Stainless Steel Coil Tube (Coiltube) — Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered continuous-length tubing product formed into a helical coil configuration. This product category encompasses seamless and welded stainless steel tubes supplied in coiled form, designed for downstream applications requiring flexibility, ease of handling, and the ability to be cut to length or formed into specific geometries without the need for butt welding at intermediate joints.
Coiltube products are distinguished from straight-length tubing by their continuous, uninterrupted coil form, which reduces material waste, minimizes handling damage, and facilitates automated processing in high-volume manufacturing environments. The product range covers both plain seamless coil tubes and inner-threaded (helical finned) coil tubes, the latter engineered to enhance surface area and thermal transfer efficiency for heat exchanger and refrigeration applications.
2. Material & Properties
2.1 Base Material Grades
- ASTM A269 / AMS 5643 — 304 (UNS S30400): Austenitic stainless steel with 18% Chromium (Cr) and 8% Nickel (Ni). Offers excellent general corrosion resistance, weldability, and formability. Suitable for food processing, chemical, and architectural applications.
- ASTM A269 / AMS 5643 — 316 (UNS S31600): Austenitic stainless steel with 16–18% Cr, 10–14% Ni, and 2–3% Molybdenum (Mo). Provides superior resistance to pitting and crevice corrosion in chloride-containing environments.
- ASTM A213 — 321 (UNS S32100): Stabilized austenitic grade with Titanium (Ti) addition. Resistant to intergranular corrosion at elevated temperatures (450–850 °C).
- ASTM A213 — 316L (UNS S31603): Low-carbon variant of 316 with enhanced weldability and resistance to sensitization during welding operations.
- ASTM A269 — 904L (UNS N08904): High-alloy austenitic grade with elevated Ni and Mo content for extreme corrosion resistance in aggressive chemical environments.
2.2 Mechanical Properties (Typical for Grade 304)
- Tensile Strength (UTS): ≥ 515 MPa (74,700 psi)
- Yield Strength (0.2% Proof): ≥ 205 MPa (29,700 psi)
- Elongation (50 mm gauge length): ≥ 40%
- Hardness (HBW): ≤ 217 (annealed condition)
- Density: 8.0 g/cm³
- Thermal Conductivity (20 °C): 16.3 W/(m·K)
- Thermal Expansion Coefficient (20–100 °C): 17.3 × 10⁻⁶ /K
- Operating Temperature Range: −196 °C to +870 °C (continuous)
2.3 Surface Finish Options
- Pickled & Passivated (P&P): Standard matte finish; removes scale and oxide layers, restoring passive chromium oxide film.
- Polished (Mirror Finish): RA ≤ 0.05 μm; achieved through multi-stage mechanical polishing and electrolytic finishing.
- Brushed Finish: Unidirectional grain texture for aesthetic and anti-fingerprint applications.
- Bead Blasted: Uniform matte surface with enhanced fatigue resistance.
3. Specifications
| Parameter | Specification Range | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 3.0 mm – 159.0 mm (1/8" – 6") | ASTM A269, ASTM A213 |
| Wall Thickness (WT) | 0.3 mm – 6.0 mm (0.012" – 0.236") | ASTM A269, EN 10217-7 |
| OD Tolerance | ±0.1 mm (small OD); ±0.3 mm (large OD) | ASTM A269 |
| Wall Thickness Tolerance | ±10% of nominal (minimum ±0.05 mm) | ASTM A269, AMS 5643 |
| Coil Inner Diameter | 500 mm – 1,200 mm (20" – 48") | Manufacturer specification |
| Coil Length (per coil) | 100 m – 500 m (328 ft – 1,640 ft) | Manufacturer specification |
| Maximum Coil Weight | Up to 2,000 kg (4,400 lbs) | Manufacturer specification |
| Manufacturing Method | Seamless (Cold Drawn / Cold Rolled) or ERW (Electric Resistance Welded) | ASTM A269, ASTM A554 |
| End Condition | Plain end, Beveled, Threaded (NPT/BSP), or Formed | ASME B1.20.1, BS 84 |
| Heat Treatment | Annealed (Solution Annealed) at 1010–1150 °C, followed by water quench | ASTM A269 |
| Inner Thread Specification | Helical fin height: 0.5–1.5 mm; Fin pitch: 2.0–5.0 mm | Custom / OEM specification |
| Delivery Condition | Coiled on wooden spools or steel drums with protective wrapping | ISO 11607 (packaging) |
4. Manufacturing Process
4.1 Seamless Coil Tube Production
- Raw Material Preparation: Hot-rolled stainless steel billets or ingots conforming to ASTM A269 chemical composition requirements are inspected via spectrographic analysis (OES) and certified with mill test reports (MTR).
- Piercing & Hot Rolling: Billets are heated to 1,150–1,250 °C and pierced to form hollow rounds, followed by hot rolling or hot extrusion to reduce to semi-finished tube dimensions.
- Annealing (Intermediate): Tubes are annealed at 1,050–1,100 °C in a protective atmosphere (endothermic gas or vacuum) to relieve residual stresses and restore ductility.
