Spiral Coil Tube (Coil Tube) for Industrial Drying Systems
Product Overview
The Spiral Coil Tube (Coil Tube), manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered stainless steel coiled tubing product designed primarily for industrial drying applications, including but not limited to the thermal drying of white carbon black (Silica, SiO₂), chemical intermediates, and fine particulate powders. The spiral coil geometry provides an exceptionally high surface-area-to-volume ratio, enabling efficient heat transfer between the process medium (typically hot air, steam, or thermal oil) and the material being dried. This product is integral to spiral coil tube dryers, where the coiled configuration ensures uniform residence time, consistent temperature distribution, and compact equipment footprint.
As a specialized component within the broader category of stainless steel coiled tubes, this product bridges metallurgical engineering and process engineering, demanding rigorous material selection, dimensional accuracy, and corrosion resistance to withstand the demanding environments of continuous thermal processing operations.
Material & Properties
The Spiral Coil Tube is fabricated from high-grade stainless steel alloys selected to balance corrosion resistance, mechanical strength, thermal conductivity, and long-term service durability. The following materials are commonly specified:
- Austenitic Stainless Steel 304 (UNS S30408): The standard grade offering excellent general corrosion resistance, good formability, and weldability. Chromium (Cr) content of 18–20% and Nickel (Ni) content of 8–10.5% provide a robust passive oxide layer suitable for most non-aggressive drying environments.
- Austenitic Stainless Steel 316 (UNS S31608): Enhanced corrosion resistance due to the addition of 2–3% Molybdenum (Mo), making it suitable for environments involving chlorides, mild acids, or aggressive chemical vapors encountered in certain white carbon black production processes.
- High-Nickel Alloy Steel 316L (UNS S31603): Low-carbon variant (C ≤ 0.03%) designed to prevent sensitization and intergranular corrosion during welding operations, essential for seamless coil fabrication.
- Duplex Stainless Steel 2205 (UNS S31803): Available for high-pressure or high-temperature applications requiring superior yield strength (≥ 450 MPa) and resistance to stress corrosion cracking (SCC).
Mechanical and Thermal Properties
| Property | Grade 304 | Grade 316 | Grade 316L | Grade 2205 |
|---|---|---|---|---|
| Yield Strength (MPa) | ≥ 205 | ≥ 205 | ≥ 170 | ≥ 450 |
| Tensile Strength (MPa) | 515–730 | 485–720 | 450–690 | 550–800 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 40 | ≥ 25 |
| 16.3 | 14.6 | 14.6 | 14.6 | |
| Maximum Service Temperature (°C) | 870 | 870 | 870 | 300 (reduced pressure) |
| Corrosion Resistance (Pitting Resistance Equivalent Number, PREN) | 19 | 24–26 | 24–26 | 34–38 |
Specifications
| Parameter | Specification |
|---|---|
| Product Designation | Spiral Coil Tube (Coil Tube), Catalog No. 1488 |
| Tube Outer Diameter (OD) | 6.35 mm – 50.8 mm (¼" – 2") |
| Tube Wall Thickness | 0.5 mm – 3.0 mm |
| Coil Diameter (Center-to-Center) | 100 mm – 2,000 mm |
| Coil Length | 1 m – 500 m (customizable per project requirement) |
| Helix Pitch | 15 mm – 100 mm (adjustable for flow resistance optimization) |
| Surface Finish | 2B Mill Finish, BA (Bright Annealed), or Electropolished (Ra ≤ 0.4 μm) |
| End Preparation | Plain end, beveled end (37°), or threaded connection (BSPT/NPT) |
| Dimensional Tolerance | OD: ±0.05 mm; Wall Thickness: ±0.03 mm; Coil Diameter: ±1.0 mm |
| Pressure Rating | Up to 2.5 MPa (at 200°C), subject to wall thickness and grade |
| Operating Temperature Range | −196°C to 870°C (Grade-dependent) |
| Standards Compliance | ASTM A269, ASTM A213, EN 10216-5, GB/T 14976 |
Manufacturing Process
The fabrication of the Spiral Coil Tube follows a rigorously controlled multi-stage manufacturing process to ensure dimensional accuracy, metallurgical integrity, and long-term reliability:
- Raw Material Inspection: Incoming stainless steel bars or seamless tubes undergo spectrographic analysis (Optical Emission Spectrometry, OES) to verify chemical composition compliance with the specified grade. Mill Test Certificates (MTC) conforming to EN 10204 3.1 are reviewed and archived.
