Stainless Steel Coil Tube (盘管) — Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (盘管 Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered tubular product formed into continuous coil configurations. These coil tubes are specifically designed for integration into fan coil units (FCU), HVAC systems, heat exchangers, and fluid transfer applications where compact spatial footprint and efficient thermal performance are critical. The coil tube geometry maximizes surface area within a confined volume, enabling superior heat exchange efficiency while maintaining structural integrity under cyclic thermal and pressure loading.
This product line addresses the key design and construction challenges identified in industry literature regarding fan coil unit integration, including concerns related to coil alignment, vibration damping, flow distribution uniformity, and long-term corrosion resistance in humid operating environments.
2. Material & Properties
2.1 Material Grades
- SUS 304 (ASTM 304 / 1.4301) — Austenitic stainless steel with excellent general corrosion resistance; suitable for most HVAC and fluid handling applications.
- SUS 316 (ASTM 316 / 1.4401) — Molybdenum-enhanced austenitic grade offering superior resistance to pitting and crevice corrosion in chloride-rich environments.
- SUS 321 (ASTM 321 / 1.4541) — Titanium-stabilized grade for elevated-temperature service exceeding 400 °C, resistant to intergranular corrosion.
2.2 Mechanical Properties (Typical, Annealed Condition)
| Property | SUS 304 | SUS 316 | SUS 321 |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 515 | ≥ 520 |
| Yield Strength (0.2% Offset, MPa) | ≥ 205 | ≥ 170 | ≥ 205 |
| Elongation (% at Break) | ≥ 40 | ≥ 40 | ≥ 40 |
| Density (g/cm³) | 7.93 | 8.00 | 7.93 |
| Thermal Conductivity (W/m·K at 20 °C) | 16.3 | 14.6 | 16.3 |
| Thermal Expansion Coefficient (10⁻⁶/K, 20–100 °C) | 17.3 | 16.0 | 17.3 |
| Maximum Service Temperature (°C) | 870 | 870 | 900 |
2.3 Surface Finish Options
- 2B (Cold Rolled & Bright Annealed) — Standard mill finish with good appearance and corrosion resistance.
- No. 4 Brushed — Uniform unidirectional grain pattern; suitable for visible applications.
- Mirror (8K) — Highly polished finish for aesthetic and hygienic requirements.
- Pickled & Passivated — Deoxidized surface with enhanced passive film for maximum corrosion protection.
3. Dimensions & Specifications
| Parameter | Specification Range | Unit |
|---|---|---|
| Outer Diameter (OD) | 6.0 – 25.4 | mm |
| Wall Thickness | 0.3 – 1.5 | mm |
| Bend Radius (Minimum) | 1.5 × OD | — |
| Coil Pitch (Center-to-Center) | 10.0 – 50.0 | mm |
| Coil Length (Uncoiled) | Up to 12,000 | mm |
| Coil Diameter (Overall) | 150 – 800 | mm |
| Tolerance on OD (±) | 0.1 | mm |
| Tolerance on Wall Thickness (±) | 0.05 | mm |
| Maximum Operating Pressure | 1.6 – 4.0 | MPa |
| Hydrostatic Test Pressure | 1.5 × Operating Pressure | MPa |
4. Manufacturing Process
- Raw Material Inspection — Incoming stainless steel strip undergoes spectroscopic analysis (PMI) for chemical composition verification and visual inspection for surface defects.
- Slitting & Edge Trimming — Cold-rolled strip is slit to precise width tolerances (±0.1 mm) using precision slitting lines with blade angle compensation.
- Coil Forming (Cold Bending) — Strip is fed through CNC-controlled bending stations with progressive die sets to achieve uniform bend radii without wall thinning or ovalization exceeding 5%.
- Welding (if applicable) — TIG (Gas Tungsten Arc Welding) or orbital welding is employed for seamless closure or end connections, with full-penetration welds verified by radiographic inspection.
- Heat Treatment / Annealing — Solution annealing at 1050–1150 °C followed by controlled cooling to relieve residual stresses from cold forming and restore full austenitic microstructure.
- Pickling & Passivation — Immersion in mixed acid solution (HNO₃ + HF) to remove oxide scale, followed by passivation treatment to establish a stable chromium oxide passive layer (≥ 100 Å thickness).
- Dimensional Inspection — Coordinate Measuring Machine (CMM) and laser scan verification of coil geometry, pitch uniformity, and dimensional compliance.
- Pressure Testing — Each coil tube assembly undergoes hydrostatic or pneumatic pressure testing to confirm leak-free integrity at 1.5× rated operating pressure, held for a minimum of 10 minutes.
5. Applications
- Fan Coil Units (FCU) — Primary application domain; coil tubes serve as the core heat exchange element in chilled water and hot water FCU systems for commercial and residential HVAC.
- Automotive Radiators & Intercoolers — Compact coil configurations for engine cooling and turbocharger air-to-air heat exchange.
- Process Heat Exchangers — Shell-and-coil heat exchangers in chemical processing, pharmaceutical manufacturing, and food-grade applications.
- Refrigeration & Cryogenic Systems — Evaporator and condenser coils operating under refrigerant service conditions.
- Marine & Offshore Equipment — Corrosion-resistant coil assemblies for seawater cooling and ballast systems.
- Medical & Laboratory Equipment — Hygienic-grade coil tubes for autoclavable sterilization systems and analytical instruments.
6. Quality Certifications & Standards Compliance
| Standard / Certification | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 3834-2 | Quality Requirements for Welding of Steel and Nickel Alloys |
| EN 10204 Type 3.1 | Inspection Certificate — Material Test Report |
| ASTM A213 / A269 | Seamless & Welded Stainless Steel Tubing |
| ASME B31.3 / B31.9 | Piping Code Compliance (Process & Refrigeration) |
| CE Marking (PED 2014/68/EU) | Pressure Equipment Directive Compliance |
| RoHS 2011/65/EU | Restriction of Hazardous Substances |
7. Unique Selling Points
- Precision Coil Geometry — CNC-controlled forming ensures pitch uniformity within ±0.2 mm, guaranteeing consistent flow distribution and preventing hot spots in heat exchanger service.
- Superior Corrosion Resistance — Full pickling and passivation treatment delivers a minimum passive film thickness of 100 Å, extending service life beyond 20 years in aggressive environments.
- Design-Construction Integration — Products are engineered with specific attention to the installation challenges documented in fan coil unit design literature, including optimized inlet/outlet configurations for reduced pressure drop and minimized vibration transmission.
- Customizable Configurations — Flexible manufacturing capability supports bespoke coil dimensions, pitch variations, and multi-pass arrangements tailored to specific thermal duty requirements.
- Traceability & Documentation — Full material traceability from mill heat number through final inspection, with comprehensive EN 10204 Type 3.1 documentation for every batch.
Technical Note: Wenzhou Jixing Metal Materials Co., Ltd maintains a dedicated R&D focus on optimizing coil tube performance for fan coil unit applications, incorporating lessons from industry-wide design reviews to deliver products that minimize common construction defects including coil misalignment, uneven fin spacing, and inadequate support point spacing.