Stainless Steel Coil Tube (Coiltube) — Product No. 289
1. Product Overview
The Stainless Steel Coil Tube (Coiltube), Product No. 289, is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd., a leading supplier of stainless steel pipe and tube solutions in China. This product is designed specifically for applications requiring efficient heat transfer and fluid conveyance in complex flow geometries, including but not limited to stirred tank reactors (STRs), heat exchangers, chemical processing systems, and process engineering equipment.
Coiltube products represent a specialized category within the stainless steel tube family, characterized by their helical or spiral wound configuration. The coiled geometry provides a significantly larger surface-to-volume ratio compared to straight tubes of equivalent length, making them particularly advantageous in heat exchange applications where maximizing thermal contact area is critical. The coil structure also introduces secondary flow patterns — including Dean vortices — that enhance turbulence and improve both convective heat transfer coefficients and mixing efficiency within confined geometries.
Based on rigorous Computational Fluid Dynamics (CFD) analysis and numerical simulation studies, the flow and heat transfer characteristics of coil tubes vary substantially depending on the coil structural parameters, including coil diameter, tube diameter, pitch, number of turns, and orientation. These numerical investigations have demonstrated that the Nusselt number (Nu) and friction factor (f) in coiled configurations are strongly influenced by the Darcy number (Da), Richardson number (Ri), and the Curvature ratio (D/d), where D is the coil mean diameter and d is the tube outer diameter. Understanding these relationships is essential for optimizing coil tube design in industrial applications.
2. Material & Properties
2.1 Base Material Options
Wenzhou Jixing Metal Materials Co., Ltd. offers Stainless Steel Coil Tubes in a range of austenitic stainless steel grades, each selected to meet specific corrosion resistance, mechanical strength, and temperature performance requirements:
- 304 / 304L (UNS S30400 / S30403) — The most versatile austenitic grade, offering excellent general corrosion resistance, formability, and weldability. Suitable for food-grade, pharmaceutical, and general chemical applications.
- 316 / 316L (UNS S31600 / S31603) — Enhanced resistance to pitting and crevice corrosion due to the addition of 2–3% molybdenum. Preferred for marine environments, chemical processing, and acidic media.
- 321 (UNS S32100) — Stabilized with titanium, providing superior resistance to intergranular corrosion at elevated temperatures (450–850 °C).
- 316Ti (UNS S31635) — Combines the molybdenum content of 316 with titanium stabilization for improved high-temperature strength and corrosion resistance.
- 904L (UNS N08904) — High-alloy austenitic grade with superior resistance to non-oxidizing acids and reducing environments.
2.2 Key Material Properties
| Property | 304L | 316L | 321 | 904L |
|---|---|---|---|---|
| Chromium (Cr) | 18–20% | 16–18% | 17–19% | 19–23% |
| Nickel (Ni) | 8–12% | 10–14% | 9–12% | 23–25% |
| Molybdenum (Mo) | — | 2–3% | — | 4–5% |
| Titanium (Ti) | — | — | 5 × (C − 0.02) min | — |
| Carbon (C) Max | 0.03% | 0.03% | 0.08% | 0.08% |
| Density (g/cm³) | 7.93 | 8.00 | 7.98 | 8.10 |
| Thermal Conductivity (W/m·K) @ 20 °C | 16.3 | 16.3 | 14.6 | 11.4 |
| Thermal Expansion (μm/m·K) @ 20–100 °C | 17.2 | 16.0 | 16.4 | 13.7 |
| Yield Strength (MPa) min | 170 | 170 | 205 | 205 |
| Tensile Strength (MPa) min | 485 | 485 | 515 | 550 |
2.3 Surface Finish Options
- 2B Finish — Cold-rolled, annealed, and pickled; standard industrial surface with moderate reflectivity.
- No. 4 Brushed Finish — Uniform matte appearance with fine parallel grain lines; suitable for visible applications.
- Electropolished (EP) — Electrochemical surface treatment achieving Ra ≤ 0.5 μm; meets FDA and pharmaceutical hygiene standards.
- Precision Ground Finish — Ra ≤ 0.2 μm; used in high-purity chemical and semiconductor applications.
