Stainless Steel Coil Tube (Coiltube) — Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd (Catalog No. 1439). Designed primarily for integration into coil-type and shell-and-tube (列管式) heat exchangers, this product represents a critical element in thermal management systems across chemical, pharmaceutical, food processing, and energy industries.
Unlike conventional straight tube bundles, coil tubes are formed into helical, spiral, or U-shaped geometries that maximize the heat transfer surface area within a compact footprint. This geometry facilitates enhanced turbulence and convective heat transfer coefficients, making coil tubes particularly advantageous in applications requiring high thermal efficiency with minimized pressure drop.
Key Distinction: The coil tube configuration described herein aligns with the principles outlined in the technical literature on Coil-Type and Shell-and-Tube Glass Heat Exchangers, which emphasizes the synergistic relationship between tube geometry, material integrity, and thermal performance in heat exchange systems.
2. Material & Properties
2.1 Base Material
Coil tubes are fabricated from high-purity austenitic stainless steel grades, selected based on the operational environment and corrosive media encountered:
- SAE 304 / AISI 304 (UNS S30400): General-purpose corrosion resistance; carbon ≤ 0.08%
- SAE 304L / AISI 304L (UNS S30403): Low-carbon variant (C ≤ 0.03%) for welding-intensive applications
- SAE 316 / AISI 316 (UNS S31600): Enhanced chloride resistance with Mo (2.0–3.0%) addition
- SAE 316L / AISI 316L (UNS S31603): Low-carbon 316 for severe corrosive environments
- SAE 321 / AISI 321 (UNS S32100): Stabilized with Ti for elevated-temperature service
- SAE 310S / AISI 310S (UNS S31008): High-temperature oxidation resistance (up to 1150°C)
2.2 Physical & Mechanical Properties (Typical — Grade 304/316)
| Property | Grade 304 | Grade 316 | Test Standard |
|---|---|---|---|
| Density (kg/m³) | 7,930 | 8,000 | ASTM A213 |
| Thermal Conductivity (W/m·K, 20°C) | 16.3 | 16.3 | ASTM E153 |
| Specific Heat (J/kg·K, 20°C) | 500 | 500 | ASTM E1225 |
| Tensile Strength (MPa, min) | 515 | 515 | ASTM A213/A269 |
| Yield Strength (MPa, min) | 205 | 205 | ASTM A213/A269 |
| Elongation (%) | ≥ 40 | ≥ 40 | ASTM A213/A269 |
| Maximum Service Temperature (°C) | 870 | 870 | ASME BPV Code |
| Minimum Service Temperature (°C) | −196 | −196 | ASTM A213 |
| Corrosion Resistance (Pitting, PREN) | 18–20 | 24–26 | ASTM G48 |
2.3 Surface Finish Options
- 2B Annealed: Standard mill finish, Ra ≤ 0.5 μm
- Pickled & Passivated: Chromia-rich passive layer for enhanced corrosion resistance
- Electropolished (EP): Ra ≤ 0.25 μm; suitable for pharmaceutical and food-grade applications (3-A Sanitary Standard)
- Bearings-Grade Polished: Ra ≤ 0.1 μm; for ultra-pure process streams
3. Specifications
3.1 Dimensional Parameters
| Parameter | Specification Range | Tolerance | Standard Reference |
|---|---|---|---|
| Outer Diameter (OD) | 6.0 – 50.8 mm (¼" – 2") | ±0.1 mm | ASTM A213 / A269 |
| Wall Thickness | 0.5 – 4.0 mm | ±10% of nominal | ASTM A213 |
| Coil Pitch (Center-to-Center) | 15 – 200 mm (configurable) | ±0.5 mm | Manufacturer Spec. |
| Coil Diameter | 100 – 2000 mm | ±2 mm | Manufacturer Spec. |
| Number of Turns | 1 – 500+ | ±1 turn | Per Customer Drawing |
| Tube Length (Developed) | 1 – 500 m (per coil) | ±1% | Per Order |
| End Preparation | Plain, Beveled (37°/60°), or Flanged | Per ASME B16.25 | ASME B16.25 |
| Heat Treatment | Solution Annealed (1050–1150°C) + Water Quenched | — | ASTM A213 |
3.2 Chemical Composition (Typical, wt%)
| Element | C | Mn | P | S | Si | Cr | Ni | Mo | N |
|---|---|---|---|---|---|---|---|---|---|
| 304 | ≤0.08 | ≤2.00 | ≤0.045 | ≤0.030 | ≤1.00 | 18.0–20.0 | 8.0–10.5 | — | — |
| 316 | ≤0.08 | ≤2.00 | ≤0.045 | ≤0.030 | ≤1.00 | 16.0–18.0 | 10.0–14.0 | 2.0–3.0 | — |
| 316L | ≤0.03 | ≤2.00 | ≤0.045 | ≤0.030 | ≤1.00 | 16.0–18.0 | 10.0–14.0 | 2.0–3.0 | — |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Procurement: Cold-rolled stainless steel strip or seamless pipe stock sourced from certified mills (e.g., Outokumpu, POSCO, Tsingshan), accompanied by full mill test certificates (MTC, EN 10204 3.1).
