Stainless Steel Coil Tube — Series 711 (Wenzhou Jixing Metal Materials Co., Ltd)
1. Product Overview
The Stainless Steel Coil Tube (Product No. 711) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered tubular component formed into a continuous helical or serpentine coil configuration. This product is designed for demanding thermal management applications, particularly in heating, ventilation, and air conditioning (HVAC) systems, heat exchangers, and industrial process cooling/heating circuits. The coil geometry maximizes heat transfer surface area within a compact volumetric envelope, making it an ideal solution for fan coil units (FCUs), chiller systems, and refrigeration condensers/evaporators.
Unlike straight tube sections, coil tubes offer superior thermal performance under variable operating conditions. Research into the effects of variable operating conditions on fan coil unit performance has demonstrated that properly designed coil tubes maintain stable heat transfer coefficients and flow resistance characteristics across a wide range of flow rates, temperatures, and pressure differentials — a critical requirement for energy-efficient HVAC systems.
2. Material & Properties
2.1 Base Alloy
The coil tube is fabricated from austenitic stainless steel conforming to industry-standard grades, with the primary options being:
- AISI 304 (UNS S30400 / 1.4301) — General-purpose grade offering excellent corrosion resistance, formability, and weldability. Suitable for most HVAC and food-grade applications.
- AISI 316L (UNS S31603 / 1.4404) — Enhanced molybdenum-bearing grade providing superior resistance to pitting and crevice corrosion in aggressive chemical environments, seawater, and high-chloride applications.
- AISI 321 (UNS S32100 / 1.4541) — Titanium-stabilized grade for elevated-temperature service where sensitization resistance is critical.
2.2 Mechanical Properties
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa (304); ≥ 510 MPa (316L) | ASTM A269 / EN 10216-5 |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ASTM A269 |
| Elongation (A50mm) | ≥ 35% | ASTM A269 |
| Hardness (HV10) | ≤ 210 HV | ISO 6507 |
| Impact Energy (KV2, -40°C) | ≥ 47 J (304L/316L) | ASTM A269 |
2.3 Thermal & Corrosion Properties
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (AISI 304); 14.6 W/(m·K) at 20°C (AISI 316L)
- Coefficient of Thermal Expansion: 17.3 × 10-6 /°C (20–300°C)
- Pitting Resistance: PREN ≥ 18 (304); PREN ≥ 24 (316L) per ASTM G48
- Intergranular Corrosion: Passes ASTM A262 Practice E (48-hour, 10% citric acid, 60°C)
- Maximum Service Temperature: 870°C (oxidation resistance limit in continuous air)
2.4 Surface Finish
- Standard: 2B (cold-rolled, annealed, pickled) — Ra ≤ 0.8 μm
- Optional: No. 4 Brushed (Ra ≤ 1.6 μm), Electropolished (Ra ≤ 0.25 μm), or Passivated (per AMS 2700 Type II)
- Internal Surface: Clean, scale-free; free from embedded particles, weld spatter, and mechanical damage
3. Specifications
| Parameter | Specification | Tolerance |
|---|---|---|
| Outer Diameter (OD) | Φ 3.0 – Φ 22.0 mm (standard); up to Φ 50.8 mm (special order) | ± 0.05 mm (OD ≤ 6 mm); ± 0.1 mm (OD > 6 mm) |
| Wall Thickness | 0.25 – 1.50 mm | ± 0.02 mm (t ≤ 0.5 mm); ± 0.05 mm (t > 0.5 mm) |
| Coil Pitch (Helical) | 15 – 150 mm (adjustable per design) | ± 0.5 mm |
| Coil Diameter (Mean) | Φ 50 – Φ 500 mm | ± 1.0 mm |
| Tube Length (Total Unwound) | 1 – 30 m (standard); up to 100 m (continuous coil) | ± 10 mm |
| Minimum Bend Radius | ≥ 3 × OD (standard); ≥ 2 × OD (cold-worked 304L) | — |
| Roundness | ≤ 0.05 mm | — |
| Concentricity | ≤ 0.05 mm | — |
| End Condition | Clean-cut, deburred, or flared per customer drawing | — |
| Applicable Standards | ASTM A269/A269M, ASTM B730, EN 10216-5, ISO 14612 | — |
4. Manufacturing Process
The coil tube production process at Wenzhou Jixing Metal Materials Co., Ltd follows a rigorous multi-stage manufacturing protocol to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection & Inspection: Cold-rolled stainless steel strip (coil) is sourced from certified mills (e.g., Outokumpu, ThyssenKrupp, or domestic equivalents) with full mill test certificates (MTC) per EN 10204 3.1. Incoming inspection includes chemical composition verification (OES/SEM), grain size assessment, and surface defect examination.
- Tube Forming (Cold Roll Forming): The flat strip is fed through a series of progressively shaped roller dies to form a seamless circular tube cross-section. This cold-forming process produces a tube with superior mechanical properties due to strain hardening, with no weld seam discontinuities.
