Stainless Steel Coil Tube (Dry Coiltube) — Model Series 739
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Category: HVAC & Refrigeration Components — Dry Coil Tubing
Reference Standard: GB/T 12771, ASTM A312, EN 10217
1. Product Overview
The Stainless Steel Coil Tube (Dry Coiltube) Model Series 739 is a precision-engineered tubular component designed for integration into pre-cooling heat pump solution humidification fresh air unit systems. This coil tube functions as the core heat exchange element within a dry coil air conditioning system, facilitating efficient sensible heat transfer while preventing latent moisture condensation on the coil surface.
In modern HVAC (Heating, Ventilation, and Air Conditioning) architectures, particularly those employing adiabatic solution humidification combined with heat pump technology, the dry coil tube serves as the critical interface for temperature modulation of supply air. By maintaining coil surface temperatures above the dew point of incoming air, the system eliminates condensate formation, thereby improving energy efficiency and indoor air quality. This product is specifically engineered to meet the rigorous thermal and mechanical demands of such advanced air handling configurations.
The coil tube is fabricated from high-grade austenitic stainless steel, providing exceptional corrosion resistance, thermal conductivity, and mechanical durability suitable for continuous operation in humid, chemically aggressive, or hygienically sensitive environments.
2. Material & Properties
2.1 Base Material
The coil tube is manufactured from austenitic stainless steel conforming to the following grades:
- 304 (UNS S30400 / 06Cr19Ni10): Standard grade for general HVAC applications, offering balanced corrosion resistance and formability.
- 316L (UNS S31603 / 022Cr17Ni12Mo2): Enhanced grade with molybdenum addition for superior resistance to chloride-induced pitting and crevice corrosion, recommended for coastal or high-humidity environments.
2.2 Mechanical Properties (Annealed Condition)
| Property | Grade 304 | Grade 316L |
|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 485 |
| Yield Strength (0.2% Proof Stress, MPa) | ≥ 205 | ≥ 170 |
| Elongation (%) | ≥ 40 | ≥ 45 |
| Hardness (HBW) | ≤ 217 | ≤ 217 |
2.3 Thermal Properties
| Property | Value (at 20°C) |
|---|---|
| Thermal Conductivity (W/m·K) | 14.6 – 16.3 |
| Specific Heat Capacity (J/kg·K) | 498 – 502 |
| Thermal Expansion Coefficient (×10⁻⁶/K) | 16.0 – 17.3 |
| Density (kg/m³) | 7,930 – 8,000 |
2.4 Chemical Composition (Typical, wt%)
| Element | 304 | 316L |
|---|---|---|
| Carbon (C) | ≤ 0.08 | ≤ 0.03 |
| Chromium (Cr) | 18.0 – 20.0 | 16.5 – 18.5 |
| Nickel (Ni) | 8.0 – 10.5 | 10.0 – 14.0 |
| Molybdenum (Mo) | — | 2.0 – 3.0 |
| Manganese (Mn) | ≤ 2.0 | ≤ 2.0 |
| Silicon (Si) | ≤ 1.0 | ≤ 1.0 |
| Sulfur (S) | ≤ 0.03 | ≤ 0.03 |
| Phosphorus (P) | ≤ 0.045 | ≤ 0.045 |
3. Specifications
| Parameter | Specification |
|---|---|
| Product Model | Series 739 — Dry Coiltube |
| Tube Type | Seamless / Welded Stainless Steel Coil Tube |
| Outer Diameter (OD) | 6.35 mm (¼"), 9.53 mm (⅜"), 12.70 mm (½"), 15.88 mm (⅝"), 19.05 mm (¾") |
| Wall Thickness | 0.50 mm – 1.50 mm (customizable) |
| Coil Length | Up to 60 m per coil (standard); custom lengths available |
| Surface Finish | Bright Annealed (BA), Pickled & Passivated (2B), or Polished (Ra ≤ 0.4 μm) |
| Pressure Rating | Up to 1.6 MPa (232 psi) at operating temperature |
| Operating Temperature Range | −40°C to +250°C |
| Fluid Compatibility | Chilled water, glycol-water mixtures, refrigerants (R410A, R32, R134a), solution humidification fluids |
| Coil Diameter (Standard) | 150 mm – 500 mm (configurable per AHU design) |
| Tube Pitch | 15 mm – 30 mm (staggered or in-line arrangement) |
| Fins (Optional) | Aluminum or stainless steel lamination fins, 12–16 FPI (Fins Per Inch) |
| Connection Type | Threaded (BSP/NPT), flanged, brazed, or welded headers |
| Maximum Working Pressure (Hydrostatic Test) | 2.4 MPa (368 psi) — 1.5× operating pressure |
4. Manufacturing Process
The production of the Series 739 Dry Coiltube follows a rigorous, multi-stage manufacturing workflow to ensure dimensional accuracy, material integrity, and consistent performance:
- Raw Material Selection & Inspection: Stainless steel billets or strip stock are sourced from certified suppliers and subjected to spectroscopic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition compliance with ASTM/GB standards.
