Stainless Steel Coil Tube (Coiltube) — HVAC & Industrial Heat Exchange Application
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed primarily for heat exchange applications in central air conditioning (CAC) systems, fan coil units (FCU), and industrial thermal management equipment. This product is supplied in coiled form to facilitate continuous feed during downstream fabrication processes such as bending, welding, and brazing into heat exchanger cores.
As a critical component in evaporator and condenser assemblies, the coil tube must exhibit superior thermal conductivity, corrosion resistance, mechanical durability, and dimensional accuracy. Wenzhou Jixing Metal Materials Co., Ltd. specializes in producing coil tubes that meet the rigorous demands of HVACR (Heating, Ventilation, Air Conditioning, and Refrigeration) industries worldwide, ensuring reliable long-term performance under cyclic thermal and chemical stress conditions.
Key Insight from Field Experience: Analysis of central air conditioning fan coil unit (FCU) maintenance data indicates that coil tube integrity is the single most critical factor determining service life and energy efficiency. Tubes exhibiting wall thinning, intergranular corrosion, or dimensional deviation beyond tolerance lead to refrigerant leakage, reduced heat transfer efficiency, and premature system failure. Proper material selection and manufacturing quality are therefore paramount.
2. Material & Properties
2.1 Base Material Grades
- AISI 304 / ASTM A213 TP304 (UNS S30400) — General-purpose austenitic stainless steel with excellent corrosion resistance and formability
- AISI 316 / ASTM A213 TP316 (UNS S31600) — Enhanced chloriding resistance due to molybdenum (Mo) addition
- AISI 316L / ASTM A213 TP316L (UNS S31603) — Low-carbon variant for superior weldability and resistance to intergranular corrosion
- Copper-Stainless Composite — Stainless steel outer layer bonded to copper inner layer for combined thermal and corrosion performance
2.2 Mechanical Properties (Typical Values)
| Property |
AISI 304 |
AISI 316 |
Unit |
| Tensile Strength (UTS) |
≥ 515 |
≥ 515 |
MPa |
| Yield Strength (0.2% Offset) |
≥ 205 |
≥ 205 |
MPa |
| Elongation (A50mm) |
≥ 40 |
≥ 40 |
% |
| Hardness (HV10) |
≤ 210 |
≤ 210 |
Vickers |
| Thermal Conductivity (20°C) |
16.3 |
14.6 |
W/(m·K) |
| Thermal Expansion Coefficient (20–100°C) |
17.3 |
16.6 |
×10⁻⁶/K |
| Density |
8.00 |
8.03 |
g/cm³ |
2.3 Chemical Composition (wt%)
| Element |
C |
Mn |
P |
S |
S i |
Cr |
Ni |
Mo |
| 304 |
≤ 0.08 |
≤ 2.00 |
≤ 0.045 |
≤ 0.030 |
≤ 1.00 |
18.0–20.0 |
8.0–10.5 |
— |
| 316 |
≤ 0.08 |
≤ 2.00 |
≤ 0.045 |
≤ 0.030 |
≤ 1.00 |
16.0–18.0 |
10.0–14.0 |
2.0–3.0 |
| 316L |
≤ 0.03 |
≤ 2.00 |
≤ 0.045 |
≤ 0.030 |
≤ 1.00 |
16.0–18.0 |
10.0–14.0 |
2.0–3.0 |
3. Specifications
3.1 Dimensional Parameters
| Parameter |
Specification / Range |
Standard Reference |
| Outer Diameter (OD) |
Φ 3.0 mm – Φ 16.0 mm (typical: Φ 6.35 mm, Φ 9.52 mm, Φ 12.7 mm) |
ASTM A213 / GB/T 12771 |
| Wall Thickness (WT) |
0.30 mm – 1.50 mm (typical: 0.50 mm, 0.65 mm, 0.80 mm) |
ASTM A213 / EN 10217 |
| Coil Inner Diameter (CID) |
Φ 200 mm – Φ 600 mm |
Manufacturer Specification |
| Coil Length (Per Coil) |
150 m – 500 m (customizable) |
— |
| OD Tolerance |
± 0.05 mm (precision grade); ± 0.10 mm (standard grade) |
ASTM A213 |
| WT Tolerance |
± 10% of nominal |
ASTM A213 |
| Straightness |
≤ 0.5 mm/m |
ISO 12163 |
| Surface Finish |
2B Annealed / No. 4 Brushed / Mirror (Ra ≤ 0.4 μm) |
ASTM A480 |
| End Condition |
Plain / Beveled / Flared / Threaded (on request) |
— |
3.2 Performance Specifications
| Performance Parameter |
Value / Requirement |
| Hydrostatic Test Pressure |
1.5 × working pressure, minimum 6.0 MPa |
| Refrigerant Compatibility |
R410A, R32, R134a, R407C, NH₃, CO₂ (R744) |
| Operating Temperature Range |
−196 °C to +870 °C (304); −196 °C to +870 °C (316) |
| Service Life (Design) |
≥ 15 years under normal HVAC operating conditions |
| Corrosion Rate (in seawater, 316L) |
< 0.02 mm/year |
| Maximum Operating Pressure |
2.5 MPa (standard); 4.0 MPa (high-pressure grade) |
4. Manufacturing Process
4.1 Process Flow Overview
- Raw Material Procurement: Selection of certified stainless steel strip (cold-rolled, annealed) from qualified mill suppliers with full chemical and mechanical traceability.
