Stainless Steel Coil Tube (Coiltube) — Technical Specification
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd
Product Category: Literature & Technical Documentation — Series No. 930
Reference Application: FP-68WA Fan Coil Unit (风机盘管机组)
1. Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered tubular product manufactured in continuous coil form, specifically designed for use in HVAC (Heating, Ventilation, and Air Conditioning) systems, heat exchanger assemblies, and thermal transfer applications. The product is produced to meet the rigorous dimensional tolerances and metallurgical requirements stipulated for integration into fan coil units such as the FP-68WA series.
Unlike conventional pipe segments delivered in fixed lengths, Coiltube is wound onto steel reels, offering significant advantages in material utilization, transportation efficiency, and downstream processing continuity. The coil format enables seamless feeding into automated forming, bending, and welding lines, thereby reducing waste and improving production throughput in heat exchanger manufacturing environments.
2. Material & Properties
2.1 Base Alloy Composition
The primary grade employed for stainless steel Coiltube in HVAC and thermal applications is AISI 304 (UNS S30400), with AISI 316 (UNS S31600) available for enhanced corrosion resistance in aggressive environments. The chemical composition adheres to ASTM A213/A269 and GB/T 14976 standards.
| Element | AISI 304 (Max %) | AISI 316 (Max %) |
|---|---|---|
| Carbon (C) | 0.08 | 0.08 |
| Manganese (Mn) | 2.00 | 2.00 |
| Phosphorus (P) | 0.045 | 0.045 |
| Sulfur (S) | 0.030 | 0.030 |
| Silicon (Si) | 1.00 | 1.00 |
| Chromium (Cr) | 18.0 – 20.0 | 16.0 – 18.0 |
| Nickel (Ni) | 8.0 – 10.5 | 10.0 – 14.0 |
| Molybdenum (Mo) | — | 2.0 – 3.0 |
2.2 Mechanical Properties
- Tensile Strength (UTS): ≥ 515 MPa (AISI 304), ≥ 515 MPa (AISI 316)
- Yield Strength (0.2% Offset): ≥ 205 MPa
- Elongation: ≥ 40% (in 50 mm gauge length)
- Hardness (Annealed): ≤ 200 HB (Brinell)
- Operating Temperature Range: −196 °C to +870 °C (oxidation resistance)
2.3 Surface Finish Options
- 2B Finish: Cold-rolled and annealed in protection, bright annealed — typical surface roughness Ra 0.4–0.8 μm
- No. 4 Brushed: Directional satin finish, Ra 0.8–1.6 μm
- Bright Annealed (BA): Mirror-like finish for aesthetic applications, Ra ≤ 0.2 μm
- Pickled & Passivated: Removal of mill scale with chromic acid passivation for maximum corrosion resistance
3. Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | φ6.0 mm – φ12.7 mm (typical for HVAC coil applications) | ASTM A213 / GB/T 14976 |
| Wall Thickness | 0.30 mm – 1.00 mm | ASTM A269 |
| OD Tolerance | ±0.05 mm (precision grade) | — |
| Wall Thickness Tolerance | ±10% of nominal | — |
| Coil Inner Diameter (ID) | φ200 mm / φ300 mm / φ500 mm | — |
| Coil Outer Diameter (max) | ≤ φ1500 mm | — |
| Coil Length (unwound) | 50 m – 500 m (continuous) | — |
| Coil Weight | Up to 2,500 kg per coil | — |
| End Form | Seamless / Welded (ERW) | ASTM A213 Type 304 TP |
| Heat Treatment | Annealed (Solution Annealed at 1050–1150 °C, water quenched) | — |
| Delivery Condition | Annealed & Pickled (A&P) / Annealed & Bright (A&BA) | — |
| Corrosion Resistance | Equivalent to 304/316 plate in neutral and mildly acidic environments | ASTM A967 |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Sourcing: Hot-rolled stainless steel strip (HSS) procured from certified mills (e.g., Tsingshan, Outokumpu, POSCO), conforming to ASTM A480/A240.
- Slitting & Leveling: Strip is slit to required width and tension-levelled to ensure flatness within ±0.2% of width.
- Pipe Forming (ERW): Cold-rolled electric resistance welding (ERW) process using high-frequency current (HF-ERW) to produce continuous tubular form. Forming rollers progressively reduce strip width to form a spiral coil.
- Weld Heat Treatment: Post-weld annealing at 1,080–1,150 °C in a protective atmosphere (endothermic gas or vacuum) to dissolve carbides and restore full austenitic properties at the weld seam.
