Stainless Steel Coil Tube (Coil Tube) — Technical Product Specification
1. Product Overview
The Stainless Steel Coil Tube is a precision-engineered tubular product supplied in continuous coiled form, designed for seamless integration into thermal management systems, fluid conveyance networks, and industrial heat exchange assemblies. This product category is particularly significant in the domain of Fan Coil Unit (FCU) systems, where coil tubes serve as the primary heat transfer medium, coupling directly with room thermal characteristics to regulate indoor climate conditions.
Based on research findings in the field of "On/Off Control of Fan Coil Units Coupled with Room Thermal Characteristics," the coil tube's thermal response dynamics, surface heat transfer coefficients, and flow resistance characteristics are critical parameters that directly influence system efficiency, control accuracy, and occupant comfort. Wenzhou Jixing Metal Materials Co., Ltd. manufactures coil tubes that meet the stringent geometric tolerances, surface quality requirements, and metallurgical specifications demanded by advanced HVAC (Heating, Ventilation, and Air Conditioning) applications.
2. Material & Properties
Stainless steel coil tubes are fabricated from austenitic and ferritic stainless steel grades, each offering distinct advantages for specific service environments:
- Austenitic Grades (e.g., 304 / 304L, 316 / 316L): Provide superior corrosion resistance, excellent formability, and non-magnetic properties. Ideal for applications involving aggressive media, high-temperature service, and hygienic environments.
- Ferritic Grades (e.g., 430, 439): Offer enhanced resistance to stress corrosion cracking and thermal fatigue, with cost advantages. Suitable for condensate drainage and moderate-temperature heat exchange duties.
- Duplex Grades (e.g., 2205): Deliver combined high yield strength and corrosion resistance for demanding pressure and chemical environments.
Key Metallurgical Properties
- Corrosion Resistance: Chromium content ≥ 18% forms a self-healing passive oxide layer (Cr₂O₃), providing resistance to pitting, crevice corrosion, and intergranular corrosion.
- Thermal Conductivity: 14–16 W/(m·K) for austenitic grades, enabling efficient heat transfer in coil assemblies.
- Temperature Range: Continuous service from cryogenic temperatures (−196 °C) up to 870 °C without loss of mechanical integrity.
- Surface Finish: Available in 2B, No. 1 (Pickled), or Mirror (8K) finishes to minimize flow resistance and facilitate cleaning.
3. Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 108 mm | ASTM A269 / ASTM A554 |
| Wall Thickness | 0.3 mm – 4.0 mm | ASTM A269 / EN 10216-5 |
| Coil Inner Diameter | 300 mm – 600 mm | Manufacturer's standard |
| Coil Length (per coil) | 50 m – 500 m | Customizable |
| Material Grades | 304, 304L, 316, 316L, 321, 310S, 430, 2205 | ASTM / EN / JIS |
| Surface Treatment | 2B, BA (Bright Annealed), No. 1 Pickled, Mirror Polish | ASTM A478 |
| Dimensional Tolerance (OD) | ±0.05 mm – ±0.10 mm | ASTM A213 |
| Dimensional Tolerance (Wall) | ±10% of nominal | ASTM A213 |
| Max. Operating Pressure | Up to 4.0 MPa (grade-dependent) | ASME B31.3 |
| Coiling Method | Random coil or uniform spiral coil | — |
| End Treatment | Plain, beveled, or threaded | Per customer requirement |
| Delivery Condition | Annealed & Pickled, or Solution Heat Treated | ASTM A213 |
4. Manufacturing Process
The production of high-precision stainless steel coil tubes follows a rigorous multi-stage manufacturing sequence:
- Slab Casting & Hot Rolling: Stainless steel ingots are cast via continuous casting (CC) and subsequently hot-rolled into seamless tube blanks at temperatures above the recrystallization point (typically 1050–1200 °C).
- Piercing & Extrusion: Hot-rolled slabs are pierced and extruded through dies to form seamless hollow tubes with controlled wall thickness ratios.
- Cold Drawing & Sizing: Tubes are cold-drawn through precision dies to achieve exact dimensional tolerances (±0.05 mm OD), enhanced surface finish, and improved mechanical properties. Multiple drawing passes may be employed for tight-tolerance applications.
- Intermediate Annealing: Periodic solution annealing at 1050–1150 °C relieves cold work hardening, restores ductility, and dissolves precipitated carbides to maintain corrosion resistance.
