Stainless Steel Coil Tube (Coiltube) — HVAC & Industrial Application Series
Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered continuous tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Designed primarily for integration into fan coil units (FCUs), air handling systems, and industrial heat exchangers, this coil tube delivers superior thermal conductivity, corrosion resistance, and structural integrity under cyclic thermal loading. The product is supplied in continuous coiled form, enabling seamless integration into automated assembly lines and minimizing on-site fabrication waste.
Rooted in the applied analysis of air volume testing for fan coil units, the coil tube geometry and dimensional tolerances are optimized to ensure uniform airflow distribution, minimized pressure drop across the coil assembly, and maximized heat transfer efficiency between the working fluid and ambient air.
Material & Properties
The coil tube is fabricated from austenitic stainless steel grades, selected for their exceptional resistance to corrosion, oxidation, and mechanical fatigue under repeated thermal cycling. The primary material specifications are as follows:
- Grade 304 (UNS S30400): 18% Chromium, 8% Nickel — General-purpose corrosion resistance suitable for HVAC and food-grade applications.
- Grade 316 (UNS S31600): 16–18% Chromium, 10–14% Nickel, 2–3% Molybdenum — Enhanced resistance to chlorides, acidic environments, and marine atmospheres.
- Grade 321 (UNS S32100): Titanium-stabilized — Superior resistance to intergranular corrosion at elevated temperatures above 450°C.
Key material properties include:
- Tensile Strength: ≥ 515 MPa (Grade 304); ≥ 580 MPa (Grade 316)
- Elongation at Break: ≥ 40%
- Thermal Conductivity (20°C): 16.3 W/(m·K) (Grade 304); 14.6 W/(m·K) (Grade 316)
- Maximum Service Temperature: 870°C (Grade 304); 870°C (Grade 316)
- Corrosion Resistance: Equivalent to or exceeding ASTM A240/A270 standards
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm, 9.52 mm, 12.70 mm, 15.88 mm, 19.05 mm (customizable) | ASTM A270 / EN 10216-5 |
| Wall Thickness | 0.50 mm – 2.00 mm (customizable) | ISO 4200 |
| Coil Length (Continuous) | 50 m – 500 m per coil (standard); up to 1,000 m on request | Manufacturer Specification |
| Coil Inner Diameter (ID) | 200 mm – 600 mm (adjustable for logistics) | Manufacturer Specification |
| Surface Finish | 2B (cold-rolled), BA (Bright Annealed), No. 4 (Brushed), Mirror (8K) | ASTM A480 |
| Dimensional Tolerance (OD) | ± 0.05 mm (Precision grade); ± 0.10 mm (Standard grade) | EN 10217-7 |
| Dimensional Tolerance (Wall) | ± 0.02 mm (Precision grade); ± 0.05 mm (Standard grade) | EN 10217-7 |
| Roundness Tolerance | ≤ 0.02 mm | ISO 80359 |
| Seam Type | Welded (TIG / Laser); Seamless available on request | ASTM A270 Type 1 / Type 2 |
| End Condition | Plain, Beveled, Flanged, or Threaded (per customer drawing) | Custom |
| Packaging | Wooden reel / Steel drum with moisture barrier; vacuum-sealed for export | ISO 2801 (Packaging) |
Manufacturing Process
The production of the Stainless Steel Coil Tube follows a rigorous multi-stage manufacturing workflow designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Procurement: Cold-rolled stainless steel strip is sourced from certified mills (e.g., Outokumpu, POSCO, Taigang) with full chemical composition traceability via Heat Treatment Number (HTN) documentation.
- Coil Slitting & Leveling: The master coil is slit to the required strip width using a precision slitting line, followed by tension leveling to eliminate coil set and ensure flatness within ± 0.1 mm/m.
- Forming (Roll Forming / Pipe Making): The leveled strip is fed through a series of precision die sets in a continuous pipe-making machine. The forming process utilizes either the roll-bending method (for welded tube) or the extrusion method (for seamless tube). Roller tooling is manufactured from hardened tool steel (HRC 60–62) to minimize surface transfer defects.
- Welding (if applicable): For welded coil tube, the seam is closed using Gas Tungsten Arc Welding (GTAW / TIG) with argon shielding gas (99.99% purity) to prevent oxidation. Laser welding is available for thinner wall specifications (≤ 0.8 mm) to achieve a narrower heat-affected zone (HAZ) and superior weld integrity.
