves resistance to pitting and crevice corrosion
- Carbon (C): ≤ 0.08% — limits sensitization and intergranular corrosion risk
3. Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | Φ 6.0 mm – Φ 219.0 mm (custom sizes available) |
| Wall Thickness (WT) | 0.5 mm – 12.0 mm |
| Coil Length (Continuous) | 20 m – 500 m (per coil, depending on diameter and wall thickness) |
| Coil Weight | 0.5 tons – 3.0 tons per coil |
| Manufacturing Method | ERW (Electric Resistance Welded) / Seamless (for larger diameters) |
| Surface Finish | 2B, BA (Bright Annealed), No.4 Brushed, Mirror (Ra ≤ 0.4 μm) |
| Tolerance — OD | ± 0.05 mm (precision grade) / ± 0.1 mm (standard grade) |
| Tolerance — Wall Thickness | ± 0.02 mm (precision grade) / ± 0.05 mm (standard grade) |
| End Condition | Plain cut, beveled (per ASME B16.25), or custom |
| Protective Coating | None (passivated) / PVC cap ends / wooden crate packaging |
4. Manufacturing Process
4.1 Process Flow
- Coil Uncoiling & Leveling: Cold-rolled stainless steel strip (slit coil) is fed through a leveling unit to eliminate coil set and ensure flatness prior to forming.
- Forming & Welding (ERW): The leveled strip is progressively rolled through a series of forming rolls into a tubular shape. The edges are then fused using Electric Resistance Welding (ERW) with precise current and pressure control.
- Heat Treatment / Solution Annealing: The welded tube undergoes solution annealing at 1050–1100 °C followed by controlled cooling to restore full austenitic structure and relieve residual welding stresses.
- Surface Finishing: The annealed tube is pickled and passivated (or polished to the required finish grade) to remove scale and establish a stable chromium oxide passive layer.
- Coiling: The continuous tube is wound into a controlled helical coil on a precision coiling machine. Tension is carefully managed to prevent deformation or ovality.
- Non-Destructive Testing (NDT): 100% inline inspection via eddy current testing (ECT) and/or ultrasonic testing (UT) to detect weld seams, wall thickness deviations, and internal/external defects.
- Final Inspection & Packaging: Dimensional verification, visual inspection, and protective packaging for shipment.
4.2 Weld Seam Integrity
For applications involving high structural loads — such as trailer chassis pipe joints — the weld seam strength is a critical design parameter. The ERW process, when properly controlled, produces a weld zone with mechanical properties comparable to the base metal. The weld seam undergoes:
- Weld Seam Inspection: 100% eddy current testing to detect cracks, lack of fusion, and porosity
- Weld Bead Removal: Internal weld bead grinding (for pressure applications) or external bead polishing
- Weld Zone Microstructure Verification: Metallographic examination to confirm complete austenitic transformation and absence of martensite or sigma phase
- Impact Testing: Charpy V-notch impact testing on weld zone samples at design service temperatures
5. Applications
5.1 Heavy-Duty Trailer Chassis Systems
Coil tubes are extensively used in the fabrication of trailer chassis frames, cross-members, and suspension mounting points for heavy-load trailers (including 63-ton capacity granular material mixing machine trailers). The continuous coil form allows automated roll-forming of chassis components without intermediate welds, significantly improving structural fatigue life and reducing maintenance intervals.
5.2 Additional Applications
- Industrial Piping Systems: Chemical processing, food and beverage, pharmaceutical, and semiconductor clean-room piping
- Automotive & Transportation: Exhaust systems, fuel lines, structural brackets, and roll cages
- Architecture & Construction: Handrails, decorative trim, structural supports, and building facades
- Heat Exchangers & Boilers: Tubular heat exchanger elements, boiler tubes, and condensers
- Medical Devices: Surgical instrument tubing, implant components, and hospital equipment frames
- Aerospace: Hydraulic lines, fuel system tubing, and structural brackets (Grade 321 / 347)
6. Quality Certifications & Standards Compliance
6.1 Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health and Safety Management
- EN 10204 3.1 — Third-party material certification
- CE Marking — Conformity with European directives (where applicable)
- ASME Stamp — Pressure vessel and piping component certification (where applicable)
- PED (Pressure Equipment Directive) 2014/68/EU — Compliance for pressure applications
6.2 Testing & Inspection Protocol
| Test Method | Standard | Purpose |
|---|---|---|
| Hydrostatic Pressure Test | ASTM A269 / EN 10216-5 | Verify weld integrity and detect leaks |
| Eddy Current Testing (ECT) | ASTM A395 | 100% inline detection of weld defects and wall thickness deviations |
| Ultrasonic Testing (UT) | ASTM E317 / ASME BPV Section V | Detect internal volumetric and planar defects |
| Chemical Composition Analysis | ASTM E415 / E1268 | Verify alloy content via optical emission spectroscopy (OES) |
| Tensile & Yield Testing | ASTM E8 / EN 10002-1 | Confirm mechanical properties meet grade specifications |
| Intergranular Corrosion Test | ASTM A269 (Appendix X) / EN 10216-5 | Verify resistance to sensitization-induced corrosion |
| Dimensional Inspection | ASTM A269 / GB/T 12771 | Verify OD, wall thickness, straightness, and ovality tolerances |
| Pickling & Passivation Verification | ASTM A967 | Confirm surface cleanliness and passive layer formation |
6.3 Traceability
Every coil tube lot is assigned a unique heat number and coil identification code. Full traceability from raw material mill certificate through final inspection is maintained, enabling complete supply chain accountability. Material certificates (EN 10204 3.1) are provided with each shipment, including chemical composition, mechanical test results, NDT reports, and dimensional inspection data.
7. Unique Selling Points
- Seamless Continuous Length: Eliminates butt welds in fabrication, reducing stress concentration and improving fatigue life — critical for heavy-load structural applications such as trailer chassis systems
- Precision Dimensional Control: Tolerances as tight as ±0.02 mm on wall thickness, enabling direct use in high-precision applications without secondary machining
- 100% NDT Coverage: Every meter of coil tube undergoes inline eddy current and ultrasonic inspection, ensuring zero-defect delivery
- Multi-Grade Availability: Full range of austenitic grades (304, 316, 321, 316L, 321, 904L, etc.) to match specific corrosion and mechanical requirements
- Custom Surface Finishes: From industrial 2B finish to precision mirror polish (Ra ≤ 0.4 μm), accommodating diverse aesthetic and functional needs
- Weld Seam Optimization: ERW process with controlled heat input produces a weld zone with mechanical properties equivalent to the base metal, validated by Charpy impact testing
- Full Traceability: Heat-number traceability from raw material to finished product with comprehensive third-party certification
- Cost Efficiency: Continuous coil supply reduces material waste (compared to cut-length pipe), minimizes fabrication labor, and accelerates production throughput
Reference Document: Technical analysis informed by "63-Ton Black Granular Material Mixing Machine Trailer Chassis Pipe Joint Weld Strength Design" — a study examining weld joint integrity optimization for heavy-load trailer chassis applications, directly applicable to the structural design considerations of coil tube selection in trailer manufacturing.