- Pickling & Descaling: Acid pickling (mixed HNO₃/HF solution) removes scale and oxide layers formed during hot working.
- Cold Drawing / Cold Rolling: Tubes are drawn through calibrated dies with a lubricant (soap solution or phosphate coating) to achieve precise dimensional tolerances. Multiple passes are employed for thin-wall tubes (WT < 1.0 mm).
- Final Annealing: Solution annealing at 1,010–1,150 °C followed by rapid cooling to achieve the required mechanical properties and corrosion resistance.
- Coiling: Continuous-length tubes are coiled onto precision-wound spools using controlled tension to prevent deformation or ovality.
4.2 Inner Threaded Coil Tube — Finishing Process Quality Control
The finishing (精整) process for inner-threaded coil tubes is a critical quality control stage that determines the final dimensional accuracy, surface integrity, and functional performance of the product. Based on established quality control methodologies, the following control points are implemented:
- Pre-Finishing Inspection: Incoming tubes are verified for OD, WT, and surface condition using ultrasonic thickness gauges (UT) and visual inspection. Any tubes exceeding tolerance limits (±10% WT deviation) are rejected prior to threading.
- Helical Threading / Fin Forming: Internal helical fins are formed using precision rotary or rotary-perforation tooling. The threading depth, fin height, and pitch are controlled to ±0.1 mm tolerance. Tool wear is monitored via dimensional sampling at 15-minute intervals.
- Dimensional Verification: Post-threading inspection employs bore gauges and optical comparators to verify inner diameter (ID), fin height, and thread continuity. Statistical Process Control (SPC) charts (X̄-R charts) are maintained to detect process drift.
- Surface Integrity Check: Tubes are inspected for tool marks, burrs, and surface defects using borescopic examination. Eddy current testing (ECT) is performed on 100% of production to detect internal cracks or wall thinning.
- Final Cleaning & Passivation: Tubes undergo ultrasonic cleaning to remove metal chips and lubricant residues, followed by passivation treatment (5% HNO₃ solution, 20–30 minutes) to restore the protective chromium oxide layer.
- Packaging & Traceability: Each coil is labeled with heat number, lot traceability code, and inspection certificate. Protective end caps and moisture-absorbent desiccant packets are included.
4.3 Welded Coil Tube Production (ERW)
- Strip Uncoiling & Leveling: Cold-rolled stainless steel strip is uncoiled and leveled to ensure flatness and consistent thickness.
- Forming: Strip is progressively formed through a series of rolls into a tube shape.
- Welding: High-frequency electric resistance welding (ERW) fuses the seam with precise current and speed control.
- Weld Inspection: 100% ultrasonic weld testing (UT) or magnetic particle inspection (MPI) of the longitudinal seam.
- Heat Treatment & Sizing: Post-weld annealing and sizing to achieve final dimensions and mechanical properties.
- Coiling & Packaging: Similar to seamless production.
5. Applications
- Heat Exchangers & Refrigeration Systems: Inner-threaded coil tubes are used as condenser and evaporator tubes in air-conditioning units, chillers, and industrial refrigeration systems. The helical fins increase internal surface area by up to 200%, enhancing heat transfer coefficients.
- Automotive Industry: Coil tubes are used for automotive radiators, intercoolers, and fuel lines due to their formability and corrosion resistance.
- Food & Beverage Processing: 316L coil tubes are employed in hygienic fluid transfer lines, pasteurization systems, and CIP (Clean-In-Place) circuits where sanitary standards (FDA 21 CFR, EHEDG) are required.
- Pharmaceutical & Biotechnology: Precision-drawn coil tubes serve as components in bioreactors, chromatography columns, and sterile fluid distribution systems.
- Oil & Gas / Petrochemical: 904L and duplex stainless steel coil tubes are used in subsea pipelines, heat exchangers, and chemical processing units exposed to sour gas (H₂S) and chloride environments.
- Power Generation: Boiler tubes, superheater tubes, and condensate lines in fossil fuel and nuclear power plants.
- Architectural & Decorative: Coil tubes are formed into handrails, railings, furniture frames, and structural elements in architectural applications.
- Medical Equipment: Endoscope sheaths, surgical instrument tubing, and implant-grade fluid delivery lines.
6. Quality Certifications & Standards Compliance
| Certification / Standard | Scope of Compliance |
|---|---|
| ISO 9001:2015 | Quality Management System (QMS) certification covering all manufacturing and inspection processes |
| ISO 14001:2015 | Environmental Management System certification |
| ASTM A269 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Similar Severe Service |
| ASTM A213 | Standard Specification for Seamless Austenitic Stainless Steel Boiler, Heat-Exchanger, and Heat-Treating Tubes |
| EN 10217-7 | Non-alloy and alloy steel tubes for mechanical and thermal uses — Technical delivery conditions for austenitic stainless steel tubes |
| AMS 5643 / AMS 5663 | Aerospace Material Specifications for wrought austenitic stainless steel tubing |
| ASME BPE | Bioprocessing Equipment standard for pharmaceutical-grade tubing (where applicable) |