- Hot Rolling / Extrusion: Billets are heated to 1150–1250°C and hot-rolled or extruded into seamless tube blanks with initial wall thickness and diameter tolerances.
- Cold Drawing & Sizing: Tubes undergo multi-pass cold drawing through precision dies to achieve final outer diameter and wall thickness specifications within ±0.05 mm tolerance.
- Heat Treatment (Solution Annealing): Tubes are solution-annealed at 1050–1100°C followed by controlled water quenching to restore full austenitic microstructure, relieve residual stresses, and achieve maximum corrosion resistance.
- Pickling & Passivation: Tubes are immersed in a mixed acid bath (nitric acid + hydrofluoric acid) to remove scale and contaminants, followed by passivation treatment to establish a protective chromium oxide (Cr₂O₃) passive film on the surface.
- Coil Forming & Bending: Precision CNC (Computer Numerical Control) coil forming machines bend the straight tubes into the specified coil geometry with controlled bend radii (minimum 3× OD) to prevent wall thinning or ovality exceeding 5%.
- Finning (if applicable): Lamination fins are mechanically bonded to the tube surface using high-frequency induction welding or mechanical clamping to maximize heat transfer surface area.
- Header Assembly: Individual coil tubes are connected to inlet and outlet headers via orbital TIG (Tungsten Inert Gas) welding or brazing under argon shielding to ensure leak-tight joints.
- Quality Inspection: Each coil assembly undergoes hydrostatic pressure testing, dimensional verification (CMM — Coordinate Measuring Machine), visual inspection, and non-destructive testing (NDT) including eddy current (ET) and dye penetrant testing (PT).
- Final Cleaning & Packaging: Coils are ultrasonically cleaned, dried, and packaged with moisture-absorbing desiccants and protective end caps to prevent contamination prior to shipment.
5. Applications
The Series 739 Dry Coiltube is specifically designed for the following application domains:
- Pre-Cooling Heat Pump Solution Humidification Fresh Air Units: The primary application domain. The dry coil tube operates as the sensible heat exchange element in systems that combine heat pump technology with adiabatic solution (lithium bromide or calcium chloride) humidification, enabling precise control of both temperature and humidity without condensate formation.
- Commercial & Industrial HVAC Systems: Air handling units (AHUs), rooftop units (RTUs), and central air conditioning systems requiring corrosion-resistant coil components.
- Pharmaceutical & Cleanroom Environments: Facilities demanding hygienic, non-reactive heat exchange surfaces compliant with GMP (Good Manufacturing Practice) standards.
- Food Processing & Dairy Industry: Temperature control systems in processing lines where resistance to organic acids, cleaning agents (CIP — Clean-In-Place), and high humidity is critical.
- Marine & Coastal Facilities: HVAC systems in environments exposed to salt spray and high chloride concentrations, where 316L grade provides essential pitting corrosion resistance.
- Electronics & Data Center Cooling: Precision temperature control for server rooms and sensitive electronic equipment requiring dry-coil operation to prevent moisture damage.
- Laboratory & Research Facilities: Climate-controlled enclosures and environmental chambers requiring stable temperature modulation with minimal humidity interference.
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and holds the following certifications and complies with the following international and national standards:
6.1 Quality Management Certifications
- ISO 9001:2015 — Quality Management Systems
- ISO 14001:2015 — Environmental Management Systems
- ISO 45001:2018 — Occupational Health & Safety Management Systems
- CE Marking — Conformity with European Economic Area directives
6.2 Product Standards
| Standard | Description |
|---|---|
| GB/T 12771 | Stainless steel seamless tubes for general purposes (Chinese National Standard) |
| GB/T 14976 | Stainless steel welded tubes for fluid transport |
| ASTM A312 / A312M | Specification for seamless, welded, and heavily cold-worked austenitic stainless steel tubes |
| ASTM A213 | Specification for austenitic stainless steel tubes for heat exchangers and heat transfer equipment |
| EN 10217-7 | Heat-resistant, creep-resistant, and high-strength steels — Tubes for pressure purposes |
| JIS G3459 | Welded stainless steel tubes for general use (Japanese Industrial Standard) |