Stainless Steel Coil Tube (Coiltube) — Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered, continuous-length tubular product supplied in coil form. Designed primarily for integration into Fan Coil Units (FCU), Heat Exchangers, Refrigeration Systems, and Hydronic Piping Networks, this product combines the corrosion resistance and structural integrity of austenitic stainless steel with the manufacturing efficiency afforded by coil-form processing. The product adheres to international standards including ASTM A269, ASTM A778, ISO 3506, and relevant national specifications governing stainless steel tubing for HVAC and industrial applications.
This specification document draws upon professional standards governing fan coil unit design and performance, ensuring that the coil tube meets the thermal, mechanical, and hygienic requirements stipulated in industry guidelines such as those referenced in 《关于风机盘管专业标准的几点商榷意见》 (Discussions on Professional Standards for Fan Coil Units).
2. Material & Properties
2.1 Base Materials
- AISI 304 (UNS S30400) — General-purpose austenitic grade with excellent corrosion resistance; ideal for HVAC and food-grade applications.
- AISI 316 (UNS S31600) — Molybdenum-bearing grade offering superior resistance to chlorides and aggressive chemical environments.
- AISI 316L (UNS S31603) — Low-carbon variant of 316, preferred for welded assemblies and cryogenic service.
- AISI 321 (UNS S32100) — Titanium-stabilized grade suitable for elevated temperature service.
2.2 Mechanical Properties (Annealed Condition)
| Property | 304 / 304L | 316 / 316L | 321 |
|---|---|---|---|
| Tensile Strength (ASTM B557) | ≥ 515 MPa (≥ 75 ksi) | ≥ 515 MPa (≥ 75 ksi) | ≥ 515 MPa (≥ 75 ksi) |
| Yield Strength (0.2% Offset) | ≥ 205 MPa (≥ 30 ksi) | ≥ 205 MPa (≥ 30 ksi) | ≥ 205 MPa (≥ 30 ksi) |
| Elongation (50 mm gauge length) | ≥ 40% | ≥ 40% | ≥ 40% |
| Hardness (Rockwell B) | ≤ 95 HRB | ≤ 95 HRB | ≤ 95 HRB |
2.3 Chemical Composition (wt%)
| Element | 304 / 304L | 316 / 316L | 321 |
|---|---|---|---|
| C (Carbon) | ≤ 0.08 / ≤ 0.03 | ≤ 0.08 / ≤ 0.03 | ≤ 0.08 |
| Cr (Chromium) | 18.0 – 20.0 | 16.0 – 18.0 | 17.0 – 19.0 |
| Ni (Nickel) | 8.0 – 10.5 | 10.0 – 14.0 | 9.0 – 12.0 |
| Mo (Molybdenum) | — | 2.0 – 3.0 | — |
| Si (Silicon) | ≤ 1.00 | ≤ 1.00 | ≤ 1.00 |
| Mn (Manganese) | ≤ 2.00 | ≤ 2.00 | ≤ 2.00 |
| Ti (Titanium) | — | — | 5 × (C+0.02) – 0.70 |
| P (Phosphorus) | ≤ 0.045 | ≤ 0.045 | ≤ 0.045 |
| S (Sulfur) | ≤ 0.030 | ≤ 0.030 | ≤ 0.030 |
2.4 Thermal & Physical Properties
- Thermal Conductivity (at 20°C): 16.3 W/(m·K) for 304; 14.6 W/(m·K) for 316
- Specific Heat Capacity (at 20°C): ~478 J/(kg·K)
- Thermal Expansion Coefficient (20–315°C): 17.3 × 10⁻⁶ /°C
- Density: 8.00 g/cm³
- Maximum Service Temperature: 870°C (304); 870°C (316)
3. Specifications
3.1 Dimensional Specifications
| Parameter | Specification | Tolerance | Reference Standard |
|---|---|---|---|
| Outer Diameter (OD) | 3.18 mm – 50.80 mm (1/8" – 2") | ±0.05 mm (OD ≤ 6 mm); ±0.10 mm (OD > 6 mm) | ASTM A778 / GB/T 12771 |
| Wall Thickness (WT) | 0.30 mm – 3.00 mm | ±10% of nominal | ASTM A778 / GB/T 12771 |
| Coil Inner Diameter (CID) | 300 mm – 600 mm | ±10 mm | Manufacturer standard |
| Coil Length (per coil) | 50 m – 300 m (continuous) | ±5% | — |
| Roundness (eccentricity) | — | ≤ 5% of OD | ASTM A778 |
| Straightness (uncoiled) | — | ≤ 0.5 mm/m | ASTM A778 |
3.2 Surface Finish Options
| Finish Type | Surface Roughness (Ra) | Application |
|---|---|---|
| Commercial Annealed (No. 1) | ≤ 1.6 μm | General industrial piping |
| Pickled & Passivated | ≤ 0.8 μm | Food-grade, pharmaceutical |
| Mirror Polished | ≤ 0.2 μm | Decorative, semiconductor |
| Electro-Polished | ≤ 0.1 μm | Critical sanitary, bioprocessing |
4. Manufacturing Process
4.1 Production Flow
- Strip Preparation — Cold-rolled stainless steel strip is sourced from certified mill producers, inspected for dimensional accuracy, surface quality, and chemical composition via X-ray Fluorescence (XRF) spectrometry.
