Stainless Steel Spiral Coil Tube (Coiltube) — Technical Specification
1. Product Overview
The Stainless Steel Spiral Coil Tube (hereinafter referred to as "Coiltube" or "Spiral Coil Tube") is a continuous, helically wound tubular product manufactured by cold-forming stainless steel strip or seamless tube through a precision coil winding machine. Unlike straight pipe sections that require cutting and welding, the spiral coil tube is produced in a single uninterrupted length, eliminating longitudinal weld seams and thereby significantly enhancing structural integrity, pressure containment capability, and corrosion resistance.
This product line, developed and supplied by Wenzhou Jixing Metal Materials Co., Ltd., is engineered for applications demanding high flow efficiency, compact installation footprints, and superior mechanical performance under cyclic thermal and pressure loading. The coil tube is formed through a controlled spiral winding process in which the feed roller displacement parameters are precisely calculated to govern helix geometry, pitch consistency, and dimensional accuracy.
2. Material & Properties
2.1 Grade Composition
The Coiltube is manufactured from austenitic and duplex stainless steel grades conforming to international standards. Commonly utilized grades include:
- SAE 304 / UNS S30400 — General-purpose austenitic stainless steel with excellent corrosion resistance and formability.
- SAE 316L / UNS S31603 — Low-carbon austenitic grade with added molybdenum (Mo) content (2.0–3.0%) for enhanced resistance to pitting and crevice corrosion in chloride environments.
- SAE 321 / UNS S32100 — Stabilized grade with titanium (Ti) addition to prevent sensitization during high-temperature exposure.
- SAE 316Ti / UNS S31635 — Titanium-stabilized variant of 316L for elevated-temperature service.
- SAE 904L / UNS N08904 — High-alloy austenitic grade for aggressive chemical processing environments.
2.2 Mechanical Properties (Typical for SA 316L)
| Property | Specification Value | Test Standard |
|---|---|---|
| Tensile Strength (Ultimate) | ≥ 485 MPa (70,300 psi) | ASTM A270 / A269 |
| Yield Strength (0.2% Offset) | ≥ 170 MPa (24,650 psi) | ASTM A270 / A269 |
| Elongation (at Break) | ≥ 40% (min. 30% in finished product) | ASTM A270 |
| Hardness (Rockwell B) | ≤ 95 HRB | ASTM A270 |
| Density | 8.0 g/cm³ | — |
| Thermal Conductivity (at 20 °C) | 16.3 W/(m·K) | — |
| Thermal Expansion Coefficient (20–100 °C) | 17.3 × 10⁻⁶ /°C | — |
2.3 Chemical Composition (SAE 316L — Typical)
| Element | Specification (wt%) |
|---|---|
| Carbon (C) | ≤ 0.03 |
| Chromium (Cr) | 16.0 – 18.0 |
| Nickel (Ni) | 10.0 – 14.0 |
| Molybdenum (Mo) | 2.0 – 3.0 |
| Iron (Fe) | Balance |
| Chloride (Cl) | ≤ 0.03 |
| Sulfur (S) | ≤ 0.03 |
3. Specifications
3.1 Geometric and Dimensional Parameters
| Parameter | Range / Value | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ 3.0 mm – Φ 50.8 mm | ASTM A269 / A270 |
| Wall Thickness (WT) | 0.3 mm – 3.0 mm | ASTM A269 |
| Coil Mean Diameter | Φ 200 mm – Φ 6,000 mm (customizable) | Enterprise Standard |
| Helix Pitch (P) | 5 mm – 150 mm (adjustable per application) | Enterprise Standard |
| Helix Angle (α) | 1° – 45° (calculated from feed roller displacement) | Enterprise Standard |
| Continuous Length | Up to 500 m (single coil, no longitudinal weld) | — |
| Surface Finish | Bright Annealed (BA), No. 4 Brushed, or 2B Finish | ASTM A270 |
| Tolerance on OD | ± 0.05 mm – ± 0.15 mm (depending on diameter) | ASTM A269 |
| Tolerance on Wall Thickness | ± 10% of nominal | ASTM A269 |
3.2 Feed Roller Displacement Parameters
A critical differentiator of this Coiltube product lies in the precision calculation of the feed roller displacement parameters (进给辊位移参数) during the spiral winding process. These parameters govern the helix geometry and are derived from the following kinematic relationships:
| Parameter Symbol | Definition | Calculation / Relationship |
|---|---|---|
| F | Feed roller linear displacement per revolution | F = P / (2π) × d / D (where P is pitch, d is tube OD, D is coil mean diameter) |
| P | Helix pitch (axial advance per complete turn) | P = D × tan(α) |
| α | Helix angle (angle between tube axis and coil plane) | α = arctan(P / πD) |
| D | Coil mean diameter | Specified per design requirement |
| vf | Feed roller velocity | vf = F × n (where n is rotational speed of coil axis) |
| R | Forming ratio (bending radius to wall thickness) | R = d / (2 × t) — must exceed minimum forming limit to prevent cracking |
The feed roller displacement is calculated iteratively to account for material springback, plastic deformation during cold bending, and the accumulated strain along the coil length. The displacement profile is programmed into the CNC-controlled coil winding machine to ensure pitch uniformity within ± 0.5 mm over the entire coil length.