- Coil Forming (Tube Coiling): Straight tubes are cold-formed into helical coils using CNC-controlled coiling machines. The forming process maintains dimensional accuracy and prevents work-hardening-induced residual stresses.
- Heat Treatment (Solution Annealing): Coils are solution-annealed at 1050–1150°C followed by rapid water quenching to restore full austenitic microstructure, eliminate carbide precipitation, and ensure maximum ductility and corrosion resistance.
- Pickling & Passivation: Immersion in mixed acid solutions (HNO₃/HF or HNO₃/HCl) to remove scale and oxide films, followed by passivation to establish a stable chromium oxide (Cr₂O₃) surface layer.
- Surface Finishing (Optional): Electropolishing or mechanical polishing to achieve specified surface roughness (Ra) for sanitary or ultra-pure applications.
- Non-Destructive Testing (NDT): 100% eddy current testing (ECT) for wall thickness and internal defect detection; hydrostatic testing at 1.5× working pressure for pressure integrity verification.
- Dimensional Inspection: CMM (Coordinate Measuring Machine) verification of coil geometry, OD, wall thickness, and pitch accuracy.
- Final Packaging & Dispatch: Protective end caps, moisture-proof wrapping, and wooden crate or pallet packaging for shipment.
4.2 Critical Process Controls
- Coil Forming Tension Control: Closed-loop servo systems ensure uniform bending radius and prevent ovality exceeding 1% of OD.
- Interpass Temperature Monitoring: During multi-pass coiling, interpass temperatures are maintained below 300°C to prevent sensitization (chromium carbide precipitation at 450–850°C).
- Grain Structure Control: Solution annealing parameters are calibrated to achieve ASTM E112 grain size of ≥ 5 for optimal fatigue resistance.
5. Applications
5.1 Heat Exchanger Systems
Coil tubes serve as the primary heat transfer elements in the following heat exchanger configurations, as referenced in the study of Coil-Type and Shell-and-Tube Glass Heat Exchangers:
- Coil-Type (盘管式) Heat Exchangers: Helical coils immersed in liquid baths for heating/cooling of process fluids; commonly used in chemical reactors, reboilers, and condensers.
- Shell-and-Tube (列管式) Heat Exchangers: Coil tubes arranged in tubular bundles within a pressure shell, facilitating shell-side and tube-side heat exchange in power generation, petrochemical refining, and HVAC systems.
- Glass-Lined Heat Exchangers: Where glass-lined steel provides additional chemical inertness, stainless steel coil tubes may serve as internal heating/cooling elements.
5.2 Industry-Specific Applications
| Industry | Application | Recommended Grade | Operating Conditions |
|---|---|---|---|
| Chemical Processing | Reactor coils, heat recovery exchangers | 316 / 316L | 50–300°C; acidic/alkaline media |
| Pharmaceutical | CIP/SIP heating coils, pasteurization | 316L (EP finish) | 80–150°C; GMP-compliant |
| Food & Beverage | Pasteurization, sterilization, UHT processing | 304L / 316L (EP finish) | 60–140°C; 3-A Sanitary |
| Petrochemical | Crude oil preheating, distillation coils | 316 / 321 | 200–450°C; H₂S/SO₂ environments |
| Power Generation |