- Coil Forming (Cold Rolling) — The strip is fed through a series of precision roll stands with controlled reduction rates to achieve the target OD and wall thickness. Roll gap is continuously monitored via laser measurement systems.
- Welding (if applicable) — For welded coil tube, high-frequency induction welding or TIG welding is employed with inert gas (Argon) shielding to prevent oxidation at the weld seam. Seam quality is verified by eddy current testing.
- Heat Treatment (Annealing) — The formed tube is annealed in a protective atmosphere (hydrogen or vacuum) at 1050°C – 1150°C, followed by controlled cooling to restore full austenitic microstructure, relieve residual stresses, and achieve the required mechanical properties.
- Pickling & Passivation — Surface scale is removed via acid pickling (HNO₃/HF blend), followed by passivation to establish a chromium oxide protective layer.
- Dimensional Inspection — Each coil undergoes automated OD/WT measurement, roundness verification, and length measurement. Samples are subjected to hydrostatic pressure testing per ASTM A778.
- Coiling & Packaging — The finished tube is wound onto a core with appropriate flange protection, wrapped in moisture-barrier film, and labeled with material certification data.
4.2 Process Control Parameters
| Process Step | Key Parameter | Control Range |
|---|---|---|
| Coil Forming | Total Reduction Ratio | 15% – 25% per pass |
| Welding (HF) | Weld Power / Travel Speed | 15 – 45 kW / 6 – 12 m/min |
| Annealing | Temperature / Dwell Time | 1050 – 1150°C / 30 – 60 min |
| Annealing | Atmosphere Dew Point | ≤ -60°C |
| Hydrostatic Test | Test Pressure | 6.3 MPa (minimum) or per formula |
5. Applications
5.1 Primary Applications
- Fan Coil Units (FCU) — The coil tube serves as the heat exchange element in FCUs used in commercial and residential HVAC systems. Its high thermal conductivity and resistance to scaling ensure long-term efficiency in air-side heat transfer.
- Chilled Water & Hot Water Piping — Continuous coil form enables seamless installation in hydronic distribution systems with minimal joint count, reducing leakage risk.
- Refrigeration & Air Conditioning — Used in evaporator and condenser coil assemblies where frost resistance and chemical inertness are critical.
- Food & Beverage Processing — 316L-grade coil tube in electropolished finish meets FDA and 3-A Sanitary Standards for milk, juice, and brewery piping.
- Pharmaceutical & Bioprocessing — Clean-in-Place (CIP) compatible tubing for CIP/SIP systems in GMP-regulated environments.
- Chemical Processing — 316/316L coil tube for transfer of aggressive chemicals, acids, and caustic solutions.
- Automotive Heat Exchangers — Compact coil assemblies for engine cooling, HVAC, and fuel cell thermal management.
5.2 Industry-Specific Performance Requirements
For Fan Coil Unit applications, the coil tube must satisfy minimum thermal performance coefficients (U-value ≥ 150 W/(m²·K) for air-to-water configurations), maintain structural integrity under cyclic thermal loading (ΔT up to 60°C), and comply with hygienic design principles that prevent microbial colonization within the tube bore. Surface roughness of ≤ 0.8 μm (Ra) is recommended for water-side applications to minimize fouling resistance.
6. Quality Certifications & Compliance
6.1 Certifications
- ISO 9001:2015 — Quality Management System certification for manufacturing operations