- Surface Treatment: Pickling in mixed acid (HNO₃ + HF) bath to remove oxide scale; passivation with citric acid or dilute nitric acid per ASTM A967.
- Dimensional Inspection: Inline laser measurement of OD, wall thickness, and roundness; ultrasonic testing for internal defects.
- Coiling & Packaging: Finished tube wound onto steel cores, wrapped with moisture-barrier film, and palletized with desiccant packs for export readiness.
4.2 Process Control
Statistical Process Control (SPC) is applied at critical control points (CCPs) including weld seam quality, dimensional accuracy, and surface finish. Each production lot undergoes:
— Chemical composition verification via XRF (X-ray Fluorescence) spectrometry
— Hydrostatic pressure testing at 2.5× working pressure
— Visual and eddy current inspection of weld seams
— Mechanical property testing per ASTM E8/E8M
5. Applications
5.1 HVAC — Fan Coil Units (FP-68WA Series)
The primary application domain for this Coiltube product is the manufacture of fan coil units, specifically the FP-68WA model series. In this context, the stainless steel coil tube serves as the heat exchanger tube through which chilled water or hot water circulates, transferring thermal energy to the airstream. Key performance requirements include:
- High thermal conductivity (≥ 16 W/m·K for AISI 304) for efficient heat transfer
- Corrosion resistance against condensate (pH 5.0–6.5) and refrigerant fluids
- Dimensional precision for tight integration with aluminum fins (fin-to-tube brazing or mechanical crimping)
- Long service life exceeding 20 years under continuous cyclic thermal loading
5.2 Additional Applications
- Condenser & Evaporator Coils: Refrigeration and air conditioning heat exchangers
- Industrial Process Heat Exchangers: Shell-and-tube and plate-fin configurations
- Water Heating Systems: Domestic and commercial water heater coils
- Automotive Thermal Management: Engine coolant tubes and intercoolers
- Food & Pharmaceutical Processing: Sanitary-grade heat transfer coils (AISI 316L)
- Marine & Offshore: Seawater heat exchanger tubing (AISI 316 with Mo content)
6. Quality Certifications & Standards Compliance
| Standard / Certification | Scope |
|---|---|
| ASTM A213 / A213M | Seamless austenitic stainless steel tubing for high-temperature service |
| ASTM A269 / A269M | Welded austenitic stainless steel tubing, general applications |
| GB/T 14976 | Chinese national standard for seamless stainless steel tubes |
| EN 10217-7 | European standard for stainless steel tubes, technical delivery conditions |
| ISO 9001:2015 | Quality Management System certification |
| ISO 14001:2015 | Environmental Management System certification |
| CE Marking | Conformity with EU machinery and pressure equipment directives |
| Mill Test Certificate (MTC) | EN 10204 Type 3.1 — full chemical and mechanical data per heat number |
7. Unique Selling Points
The Coiltube product from Wenzhou Jixing Metal Materials Co., Ltd distinguishes itself in the global stainless steel tube market through the following competitive advantages:
- Continuous Coil Format: Eliminates butt-weld joints found in fixed-length pipe, reducing leak points and improving heat exchanger reliability by up to 40% compared to segment-welded alternatives.
- Precision Dimensional Control: OD tolerance of ±0.05 mm ensures optimal fin engagement and brazing quality in automated heat exchanger assembly lines.
- Full Material Traceability: Each coil is heat-number stamped and linked to a digital quality dossier containing complete chemical, mechanical, and non-destructive testing data.
- Customizable Specifications: Flexible configuration of OD, wall thickness, surface finish, and coil dimensions to match specific OEM requirements for fan coil unit manufacturers.
- Cost-Effective Delivery: Coil format reduces transportation costs by 25–35% compared to straight-length pipe delivery, while minimizing offcut waste in downstream forming operations.
- Environmental Compliance: Production processes adhere to RoHS, REACH, and conflict-free mineral regulations; pickling waste is treated in an on-site effluent treatment plant meeting local discharge standards.
8. Technical Summary
In conclusion, the Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd represents a premium-grade tubular product engineered for demanding thermal management applications. Its metallurgical integrity, dimensional precision, and corrosion resistance make it an ideal substrate for fan coil unit heat exchangers, particularly in the FP-68WA series. The product embodies the intersection of metallurgical science, manufacturing engineering, and systems integration — delivering reliable performance across the full lifecycle of HVAC equipment deployment.