Stainless Steel Coil Tube (Coiltube) — Technical Product Specification
1. Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd., designed for thermal exchange and fluid conveyance applications in industrial and commercial HVAC (Heating, Ventilation, and Air Conditioning) systems. The product is supplied in continuous coil form, enabling downstream fabrication into heat exchangers, fan coil units (FCUs), condenser coils, evaporator coils, and refrigeration circuits without the need for secondary cutting or welding at the point of installation.
This specification draws upon the thermodynamic research framework established in the study titled "Equivalent Thermal Calculation Method for Fan Coil Units under Dry and Wet Conditions", which provides a rigorous analytical basis for evaluating the thermal performance of coil tube assemblies operating across both dry-bulb and wet-bulb environmental regimes. The Coiltube product is engineered to satisfy the stringent thermal efficiency requirements identified in this research, ensuring reliable heat transfer under all operational conditions.
2. Material & Properties
2.1 Base Material
The Coiltube is fabricated from high-purity austenitic stainless steel conforming to the following international material designations:
- AISI 304 / UNS S30400 — The primary grade, offering excellent corrosion resistance, weldability, and formability for general-purpose thermal exchange applications.
- AISI 316L / UNS S31603 — A low-carbon, molybdenum-enhanced variant specified for aggressive chemical environments, marine applications, and high-chloride-iodide service conditions.
- AISI 321 / UNS S32100 — Titanium-stabilized grade recommended for sustained elevated-temperature service exceeding 450 °C, providing superior resistance to intergranular corrosion.
2.2 Key Mechanical and Physical Properties
| Property | AISI 304 | AISI 316L | AISI 321 |
|---|---|---|---|
| Tensile Strength (MPa, min.) | 515 | 485 | 515 |
| Yield Strength (MPa, min.) | 205 | 170 | 205 |
| Elongation (% min., 50 mm gauge) | 40 | 40 | 40 |
| Density (g/cm³, 20 °C) | 7.93 | 7.98 | 7.93 |
| Thermal Conductivity (W/m·K, 100 °C) | 16.3 | 14.6 | 16.3 |
| Specific Heat Capacity (kJ/kg·K, 25 °C) | 0.50 | 0.50 | 0.50 |
| Linear Thermal Expansion (×10⁻⁶/°C, 20–100 °C) | 17.3 | 17.5 | 17.3 |
| Maximum Service Temperature (°C) | 870 | 870 | 900 |
2.3 Surface Finish
The internal and external surfaces of the Coiltube are finished to a 2B cold-rolled finish (Ra ≤ 0.4 µm) as standard. Upon customer request, the following alternative surface treatments are available:
- Pickled & Passivated (P&P) — Removes oxide scale and restores the passive chromium-oxide layer for enhanced corrosion resistance.
- Mirror Polish (No. 7 / No. 8) — Ra ≤ 0.1 µm, suitable for food-grade and pharmaceutical applications requiring high sanitary standards.
- Electropolished (EP) — Electrochemical surface refinement achieving Ra ≤ 0.2 µm with superior biocompatibility and chemical inertness.
3. Specifications
| Parameter | Specification |
|---|---|
| Product Designation | Stainless Steel Coil Tube (Coiltube) — Catalog No. 1123 |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd. |
| Tube Form | Continuous Cold-Drawn Coil (Uncoiled Length: 50 m – 300 m per spool, customizable) |
| Outer Diameter (OD) | 6.0 mm – 25.4 mm (standard range); up to 50.8 mm upon special order |
| Wall Thickness | 0.3 mm – 1.5 mm (tolerance ±0.05 mm) |
| Inner Diameter (ID) | Calculated per OD and wall thickness; tolerance ±0.05 mm |
| Roundness | ≤ 0.1% of nominal OD |
| Coil Diameter (Spool OD) | 500 mm – 1,200 mm (configurable to customer requirement) |
| Minimum Bend Radius | ≥ 2× OD (cold bending); ≥ 1.5× OD (hot bending) |
| Maximum Operating Pressure | Up to 1.6 MPa (PN16); up to 4.0 MPa (PN40) for heavy-wall variants |
| Operating Temperature Range | −196 °C (cryogenic) to +870 °C (continuous) |
| Applicable Standards | ASTM A213, ASTM A269, EN 10216-5, GB/T 14976, JIS G3459 |
| Coil Packaging | Wooden spool with moisture-absorbent desiccant; stretch-wrapped in PE film |
| Standard Coil Length | 100 m (default); 50 m – 300 m available on request |
4. Manufacturing Process
The production of the Stainless Steel Coil Tube follows a rigorous multi-stage cold-work pipeline designed to ensure dimensional accuracy, metallurgical integrity, and surface quality. The process flow is outlined below:
- Hot-Rolled Coil Uncoiling and Cleaning — The raw material, supplied as a hot-rolled stainless steel coil, is uncoiled and subjected to high-pressure water jet cleaning to remove surface contaminants, scale, and mill oils.
- Acid Pickling and Passivation — The coil is immersed in a mixed acid bath (typically HNO₃/HF or H₂SO₄/HNO₃) to dissolve residual iron oxide scale. A subsequent passivation treatment re-establishes the native chromium oxide passive film, critical for long-term corrosion resistance.
- Cold Drawing (Multi-Pass) — The pickled coil is fed through a series of precision-drawn tungsten carbide (WC) or boron carbide (B₄C) die sets. Multiple drawing passes progressively reduce the outer diameter and wall thickness to the target specification. The drawing lubricant is formulated to minimize surface defects and ensure uniform plastic deformation.
