Stainless Steel Heating Coil Tube (Coil Tube) — Technical Product Specification
1. Product Overview
The Stainless Steel Heating Coil Tube (hereinafter referred to as "Coil Tube") is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Wenzhou Jixing Metal Materials Co., Ltd.), specifically designed for radiant heating systems, hydronic heating loops, and thermal energy transfer applications. The Coil Tube is formed from high-grade austenitic stainless steel strip through a continuous cold-rolling and spiral-coiling process, producing a seamless helical tube configuration that maximizes heat exchange surface area within a compact spatial footprint.
Unlike conventional straight-section stainless steel pipe systems that require extensive welding at field installation, the Coil Tube is supplied in continuous helical form, eliminating the need for field welding in most applications. This design significantly reduces installation labor costs, minimizes potential leak points, and ensures long-term structural integrity under cyclic thermal loading conditions.
Key Design Philosophy: The Coil Tube represents the optimal intersection of thermal efficiency, mechanical durability, and installation convenience in modern hydronic heating infrastructure.
2. Material & Properties
2.1 Base Material Grades
The Coil Tube is primarily fabricated from the following austenitic stainless steel grades, selected for their superior corrosion resistance, thermal conductivity, and mechanical properties at elevated operating temperatures:
- SUS304 (ASTM A213 TP304 / EN 1.4301): The most widely used grade, containing approximately 18% Chromium (Cr) and 8% Nickel (Ni), offering excellent general corrosion resistance and formability. Suitable for most residential and commercial heating applications.
- SUS316 (ASTM A213 TP316 / EN 1.4401): Enhanced grade with 2–3% Molybdenum (Mo) addition, providing superior resistance to pitting and crevice corrosion. Recommended for coastal environments, geothermal applications, and systems utilizing aggressive water treatment chemicals.
- SUS321 (ASTM A213 TP321 / EN 1.4541): Titanium (Ti) stabilized grade, designed to resist intergranular corrosion at temperatures between 425°C and 870°C. Suitable for high-temperature industrial heating loops.
- SUS316L (ASTM A213 TP316L / EN 1.4431): Low-carbon variant of SUS316 with carbon content ≤0.03%, offering enhanced weldability and resistance to sensitization during welding operations.
2.2 Mechanical Properties (Annealed Condition)
| Property | Test Method | SUS304 | SUS316 | SUS321 |
|---|---|---|---|---|
| Tensile Strength (Rm) | ASTM A370 / EN ISO 6892-1 | ≥ 515 MPa | ≥ 515 MPa | ≥ 515 MPa |
| Yield Strength (Rp0.2) | ASTM A370 / EN ISO 6892-1 | ≥ 205 MPa | ≥ 205 MPa | ≥ 205 MPa |
| Elongation (A50) | ASTM A370 / EN ISO 6892-1 | ≥ 40% | ≥ 40% | ≥ 40% |
| Hardness (HBW) | ASTM E10 / EN ISO 6507 | ≤ 210 | ≤ 210 | ≤ 210 |
| Thermal Conductivity (25°C) | ASTM E1225 | 16.3 W/(m·K) | 14.6 W/(m·K) | 15.0 W/(m·K) |
| Operating Temperature Range | — | −196°C to +870°C | −196°C to +870°C | −196°C to +900°C |
| Corrosion Resistance (pH 3–10) | ASTM G48 | Excellent | Superior | Excellent |
2.3 Chemical Composition (Maximum % by Weight)
| Grade | C | Si | Mn | P | S | Cr | Ni | Mo | Other |
|---|---|---|---|---|---|---|---|---|---|
| SUS304 | 0.08 | 1.00 | 2.00 | 0.045 | 0.030 | 18.0–20.0 | 8.0–10.5 | — | Ti ≤ 0.70 |
| SUS316 | 0.08 | 1.00 | 2.00 | 0.045 | 0.030 | 16.0–18.0 | 10.0–14.0 | 2.0–3.0 | — |
| SUS321 | 0.08 | 1.00 | 2.00 | 0.045 | 0.030 | 17.0–19.0 | 9.0–12.0 | — | 5Ti–8Al |
3. Specifications
3.1 Dimensional Specifications
| Parameter | Specification / Range | Tolerance | Reference Standard |
|---|---|---|---|
| Outer Diameter (OD) | 8 mm – 32 mm (standard); 38 mm – 60 mm (custom) | ±0.15 mm | ASTM A213 / EN 10216-5 |
| Wall Thickness (WT) | 0.4 mm – 1.5 mm (standard); 1.6 mm – 3.0 mm (custom) | ±10% | ASTM A213 / EN 10216-5 |