4. Manufacturing Process
4.1 Process Flow
- Material Inspection & Receiving: Incoming stainless steel seamless tube or precision-welded tube undergoes 100% visual inspection, dimensional verification (OD and WT via ultrasonic thickness gauge), and chemical composition confirmation (spectrometric analysis per ASTM E415).
- Pre-treatment & Surface Preparation: Tubes are degreased using ultrasonic cleaning baths and chemically passivated (nitric acid or citric acid passivation per ASTM A967) to remove surface contaminants and establish a protective chromium oxide film.
- Forming Die Setup & Parameter Programming: The coil winding machine's feed roller system is configured based on the calculated displacement parameters. Forming dies (typically 3-roll or 4-roll configuration) are set to the target OD and wall thickness with clearance compensation for springback.
- Spiral Winding (Cold Forming): The tube is fed through the forming rolls while the feed rollers advance the tube axially at a precisely controlled rate synchronized with the rotational speed of the coil mandrel. The helix is formed through controlled plastic deformation. The feed roller displacement is continuously monitored by encoders and feedback-controlled to maintain dimensional accuracy.
- Heat Treatment (if required): For applications requiring stress relief (e.g., high-pressure service), the formed coil may undergo post-forming annealing at 870–900 °C followed by controlled cooling, per ASTM A270 requirements.
- Final Inspection & Testing: Each coil undergoes hydrostatic pressure testing (typically 1.5× working pressure, per ASTM A269), dimensional verification (pitch, OD, WT at multiple points along the coil length), and surface inspection. Non-destructive testing (NDT) including eddy current (per ASTM E309) and dye penetrant inspection (per ASTM E165) is performed as specified.
- Packaging & Dispatch: Coils are wound onto protective cores, wrapped in moisture-barrier film, and packed in wooden crates or export-grade containers with desiccant for international shipment.
4.2 Key Process Parameters
| Process Stage | Critical Parameter | Control Range |
|---|---|---|
| Spiral Winding | Forming Roll Pressure | 15 – 80 kN (depending on tube size and grade) |
| Spiral Winding | Feed Roller Speed | 0.5 – 15.0 m/min |
| Spiral Winding | Coil Rotation Speed | 0.1 – 5.0 RPM |
| Spiral Winding | Springback Compensation | 2° – 8° overbend angle |
| Hydrostatic Testing | Test Pressure | 1.5 × MAOP (Maximum Allowable Operating Pressure) |
| Hydrostatic Testing | Hold Time | ≥ 30 seconds (min.) |
5. Applications
The stainless steel spiral coil tube is a versatile component employed across multiple industries where continuous, weld-free tubular geometry provides distinct advantages in fluid handling, heat exchange, and structural applications:
- Heat Exchangers & Refrigeration Systems: Spiral coil tubes serve as the primary heat transfer element in air-cooled heat exchangers, refrigeration evaporators/condensers, and cooling towers. The helical geometry maximizes surface area within a compact volume, enhancing heat transfer efficiency by 30–50% compared to straight tube arrangements.
- Chemical & Petrochemical Processing: Used in heat exchangers, reactors, and fluid transfer lines where resistance to aggressive chemical media (acids, chlorides, caustics) is paramount. Grades 316L and 904L are preferred for these applications.
- Food & Beverage Industry: Sanitary-grade coil tubes (BA finish, Ra ≤ 0.4 μm) are used in pasteurization systems, CIP (Clean-In-Place) loops, and process piping where hygienic standards (3-A Sanitary Standards, FDA 21 CFR) must be met.
- Pharmaceutical Manufacturing: GMP-compliant coil assemblies for sterile fluid transfer, steam sterilization loops, and bioreactor heat exchange systems.
- Power Generation: Spiral coils are employed in condensers, feedwater heaters, and desuperheaters in thermal power plants