Stainless Steel Coil Tube (Coiltube) — Product No. 1301
Product Overview
The Stainless Steel Coil Tube (Coiltube) produced by Wenzhou Jixing Metal Materials Co., Ltd. is a continuous-length, coiled stainless steel tubing product engineered for demanding industrial, HVAC, and heating applications. Unlike straight-length stainless steel tubes, coil tubes are wound into compact, continuous coils that maximize material utilization, reduce welding joints, and facilitate automated forming and processing downstream. This product is particularly suited for applications requiring high thermal conductivity, corrosion resistance, and mechanical integrity under cyclic thermal loading conditions — properties that are critical in fan coil unit (FCU) systems and district heating renovation projects.
Coil tubes represent a significant advancement in stainless steel tube manufacturing, offering continuous production capability at high speeds, superior dimensional consistency, and reduced material waste compared to traditional cut-length tube production. The coil configuration also simplifies logistics and storage, as large quantities of tubing can be stored in a single coil package rather than numerous individual lengths.
Material & Properties
Base Material Grades
- Austenitic Stainless Steels: Primarily Grade 304 (UNS S30408) and Grade 316 (UNS S31608), providing excellent general corrosion resistance and formability.
- Super Austenitic Grades: Grade 316L (UNS S31603) with reduced carbon content (< 0.03% C) for enhanced resistance to intergranular corrosion (IGC) in welding and heat-affected zones.
- Specialty Grades (upon request): Grade 321 (UNS S32100) with titanium stabilization, and Grade 347 (UNS S34700) with niobium stabilization, suitable for elevated-temperature service exceeding 600 °C.
Mechanical Properties (Typical, Annealed Condition)
- Tensile Strength (UTS): ≥ 515 MPa (Grade 304); ≥ 515 MPa (Grade 316)
- Yield Strength (0.2% Offset): ≥ 205 MPa
- Elongation at Break: ≥ 40% (per ASTM A269 / EN 10216-5)
- Hardness (Rockwell B): 80–95 HRB (annealed); up to 35 HRC (cold-worked/hardened condition)
- Density: 7.93 g/cm³
Chemical Composition (Typical, wt%)
- Carbon (C): ≤ 0.08% (standard); ≤ 0.03% (low-carbon/L grade)
- Chromium (Cr): 18.0–20.0% — primary contributor to passive oxide film formation and general corrosion resistance.
- Nickel (Ni): 8.0–10.5% — stabilizes the austenitic crystal structure (Face-Centered Cubic, FCC) and enhances ductility.
- Molybdenum (Mo): 2.0–3.0% (Grade 316) — improves pitting and crevice corrosion resistance, particularly in chloride-containing environments.
- Titanium (Ti): 5×(C−0.02)% to 0.70% (Grade 321) — carbide scavenger preventing chromium depletion at grain boundaries.
Corrosion Resistance Characteristics
- Excellent resistance to atmospheric corrosion, dilute organic and inorganic acids, and alkaline solutions.
- Grade 316/316L offers superior resistance to pitting corrosion in marine and chemical processing environments (Critical Pitting Temperature, CPT: > 35 °C in 3.5% NaCl solution).
- Passive film (Cr₂O₃) self-repairs in oxidizing environments, ensuring long-term service life without maintenance coatings.
Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ 6 mm – Φ 51 mm (custom sizes available) | ASTM A269 / EN 10216-5 |
| Wall Thickness (WT) | 0.5 mm – 3.0 mm | ASTM A269 / EN 10216-5 |
| Coil Length (Continuous) | 200 m – 1,000 m (typical); up to 2,000 m on request | Manufacturer Specification |
| Coil Inner Diameter (ID) | Φ 500 mm – Φ 1,000 mm | Manufacturer Specification |
| Coil Weight | 500 kg – 2,000 kg (depending on tube size) | Manufacturer Specification |
| Tolerance on OD | ± 0.05 mm (precision); ± 0.1 mm (standard) | ASTM A269 |
| Tolerance on Wall Thickness | ± 10% (standard); ± 5% (precision) | ASTM A269 |
| Surface Finish | Mirror Polish (Ra ≤ 0.25 μm), Electropolished, No. 4 Brushed, 2B (Cold-Rolled & Annealed) | ASTM A269 / ISO 11404 |
| End Form | Open End, Flat-End, Beveled End (45°), Threaded (BSP/NPT) | ASTM A269 / EN 10226 |
| Heat Treatment | Solution Annealed (1050–1150 °C) + Water Quenched; Stress-Relieved; Cold-Worked (1/4-HW, 1/2-HW, HW) | ASTM A269 |
| Welding Type (if welded) | Continuous TIG Welding (GTAW), Orbital TIG, Laser Welding | ISO 13707 |
| Heat Exchanger Type | Plate & Fin, Double-Pipe, Spiral-Wound, Air-Cooling Coil | ASHRAE 90.1 / EN 14511 |
| Maximum Operating Temperature | −196 °C to +870 °C (Grade 304); −196 °C to +870 °C (Grade 316) | ASTM A269 |
| Maximum Operating Pressure | Up to 20 MPa (design-dependent) | ASME B31.3 |
| Applicable Standards | ASTM A269, ASTM A270, EN 10216-5, EN 10217-7, ISO 13707, JIS G3459 | — |
Manufacturing Process
1. Raw Material Preparation
High-purity stainless steel billets or continuous casting slabs are sourced from certified producers with traceable chemical composition documentation. Incoming material undergoes rigorous inspection including Visual Testing (VT), Ultrasonic Testing (UT) for internal defects, and Spectrographic Analysis (OES) for chemical verification. Non-conforming material is rejected at this stage to ensure downstream quality consistency.
2. Hot Rolling & Seamless Tube Formation
For seamless coil tubes, the manufacturing begins with hot rolling of slabs into round or square billets. The billets are then pierced through a mandrel on a rotary piercing mill (RPM) or continuous tube mill to form hollow tubes. The hot-rolled tube undergoes a series of hot-drawing or hot-rolling passes to achieve approximate final dimensions. Alternatively, for welded coil tubes, cold-rolled stainless steel strip is fed into a roll-forming machine where it is progressively shaped into a circular cross-section.
3. Cold Drawing & Sizing
The hot-rolled tube is annealed and pickled to remove scale and restore ductility. It is then cold-drawn through precision dies (plunger or capstan drawing) to achieve the required final dimensions with tight tolerances. For precision applications, multi-stage cold drawing with intermediate annealing cycles is employed to achieve dimensional accuracy within ± 0.05 mm. The cold working process introduces beneficial work hardening, improving the mechanical strength while maintaining adequate ductility.
4. Welding (for Welded Coil Tubes)
For welded coil tubes, the formed strip is welded along the longitudinal seam using one of the following methods:
- Transverse Arc Welding (TAW): Gas Tungsten Arc Welding (GTAW/TIG) with inert gas shielding (Argon or Helium). This is the most common method for stainless steel coil tubes, producing high-quality welds with minimal heat-affected zone (HAZ).
- Orbital TIG Welding: Automated circumferential welding for end joints in heat exchanger applications.
- Laser Welding: High-speed, narrow HAZ welding suitable for thin-wall tubes (< 1.0 mm) with superior weld aesthetics and minimal distortion.
Weld quality is verified through Radiographic Testing (RT), Dye Penetrant Testing (PT), or Eddy Current Testing (ECT) per ISO 13707 requirements.
5. Annealing & Surface Treatment
Following forming and welding, the coil tube undergoes solution annealing in a controlled-atmosphere furnace (hydrogen or vacuum) at temperatures between 1050 °C and 1150 °C. This treatment dissolves precipitated chromium carbides (Cr₂₃C₆), restores full austenitic microstructure, and eliminates residual stresses. The tube is then rapidly quenched in water or air to lock in the solution-treated condition. Post-annealing surface treatment includes:
- Pickling: Immersion in mixed acid bath (HNO₃ + HF or citric acid) to remove oxide scale.
- Passivation: Treatment with 20–30% nitric acid or citric acid to enhance the protective chromium oxide passive film.
