304 Austenitic Stainless Steel Coil Tube (Coiltube) — Wenzhou Jixing Metal Materials Co., Ltd.
1. Product Overview
The 304 Austenitic Stainless Steel Coil Tube (also referred to as Coiltube or Coil Pipe) is a continuously wound tubular product manufactured from UNS S30400 / AISI 304 grade austenitic stainless steel. As the 18Cr-8Ni base alloy of the austenitic family, this product represents the cornerstone of commercial stainless steel applications worldwide. Its designation as a general-purpose austenitic grade reflects its versatile corrosion resistance against atmospheric environments and weakly aggressive chemical media, making it the single most widely consumed stainless steel grade in global industrial markets.
Wenzhou Jixing Metal Materials Co., Ltd. supplies this product in continuous coil form, enabling efficient downstream processing—including straightening, cutting, bending, and forming—without the need for seam-welding of discrete tube lengths. The coil configuration significantly reduces material waste, improves production throughput, and supports automated manufacturing workflows in high-volume industries.
2. Material Composition & Properties
2.1 Chemical Composition (Typical, wt%)
| Element | Specification Range | Function |
|---|---|---|
| Carbon (C) | ≤ 0.08% | Controls precipitation and weldability |
| Chromium (Cr) | 18.0 – 20.0% | Primary corrosion resistance element; forms passive Cr₂O₃ film |
| Nickel (Ni) | 8.0 – 10.5% | Stabilizes austenitic crystal structure; enhances ductility |
| Manganese (Mn) | ≤ 2.0% | Partial nickel substitution; aids deoxidation |
| Silicon (Si) | ≤ 1.0% | Deoxidizer; improves high-temperature oxidation resistance |
| Phosphorus (P) | ≤ 0.045% | Impurity control; limits cold-cracking susceptibility |
| Sulfur (S) | ≤ 0.030% | Impurity control; minimizes hot-shortness during rolling |
| Iron (Fe) | Balance | Base matrix element |
2.2 Mechanical Properties (Annealed Condition)
| Property | Typical Value | Test Standard |
|---|---|---|
| Tensile Strength (UTS) | ≥ 515 MPa (≥ 75 ksi) | ASTM A270 / GB/T 12771 |
| Yield Strength (0.2% Offset) | ≥ 205 MPa (≥ 30 ksi) | ASTM A270 / GB/T 12771 |
| Elongation (in 50 mm) | ≥ 40% | ASTM A270 / GB/T 12771 |
| Hardness (Rockwell B) | ≤ 95 HRB | ASTM A270 |
| Density | 8.0 g/cm³ | — |
| Thermal Conductivity (20°C) | 16.3 W/(m·K) | — |
| Electrical Resistivity (20°C) | 0.74 Ω·mm²/m | — |
| Modulus of Elasticity | 193 GPa (28 × 10⁶ psi) | — |
2.3 Corrosion Resistance Characteristics
- Atmospheric Corrosion: Excellent resistance to urban, rural, and industrial atmospheres; suitable for outdoor architectural applications without protective coating.
- Weak Chemical Media: Resistant to dilute inorganic acids (H₂SO₄, HNO₃, H₃PO₄ below critical concentrations), organic acids (citric, acetic, lactic), and alkaline solutions at ambient to moderate temperatures.
- Pitting & Crevice Corrosion: Moderate resistance; susceptible to chloride-induced pitting above ~200 ppm Cl⁻ at elevated temperatures. For aggressive chloride environments, upgraded grades (316L, 904L) are recommended.
- Intergranular Corrosion: The low-carbon variant (304L, C ≤ 0.03%) provides superior resistance to sensitization during welding or heat treatment in the 450–850°C temperature range.
- Passivation: Self-healing chromium oxide passive film (Cr₂O₃) reforms rapidly in oxidizing environments, providing continuous long-term protection.
3. Product Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Material Grade | UNS S30400 / AISI 304 / EN 1.4301 / GB 06Cr19Ni10 | ASTM A270 / EN 10216-5 / GB/T 12771 |
| Product Form | Continuous Coil Tube (Coiltube) | — |
| Outer Diameter (OD) | 6.0 – 168.3 mm (¼" – 6⅝") | ASTM A554 / GB/T 12771 |
| Wall Thickness (WT) | 0.5 – 6.0 mm (0.020" – 0.236") | ASTM A554 / GB/T 12771 |
| Coil Length | 5,000 – 15,000 mm (standard); custom lengths available | — |
| Surface Finish | No. 1 (Hot Rolled), 2B (Cold Rolled & Annealed), BA (Bright Annealed), No. 4 (Brushed), Mirror (8K) | ASTM A480 / GB/T 4237 |
| Manufacturing Method | Seam-welded (ERW, TIG) or Weldless (Cold-Drawn) | ASTM A270 |
| Heat Treatment | Full Annealing (Solution Annealing) at 1010–1150°C, followed by water or air quench | — |
| Tolerance (OD) | ± 0.05 mm (precision grades); ± 1.0% (standard) | ASTM A554 |
| Tolerance (WT) | ± 0.03 mm (precision grades); ± 10% (standard) | ASTM A554 |
| Coil ID | 508 mm (20"), 610 mm (24") — standard | — |
| Packaging | Wooden reel or steel ring, wrapped in VCI (Vapor Corrosion Inhibitor) paper and stretch film | — |
4. Manufacturing Process
The production of 304 stainless steel coil tube at Wenzhou Jixing follows a rigorous multi-stage metallurgical and mechanical processing workflow designed to ensure dimensional accuracy, microstructural integrity, and surface quality:
- Raw Material Selection: High-purity 304-grade stainless steel strip is sourced from certified mills (e.g., POSCO, Outokumpu, Taigang, or Baosteel), with incoming chemical composition verified via Optical Emission Spectrometry (OES) to confirm compliance with ASTM A270 / EN 10216-5 requirements.