- Hot Rolling / Cold Drawing: The base tube is produced via hot rolling followed by cold drawing to achieve the required outer diameter and wall thickness tolerances. Cold working enhances mechanical properties through work hardening while maintaining the austenitic microstructure.
- Solution Annealing: The drawn tube is solution-annealed at 1010–1150°C in a controlled atmosphere furnace to dissolve any carbide precipitates, restore full corrosion resistance, and relieve residual stresses introduced during cold forming.
- Spiral Coiling (Coil Forming): The annealed tube is fed through precision coil-forming dies using either a push-through or pull-through coiling method. The forming process is carefully controlled to prevent tube flattening, ovality distortion, or micro-cracking at the inner bend radius. The minimum bend diameter is maintained at ≥ 6× the tube OD to preserve structural integrity.
- Welding (if applicable): For coil assemblies requiring internal spiral welds or connection joints, Gas Metal Arc Welding (GMAW) or Shielded Metal Arc Welding (SMAW) with matching filler metals (e.g., ER308L for Grade 304) is employed. Weld seams are inspected via Dye Penetrant Testing (DPT) or Ultrasonic Testing (UT).
- Surface Treatment: Optional electropolishing is performed to achieve ultra-low surface roughness (Ra ≤ 0.4 μm), removing the surface contamination layer and enhancing the passive film for improved corrosion resistance and ease of cleaning in hygienic or chemical processing applications.
- Final Quality Control: Completed coil tubes undergo dimensional verification (caliper measurement, coil diameter gauge), hydrostatic pressure testing at 1.5× the design pressure, and visual inspection for surface defects, weld integrity, and dimensional conformity.
Applications
The Spiral Coil Tube finds extensive application across multiple industrial sectors, particularly in thermal processing systems:
- White Carbon Black (Precipitated Silica) Drying: The primary application as referenced in technical literature. The spiral coil tube dryer utilizes the coiled geometry to maximize heat exchange surface area, enabling efficient thermal drying of wet silica slurry. Hot air or steam flows through the coil while the wet material contacts the outer surface, achieving rapid and uniform drying with low energy consumption.
- Chemical Powder Drying: Suitable for drying titanium dioxide (TiO₂), talc, kaolin, and other mineral powders where stainless steel corrosion resistance is required.
- Food and Pharmaceutical Processing: Electropolished coil tubes are used in heat exchangers and drying systems for food-grade and pharmaceutical-grade powders, meeting FDA and EU GMP (Good Manufacturing Practice) requirements.
- Heat Exchanger Coils: The spiral coil geometry is widely employed in shell-and-coil heat exchangers for process cooling and heating applications in petrochemical, pharmaceutical, and food industries.
- Industrial Oven and Furnace Heating Elements: Coil tubes serve as heating media conduits in continuous drying ovens and conveyor dryers.
- Gas Processing and Separation: Spiral coils used in gas separation and adsorption systems where stainless steel durability is essential.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework to ensure product reliability and regulatory compliance:
- ISO 9001:2015 — Quality Management Systems certification, demonstrating adherence to international quality management standards.
- ISO 14001:2015 — Environmental Management Systems certification, reflecting commitment to sustainable manufacturing practices.
- EN 10204 3.1 — Mill Test Certificates providing full chemical and mechanical property documentation for each production batch.
- NACE MR0175 / ISO 15156 — Compliance for sour service applications (where applicable), ensuring resistance to sulfide stress cracking.
- CE Marking — Conformity with European Union directives for pressure equipment and industrial components.
- Third-Party Inspection — Available upon request by recognized inspection bodies (e.g., SGS, BV, TUV) for end-user verification.
Unique Selling Points
- Optimized Spiral Geometry: The precisely engineered helix pitch and coil diameter maximize heat transfer efficiency while minimizing pressure drop, offering superior drying performance compared to conventional straight-tube configurations.
- Customizable Configuration: Full range of dimensions, materials, and surface finishes available to meet specific process requirements, enabling tailored solutions for diverse industrial drying applications.
- Corrosion-Resistant Construction: High-grade austenitic stainless steel provides exceptional resistance to oxidation, acid attack, and chloride-induced pitting, ensuring extended service life in aggressive chemical environments.
- Compact Footprint: The coiled design significantly reduces equipment volume and installation space compared to equivalent-length straight tube systems, facilitating integration into space-constrained process plants.
- Proven Track Record in Silica Drying: Direct application in white carbon black drying processes, validated through extensive technical literature and field deployment, ensuring reliable performance in demanding particulate drying scenarios.