Stainless Steel Cooling Coil Tube — Industrial Roasting Furnace Application
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. (温州吉兴金属材料有限公司)
Product Reference No.: 241
Classification: Technical Literature & Engineering Application Research
1. Product Overview
The Stainless Steel Cooling Coil Tube (盘管, Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed for high-temperature thermal management applications, particularly within industrial roasting furnaces (焙烧炉, Roasting Furnace). These coil tubes serve as critical heat exchange elements, circulating cooling medium (typically water or thermal oil) through serpentine-configured tubing to dissipate intense radiant and convective heat loads generated during ore processing, calcination, and sintering operations.
This product line has been the subject of rigorous engineering research, specifically documented in the technical study titled "109 m² Roasting Furnace Cooling Coil Tube Leakage Analysis and Research on Extending Coil Tube Service Life". The findings from this research have been integrated into subsequent manufacturing iterations, resulting in enhanced durability, reduced failure rates, and significantly extended operational lifecycles under severe thermal cycling conditions.
Unique Selling Points
- Extended Service Life: Incorporates metallurgical optimizations derived from failure analysis of 109 m² roasting furnace installations, reducing premature leakage incidents by up to 60%.
- Thermal Stability: Maintains structural integrity under continuous operating temperatures of 800–1200°C on the hot side, withstanding repeated thermal cycling without significant creep deformation.
- Leakage Resistance: Enhanced weld integrity and wall thickness uniformity minimize through-wall corrosion and stress corrosion cracking (Stress Corrosion Cracking, SCC).
- Custom Coil Configuration: Available in customized coil diameters, pitch configurations, and layout geometries tailored to specific furnace architecture.
2. Material & Properties
The coil tubes are fabricated from high-performance austenitic and austenitic-ferritic stainless steel grades selected for their exceptional resistance to oxidation, scaling, and thermal fatigue in aggressive industrial atmospheres.
Primary Material Grades
- 310S (UNS S31008): General-purpose high-temperature coil tube material with excellent oxidation resistance up to 1150°C.
- 309S (UNS S30908): Enhanced nickel content for superior resistance to thermal cracking and scaling at elevated temperatures.
- 347H (UNS S34709): Columbium-stabilized grade offering superior resistance to intergranular corrosion and sensitization during welding.
- 321H (UNS S32109): Titanium-stabilized grade for applications requiring resistance to chlorinated environments.
- Super Alloy Options: Custom grades including Incoloy 800H, Alloy 617, and Hastelloy for extreme-temperature and highly corrosive service conditions.
Key Mechanical Properties (Typical, Annealed Condition)
| Property | Grade 310S | Grade 309S | Grade 347H |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 515 | ≥ 515 | ≥ 485 |
| Yield Strength (MPa) | ≥ 205 | ≥ 205 | ≥ 170 |
| Elongation (%) | ≥ 35 | ≥ 35 | ≥ 40 |
| Maximum Continuous Service Temperature (°C) | 1150 | 1100 | 900 |
| Thermal Expansion Coefficient (×10⁻⁶/°C) | 17.0 | 16.5 | 17.3 |
| Thermal Conductivity (W/m·K, at 100°C) | 24.7 | 22.0 | 25.4 |
Chemical Composition (wt%, Typical)
| Element | 310S | 309S | 347H |
|---|---|---|---|
| C | ≤ 0.08 | ≤ 0.08 | ≤ 0.08 |
| Cr | 24.0–26.0 | 22.0–24.0 | 17.0–19.0 |
| Ni | 19.0–22.0 | 12.0–15.0 | 9.0–13.0 |
| Nb (Columbium) | — | — | 10×C to 1.0 |
| Si | ≤ 1.5 | ≤ 1.0 | ≤ 1.0 |
| Mn | ≤ 2.0 | ≤ 2.0 | ≤ 2.0 |
3. Specifications
| Parameter | Specification / Range |
|---|---|
| Outer Diameter (OD) | Φ25 mm – Φ57 mm (customizable up to Φ114 mm) |
| Wall Thickness | 1.5 mm – 6.0 mm (minimum 2.5 mm recommended for furnace service) |
| Coil Bend Radius | ≥ 3.0 × OD (to minimize residual stress and prevent cracking) |
| Coil Pitch (Center-to-Center) | 50 mm – 200 mm (configurable per furnace design) |
| Tube Length per Coil | 3 m – 50 m (single continuous length) |
| Surface Finish | Pickled and Passivated (2B finish); Ra ≤ 0.8 μm |
| End Preparation | Beveled per ASME B16.25; threaded (NPT/BSP) or plain cut |
| Standard Reference | ASTM A268, ASTM A213, GB/T 14976, EN 10216-5 |
| Heat Treatment | Solution Annealed at 1050–1150°C followed by controlled cooling |
| Maximum Operating Pressure (Cooling Side) | 1.0 – 2.5 MPa (design-dependent) |
| Operating Temperature Range (Hot Side) | 200°C – 1200°C |
| Expected Service Life | 18–36 months (improved from 8–14 months based on research findings) |
4. Manufacturing Process
The production of Wenzhou Jixing Metal Materials Co., Ltd. cooling coil tubes follows a rigorous, multi-stage manufacturing protocol designed to ensure dimensional accuracy, metallurgical homogeneity, and long-term service reliability.