| Coil Pitch (Helical Spacing) | 50 mm – 150 mm (adjustable per design) | ±2 mm | Project-specific |
| Coil Diameter (Bundle OD) | 200 mm – 1200 mm | ±5 mm | Project-specific |
| Tube Length per Coil | 5 m – 500 m (continuous, no field welding required) | ±1% | — |
| Surface Finish | Ba < 0.8 μm (2B finish); Ra < 0.5 μm (electropolished) | — | ASTM A403 / EN 10217 |
| Pressure Rating | Up to 1.6 MPa (standard); up to 4.0 MPa (heavy-wall) | — | EN 10216-5 / ASME B31.9 |
| Operating Medium | Water, glycol-water mixtures, thermal oil (up to 350°C) | — | — |
| Connection Type | Flanged, threaded, compression fitting, or direct weld | — | ASME B16.1 / EN 1092-1 |
3.2 Standard Coil Configurations
| Model Designation | OD × WT (mm) | Coil Pitch (mm) | Coil Bundle OD (mm) | Tube Length (m) | Typical Application |
|---|---|---|---|---|---|
| JX-HT-0815 | 8.0 × 0.8 | 75 | 300 | 100 | Residential underfloor heating |
| JX-HT-1020 | 10.0 × 1.0 | 100 | 500 | 200 | Commercial radiant heating |
| JX-HT-1225 | 12.0 × 1.2 | 125 | 600 | 250 | Industrial process heating |
| JX-HT-1630 | 16.0 × 1.5 | 150 | 800 | 300 | Large-scale hydronic systems |
| JX-HT-2040 | 20.0 × 2.0 | 150 | 1000 | 400 | Heavy-duty industrial heating |
4. Manufacturing Process
4.1 Process Flow Overview
The manufacturing of the Stainless Steel Heating Coil Tube follows a rigorous multi-stage production sequence adhering to ISO 9001:2015 quality management protocols:
- Raw Material Procurement & Incoming Inspection: Cold-rolled stainless steel strip is sourced from certified mills (e.g., POSCO, Outokumpu, Taigang). Each batch undergoes spectrographic analysis (OES) to verify chemical composition, and mechanical testing to confirm tensile and elongation properties meet the specified grade requirements.
- Strip Annealing & Pickling: The cold-rolled strip is subjected to solution annealing at 1050°C–1100°C in a protective atmosphere (95% N₂ / 5% H₂) to relieve cold-work stresses and restore full austenitic microstructure. Subsequent pickling in a mixed acid bath (HNO₃ + HF) removes oxide scale, followed by passivation to restore the protective chromium oxide layer.
- Edge Milling & Slitting: The annealed coil is edge-milled to remove burrs and defects, then slit to the precise width required for the target tube outer diameter. Width tolerance is maintained within ±0.1 mm to ensure uniform tube dimensions throughout the coil length.
- Forming & Welding (ERW / Laser Welding): The strip is fed through precision roll-forming dies that progressively bend it into a tubular cross-section. The longitudinal seam is sealed using either Electric Resistance Welding (ERW) or high-frequency Laser Welding. Laser welding is preferred for wall thicknesses below 1.0 mm, producing a weld seam with a width-to-strength ratio superior to ERW. The weld seam is subsequently ground flush to achieve a smooth internal surface, critical for minimizing flow resistance in hydronic applications.
- Post-Weld Annealing: The formed tube undergoes stress-relief annealing at 850°C–900°C to eliminate residual welding stresses and ensure uniform mechanical properties along the weld seam and base metal.
- Spiral Coiling (Helical Winding): The straight tube is fed through a precision coiling head that winds it into a helical configuration at the specified coil pitch and bundle diameter. The coiling process is computer-controlled (CNC) to maintain constant pitch accuracy (±2 mm) and prevent tube deformation. A spring-back compensation algorithm ensures dimensional stability after the tube is released from the coiling fixture.
- End Finishing & Connection Fabrication: Coil ends are prepared with the specified connection type (flange welding, thread machining, or compression fitting installation). End caps are installed to prevent ingress of contaminants during storage and transport.
- Final Inspection & Testing: Each coil undergoes hydrostatic pressure testing at 1.5×