Stainless Steel Coil Tube (Coiltube) — Enamel-Lined PTFE Composite Coil Tube Condenser
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd (温州吉兴金属材料有限公司)
Product Catalogue No.: 1221
Classification: Literature & Technical Reference (文献学习)
Document Type: Technical Specification & Learning Summary
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular component fabricated in a continuous helical or spiral configuration, designed for integration into heat exchange systems. This product line is specifically developed for use in Enamel-Lined PTFE (Polytetrafluoroethylene) Composite Coil Tube Condensers — a hybrid heat exchanger architecture that combines the corrosion resistance of enamel glazing with the chemical inertness of PTFE and the thermal efficiency of stainless steel coil tubing.
Coil tubes serve as the primary heat transfer surface within condensers, evaporators, and reactors. Their compact spiral geometry maximizes surface-area-to-volume ratio, enabling high thermal flux density within confined installation footprints. The coil tube product from Wenzhou Jixing Metal Materials Co., Ltd is engineered to withstand aggressive chemical environments, high-pressure differentials, and thermal cycling conditions commonly encountered in petrochemical, pharmaceutical, and fine chemical processing industries.
2. Material & Properties
2.1 Base Material Composition
The coil tube is manufactured from austenitic stainless steel grades conforming to international standards. The primary material grades include:
- AISI 304 (UNS S30408): General-purpose austenitic stainless steel offering excellent corrosion resistance, formability, and weldability. Chromium content ≥18%, Nickel content ≥8%.
- AISI 316 (UNS S31608): Molybdenum-enhanced austenitic stainless steel providing superior resistance to pitting and crevice corrosion, particularly in chloride-containing environments. Molybdenum content 2.0%–3.0%.
- AISI 316L (UNS S31603): Low-carbon variant of 316L with carbon content ≤0.03%, suitable for applications requiring sensitization resistance at high temperatures.
- AISI 321 (UNS S32100): Titanium-stabilized austenitic stainless steel offering enhanced resistance to intergranular corrosion at elevated temperatures (450°C–850°C).
2.2 Composite Coating System
In the Enamel-Lined PTFE Composite configuration, the stainless steel coil tube undergoes a multi-layer coating process:
- Inner Layer — PTFE (Polytetrafluoroethylene): Applied via suspension or dispersion coating method. Provides exceptional chemical inertness against nearly all acids, bases, and organic solvents. Operating temperature range: −200°C to +260°C. Friction coefficient: 0.04–0.10 (one of the lowest known solid lubricants).
- Outer Layer — Enamel (Vitreous Enamel / Glass Fusing): Fused at temperatures of 800°C–850°C, creating a glass-to-steel bond with adhesion strength ≥15 N/mm². Provides mechanical protection and additional chemical barrier.
- Intermediate Adhesion Promoter Layer: A proprietary primer layer ensuring cohesive bonding between the PTFE coating and the enamel glaze, preventing delamination under thermal cycling.
2.3 Key Physical & Mechanical Properties
| Property | Specification | Test Standard |
|---|---|---|
| Density (Stainless Steel Base) | 7.90–8.00 g/cm³ | ASTM A270 |
| Thermal Conductivity (304 Grade, 20°C) | 16.3 W/(m·K) | ASTM E1461 |
| Thermal Conductivity (316 Grade, 20°C) | 14.6 W/(m·K) | ASTM E1461 |
| Thermal Expansion Coefficient (20°C–100°C) | 17.3 × 10⁻⁶ /°C | ASTM E228 |
| Tensile Strength (304 Grade) | ≥515 MPa | ASTM A270 |
| Tensile Strength (316 Grade) | ≥485 MPa | ASTM A270 |
| Yield Strength (0.2% Offset) | ≥205 MPa | ASTM A270 |
| Elongation at Break | ≥40% | ASTM A270 |
| PTFE Coating Thickness | 200–500 μm | ASTM D3639 |
| Enamel Layer Thickness | 0.3–0.8 mm | GB/T 9791 |
| Enamel Adhesion Strength | ≥15 N/mm² | GB/T 9791.4 |
| Operating Pressure (Typical) | 0.6–2.5 MPa (gauge) | ASME BPV Code VIII |
| Operating Temperature Range | −20°C to +260°C | Manufacturer Specification |
3. Specifications
3.1 Dimensional Parameters
| Parameter | Range / Value | Unit |
|---|---|---|
| Outer Diameter (OD) | 6.0 – 50.8 | mm |
| Wall Thickness | 0.5 – 2.0 | mm |
| Inner Diameter (ID) | 4.0 – 46.8 | mm |
| Coil Pitch (Spacing) | 8.0 – 30.0 | mm |
| Coil Diameter (Helix) | 50 – 600 | mm |
| Tube Length per Coil | 1 – 50 | m |
| Tolerance on OD | ±0.05 (Precision) / ±0.10 (Standard) | mm |
| Tolerance on Wall Thickness | ±10% (Standard) / ±5% (Precision) | % |
| Straightness Deviation | ≤1.0 | mm/m |
| End Form | Plain / Beveled / Flanged / Threaded | — |
3.2 Surface Finish
| Surface Condition | Roughness (Ra) | Application |
|---|---|---|
| Mill Annealed (Standard) | 0.5 – 1.6 | General heat exchange |
| Pickled & Passivated (P&P) | 0.2 – 0.8 | Pharmaceutical / food grade |
| Electropolished | 0.05 – 0.25 | Biochemical / ultra-pure |
| PTFE-Coated Interior | 0.1 – 0.5 (coating surface) | Corrosive chemical service |
3.3 Applicable Standards & Codes
- ASTM A270 / A270M: Standard Specification for Seamless and Wrought Austenitic Chromium-Stainless Steel Tubing for Boiler, Heat Exchanger, and Similar Heat Transfer Applications
- ASTM A554: Standard Specification for Seamless Austenitic Stainless Steel Tubing for Chemical and Heat-Transfer Service
- EN 10217-7: Heat-resistant, creep-resistant and high-strength steels — Seamless tubes for high temperature applications — Part 7: Technical delivery conditions for austenitic tubes
- GB/T 14976: Chinese National Standard for Cold-rolled (or Cold-drawn) Seamless Stainless Steel Tubes for Fluid Transport
- ASME BPV Code Section VIII: Rules for Construction of Pressure Vessels
- GB/T 9791: Chinese National Standard for Enamel-lined Steel Equipment
- ASTM D3639: Standard Test Method for PTFE Coatings on Metal Substrates
4. Manufacturing Process
4.1 Process Flow Overview
The manufacturing of the Stainless Steel Coil Tube for the Enamel-Lined PTFE Composite Condenser follows a rigorous multi-stage production sequence:
- Raw Material Inspection: Incoming stainless steel seamless tube billets or rolled coils undergo spectroscopic analysis (OES) to verify chemical composition, and ultrasonic testing (UT) to detect internal defects. Material traceability is maintained through heat-number documentation.