- Polishing: Mechanical or electrochemical polishing to achieve mirror finish (Ra ≤ 0.25 μm) for sanitary and pharmaceutical applications.
6. Coiling & Packaging
The finished tube is wound into coils of the specified inner diameter using an automated coiler. The coil is secured with steel strapping or bands and wrapped in protective film or paper to prevent surface damage during handling and transport. Each coil is labeled with product identification, heat number, chemical composition, mechanical properties, and applicable standard reference.
Applications
1. Heating, Ventilation & Air Conditioning (HVAC) Systems
Stainless steel coil tubes are extensively used in fan coil units (FCUs), air handling units (AHUs), and chiller coils for heating and cooling applications. Their high thermal conductivity (14–16 W/m·K for austenitic grades), combined with resistance to corrosion from condensate and humid air, makes them ideal for evaporator and condenser coils. In heating renovation projects, stainless steel coil tubes replace legacy copper coils, offering superior durability, longer service life, and reduced maintenance costs. The continuous coil form allows for efficient manufacturing of finned tube heat exchangers with minimal waste.
2. District Heating & Radiator Systems
In centralized district heating networks and building heating renovation projects, stainless steel coil tubes serve as efficient heat transfer elements. Their ability to withstand cyclic thermal loading (repeated heating and cooling) without fatigue failure, coupled with resistance to scaling and corrosion from treatment chemicals, ensures reliable long-term operation. The coil configuration facilitates the manufacture of compact, high-surface-area heat exchangers suitable for space-constrained installation environments.
3. Chemical Processing & Petrochemical Industry
Grade 316/316L coil tubes are employed in chemical reactors, heat exchangers, condensers, and process piping systems where resistance to aggressive chemical media (acids, alkalis, chlorides) is critical. The continuous coil form enables the production of complex heat exchanger geometries (spiral-wound, plate-fin) with high heat transfer efficiency.
4. Food Processing & Pharmaceutical Industry
Mirror-polished stainless steel coil tubes meet the stringent hygiene requirements of food processing (CIP/SIP compatible) and pharmaceutical manufacturing. The smooth surface finish (Ra ≤ 0.25 μm) prevents bacterial adhesion and facilitates automated cleaning-in-place (CIP) procedures. Applications include pasteurization coils, condensers, and process tubing in breweries, dairy plants, and bioreactor systems.
5. Marine & Offshore Engineering
Grade 316L and duplex stainless steel coil tubes are used in marine cooling systems, ballast water treatment, and offshore platform piping. Molybdenum-enhanced grades provide exceptional resistance to pitting and crevice corrosion in seawater environments, ensuring structural integrity over extended service periods.
6. Automotive & Aerospace
Lightweight, high-strength stainless steel coil tubes are used in automotive exhaust systems, turbocharger manifolds, and aerospace heat exchangers. The coil form allows for complex forming and bending operations required by modern vehicle architectures, while maintaining the mechanical properties necessary for high-temperature exhaust gas environments.
Quality Certifications
International Standards Compliance
- ASTM A269 / A269M: Standard Specification for Seamless and Wrought Steel Tube, Austenitic Cr-Ni Alloy (General Requirements).
- ASTM A270 / A270M: Standard Specification for Seamless and Welded Austenitic Chromium-Chromium-Nickel Stainless Steel Tubing for Chemical and Similar Severe Service.
- EN 10216-5: Technical Delivery Conditions for Seamless and Welded Tubes of Austenitic Stainless Steels for General Purposes.
- EN 10217-7: Technical Delivery Conditions for Seamless Tubes of Austenitic Stainless Steels for Pressure Purposes.
- ISO 13707: Welded Tubes and Pipes of Stainless Steel — Technical Delivery Conditions.
- JIS G3459: Japanese Industrial Standard for Stainless Steel Tubes.
- ASME SA-213: Standard Specification for Seamless Austenitic Chromium-Chromium-Nickel Alloy Heat-Exchanger and Heat-Tr ansformer Tubes.
Quality Management Systems
- ISO 9001:2015: Quality Management Systems — Requirements.
- ISO 14001:2015: Environmental Management Systems — Requirements.
- ISO 45