- Coil Winding: The formed straight tube is wound into the specified coil geometry using a CNC-controlled coiling machine. The winding parameters (pitch, coil diameter, tension) are precisely controlled to maintain uniform curvature without introducing plastic deformation, residual stresses, or geometric deviations.
- Stress Relief Annealing (Optional): For applications requiring reduced residual stresses, the formed coil tube may undergo solution annealing at 1050–1100°C followed by controlled water quenching, restoring full austenitic properties and eliminating cold-work hardening.
- Pickling & Passivation: The coil tube undergoes acid pickling (HNO3/H2SO4 blend) to remove surface oxides, followed by passivation treatment to establish a stable chromium oxide (Cr2O3) protective film. This ensures long-term corrosion resistance.
- Quality Control & Testing: Each batch undergoes dimensional verification (laser micrometry), hydrostatic pressure testing (1.5 × design pressure, minimum 30 seconds), visual inspection (100% coverage), and periodic destructive testing (tensile, hardness, intergranular corrosion per ASTM A262).
- Packaging: Finished coil tubes are wrapped in protective film, placed in wooden crates or cardboard boxes with moisture-absorbing desiccants, and labeled with batch traceability information.
5. Applications
The stainless steel coil tube (Series 711) finds extensive application across multiple industries due to its corrosion resistance, thermal performance, and formability:
- HVAC Systems: Primary component in fan coil units (FCUs), air handling units (AHUs), chilled beams, and radiators. The coil geometry provides high heat transfer efficiency under variable air flow and temperature conditions.
- Refrigeration & Air Conditioning: Evaporator and condenser coils for commercial refrigeration units, heat pumps, and split-system air conditioners.
- Heat Exchangers: Plate-and-fin heat exchangers, shell-and-coil exchangers, and air-cooled condensers in industrial process plants.
- Food & Beverage Industry: Pasteurization coils, cooling jackets, and sanitary process lines where hygienic design and corrosion resistance are paramount (FDA-compliant 316L available).
- Pharmaceutical & Biotech: Bioreactor cooling coils, CIP (Clean-in-Place) loop tubing, and sterile process heat exchangers requiring electropolished surfaces.
- Marine & Offshore: Seawater cooling coils, desalination plant components, and marine HVAC systems where chloride-induced pitting corrosion is a concern (316L/2205 duplex grades).
- Automotive: Intercooler tubes, engine cooling circuits, and heat recovery systems.
- Solar Thermal: Collector tube coils in solar water heating systems and concentrated solar power (CSP) plants.
6. Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management system and holds the following certifications:
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health and Safety Management System
- CE Marking — Conformity with European pressure equipment directive (PED 2014/68/EU) where applicable
- EN 10204 3.1 — Material Test Certificate (MTC) issued for every production batch
- RoHS & REACH Compliance — Restriction of hazardous substances; chemical compliance for EU market
- Third-Party Inspection: Available upon request (SGS, Bureau Veritas, TÜV)
7. Unique Selling Points
Variable Operating Condition Resilience: Research-based design philosophy ensures that the coil tube maintains consistent thermal-hydraulic performance across varying flow rates, inlet temperatures, and pressure differentials — a critical advantage in HVAC applications where operating conditions are inherently dynamic.
- Seamless Construction: Cold roll-formed process eliminates weld seams, removing potential corrosion initiation sites and ensuring uniform mechanical properties throughout the tube wall.
- Precision Dimensional Control: CNC-driven coiling ensures consistent pitch and diameter tolerances, enabling seamless integration into precision-engineered heat exchanger assemblies.
- Full Material Traceability: Every coil tube is traceable to its raw material mill certificate, enabling complete supply chain transparency.
- Customization Capability: Flexible manufacturing capability allows customization of OD, wall thickness, coil geometry, pitch, surface finish, and end preparation to meet specific customer requirements.
- Extended Service Life: Austenitic stainless steel construction provides corrosion resistance exceeding 50 years in typical HVAC environments, significantly reducing lifecycle maintenance costs.
- Hygienic Design: Electropolished internal surfaces (Ra ≤ 0.25 μm) prevent bacterial adhesion and facilitate CIP cleaning — essential for food, beverage, and pharmaceutical applications.
8. Technical Data Summary
| Item | Specification |
|---|---|
| Product Number | 711 |
| Product Name | Stainless Steel Coil Tube (盘管 / Coil Tube) |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd |
| Material Grades | AISI 304, 304L, 316L, 321 (custom grades available) |
| Forming Process | Cold roll forming + CNC coil winding |
| Surface Treatment | Pickled & passivated (standard); Electropolished (optional) |
| Pressure Test | Hydrostatic, 1.5 × design pressure |
| Standards Compliance | ASTM A269, ASTM B730, EN 10216-5, ISO 14612 |
| Minimum Order Quantity | 500 pieces (standard configurations); negotiable for custom orders |
| Lead Time | 15–25 days (standard); 30–45 days (custom) |
Note: All specifications are subject to revision without prior notice. Customers requiring non-standard configurations or additional testing protocols should contact Wenzhou Jixing Metal Materials Co., Ltd for a formal quotation and technical consultation.