Stainless Steel Coil Tube (Coiltube) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube), manufactured by Wenzhou Jixing Metal Materials Co., Ltd, is a precision-engineered tubular product formed through continuous coiling processes. This product is designed for demanding applications in HVAC (Heating, Ventilation, and Air Conditioning), heat exchange systems, and industrial process engineering. The coil tube geometry provides superior heat transfer efficiency, compact installation profiles, and enhanced fluid dynamics characteristics compared to straight tube alternatives.
This product line draws upon advanced thermal performance testing methodologies, including those outlined in research on Fan Coil Unit (FCU) thermal performance evaluation, ensuring that the coil tube meets stringent operational requirements for heat exchange applications. The product is catalogued under reference number 1201 in the manufacturer's technical documentation system.
2. Material Composition & Mechanical Properties
2.1 Commonly Available Grades
- AISI 304 / EN 1.4301 — General purpose austenitic stainless steel with excellent corrosion resistance and formability
- AISI 316 / EN 1.4401 — Molybdenum-enhanced austenitic grade for superior resistance to pitting and crevice corrosion
- AISI 316L / EN 1.4404 — Low-carbon variant of 316 for improved weldability and resistance to sensitization
- AISI 321 / EN 1.4541 — Titanium-stabilized grade for elevated temperature applications
- AISI 310S / EN 1.4845 — High-temperature austenitic grade for furnace and combustion applications
2.2 Typical Chemical Composition (AISI 304)
| Element | Specification (%) |
|---|---|
| Carbon (C) | ≤ 0.08 |
| Manganese (Mn) | ≤ 2.00 |
| Phosphorus (P) | ≤ 0.045 |
| Sulfur (S) | ≤ 0.030 |
| Silicon (Si) | ≤ 1.00 |
| Chromium (Cr) | 18.00 – 20.00 |
| Nickel (Ni) | 8.00 – 10.50 |
| Iron (Fe) | Balance |
2.3 Mechanical Properties (Solution Annealed Condition)
| Property | Specification |
|---|---|
| Tensile Strength (UTS) | ≥ 515 MPa (75 ksi) |
| Yield Strength (0.2% Offset) | ≥ 205 MPa (30 ksi) |
| Elongation (in 50 mm gauge) | ≥ 40% |
| Hardness (Brinell) | ≤ 217 HB |
| Density | 7.93 g/cm³ |
| Thermal Conductivity (20°C) | 16.3 W/(m·K) |
| Thermal Conductivity (100°C) | 21.5 W/(m·K) |
| Thermal Expansion (20–100°C) | 17.3 × 10⁻⁶ /K |
| Maximum Service Temperature | 870°C (1600°F) — non-oxidizing |
3. Product Specifications
3.1 Dimensional Parameters
| Parameter | Range / Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm – 50.8 mm (¼" – 2") | ASTM A554 / EN 10217 |
| Wall Thickness (WT) | 0.5 mm – 3.0 mm | ASTM A554 / EN 10217 |
| Coil Diameter (CD) | 100 mm – 300 mm (4" – 12") | Manufacturer Specification |
| Coil Length (per bundle) | 5 m – 50 m (configurable) | Custom Order |
| Coil Pitch | 15 mm – 60 mm (adjustable) | Application-Specific |
| Number of Turns | 5 – 200 (per coil section) | Application-Specific |
| Surface Finish | Ba & Le (Bright Annealed & Pickled) / Mirror Polish / Matte | ASTM A473 |
| End Condition | Plain / Beveled / Flared / Threaded | Custom Specification |
3.2 Tolerance Standards
| Dimension | Tolerance |
|---|---|
| Outer Diameter | ± 0.10 mm (for OD ≤ 25 mm); ± 0.15 mm (for OD > 25 mm) |
| Wall Thickness | ± 10% of nominal |
| Coil Diameter | ± 3 mm |
| Roundness | ≤ 5% of OD |
| Straightness (uncoiled) | ≤ 1.5 mm/m |
4. Manufacturing Process
4.1 Production Workflow
- Raw Material Procurement: Cold-rolled stainless steel strip or wire rod sourced from certified mills, with full mill test certificates (MTC) per EN 10204 Type 3.1 or ASTM equivalent.
- Wire Drawing / Strip Slitting: Raw material is processed to precise dimensional specifications through multi-stage cold drawing or precision slitting operations.
- Tube Forming: The formed strip is passed through progressive die sets to create seamless tubing with uniform wall thickness. For wire-based production, drawing through tungsten carbide (WC) dies achieves final OD and WT.
- Solution Annealing: Tubes are heated to 1050–1150°C in a controlled atmosphere furnace (protective gas: nitrogen or argon) to dissolve carbides, restore full solution-annealed condition, and relieve internal stresses.
- Pickling & Descaling: Post-annealing oxide scale is removed using citric acid or mixed acid (HNO₃ + HF) baths, followed by thorough water rinsing and passivation treatment.
- Coil Forming: The annealed tubing is precisely wound into helical coil configurations using CNC-controlled coiling machines. Coil pitch, diameter, and number of turns are controlled to ±2% accuracy.
- End Processing: Coil ends are cut, deburred, and optionally beveled, flared, or threaded according to customer specifications.
