Stainless Steel Coil Tube (Dry Coil System) — Product No. 1035
1. Product Overview
The Stainless Steel Coil Tube (Product No. 1035) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This coil tube is specifically designed for application in Dry Coil Systems (also known as Chilled Beam Systems or Indirect Radiant Cooling Systems), where it serves as the core heat exchange element within the evaporative cooling circuitry. Unlike conventional wet coil systems, dry coil tubes operate without direct water contact, leveraging the latent heat of evaporation in adjacent sections to achieve energy-efficient thermal management.
Based on extensive research into key technologies of dry coil systems — including flow distribution uniformity, corrosion resistance in condensing environments, and thermal efficiency optimization — this product integrates advanced metallurgical and manufacturing capabilities to deliver superior performance in demanding HVAC (Heating, Ventilation, and Air Conditioning) and industrial process cooling applications.
2. Material & Properties
2.1 Base Material
The coil tube is fabricated from high-grade austenitic stainless steel, conforming to the following international standards:
- AISI 304 (UNS S30408) — General-purpose grade with excellent corrosion resistance and formability
- AISI 316L (UNS S31603) — Enhanced pitting and crevice corrosion resistance due to molybdenum (Mo) addition, suitable for aggressive chemical environments
- AISI 321 (UNS S32100) — Stabilized grade with titanium (Ti) addition for resistance to intergranular corrosion at elevated temperatures
2.2 Key Material Properties
| Property | AISI 304 | AISI 316L | AISI 321 |
|---|---|---|---|
| Chromium (Cr) Content | 18.0–20.0% | 16.0–18.0% | 17.0–19.0% |
| Nickel (Ni) Content | 8.0–10.5% | 10.0–14.0% | 9.0–12.0% | Molybdenum (Mo) Content | — | 2.0–3.0% | — |
| Titanium (Ti) Content | — | — | 5×(C−0.02)% |
| Tensile Strength (Min.) | 515 MPa | 485 MPa | 515 MPa |
| Yield Strength (0.2% Offset) | 205 MPa | 170 MPa | 205 MPa |
| Thermal Conductivity (at 20°C) | 16.3 W/(m·K) | 14.6 W/(m·K) | 16.3 W/(m·K) |
| Maximum Service Temperature | 870°C (continuous) | 870°C (continuous) | 900°C (continuous) |
| Corrosion Resistance (Pitting) | Good | Excellent | Good |
| Weldability | Excellent | Excellent | Excellent |
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Name | Stainless Steel Coil Tube (Dry Coil System) | — |
| Product Number | 1035 | Internal Catalog |
| Outer Diameter (OD) | 6.0 mm – 25.4 mm (customizable) | ASTM A213 / EN 10216-5 |
| Wall Thickness | 0.5 mm – 2.0 mm (tolerance ±0.05 mm) | ASTM A269 |
| Coil Diameter | 150 mm – 600 mm | Customer specification |
| Tube Length (per coil) | 5 m – 50 m (continuous) | — |
| Surface Finish | BA (Bright Annealed), No. 4 Brushed, or Mirror Polished (Ra ≤ 0.4 μm) | ASTM A473 / EN 10204 |
| End Form | Plain Cut, Beveled, or Flanged | Customer specification |
| Helical Pitch | 10 mm – 50 mm (adjustable for heat transfer optimization) | — |
| Hydrostatic Test Pressure | 2.0 – 6.0 MPa (depending on wall thickness) | ASTM A213 |
| Maximum Operating Pressure | 1.6 – 4.0 MPa | — |
| Maximum Operating Temperature | -40°C to +120°C (standard); up to +400°C (321 grade) | — |
| Refrigerant Compatibility | R-134a, R-410A, R-407C, R-32, Ammonia (NH₃) | ASHRAE Standard 15 |
| Coating (Optional) | Passivation Treatment, Epoxy Coating, or PTFE (Teflon) Inner Lining | ISO 23600 |
| Weight Tolerance | ±3.0% | — |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection & Inspection — Ingot verification via spectrometric analysis (OES) and mechanical testing to ensure compliance with ASTM/EN chemical composition requirements.
- Hot Rolling & Annealing — Billet material is hot-rolled to produce seamless tubes, followed by solution annealing at 1050–1150°C in a protective atmosphere (reduced hydrogen or vacuum) to restore full austenitic microstructure.
- Cold Drawing / Piercing — Tubes are cold-worked through precision dies to achieve final OD and wall thickness dimensions with tight tolerances (±0.05 mm). This cold work induces beneficial work hardening while maintaining ductility.
- Intermediate Annealing — Periodic annealing cycles during multi-pass cold drawing prevent excessive strain hardening and maintain formability for subsequent coiling operations.
- Coil Forming (Coiling) — The straight tube is helically coiled using CNC-controlled coiling machines with variable pitch control. The coil geometry is optimized to maximize heat transfer surface area while minimizing pressure drop.
- Post-Coil Annealing & Passivation — Final annealing in a controlled atmosphere furnace eliminates residual stresses. Chemical passivation (nitric acid or citric acid treatment) removes free iron from the surface, enhancing natural chromium oxide film formation.
