Stainless Steel Coil Tube — Industrial Coiled Tubing for HVAC & Process Applications
1. Product Overview
The Stainless Steel Coil Tube is a precision-engineered continuous tubular product formed into a helical coil configuration, manufactured from high-grade austenitic and duplex stainless steel grades. Unlike straight seamless or welded pipes, coil tubes are produced in long, uninterrupted lengths wound onto shipping coils, offering superior material utilization, reduced waste, and enhanced flexibility for downstream forming and bending operations. This product category is particularly critical in HVAC (Heating, Ventilation, and Air Conditioning) systems, where coiled tubing serves as the core heat exchange element in fan coil units, air handlers, and condensing systems.
Wenzhou Jixing Metal Materials Co., Ltd. supplies stainless steel coil tubes engineered to meet the rigorous demands of hygienic processing, chemical resistance, and thermal efficiency. The coiled format eliminates the need for field welding at coil lengths, reducing labor costs and improving system integrity. The product is designed with special consideration for hydraulic operating conditions, where flow dynamics, pressure differentials, and thermal cycling must be accurately modeled to ensure long-term reliability in fan coil unit systems and similar closed-loop hydraulic applications.
2. Material & Properties
Stainless steel coil tubes are fabricated from austenitic and duplex stainless steel grades that provide an optimal balance of corrosion resistance, mechanical strength, formability, and weldability. The following table outlines the key material grades available and their corresponding properties:
| Property | 304 / 304L (UNS S30400 / S30403) | 316L (UNS S31603) | 321 (UNS S32100) | Duplex 2205 (UNS S32205) |
|---|---|---|---|---|
| Standard Designation | ASTM A269 / ASME SA-269 | ASTM A269 / ASME SA-269 | ASTM A269 / ASME SA-269 | ASTM A269 / ASME SA-269 |
| Chromium Content (%) | 18.0 – 20.0 | 16.0 – 18.0 | 17.0 – 19.0 | 22.0 – 23.0 |
| Nickel Content (%) | 8.0 – 10.5 | 10.0 – 14.0 | 9.0 – 12.0 | 5.5 – 7.5 |
| Molybdenum Content (%) | — | 2.0 – 3.0 | — | 3.0 – 3.5 |
| Maximum Service Temperature (°C) | 870 | 870 | 900 | 300 (continuous) |
| Tensile Strength (MPa, min.) | 515 | 485 | 515 | 450 |
| Yield Strength (MPa, min.) | 205 | 170 | 205 | 450 |
| Elongation (%) | ≥ 40 | ≥ 35 | ≥ 40 | ≥ 20 |
| Pick Resistance (PREN) | 19 – 21 | 24 – 26 | 19 – 21 | 34 – 36 |
| Corrosion Resistance | General atmospheric, mild acids | Marine, chlorinated environments | High-temperature oxidation | Severe chloride, sour gas |
Key Material Characteristics:
- Corrosion Resistance: The passive chromium oxide layer (Cr₂O₃) provides self-healing protection against atmospheric, chemical, and electrochemical corrosion. 316L grade offers enhanced resistance to pitting and crevice corrosion in chlorinated and marine environments.
- Mechanical Integrity: The austenitic crystal structure ensures excellent ductility and formability, permitting tight bending radii without cracking or thinning — a critical requirement for coil tube applications involving serpentine or helical configurations.
- Hygienic Surface Finish: Available in electropolished (Ra ≤ 0.4 μm), passivated, or matte finishes to meet FDA, 3-A, and EHEDG standards for food-grade and pharmaceutical applications.
- Thermal Stability: Maintains dimensional stability and mechanical properties across a wide temperature range from cryogenic (-196 °C) to elevated service temperatures, making it suitable for thermal cycling environments.
3. Specifications
The following table presents the dimensional and performance specifications for standard stainless steel coil tube products:
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 3.00 mm – 25.40 mm (1/8" – 1") |
| Wall Thickness | 0.30 mm – 2.50 mm |
| Coil Diameter | 600 mm – 1,200 mm |
| Coil Length (Continuous) | 30 m – 300 m per coil (custom lengths available) |
| Manufacturing Standard | ASTM A269 / ASME SA-269, EN 10216-5, GB/T 14976 |
| Tolerance — OD | ±0.05 mm (precision grade); ±0.10 mm (standard grade) |
| Tolerance — Wall Thickness | ±0.03 mm (precision grade); ±0.05 mm (standard grade) |
| Surface Finish | Pickled & Passivated (P&P), Matte, Electropolished (Ra ≤ 0.4 μm), Mirror (Ra ≤ 0.2 μm) |
| Maximum Working Pressure | Up to 10.0 MPa (1450 psi), depending on OD and wall thickness |
| Maximum Service Temperature | Up to 870 °C (1600 °F) for austenitic grades |
| Minimum Bend Radius | 1.5 × OD (without springback compensation) |
| Hydrostatic Test Pressure | 1.5 × Maximum Working Pressure, per ASME B31.3 |
| Available Grades | 304, 304L, 316, 316L, 321, 310S, 316Ti, 2205 Duplex, 904L |
| Heat Treatment Condition | Solution Annealed (SA), Cold Worked (CW), Pickled & Passivated |
4. Manufacturing Process
The production of stainless steel coil tubes follows a rigorous multi-stage manufacturing process designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Procurement: Hot-rolled stainless steel strip is sourced from certified mills and subjected to incoming inspection for chemical composition (via OES — Optical Emission Spectroscopy), mechanical properties, and surface condition.