- Quality Inspection: Each batch undergoes dimensional verification (CMM or laser measurement), visual inspection, eddy current testing (ECT), and hydrostatic pressure testing.
- Packaging & Shipping: Coils are wrapped in protective film, placed on wooden pallets, and labeled with product identification, heat number, and compliance documentation.
4.2 Process Control Highlights
- Continuous Heat Treatment Monitoring: Infrared pyrometry and thermocouple arrays ensure uniform annealing temperatures across the entire batch.
- Intergranular Corrosion Resistance: Solution-annealed condition ensures freedom from carbide precipitation at grain boundaries, verified by ASTM A967 acid immersion test.
- Coil Geometry Verification: Laser scanning systems confirm coil diameter uniformity and pitch consistency throughout production runs.
5. Applications
5.1 HVAC & Thermal Systems
- Fan Coil Units (FCU): Coil tubes serve as the primary heat transfer element in fan coil units, where thermal performance is critical. Research on FCU thermal performance testing (per GB/T 19232 and ISO 13246) confirms that stainless steel coil tubes provide consistent, predictable heat exchange coefficients over extended service life.
- Chilled Water & Hot Water Systems: Coil tubes used in air handling units, unitary conditioning systems, and radiant heating panels.
- Condensers & Evaporators: Refrigeration and air conditioning coil assemblies for commercial and industrial applications.
5.2 Industrial Process Engineering
- Heat Exchanger Coils: Spiral wound coil heat exchangers for chemical processing, pharmaceutical manufacturing, and food-grade applications.
- Process Heating & Cooling: Jacketed reactor internals, tempering coils, and process circulation loops.
- Automotive & Transportation: Oil cooler coils, intercooler elements, and thermal management systems in electric vehicles (EV).
5.3 Specialty Applications
- Marine & Offshore: Condenser tubes and heat exchanger coils in marine propulsion systems and offshore platforms (AISI 316L grade).
- Medical Equipment: Sterilizable coil assemblies in autoclaves, medical gas delivery systems, and laboratory heating apparatus.
- Food & Beverage: Pasteurization coils, brewing system heat exchangers, and dairy processing equipment (FDA-compliant finishes).
- Electrical & Electronics: Transformer windings, heating element coils, and thermal management in power electronics.
6. Quality Certifications & Compliance
6.1 Standards Compliance
| Standard | Description |
|---|---|
| ASTM A554 | Standard Specification for Cold-Drawn Stainless Steel Seamless Tubing for General Application |
| ASTM A269 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Similar Severe Service |
| ASTM A270 | Standard Specification for Austenitic Stainless Steel Tubing, Seamless and Welded |
| EN 10217-1 | Non-ferrous metal tubes and pipes for pressure purposes — Technical delivery conditions for austenitic stainless steel tubes |
| EN 10217-7 | Technical delivery conditions for austenitic stainless steel tubes for heat exchangers |
| ISO 13246 | Thermal performance testing of fan coil units |
| GB/T 19232 | Chinese national standard for thermal performance testing of fan coil units |
| GB/T 14976 | Chinese standard for seamless stainless steel tubes for general engineering |
6.2 Quality Management & Certifications
- ISO 9001:2015 — Quality Management System certification for consistent manufacturing processes
- ISO 14001:2015 — Environmental Management System certification
- ISO/TS 22163 — IRIS (International Railway Industry Standard) for rail applications, where applicable
- EN 10204 Type 3.1 — Mill Test Certificates with full chemical and mechanical test results
- NACE MR0175 / ISO 15156 — Compliance for sour service applications (AISI 316L grade)
- ASME Boiler and Pressure Vessel Code — Section VIII compliance for pressure vessel applications
- EU PED (Pressure Equipment Directive 2014/68/EU) — CE marking for pressure equipment
- NSF/ANSI 61 — Drinking water system components certification (food-grade applications)
- 3-A Sanitary Standards — Dairy and food processing equipment compliance
6.3 Testing & Verification Protocol
- Dimensional Inspection: 100% inspection of OD, WT, coil diameter, and pitch using calibrated instruments
- Chemical Analysis: Spectroscopic verification (OES or XRF) of chemical composition per heat number
- Hydrostatic Pressure Test: 100% of tubes tested at 3–5× working pressure per ASTM A554
- Eddy Current Testing (ECT): Non-destructive inspection for internal and surface defects
- Intergranular Corrosion Test: ASTM A967 acid immersion test (for 304L, 316L grades)
- Mechanical Testing: Tensile and hardness testing per ASTM E8 / ASTM E92 on representative samples
- Surface Finish Verification: Ra roughness measurement (target: Ra ≤ 0.8 μm for BA finish; Ra ≤ 0.2 μm for mirror polish)
7. Unique Selling Points
Thermally Optimized Coil Geometry: The coil tube design leverages the enhanced heat transfer surface area-to-volume ratio inherent to helical geometry. Research on fan coil unit thermal performance demonstrates that properly engineered coil configurations achieve 15–30% higher heat transfer coefficients compared to equivalent straight-tube designs, while reducing system footprint and weight.
- Superior Corrosion Resistance: Austenitic stainless steel construction provides exceptional resistance to atmospheric, chemical, and aqueous corrosion, eliminating the need for protective