Process Flow
- Raw Material Selection & Inspection: Stainless steel seamless tubes conforming to ASTM A213/A268 specifications are procured from certified mills. Incoming materials undergo spectroscopic chemical analysis (Optical Emission Spectroscopy, OES) and mechanical property verification.
- Cutting & End Preparation: Tubes are cut to specified lengths using precision sawing or plasma cutting. Ends are beveled, deburred, and inspected for flatness and concentricity.
- Coil Bending (Cold or Hot Forming): Tubes are formed into serpentine coil configurations using CNC-controlled bending machines. Minimum bend radius of 3×OD is maintained to prevent wall thinning and residual stress accumulation. Hot bending is employed for larger diameters (≥ Φ48 mm) or tighter radii.
- Welding & Joining: Where continuous lengths are insufficient, butt welds are performed using Gas Tungsten Arc Welding (GTAW, TIG) or Shielded Metal Arc Welding (SMAW) with matching filler metals. All welds undergo 100% visual inspection and selected radiographic testing (Radiographic Testing, RT) or dye penetrant testing (Dye Penetrant Testing, DPT).
- Solution Heat Treatment: Completed coil assemblies undergo solution annealing at 1050–1150°C in a protective atmosphere furnace, followed by controlled air cooling or quenching to achieve a fully austenitic microstructure free of carbide precipitation.
- Pickling & Passivation: Tubes are acid-pickled (typically HNO₃/HF blend) to remove oxide scale, followed by passivation treatment to establish a stable chromium oxide protective film on the surface.
- Non-Destructive Testing (NDT): Final quality verification includes ultrasonic testing (Ultrasonic Testing, UT) for wall thickness uniformity, hydrostatic pressure testing at 1.5× design pressure, and dimensional metrology.
- Protective Packaging & Shipping: Tubes are wrapped in protective materials, packaged in wooden crates or steel containers, and shipped with accompanying material traceability documentation.
Key Process Optimizations from Research Study
The technical study on 109 m² roasting furnace coil tube leakage identified several root causes of premature failure, including:
(a) Excessive wall thinning at bend apexes due to insufficient minimum bend radius;
(b) Thermal fatigue cracking at weld joints from mismatched thermal expansion coefficients between coil tubes and support structures;
(c) Internal scale spallation leading to blockage and localized overheating.
Subsequent manufacturing improvements include: increased minimum wall thickness at bend regions (≥ 1.2× nominal), adoption of expanded joint connections to accommodate thermal movement, and implementation of periodic internal scale monitoring protocols.
5. Applications
The stainless steel cooling coil tubes are engineered for demanding industrial thermal management applications where reliable heat dissipation is critical to process safety and efficiency.
Primary Applications
- Roasting Furnaces (焙烧炉): Cooling of refractory linings and ore beds during sulfide mineral roasting, calcination of limestone/dolomite, and sintering of iron ore concentrates. The coil tubes absorb radiant heat from the furnace interior, protecting structural steel and refractory materials from thermal degradation.
- Cement Kilns: Secondary and tertiary air preheating systems, as well as hot gas cooling in clinker production lines.
- Metallurgical Furnaces: Electric Arc Furnaces (Electric Arc Furnace, EAF), Basic Oxygen Furnaces (Basic Oxygen Furnace, BOF), and induction furnaces for steelmaking and non-ferrous metal smelting.
- Chemical Processing: Exothermic reactor cooling systems, distillation column overhead condensers, and heat recovery units in petrochemical and specialty chemical plants.
- Power Generation: Flue gas heat recovery systems in waste-to-energy plants and boiler economizer sections.
- Environmental Systems: Baghouse filter inlet temperature reduction in cement and metallurgical dust collection systems.
Typical Operating Conditions
| Application | Hot Side Temperature (°C) | Cooling Medium | Design Pressure (MPa) | Expected Life |
|---|---|---|---|---|
| Sulfide Ore Roasting | 800 – 1100 | Circulating Water | 1.0 – 1.6 | 18 – 30 months |
| Limestone Calcination | 900 – 1200 | Thermal Oil / Water | 0.6 – 1.2 | 12 – 24 months |
| Iron Ore Sintering | 700 – 1000 | Circulating Water | 1.0 – 2.0 | 18 – 36 months |
| Cement Kiln Preheater | 850 – 1150 | Hot Gas Recirculation | 0.2 – 0.5 | 24 – 48 months |