- Pipe Forming & Coiling: Seamless or welded stainless steel tubes are fed through precision coiling machines equipped with CNC-controlled rollers. The coil pitch, helix diameter, and winding tension are programmatically controlled to ensure dimensional accuracy. Cold coiling is performed at ambient temperature to preserve the annealed microstructure of the austenitic steel.
- Intermediate Annealing (if required): For coils exceeding 15 m in length, stress-relief annealing is performed at 1050°C–1100°C in a controlled atmosphere (argon or vacuum) furnace, followed by rapid quenching to prevent chromium carbide precipitation at grain boundaries.
- Pickling & Passivation: The coiled tube is immersed in a mixed acid solution (HNO₃ + H₂SO₄) at 60°C–80°C to remove mill scale and surface oxides. Subsequent passivation with 20%–30% nitric acid solution forms a chromium-rich passive film (Cr₂O₃) enhancing corrosion resistance.
- PTFE Coating Application: The interior surface of the coil tube receives PTFE coating via one of the following methods:
- Suspension Coating: PTFE suspension (solid content 35%–40%) is applied by electrostatic spraying or dip-coating, followed by sintering at 280°C–320°C for 15–30 minutes.
- Dispersion Coating: PTFE dispersion is electrostatically applied to the tube interior, achieving uniform film thickness of 100–300 μm per pass.
- PTFE Impregnation: For porous pre-treatment, PTFE emulsion is vacuum-impregnated into micro-pores created by sandblasting, followed by thermal sintering.
- Enamel Application & Firing: The exterior surface receives vitreous enamel coating by dip-coating or spray application. The enamel slurry (glass frit + filler + binder) is applied at a thickness of 0.3–0.8 mm. The coil tube is then fired in a continuous belt furnace at 800°C–850°C for 30–60 minutes, achieving glass-to-steel fusion with bond strength ≥15 N/mm².
- Quality Inspection & Testing: Finished coil tubes undergo comprehensive inspection including:
- Visual inspection for coating uniformity, pinholes, and defects
- High-voltage (HV) spark test at 15–30 kV for enamel integrity
- Hydrostatic pressure test at 1.5× working pressure for 30 minutes
- Coating thickness measurement by magnetic induction or eddy current methods
- Adhesion testing per ASTM D3359 (cross-cut method) or pull-off method
- Dimensional verification using laser scanning or CMM (Coordinate Measuring Machine)
- Packaging & Dispatch: Coiled tubes are wound onto wooden spools or steel drums with protective end caps. Desiccant packs are included to prevent moisture ingress during transit. Each unit is labeled with product identification, heat number, and inspection certificate reference.
4.2 Key Manufacturing Technologies
- Computer Numerical Control (CNC) Coiling: Ensures repeatable coil geometry with pitch accuracy of ±0.5 mm and helix diameter accuracy of ±1.0 mm.
- Continuous Belt Firing Furnace: Provides uniform thermal profile across the enamel firing zone, minimizing thermal distortion and ensuring consistent glass-to-steel bond quality.
- Electrostatic PTFE Spraying: Achieves uniform coating distribution with transfer efficiency >85%, minimizing overspray and material waste.
- Online Ultrasonic Thickness Gauging: Real-time monitoring of wall thickness during the coiling process, enabling immediate corrective action for out-of-tolerance conditions.
5. Applications
5.1 Primary Application Domains
- Petrochemical Industry: Condensers for distillation columns, overhead vapor condensers, and reflux systems processing hydrocarbons, aromatics, and halogenated compounds.
- Pharmaceutical Manufacturing: Heat exchangers for solvent recovery, crystallization processes, and sterilization-in-place (SIP) systems requiring PTFE-grade chemical compatibility.
- Food & Beverage Processing: Pasteurization condensers, juice concentration systems, and dairy processing heat exchangers meeting FDA/3-A sanitary standards.
- Environmental Protection: Flue gas desulfurization (FGD) systems, wastewater treatment heat recovery, and scrubber condensation units.
- Chemical Synthesis: Reactor cooling coils for exothermic reactions involving strong acids (H₂SO₄, HNO₃, HF), alkalis (NaOH, KOH), and organic solvents.
- Textile Industry: Dyeing and finishing process condensers handling acidic and