- Heat Treatment (Solution Annealing): The formed tube undergoes solution annealing at 1050–1150°C in a controlled atmosphere (hydrogen or vacuum) to relieve residual stresses, restore austenitic microstructure, and achieve maximum corrosion resistance.
- Pickling & Passivation: Post-annealing oxide scale is removed via acid pickling (HNO₃ + HF mixture), followed by passivation treatment to establish a stable chromium oxide passive film on the surface.
- Surface Finishing: Mechanical polishing or electrolytic polishing is applied to achieve the specified surface finish (2B, BA, No. 4, or Mirror). Surface roughness (Ra) is controlled to ≤ 0.4 µm for BA finish and ≤ 0.1 µm for Mirror finish.
- Coiling & Packaging: The finished tube is wound onto a precision-machined reel at a controlled tension to prevent ovalization or kinking. The coil is wrapped in protective film, placed in a wooden reel or steel drum, and labeled with full traceability documentation.
Applications
The Stainless Steel Coil Tube is deployed across a broad spectrum of engineering domains:
- HVAC Systems — Fan Coil Units (FCUs): The primary application domain. The coil tube serves as the heat exchanger element in FCUs, where precise tube geometry and surface quality directly influence air volume distribution, coil efficiency (EER/COP), and acoustic performance. Optimized coil pitch and tube spacing minimize pressure drop while maximizing the heat transfer coefficient (U-value).
- Air Handling Units (AHUs) & Chilled Water Coils: Used as the fin-and-tube heat exchanger core in commercial and industrial air handling systems.
- Process Heat Exchangers: Shell-and-tube heat exchangers, plate heat exchangers, and evaporators in chemical, pharmaceutical, and food processing industries.
- Refrigeration & Cryogenic Systems: Evaporator and condenser coils where low-temperature ductility and fatigue resistance are critical.
- Automotive & Aerospace Thermal Management: Radiator cores, intercoolers, and battery thermal management systems (BTMS) in electric vehicles.
- Sanitary & Food-Grade Applications: Dairy processing, brewing, and pharmaceutical fluid transfer where hygienic surface finish (Ra ≤ 0.4 µm) and corrosion resistance are mandatory.
- Building Services & Radiant Heating: Underfloor heating circuits and radiant cooling panels requiring continuous, kink-free tubing.
Quality Certifications & Standards Compliance
The Stainless Steel Coil Tube product line is manufactured and certified in accordance with the following international standards and quality management frameworks:
- ISO 9001:2015 — Quality Management Systems (QMS) certification for manufacturing operations.
- ISO 14001:2015 — Environmental Management Systems certification.
- ASTM A270 / A269 — Standard Specification for Seamless, Welded, and Heavy-Walled Austenitic Stainless Steel Tubing for General Applications.
- EN 10216-5 / EN 10217-7 — European standards for welded stainless steel tubes for pressure and general purposes.
- ASME SA-213 / SA-213M — Boiler and Heat Exchanger Tubes.
- 3-A Sanitary Standards — For food-grade and pharmaceutical applications.
- CE Marking (EU Pressure Equipment Directive 2014/68/EU) — For pressure-rated applications.
- Mill Test Reports (MTR) — Full chemical composition, mechanical property, and heat treatment documentation provided with every batch.
Every production batch undergoes non-destructive testing (NDT) including eddy current testing (ECT) for weld seam integrity, hydrostatic pressure testing (to 1.5× working pressure for 30 seconds minimum), and dimensional verification via laser diameter measurement systems.
Unique Selling Points
- Optimized for Fan Coil Unit Performance: Coil tube geometry is engineered based on air volume testing methodologies, ensuring uniform airflow distribution and minimized pressure drop across the coil assembly — directly improving FCU energy efficiency and reducing fan power consumption.
- Precision Dimensional Control: Tolerances as tight as ± 0.02 mm on wall thickness and ± 0.05 mm on OD ensure consistent heat transfer performance and seamless integration with automated coil-bending and finning equipment.
- Full Traceability: Each coil is serialized with Heat Treatment Number (HTN) and batch identification, enabling complete material traceability from raw strip to finished product.
- Customization Capability: Flexible configuration of OD, wall thickness, surface finish, and coil length to meet project-specific engineering drawings and performance requirements.
- Superior Surface Quality: Available in BA and Mirror finishes with Ra values as low as 0.1 µm, eliminating nucleation sites for fouling and biofilm formation — critical for sanitary and long-life heat exchanger applications.
- Export-Ready Packaging: Vacuum-sealed, moisture-barrier packaging compliant with international shipping standards, ensuring product integrity across long-haul logistics.