Stainless Steel Coil Tube (Coiltube) — Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered continuous-length tubing product, formed into a compact coil configuration for efficient storage, transport, and downstream processing. Designed primarily for the HVAC (Heating, Ventilation, and Air Conditioning) and Independent Fresh Air System (DOAS — Dedicated Outdoor Air System) industries, this coil tube serves as a critical heat-exchange and fluid-transport component in commercial and industrial building infrastructure.
Unlike discrete-length pipe sections, coil tubing offers the distinct advantage of continuous material integrity with no intermediate weld seams, thereby minimizing leak paths and enhancing system reliability. The coil form factor reduces packaging volume by up to 60% compared to straight-length alternatives, significantly lowering logistics costs and warehouse footprint.
2. Material & Properties
2.1 Base Alloy Composition
The coil tube is fabricated from austenitic stainless steel, conforming to the following primary grades:
- AISI 304 / SUS 304 / 0Cr18Ni9 — General-purpose austenitic grade with excellent corrosion resistance and formability.
- AISI 316 / SUS 316 / 0Cr17Ni12Mo2 — Molybdenum-enhanced grade offering superior resistance to pitting and crevice corrosion in aggressive environments.
- AISI 321 / SUS 321 / 0Cr18Ni10Ti — Titanium-stabilized grade suitable for elevated-temperature applications.
2.2 Key Mechanical Properties (Typical Values for AISI 304)
- Tensile Strength (UTS): ≥ 515 MPa
- Yield Strength (0.2% offset): ≥ 205 MPa
- Elongation at Break: ≥ 40%
- Hardness (Rockwell B): ≤ 95 HRB
- Density: 8.0 g/cm³
- Thermal Conductivity (at 100°C): 16.3 W/(m·K)
- Coefficient of Thermal Expansion: 17.3 × 10⁻⁶ /°C
2.3 Surface Finish Options
- 2B Finish — Cold-rolled and annealed for a uniform matte appearance; suitable for general industrial applications.
- No. 4 Brushed Finish — Mechanically polished for aesthetic and corrosion-resistant surface characteristics.
- Mirror (8K) Finish — High-polish finish for architectural and food-grade applications.
- Pickled & Passivated — Chemical surface treatment removing scale and forming a protective chromium oxide layer.
3. Technical Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (¼" – 2") | ASTM A778 / EN 10217 |
| Wall Thickness | 0.3 mm – 3.0 mm | ASTM A778 / ASME B36.19M |
| Coil Diameter (Bundle) | 300 mm – 1,200 mm | Manufacturer Standard |
| Coil Length (Continuous) | 50 m – 500 m per coil | Manufacturer Standard |
| Dimensional Tolerance (OD) | ±0.05 mm (Precision grade); ±0.1 mm (Standard grade) | ASTM A778 |
| Dimensional Tolerance (Wall) | ±10% of nominal thickness | ASTM A778 |
| Roundness | ≤ 5% of nominal OD | ISO 1128 |
| Surface Roughness (Ra) | ≤ 0.8 μm (2B finish); ≤ 0.4 μm (8K finish) | ISO 1302 |
| Operating Temperature Range | −196°C to +870°C (AISI 304) | Material Data Sheet |
| Maximum Working Pressure | Up to 4.0 MPa (grade-dependent) | ASME B31.3 |
| End Treatment | Plain end, beveled end, or threaded end (on request) | Customer Specification |
| Corrosion Resistance | Passivation test per ASTM A967; Salt spray ≥ 1,000 hours (AISI 316) | ASTM A967 / ASTM B117 |
4. Manufacturing Process
The production of stainless steel coil tubing follows a rigorous multi-stage process ensuring dimensional accuracy, metallurgical integrity, and surface quality:
- Strip Preparation — Cold-rolled stainless steel strip (coil) is inspected for surface defects and dimensional conformity. Chemical composition is verified via optical emission spectroscopy (OES) or X-ray fluorescence (XRF) analysis.
- Forming (Semi-Automatic or Automatic) — The flat strip is fed through a series of progressively reducing rolls (forming station) to gradually shape it into a circular cross-section. The forming process is carefully calibrated to avoid work-hardening and maintain metallurgical homogeneity.