- Strip Preparation & Inspection: Incoming cold-rolled strip undergoes visual inspection for surface defects, dimensional verification (thickness gauge, width measurement), and magnetic permeability testing to confirm full austenitic microstructure. Any strip exhibiting ferrite content exceeding 1% is rejected.
- Coil Forming & Welding (Seam-Welded Route):
- Pre-formed strip is fed through a series of roll-forming stations to achieve the desired circular cross-section.
- Seam welding is performed via Electrode Resistance Welding (ERW) for high-speed production of smaller diameters, or Tungsten Inert Gas (TIG) welding for precision applications requiring superior weld quality and lower heat-affected zone (HAZ) distortion.
- Weld seams are ground and polished to achieve flush or near-flush surface profiles.
- Cold Drawing (Weldless Route): For seamless coil tube, solid billet is pierced, hot-rolled into hollow stock, and cold-drawn through precision dies to achieve final dimensions with a fully homogeneous microstructure and no weld seam.
- Solution Annealing (Stress Relief): The formed tube is annealed at 1010–1150°C in a protective atmosphere (endothermic gas or vacuum) to:
- Relieve residual stresses from forming and welding operations
- Dissolve any carbide precipitates (e.g., Cr₂₃C₆) formed during processing
- Restore full austenitic microstructure and maximum corrosion resistance
- Improve ductility and formability for downstream fabrication
- Surface Treatment:
- Pickling: Immersion in a mixed acid solution (HNO₃ + HF or HNO₃ + HCl) to remove oxide scale and mill scale.
- Passivation: Treatment with 20–30% nitric acid solution to enrich the surface chromium content and establish a stable passive film.
- Polishing/Bright Annealing: Optional surface finishing to achieve specified finish grades (2B, BA, Mirror).
- Final Inspection & Quality Control:
- Dimensional inspection (OD, WT, straightness, coil diameter)
- Chemical composition verification (OES or ICP-OES)
- Mechanical property testing (tensile, hardness)
- Corrosion testing (salt spray per ASTM B117; intergranular corrosion per ASTM A262 Practice E)
- Non-Destructive Testing (NDT): Eddy current, ultrasonic, or radiographic inspection of weld seams
- Visual inspection for surface defects, weld bead uniformity, and coating integrity
- Coiling & Packaging: The finished tube is wound onto a steel or wooden reel, protected with VCI paper and moisture-barrier stretch film, and secured with steel strapping for transport.
5. Applications
The 304 stainless steel coil tube's combination of corrosion resistance, formability, weldability, and economic accessibility makes it suitable for an extraordinarily broad range of industrial applications:
5.1 Architectural & Construction
- Structural handrails, balustrades, and guardrails
- Facade cladding tubes and decorative columns
- Window frames, door frames, and curtain wall supports
- Exhaust and ventilation ductwork
5.2 Food & Beverage Processing
- Hygienic process piping and transfer lines
- Brewery and dairy processing equipment
- Food-grade support structures and conveyor frames
- Wine and beverage fermentation vessel supports
5.3 Chemical & Pharmaceutical
- Low-pressure chemical process piping (non-aggressive media)
- Pharmaceutical equipment frames and supports
- Heat exchanger tubes (moderate service conditions)
- Laboratory instrumentation and analytical equipment housings
5.4 Automotive & Transportation
- Exhaust system components (upstream sections)
- Structural tubing for vehicle frames and roll cages
- Fuel system lines and brackets
- Electrical conduit and harness protection
5.5 General Industrial
- Machine tool frames and guardrails
- Industrial shelving and racking systems
- Agricultural equipment (irrigation pipes, greenhouse structures)
- Furniture manufacturing (tubular frames, legs, supports)
- Medical device frames and hospital equipment supports
5.6 Domestic & Consumer Products
- Appliance components (washing machine drums, oven racks)
- Lighting fixtures and lamp holders
- Water heater components and plumbing fixtures
- Consumer electronics housings and frames
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems and product certifications to ensure compliance with international and domestic standards:
| Certification / Standard | Scope | Relevance |
|---|---|---|
| ISO 9001:2015 | Quality Management System | Ensures consistent product quality and process control |
| ISO 14001:2015 | Environmental Management System | Controls environmental impact of manufacturing operations |
| ISO 45001:2018 | Occupational Health & Safety Management | Worker safety and health assurance |
| EN 10204 3.1 | Material Test Certificate | Third-party verified product certification |
| ASTM A270 | Standard for Stainless Steel Tubular Products (Seamless & Welded) | Primary product standard for tubing |
| GB/T 12771 | Chinese National Standard for Stainless Steel Tubes for General Purposes | Domestic market compliance |