- Strip Inspection: Incoming material undergoes visual inspection, ultrasonic testing (UT) for laminations, and spectroscopic analysis (OES) for compositional verification.
- Forming (ERW / Cold Roll Forming): Flat strip is progressively formed into a circular cross-section using precision roll-forming equipment with calibrated die sets. The seam is welded using Electric Resistance Welding (ERW) or left as a cold-formed tube (weld-free) depending on application requirements.
- Weld Heat-Affected Zone (HAZ) Control: For ERW tubes, post-weld internal and external grinding ensures the weld seam is flush with the tube surface, maintaining internal surface integrity for fluid flow.
- Annealing & Pickling: Tubes undergo solution annealing at 1050–1150 °C in a controlled atmosphere (vacuum or inert gas) followed by acid pickling and passivation to restore full austenitic microstructure, remove oxide scale, and establish a protective chromium oxide layer.
- Dimensional Calibration (Sizing & Straightening): Final sizing passes through precision draw rolls to achieve exact OD and WT tolerances. Straightening eliminates residual curvature.
- Coiling: The finished tube is coiled onto a mandrel at controlled tension to produce a uniform coil with consistent pitch and no kinking or flattening.
- Final Inspection & Packaging: Each coil undergoes 100% hydrostatic testing, dimensional verification, and surface quality inspection before protective wrapping and labeling.
4.2 Critical Process Parameters
- Forming Speed: 15–40 m/min (dependent on tube diameter and wall thickness)
- ERW Current: 30–60 kA with precise synchronization to strip speed
- Internal Grinding: Achieves seam flatness within ± 0.02 mm
- Annealing Atmosphere: Dew point < −60 °C to prevent re-oxidation
- Pickling Solution: HNO₃/HF mixed acid at 50–60 °C, dwell time 5–15 minutes
5. Applications
5.1 Primary Application Domains
- Central Air Conditioning (CAC) Systems: Evaporator and condenser tube coils in chiller units, air handling units (AHU), and rooftop units (RTU)
- Fan Coil Units (FCU): Heat exchange coils in commercial and residential FCU installations — the most common end-use for this product category
- Refrigeration & Cryogenic Systems: Tube bundles in industrial refrigeration condensers, evaporators, and heat recovery units
- Heat Exchangers (Plate & Shell): Coil tubes used in shell-and-tube heat exchangers for process cooling and heating
- Automotive & Transportation HVAC: Compact evaporator coils for vehicle air conditioning systems
- Food & Pharmaceutical Processing: Sanitary-grade heat exchangers requiring high corrosion resistance and cleanability
- Marine & Offshore Platforms: Seawater-cooled heat exchangers where chloride resistance (316/316L grade) is essential
5.2 Maintenance Experience Insights
Field maintenance analysis of central air conditioning fan coil units (FCU) reveals the following key findings regarding coil tube performance:
- Corrosion-induced wall thinning at the tube-to-finsheet junction is the leading cause of refrigerant leakage, accounting for approximately 60% of coil failures in coastal environments.
- Dimensional inconsistency (OD variation > 0.05 mm) causes poor fin-to-tube contact, reducing heat transfer efficiency by 15–25%.
- Weld seam defects in ERW tubes are the second most common failure mode, often manifesting as micro-cracks after 3–5 years of thermal cycling.
- Proper passivation and surface finish quality significantly extend service life in humid tropical climates.
6. Quality Certifications & Standards Compliance
6.1 Applicable Standards
- ASTM A213 / A213M — Standard Specification for Ferritic, Austenitic, and Ferritic-Austenitic Stainless Steel Tubing for Heat-Transfer and Similar Applications
- EN 10217-7 — Non-ferrous metal tubes and their alloys — Technical delivery conditions — Part 7: Seamless and welded stainless steel tubes for heat exchangers
- GB/T 12771 — Technical delivery conditions for cold-rolled stainless steel seamless tubes and welded tubes
- GB/T 14976 — Cold-rolled or cold-drawn stainless steel seamless tubes for fluid transport
- JIS G3448 — Cold-rolled stainless steel tubes for general use
- ASME B31.5 — Power Piping (for process applications)
6.2 Certifications & Compliance
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health and Safety Management
- EN 10204 Type 3.1 — Inspection Certificate issued by authorized quality control personnel
- Mill Test Report (MTR) — Full chemical analysis, mechanical properties, and heat number traceability provided per batch
- CE Marking — Conformity with European Pressure Equipment Directive (PED 2014/68/EU) where applicable
- UL / CSA — Component approval for HVAC applications in North American markets
6.3 Inspection & Testing Protocol
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