- Seam Welding — The formed tube edges are joined using high-frequency induction welding (HF-W) or gas tungsten arc welding (GTAW/TIG), depending on wall thickness. Weld parameters are monitored in real time to ensure full penetration and minimal heat-affected zone (HAZ).
- In-Line Annealing (Optional) — For high-strength grades or where stress relief is required, the tube passes through an in-line resistance or gas-fired annealing furnace to restore ductility and refine grain structure.
- Internal Cleaning / Polishing (Optional) — Abrasive brush inserts or chemical cleaning agents are used to achieve the required internal surface finish, critical for hygienic and pharmaceutical applications.
- Pickling & Passivation — The coil is immersed in an acid bath (typically a mixture of nitric and hydrofluoric acid) to remove welding scale and oxidation, followed by a passivation treatment to establish a protective chromium oxide film.
- Dimensional Inspection — Each coil undergoes ultrasonic thickness measurement, optical OD verification, and hydrostatic pressure testing to confirm compliance with specified tolerances.
- Coiling & Packaging — The continuous tube is wound onto a protective core, wrapped with moisture-barrier film, and secured with strapping bands for safe transportation.
5. Applications
5.1 HVAC & Independent Fresh Air Systems (DOAS)
In conventional fan coil independent fresh air systems, the stainless steel coil tube serves as the primary heat-exchange medium within air handling units (AHUs). The tube's continuous, seam-minimized construction ensures efficient thermal transfer between refrigerant and ambient air, while its corrosion resistance extends service life in humid indoor environments. The coil form facilitates rapid installation and reduces field labor costs.
5.2 Food & Beverage Processing
The hygienic surface finish and compliance with FDA/3-A sanitary standards make these coil tubes suitable for dairy processing lines, brewing systems, and CIP (Clean-In-Place) piping networks.
5.3 Chemical & Pharmaceutical Industries
AISI 316-grade coil tubing is employed in chemical transfer lines, reactor feed systems, and pharmaceutical clean-room piping where resistance to aggressive media and particulate generation are paramount.
5.4 Water Treatment & Desalination
Used in reverse osmosis (RO) pre-treatment systems, UV sterilization housings, and brine injection manifolds due to resistance to chloride-induced corrosion.
5.5 Solar Thermal & Geothermal Systems
The excellent thermal conductivity and wide temperature tolerance of austenitic stainless steel make coil tubing ideal for solar collector loops and geothermal heat exchange circuits.
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring traceability and performance assurance:
- ISO 9001:2015 — Quality Management System certification for consistent manufacturing processes.
- ISO 14001:2015 — Environmental Management System for sustainable production practices.
- ISO/IEC 17025 — Laboratory competence for in-house material testing and dimensional inspection.
- ASTM A778 — Standard specification for cold-drawn austenitic stainless steel tubing.
- ASME B36.19M — Standard for welded and seamless wrought austenitic stainless steel pipe dimensions.
- EN 10217-7 — European standard for austenitic stainless steel tubes for pressure purposes.
- GB/T 12771 — Chinese national standard for stainless steel welded tubes for fluid transport.
- Mill Test Certificates (MTC) — Provided per EN 10204 Type 3.1 for every shipment, including chemical analysis, mechanical test results, and dimensional verification data.
7. Unique Selling Points
Continuous Integrity: The coil tube format eliminates field welds and joint failures, providing a monolithic fluid pathway with superior leak resistance compared to segmented pipe assemblies.
Logistics Efficiency: Compact coil bundling reduces transport volume and weight per unit length, minimizing carbon footprint and warehousing requirements.
Multi-Grade Flexibility: Availability in AISI 304, 316, and 321 grades allows engineers to select the optimal corrosion-to-cost ratio for specific service conditions.
DOAS System Compatibility: Specifically engineered for integration into Dedicated Outdoor Air Systems and conventional fan coil units, ensuring optimal heat transfer coefficients and minimal pressure drop.
Full Traceability: Each coil is serialized with a unique batch number, enabling complete material traceability from raw strip mill certification through final delivery.
8. Technical Data Sheet Reference
For detailed metallurgical data, welding procedure specifications (WPS), and pressure-temperature rating charts, customers are advised to request the full Technical Data Sheet (TDS) directly from Wenzhou Jixing Metal Materials Co., Ltd. Custom specifications, including non-standard dimensions, special surface treatments, and OEM branding, are available upon request with a minimum order quantity (MOQ) subject to quotation.