3. Specifications
3.1 Geometric Dimensions
| Parameter | Specification Range | Standard Reference |
|---|---|---|
| Tube Outer Diameter (OD) | Φ 3 mm – Φ 108 mm | ASTM A213 / EN 10216-5 |
| Tube Wall Thickness | 0.3 mm – 6.0 mm | ASTM A213 / EN 10216-5 |
| Tube Inner Diameter (ID) | Calculated: ID = OD − 2 × Wall Thickness | — |
| Coil Mean Diameter (CMD) | Φ 50 mm – Φ 2000 mm | Custom specification |
| Coil Pitch (Center-to-Center) | 1.0 × OD – 10.0 × OD (adjustable) | Custom specification |
| Number of Turns | 1 turn – 500+ turns | Application-dependent |
| Tube Length per Coil | Up to 500 m per coil assembly | Custom specification |
| Overall Coil Height | Up to 3000 mm | Application-dependent |
| End Preparation | Plain, beveled, threaded, or flanged | ASME B1.20.1 / ASME B16.5 |
| Curvature Ratio (D/d) | 5 – 100 (typical range) | CFD-optimized |
3.2 Mechanical & Performance Parameters
| Parameter | Typical Value | Notes |
|---|---|---|
| Design Pressure | Up to 16 MPa (2320 psi) | Dependent on wall thickness and grade |
| Design Temperature | −196 °C to +650 °C | Cryogenic to high-temperature service |
| Heat Transfer Enhancement Factor | 1.3 – 2.5× (vs. straight tube) | Based on CFD numerical analysis |
| Pressure Drop Factor | 1.5 – 4.0× (vs. straight tube) | Function of curvature ratio and pitch |
| Surface-to-Volume Ratio Enhancement | Up to 3.0× (vs. equivalent straight tube) | Dependent on coil geometry |
3.3 Applicable Standards
- ASTM A213 — Standard Specification for Seamless Austenitic Stainless Steel Tubes for High-Temperature Service
- ASTM A554 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Similar Severe Service
- EN 10216-5 — Steel Tubes for Pressure Purposes — Non-heat-resistant Stainless Steel Tubes
- ISO 13975 — Nickel and Nickel Alloys — Welded Tubes for Pressure Purposes
- GB/T 12771 — Chinese National Standard for Stainless Steel Tubes for General Purpose
- GB/T 14976 — Chinese National Standard for Seamless Stainless Steel Tubes for Fluid Transport
4. Manufacturing Process
4.1 Process Flow
- Raw Material Procurement & Inspection — Ingot or coil stock from certified mills (e.g., Outokumpu, Voestalpine, Tsingshan) with full mill test certificates (MTC) verifying chemical composition and mechanical properties per ASTM/EN specifications.
- Hot Rolling or Cold Drawing — Production of seamless or welded precursor tubes. Seamless tubes are manufactured via the Plattner piercing process or rotary piercing, while welded tubes utilize Automatic Welding (AW) or TIG welding with full penetration.
- Heat Treatment (Annealing) — Solution annealing at 1040–1150 °C followed by rapid cooling (air or water quench) to achieve a fully austenitic microstructure with maximum ductility and corrosion resistance.
- Pickling & Passivation — Removal of oxide scale via controlled acid pickling (nitric/hydrofluoric acid blend), followed by passivation to establish a stable chromium oxide passive film (Cr₂O₃).
- Precision Coil Forming — The straight tube is fed through a precision multi-roll coiling machine equipped with CNC-controlled roll stations. The forming process maintains dimensional accuracy within ±0.1 mm tolerance while preventing ovality, kinking, or cold work hardening. The coiling radius is calculated based on the minimum bending radius for the specific tube geometry (typically 5–10 × OD for austenitic grades).
- Post-Forming Annealing (if required) — For applications requiring maximum ductility after forming, a post-forming stress relief anneal may be performed at 800–900 °C.
- End Preparation & Fitting — Cutting, beveling, threading, or flange welding of coil ends as specified. Flange welding is performed using Gas Tungsten Arc Welding (GTAW/TIG) with argon back purging to prevent oxidation of the weld root.
- Surface Treatment — Optional electropolishing, passivation, or specialized surface finishing to meet hygiene or corrosion requirements.
- Non-Destructive Testing (NDT) — Visual inspection, magnetic particle testing (MT) for surface defects, eddy current testing (ET) for subsurface integrity, and hydrostatic pressure testing per ASTM A213 requirements.
- Final Inspection & Packaging — Dimensional verification, surface quality assessment, chemical spot testing, and protective packaging (wooden crates with desiccant, or steel-to-steel wrapped coils with end caps).
4.2 CFD-Optimized Design Considerations
A distinguishing feature of Wenzhou Jixing's coil tube product line is the incorporation of numerical simulation data into the design and manufacturing process. Based on academic research into flow and heat transfer characteristics in stirred tanks under varying coil structures, the following design parameters are optimized:
- Coil Diameter-to-Tube Diameter Ratio (D/d): The curvature ratio significantly affects the secondary flow patterns (Dean vortices) within the coil. Numerical simulations indicate that D/d values between 10–30 provide optimal balance between heat transfer enhancement and acceptable pressure drop.
- Pitch Optimization: The coil pitch determines the spacing between adjacent turns, which affects both the external heat transfer to the surrounding fluid and the internal flow dynamics. CFD analysis reveals that a pitch of 2–4 × OD maximizes the local Nusselt number while minimizing inter-turn interference.
- Number of Turns & Configuration: Multi-turn helical coils, spiral coils, and segmented coil arrays exhibit different flow distribution characteristics within stirred tanks. Numerical analysis has shown that the heat transfer rate increases with the number of turns but exhibits diminishing returns beyond a critical turn count, depending on the Reynolds number (Re) of the bulk fluid.
- Orientation Effects: The vertical or horizontal orientation of the coil relative to the impeller flow field significantly influences the velocity field distribution and temperature uniformity within the stirred tank. Numerical models incorporating the k-ε turbulence model and standard wall functions have been employed to predict optimal coil placement.
5. Applications
5.1 Primary Applications
- Stirred Tank Reactors (STRs) — Jacketed or coil-heated reactors for chemical synthesis, polymerization, and biological fermentation. The coil tube