- Hydrostatic Testing — Each coil undergoes 100% hydrostatic pressure testing at 2–3× the maximum operating pressure, with full-length inspection to detect any porosity, cracks, or thin-wall defects.
- Final Inspection & Packing — Dimensional verification (OD, wall thickness, coil diameter), surface finish measurement (roughness gauge), and visual inspection. Tubes are packed in moisture-proof wrapping with desiccant bags to prevent oxidation during transit.
4.2 Key Process Technologies for Dry Coil Systems
The research on key technologies in dry coil systems highlights several critical manufacturing considerations that are integrated into the production of this product:
- Flow Distribution Uniformity — Precision coiling with controlled pitch variation ensures uniform refrigerant flow distribution across the entire coil assembly, preventing localized dry-out and optimizing heat transfer coefficients.
- Wall Thickness Consistency — Tight tolerance control (±0.05 mm) on wall thickness prevents thin-wall areas that could lead to premature corrosion or mechanical failure under cyclic thermal loading.
- Surface Roughness Optimization — Controlled surface roughness (Ra 0.2–0.8 μm) balances frictional pressure drop against convective heat transfer performance, a critical parameter in dry coil system efficiency.
- Intergranular Corrosion Resistance — Proper heat treatment prevents chromium carbide precipitation at grain boundaries, ensuring long-term resistance to intergranular corrosion in condensing environments.
5. Applications
5.1 Primary Applications
- Dry Coil Chilled Beam Systems — Used in commercial HVAC systems where dry coil tubes serve as the evaporator circuit within indirect radiant cooling panels. These systems provide superior indoor air quality (IAQ) by eliminating direct water contact with occupied spaces.
- Heat Pump Systems — Integrated into air-source and ground-source heat pump units for efficient heat exchange in both heating and cooling modes.
- Industrial Process Cooling — Applied in food processing, pharmaceutical manufacturing, and chemical plants where corrosion resistance and hygiene requirements are paramount.
- Commercial Refrigeration — Used in display cases, walk-in coolers, and supermarket refrigeration systems requiring reliable, low-maintenance heat exchange components.
- Automotive & Transportation HVAC — Lightweight coil tube assemblies for vehicle air conditioning systems, particularly in electric vehicles (EVs) where thermal management is critical.
5.2 Dry Coil System Architecture Integration
In a typical dry coil system, the stainless steel coil tube is arranged in a serpentine or helical configuration within an air-handling unit or radiant panel. The system operates on the principle of indirect evaporative cooling:
- Chilled water (typically 7–12°C) flows through the coil tube, absorbing heat from the supply air stream.
- A separate water spray section provides evaporative cooling, lowering the air temperature below the dew point without condensation on the coil surface.
- The dry coil tube maintains a surface temperature above the dew point, preventing condensation and associated microbial growth (legionella risk mitigation).
- Energy recovery wheels or plate heat exchangers further improve system COP (Coefficient of Performance).
6. Quality Certifications & Standards Compliance
6.1 Certifications
- ISO 9001:2015 — Quality Management System certification covering all manufacturing processes
- ISO 14001:2015 — Environmental Management System certification
- ISO 45001:2018 — Occupational Health and Safety Management System
- CE Marking — Conformity with European Union directives for pressure equipment and HVAC components
- TÜV Rheinland Certification — Third-party product certification for safety and performance
- SGS Testing Reports — Independent laboratory verification of material composition and mechanical properties
- EN 10204 3.1 — Inspection Certificate (Mill Test Certificate) for each batch
- NSF/ANSI 61 — Drinking water system components certification (where applicable for chilled water systems)
6.2 Applicable Standards
| Standard | Scope |
|---|---|
| ASTM A213 | Standard Specification for Seamless Austenitic Stainless Steel Tubes for High-Pressure Boilers and Heat-Exchanger Tubes |
| ASTM A269 | Standard Specification for Cold-Drawn (or Cold-Rolled) Seamless Stainless Steel Tubing |
| ASTM A473 | Standard Specification for General Requirements for Heat-Treated Bars, Forgings, and Fittings of Stainless Steel |
| EN 10216-5 | Non-Alloy and Alloy Steel Tubes — Technical Delivery Conditions — Part 5: Seamless Cold-Drawn Tubes of Austenitic Steels |
| GB/T 14976 | Chinese National Standard for Cold-Rolled Stainless Steel Tubes for Fluid Transport |
| EN 10204 | Metallurgical Products — Types of Inspection Documents |
6.3 Inspection & Testing Protocol
- Chemical Analysis — OES (Optical Emission Spectroscopy) for each heat; PM (Photoelectric Emission) for carbon and nitrogen verification
- Mechanical Testing — Tensile testing per ASTM E8; hardness testing (Rockwell B scale); impact testing (Charpy V-notch) at service temperature
- Dimensional Inspection — Ultrasonic wall thickness gauging (100% coverage); OD measurement by micrometer; coil diameter verification
- Non-Destructive Testing (NDT) — Eddy current testing for surface and near-surface defect detection; hydrostatic testing for through-thickness integrity
- Surface Quality — Roughness measurement (Ra, Rz); visual inspection under controlled lighting; passivation verification via iron contamination test (ferri-ferroxy blue test)
7. Unique Selling Points
7.1 Research-Driven Design Optimization