- Coiling & Straightening: The strip is uncoiled, straightened to remove mill curvature, and leveled to ensure uniform thickness and flatness prior to tube forming.
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Tube Forming (Cold Drawing or Seamless):
- Cold-Drawn Seamless: The flat strip is rolled into a tube shape using precision roll forming equipment, then welded using TIG (Tungsten Inert Gas) or laser welding technology. The weld seam is subsequently ground flush to achieve a near-seamless interior surface.
- Seamless Cold Drawing: A solid billet is pierced and cold-drawn through precision dies to produce true seamless tubing, which is then coiled. This method yields superior internal surface finish and eliminates weld-related stress concentrations.
- Precision Cold Drawing & Sizing: The formed tube passes through a series of precision dies and mandrels to achieve the target OD, wall thickness, and dimensional tolerances. This step also imparts work hardening for enhanced mechanical strength.
- Solution Annealing: The tube is heated to 1050–1150 °C in a controlled atmosphere furnace to relieve cold-work stresses, restore full ductility, and homogenize the microstructure. Rapid cooling (water quench or air quench) prevents sensitization and chromium carbide precipitation at grain boundaries.
- Pickling & Passivation: The annealed tube is immersed in a mixed acid solution (HNO₃/HF) to remove oxide scale and mill scale, followed by a passivation treatment to restore and enhance the natural chromium oxide passive film.
- Coiling: The finished tube is wound onto a shipping coil of the specified diameter using automated coiling equipment. The coil is secured with steel strapping and protective wrapping to prevent deformation during handling and transport.
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Quality Inspection & Testing:
- Dimensional Inspection: Automated laser gauging for OD and wall thickness along the full coil length.
- Hydrostatic Pressure Testing: 100% inline testing at 1.5× the maximum working pressure to verify weld integrity and absence of porosity or defects.
- Visual Inspection: Automated surface inspection systems detect scratches, dents, and surface inclusions.
- Chemical Analysis: Spectroscopic verification of alloy composition per ASTM E415.
- Mechanical Testing: Tensile testing per ASTM E8/E8M on representative samples.
5. Applications
Stainless steel coil tubes find extensive application across multiple industries, leveraging their corrosion resistance, mechanical strength, and hygienic properties:
5.1 HVAC & Thermal Management Systems
Coil tubes serve as the primary heat exchange element in fan coil units (FCUs), air handling units (AHUs), and condensing/evaporating coils. The coiled configuration maximizes heat transfer surface area within a compact footprint. In these applications, the tube must withstand repeated thermal cycling, condensation-induced corrosion, and continuous fluid flow under varying hydraulic conditions. Accurate system modeling — accounting for fluid dynamics, pressure drops, and heat transfer coefficients — is essential for optimizing fan coil performance and energy efficiency.
5.2 Food & Beverage Processing
Used in hygienic piping systems for dairy, brewing, and pharmaceutical processing where CIP (Clean-In-Place) and SIP (Sterilize-In-Place) protocols require seamless, corrosion-resistant, and easily cleanable tubing. Electropolished finishes prevent bacterial adhesion and facilitate thorough cleaning.
5.3 Chemical & Petrochemical Industry
316L and 904L grade coil tubes are deployed in chemical processing, acid handling, and desulfurization systems where resistance to aggressive media and high temperatures is paramount. Duplex 2205 grades offer enhanced chloride stress corrosion cracking resistance in sour gas environments.
5.4 Marine & Offshore Applications
Marine-grade 316L coil tubes are used in ballast water systems, seawater cooling circuits, and desalination plants where prolonged exposure to chloride-rich environments demands superior pitting and crevice corrosion resistance.
5.5 Medical & Pharmaceutical Equipment
High-purity coil tubing is integral to dialysis machines, medical gas delivery systems, and pharmaceutical manufacturing equipment, where biocompatibility and ultra-low particulate surface finishes are mandatory.
5.6 Heat Exchangers & Refrigeration
Coil tubes are extensively used in shell-and-tube heat exchangers, plate heat exchangers, and refrigeration evaporator/condenser coils, where their thermal conductivity and corrosion resistance ensure long service life under demanding thermal and chemical conditions.
6. Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and holds the following certifications and compliance standards:
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and customer satisfaction.
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to environmental responsibility and sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management System certification.
- CE Marking — Conformity with European Union directives for product safety, health, and environmental protection.
- ASME / ASTM Compliance — Products manufactured and tested in accordance with American Society of Mechanical Engineers and American Society for Testing and Materials standards.