- Intermediate Annealing — After each drawing pass, the tube is subjected to controlled furnace annealing (typically 1,050 °C – 1,100 °C, 10–20 minutes, followed by controlled cooling) to relieve accumulated cold-work strain, restore ductility, and prevent cracking during subsequent forming operations.
- Final Sizing and Straightening — The drawn tube undergoes final sizing through calibrated mandrel dies to achieve precise dimensional tolerances. A straightening and leveling operation ensures the tube maintains geometric straightness along its full coil length.
- Hydrostatic Pressure Testing — Every coil is subjected to a continuous hydrostatic test at 1.5× the maximum design operating pressure for a minimum dwell time of 5 seconds per unit length. Any coil exhibiting leakage or permanent deformation is rejected.
- Non-Destructive Testing (NDT) — 100% eddy current testing (ECT) and magnetic particle inspection (MPI) are performed to detect internal and surface defects including cracks, seams, and laminations.
- Coiling and Packaging — The qualified tube is wound onto a protective wooden or steel spool, secured with tension-controlled strapping, and packaged with desiccant and PE film wrapping to prevent moisture ingress and surface damage during transit.
5. Applications
The Stainless Steel Coil Tube from Wenzhou Jixing Metal Materials Co., Ltd. is engineered for a broad spectrum of thermal management and fluid transfer applications. Key deployment domains include:
- Fan Coil Units (FCUs) — The primary application domain. The Coiltube serves as the core heat exchange element in both dry and wet operating conditions. As established in the referenced thermodynamic study, the equivalent thermal calculation method validates that these coils maintain efficient heat transfer across varying humidity and temperature regimes, ensuring consistent indoor climate control performance in commercial and residential HVAC systems.
- Refrigeration and Air Conditioning Systems — Evaporator and condenser coils in chillers, heat pumps, and split-system air conditioners. The high thermal conductivity and corrosion resistance of austenitic stainless steel ensure long service life in refrigerant circuits.
- Industrial Heat Exchangers — Shell-and-tube heat exchangers, plate-fin coils, and custom thermal assemblies in chemical processing, food and beverage production, and pharmaceutical manufacturing.
- Automotive Thermal Systems — Engine oil coolers, intercoolers, and transmission fluid coolers requiring lightweight, corrosion-resistant tubing.
- Medical and Laboratory Equipment — Sanitary-grade coil assemblies for autoclaves, sterilization chambers, and pharmaceutical process piping where hygienic standards (FDA-compliant, 3-A Sanitary) are mandatory.
- Marine and Offshore Systems — Seawater cooling circuits, ballast water systems, and marine HVAC installations where AISI 316L grade provides superior resistance to chloride-induced pitting and crevice corrosion.
6. Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management and product certification framework ensuring compliance with international standards:
- ISO 9001:2015 — Quality Management System certification covering the entire manufacturing, inspection, and distribution process.
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management System certification.
- EN 10204 Type 3.1 — Material test certificates issued by an authorized inspection body, confirming material conformity with the specified grade and standard.
- CE Marking — Conformity with European Union directives for pressure equipment (PED 2014/68/EU) where applicable.
- ASME / NB Certification — National Board registration for components used in pressure vessel and heat exchanger construction (available upon request).
- Mill Test Reports (MTR) — Comprehensive chemical composition analysis (spectrometric) and mechanical test data provided with every shipment.
- Third-Party Inspection — Independent inspection services by SGS, Bureau Veritas, or TÜV available for pre-shipment verification.
7. Unique Selling Points
- Thermodynamically Validated Performance — The product specifications are aligned with the equivalent thermal calculation methodology for fan coil units under dry and wet conditions, ensuring that thermal efficiency predictions made during system design are accurately realized in field operation. This provides system integrators with high confidence in performance modeling and energy consumption forecasting.
- Full Coil Continuity — Supplied as a seamless continuous coil without butt-welds or lap joints, eliminating potential leak paths and ensuring uniform hydraulic and thermal characteristics along the entire coil length.
- Multi-Grade Availability — Customers can select from AISI 304, 316L, and 321 grades from a single supplier, simplifying procurement and ensuring consistent quality across diverse application requirements.
- Precision Cold-Formed Geometry — Tight dimensional tolerances (±0.05 mm on OD and wall thickness) and excellent roundness (≤ 0.1% of OD) enable direct integration into precision heat exchanger manufacturing without secondary machining.
- Cryogenic to High-Temperature Versatility — Operating capability spanning from liquid nitrogen temperatures (−196 °C) to continuous service at 870 °C, making the Coiltube suitable for both cryogenic and high-temperature industrial applications.
- End-to-End Quality Assurance — 100% hydrostatic testing, eddy current inspection, and magnetic particle inspection on every coil, supplemented by full traceability through heat number and batch coding.
- Customizable Spool Configuration — Coil diameter, coil length, and packaging configuration are adaptable to customer-specific logistics and fabrication requirements, reducing handling costs and installation complexity.
8. Ordering Information
Customers are advised to specify the following parameters when placing an order:
- Stainless steel grade (AISI 304 / 316L / 321 or equivalent UNS designation)
- Nominal outer diameter and wall thickness
- Required coil length and spool diameter
- Surface finish requirement (2B, P&P, mirror polish, or electropolished)
- Applicable standard and certification requirements
- Intended application and operating conditions (temperature, pressure, fluid type)
Document Reference: Technical Product Specification — Stainless Steel Coil Tube (Coiltube), Catalog No. 1123.
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Applicable Research Framework: "Equivalent Thermal Calculation Method for Fan Coil Units under Dry and Wet Conditions" — Literature Study Series, Category: Literature Learning (文献学习).