- Pickling & Descaling: Tubes are immersed in mixed acid baths (HNO₃/HF or H₂SO₄/HNO₃) to remove oxide scale and restore the passive chromium oxide surface layer.
- Coiling: Continuous tube lengths are coiled onto precision-mandrel winding machines under controlled tension to produce uniform spiral coils. Coil inner diameter and pitch are precisely controlled to prevent deformation or wrinkling.
- Quality Inspection: Each coil undergoes ultrasonic testing (UT), hydrostatic pressure testing (typically 2× working pressure), dimensional verification, and visual inspection for surface defects.
5. Applications
Primary Application Domains
- Fan Coil Unit (FCU) Systems: Coil tubes serve as the core heat exchange element in FCUs, where chilled or hot water circulates through the tube bundle to condition indoor air. The thermal coupling between the coil tube and room air directly determines on/off control strategies and system energy efficiency.
- Chilled Water & Hot Water Distribution: Coil tubes are fabricated into serpentine or zig-zag configurations for use in air handling units (AHUs), unit heaters, and fan-coil-based terminal units in commercial and residential buildings.
- Industrial Heat Exchangers: Used in plate-and-tube heat exchangers, shell-and-tube condensers, and evaporators in chemical processing, pharmaceutical manufacturing, and food & beverage industries.
- Refrigeration & Cryogenic Systems: 316L and 304L coil tubes are employed in evaporator and condenser assemblies for ammonia, refrigerant, and liquid nitrogen systems.
- Hygienic & Pharmaceutical Applications: Mirror-polished (8K finish) coil tubes meet FDA and 3-A sanitary standards for dairy processing, biotechnology, and pharmaceutical fluid transfer.
- Automotive & Aerospace: Precision coil tubes are used in fuel systems, hydraulic lines, and thermal management circuits where weight reduction and corrosion resistance are critical.
Thermal Control Relevance
Research on "On/Off Control of Fan Coil Units Coupled with Room Thermal Characteristics" demonstrates that the thermal mass, heat transfer coefficient, and flow resistance of the coil tube assembly are dominant parameters in predicting room temperature response. Optimized coil tube geometry — including tube diameter, wall thickness, coil pitch, and fin density — enables faster transient response, reduced overshoot, and improved energy efficiency in building HVAC control loops. Stainless steel coil tubes with controlled surface finish (low Ra values) minimize fouling resistance over time, maintaining design heat transfer performance throughout the service life.
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management systems and product certifications to ensure traceability, consistency, and regulatory compliance:
- ISO 9001:2015 — Quality Management System certification for consistent product quality and process control.
- ISO 14001:2015 — Environmental Management System certification for sustainable manufacturing practices.
- ASTM A269 / A554 — Compliance with American Society for Testing and Materials specifications for wrought austenitic stainless steel tube.
- EN 10216-5 — European standard for welded and seamless stainless steel tubes for general applications.
- JIS G3445 / G3459 — Japanese Industrial Standards for stainless steel tubes (seamless and welded).
- GB/T 12771 / GB/T 13296 — Chinese national standards for stainless steel tubes (welded and seamless).
- Mill Test Reports (MTRs): Each production lot is accompanied by a full chemical analysis report, mechanical test data (tensile strength, yield strength, elongation), and non-destructive testing (NDT) results.
- Hydrostatic Testing: All coils pass 100% hydrostatic pressure testing at 2× the maximum design working pressure, with zero leakage tolerance.
- Ultrasonic Testing (UT): Automated UT inspection for internal defects (inclusions, laminations, cracks) per ASTM A777.
7. Unique Selling Points
- Precision Dimensional Control: Cold-drawing processes achieve ±0.05 mm OD tolerance, critical for seamless integration into fan coil tube bundles and heat exchanger assemblies.
- Superior Surface Quality: Available in BA and mirror finishes (Ra ≤ 0.2 μm), minimizing fouling resistance and maintaining long-term heat transfer efficiency in thermal control applications.
- Full Traceability: Every coil is individually identified with heat number, grade, dimensions, and test results, enabling complete supply chain traceability.
- Custom Coiling Configuration: Flexible coil inner diameter and pitch options allow direct compatibility with existing coil-forming machinery in HVAC manufacturing.
- Multi-Grade Availability: Single-source procurement of 304, 316L, 321, 430, and 2205 grades simplifies inventory management for OEM customers.
- Thermal Performance Optimization: Material selection and surface treatment are tailored to minimize fouling factor accumulation, ensuring stable thermal conductance throughout the operational lifecycle of fan coil units and heat exchangers.