Stainless Steel Coil Tube (Coiltube) — Heat Carrier Furnace Application
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered coiled tubing product designed for high-temperature thermal systems, particularly fuel-fired hot oil furnaces (hot carrier oil heating systems). The coil tube serves as a critical heat transfer element within the furnace chamber, where thermal energy from combustion gases is efficiently transferred to the circulating thermal oil medium. The product is engineered to withstand sustained exposure to elevated flue gas temperatures while maintaining structural integrity, dimensional stability, and corrosion resistance over extended service cycles.
This coil tube product line is specifically optimized for use in coil-type fuel-fired hot oil furnaces (盘管式燃油热载体炉), where the serpentine coil arrangement maximizes the heat exchange surface area within a compact furnace volume. The design facilitates uniform heat distribution and minimizes thermal stress concentration at bend radii.
Material & Properties
Base Material Composition
The coil tube is fabricated from high-grade austenitic stainless steel, predominantly selected from the following grades depending on the application temperature and chemical environment:
- 304 (UNS S30408) — General-purpose austenitic stainless steel with excellent corrosion resistance and formability
- 321 (UNS S32100) — Titanium-stabilized variant offering superior resistance to intergranular corrosion at elevated temperatures (up to 870°C)
- 316L (UNS S31603) — Low-carbon molybdenum-bearing grade for enhanced pitting and crevice corrosion resistance in aggressive environments
- 310S (UNS S31008) — High-temperature grade suitable for sustained service up to 1150°C in oxidizing atmospheres
Mechanical Properties (Typical, Annealed Condition)
| Property | 304 | 321 | 316L | 310S |
|---|---|---|---|---|
| Tensile Strength (MPa) | ≥520 | ≥485 | ≥485 | ≥515 |
| Yield Strength (0.2% Offset, MPa) | ≥205 | ≥205 | ≥170 | ≥205 |
| Elongation (%) | ≥40 | ≥40 | ≥40 | ≥40 |
| Maximum Service Temperature (°C) | 870 | 982 | 870 | 1150 |
| Thermal Conductivity at 100°C (W/m·K) | 16.3 | 16.3 | 16.3 | 21.5 |
| Linear Thermal Expansion (×10⁻⁶/K, 20–100°C) | 17.3 | 17.3 | 17.3 | 18.0 |
Chemical Composition Requirements (ASTM A213 / A269)
| Element | 304 | 321 | 316L | 310S |
|---|---|---|---|---|
| Carbon (C) max (%) | 0.08 | 0.08 | 0.03 | 0.08 |
| Chromium (Cr) (%) | 18.0–20.0 | 17.0–19.0 | 16.0–18.0 | 24.0–26.0 |
| Nickel (Ni) (%) | 8.0–10.5 | 9.0–12.0 | 10.0–14.0 | 19.0–22.0 |
| Molybdenum (Mo) (%) | — | — | 2.0–3.0 | — |
| Titanium (Ti) (%) | — | 5×C to 0.70 | — | — |
Specifications
| Parameter | Specification |
|---|---|
| Product Category | Stainless Steel Coil Tube (Coiltube) for Hot Carrier Oil Furnace |
| Tube Outer Diameter (OD) | Φ12 mm – Φ38 mm (customizable) |
| Wall Thickness | 1.0 mm – 4.0 mm |
| Bend Radius (R) | ≥3D (D = tube outer diameter), typically R = 50–150 mm |
| Coil Inner Diameter (ID) | Φ300 mm – Φ2000 mm |
| Coil Length (per unit) | 5 m – 50 m (configurable per furnace design) |
| Surface Finish | Pickled & Passivated (2B finish), Ra ≤ 0.8 μm |
| End Preparation | Plain end / Beveled end / Threaded end (per customer specification) |
| Applicable Standards | ASTM A213, ASTM A269, EN 10216-5, GB/T 12771 |
| Design Temperature Range | −40°C to 1150°C (grade-dependent) |
| Design Pressure | Up to 2.5 MPa (typical for hot oil circulation systems) |
| Heat Treatment | Solution Annealing (1050–1150°C) followed by air/water quench |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd |
Manufacturing Process
1. Raw Material Selection & Verification
Stainless steel seamless tubes or welded tubes conforming to ASTM A213/A269 specifications are sourced from certified mills. Each batch undergoes spectroscopic analysis (OES) for chemical composition verification and mechanical property testing prior to coil forming operations.
2. Coil Forming
The straight tube is cold-formed into a helical coil using precision CNC coil bending equipment. The bending process is controlled to maintain:
- Uniform bend radius with tolerance of ±1% of nominal
- Controlled ovality (eccentricity) at bends ≤ 5% of OD
- Wall thinning at outer bend radius ≤ 15% (per ASTM A269 requirements)
- Consistent pitch (helical spacing) throughout the coil length
3. Welding (for multi-piece assemblies)
Where coil length requires joining of multiple tube segments, orbital TIG welding (GTAW) is employed. Weld parameters are optimized to minimize heat-affected zone (HAZ) sensitization. Post-weld solution heat treatment restores full austenitic microstructure and corrosion resistance.
4. Heat Treatment & Solution Annealing
The formed coil is subjected to solution annealing at 1050–1150°C in a protective atmosphere (argon or vacuum) to dissolve any carbide precipitates formed during cold forming. This restores full ductility, eliminates residual stresses, and ensures maximum corrosion resistance.
5. Surface Treatment
Post-annealing pickling and passivation removes oxide scale and forms a protective chromium oxide layer. The surface is inspected for pitting, discoloration, or contamination.
6. Non-Destructive Testing (NDT)
- Helium Leak Testing — Ensures weld integrity and coil watertightness
- Ultrasonic Testing (UT) — Detects internal defects, laminations, or wall thinning
- Visual Inspection — Assessment of surface finish, dimensional accuracy, and weld quality
- Dimensional Inspection — Verification of OD, wall thickness, bend radius, and coil geometry
7. Final Inspection & Packaging
Each coil tube assembly is accompanied by a material traceability certificate (MTC), heat treatment records, NDT reports, and dimensional inspection data. Coils are packaged with protective end caps and corrosion-inhibiting wrapping for transit.
Applications
Primary Application: Hot Carrier Oil Furnace Systems
The coil tube is the principal heat exchange component in coil-type fuel-fired hot oil furnaces (盘管式燃油热载体炉). In this configuration:
- Combustion gases from a fuel burner (natural gas, diesel, or heavy oil) flow through the furnace chamber
- Thermal energy is transferred from the flue gas to the stainless steel coil tube walls via convection and radiation
- Thermal oil (heat transfer fluid) circulates through the coil interior, absorbing heat for industrial process applications
- The flue gas temperature at the furnace outlet is calculated using empirical correlations that account for coil geometry, gas flow velocity, and heat transfer coefficients
Secondary Applications
- Industrial Process Heating — Polymer extrusion, rubber vulcanization, chemical reactors
- Boiler and Steam Generator Systems — Secondary heat exchangers in waste heat recovery
- Food Processing Equipment — Steam coils for pasteurization and sterilization
- Pharmaceutical Manufacturing — Clean-in-place (CIP) heating loops requiring sanitary-grade surfaces
- Textile Industry — Dyeing and finishing equipment requiring precise temperature control
- Wood Drying Kilns — Indirect heating systems using thermal oil circulation
Flue Gas Temperature Calculation — Engineering Considerations
Based on technical literature study, the flue gas outlet temperature (Tout) from a coil-type fuel-fired hot oil furnace can be estimated using a simplified calculation formula that incorporates:
- Combustion air excess ratio (λ)
- Fuel lower heating value (LHV)
- Heat transfer surface area of the coil tube (Acoil)
- Overall heat transfer coefficient (U)
- Thermal oil inlet temperature (Toil,in) and mass flow rate (ṁoil)
- Furnace heat loss coefficient
The coil tube geometry (diameter, wall thickness, total length, and number of turns) directly influences the effective heat transfer area and therefore the achievable flue gas outlet temperature. Optimized coil design minimizes flue gas temperature while ensuring complete fuel combustion and acceptable thermal oil outlet temperatures.
Quality Certifications & Compliance
- ISO 9001:2015 — Quality Management System certification for manufacturing processes
- EN 10204 3.1 — Material Test Certificate (MTC) per European standard
- ASTM A213 / A269 — Product specification compliance for stainless steel boiler, heat-exchanger, and condenser tubes
- GB/T 12771 — Chinese national standard for stainless steel seamless tubes for fluid transport
- CE Marking — Compliance with European Machinery Directive for pressure equipment applications
- PED 2014/68/EU — Pressure Equipment Directive compliance (where applicable for pressurized systems)
- Mill Test Reports — Chemical analysis, mechanical properties, and heat treatment documentation for each heat number
- NDT Reports — Helium leak test, ultrasonic examination, and visual inspection documentation
Unique Selling Points
- Precision Coil Geometry — CNC-controlled bending ensures uniform heat transfer performance across the entire coil assembly, eliminating thermal dead zones
- Grade Flexibility — Multiple stainless steel grade options allow tailoring to specific temperature and corrosion environments
- Thermal Stress Management — Solution-annealed microstructure provides excellent thermal fatigue resistance for cyclic heating/cooling duty
- Custom Engineering — Coil dimensions (OD, wall thickness, bend radius, total length) are fully customizable to match specific furnace chamber geometry and thermal load requirements