Stainless Steel Coil Tube (Coiltube) — Technical Product Specification
1. Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered helical heat exchange element manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Designed for integration into thermal energy systems, this product leverages the inherent advantages of stainless steel — including outstanding corrosion resistance, high thermal conductivity, and mechanical durability — to deliver reliable performance in demanding industrial and agricultural environments. The product draws upon research findings from the study "Experimental Research on Heat Transfer Performance of PEX Spiral Coil Tubes in Biogas Digesters", which validated the superior heat exchange efficiency of spiral coil geometries in enclosed thermal systems.
Unlike straight-pipe heat exchangers, the continuous helical configuration of the Coiltube maximizes the surface-area-to-volume ratio, promotes turbulent flow within the tube, and significantly enhances convective heat transfer coefficients. This makes the product particularly well-suited for biogas digester heating, geothermal heat recovery, industrial process heating, and refrigeration applications.
2. Material & Properties
2.1 Base Material
The Coiltube is fabricated from high-grade austenitic stainless steel conforming to ASTM A213 / ASME SA-213 seamless tube specifications. The primary alloy grades available include:
- 304 / 304L (UNS S30400 / S30403): General-purpose corrosion resistance with excellent weldability; suitable for most industrial and food-grade applications.
- 316 / 316L (UNS S31600 / S31603): Enhanced resistance to chlorides and acidic environments due to 2–3% molybdenum addition; ideal for marine and chemical processing contexts.
- 321 (UNS S32100): Titanium-stabilized grade offering superior resistance to intergranular corrosion at elevated temperatures (up to 870°C).
2.2 Key Physical & Mechanical Properties
- Thermal Conductivity: 14.6–16.3 W/(m·K) at 20°C (Grade 304), providing efficient radial heat transfer through the tube wall.
- Density: 8.0 g/cm³
- Operating Temperature Range: −196°C to +870°C (Grade 321); −196°C to +425°C (Grades 304/316)
- Yield Strength (0.2% Offset): ≥ 205 MPa (Grade 304); ≥ 275 MPa (Grade 316)
- Tensile Strength: ≥ 515 MPa (Grade 304); ≥ 585 MPa (Grade 316)
- Corrosion Resistance: Passivation via chromium oxide (Cr₂O₃) film; pitting resistance equivalent number (PREN) of 19 (304) or 24 (316).
3. Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) |
| Item No. | 578 |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd. |
| Tube Configuration | Continuous helical spiral coil |
| Outer Diameter (OD) | 6 mm – 51 mm (customizable) |
| Wall Thickness | 0.5 mm – 3.0 mm |
| Coil Diameter | 100 mm – 1,500 mm (adjustable per application) |
| Coil Pitch | 15 mm – 80 mm (spiral spacing) |
| Total Coil Length | 1 m – 500 m (continuous or segmented) |
| Surface Finish | Mirror polish (Ra ≤ 0.4 μm), brushed, or standard mill finish |
| End Preparation | Plain end, beveled, threaded, or socket-welded |
| Operating Pressure | Up to 16 MPa (160 bar) depending on wall thickness and diameter |
| Compliance Standards | ASTM A213, ASME SA-213, EN 10217, GB/T 12771 |
| Available Grades | 304, 304L, 316, 316L, 321, 310S (upon request) |
| Customization | Coil geometry, dimensions, and end fittings available per customer drawings |
4. Manufacturing Process
4.1 Raw Material Selection & Inspection
Virgin stainless steel seamless tubes are procured from certified mills with full mill test certificates (MTC) in accordance with EN 10204 Type 3.1. Each batch undergoes incoming inspection for chemical composition (via optical emission spectrometry), grain size verification, and hydrostatic testing.
4.2 Coil Forming
The forming process utilizes a high-precision CNC-controlled coil winding machine with the following sequence:
- Pre-Heating: For grades requiring elevated formability (e.g., 310S), tubes are pre-heated to 150–200°C to reduce springback and minimize work hardening.
- Helical Winding: The tube is drawn through a series of guided rollers and formed around a mandrel of the specified coil diameter. The CNC system controls coil pitch, winding speed, and tension to ensure geometric accuracy within ±0.5 mm tolerance.
- Springback Compensation: Computational algorithms pre-adjust the winding parameters to compensate for elastic recovery, ensuring the final coil diameter matches the design specification.
4.3 Post-Forming Treatment
- Solution Annealing: Tubes are annealed at 1050–1100°C followed by controlled cooling to relieve residual stresses introduced during forming and restore full corrosion resistance.
- Pickling & Passivation: Immersion in a citric acid or nitric acid bath removes oxide scale and establishes a protective chromium oxide passive film.
- Surface Finishing: Electropolishing or mechanical polishing is applied for food-grade or pharmaceutical applications to achieve Ra ≤ 0.4 μm surface roughness.
4.4 Quality Control & Testing
- Dimensional Inspection: Coordinate measuring machine (CMM) verification of coil diameter, pitch uniformity, and total length.
- Pressure Testing: Hydrostatic or pneumatic testing at 1.5× the maximum operating pressure, held for a minimum of 60 seconds with zero pressure drop.
- Visual & NDT Inspection: Dye penetrant testing (PT) or eddy current testing (ET) on coil seams and end preparations to detect surface and near-surface defects.
- Corrosion Testing: Salt spray testing (ASTM B117) for a minimum of 1,000 hours with no pitting or corrosion observed on Grades 316/316L.
5. Applications
5.1 Biogas Digester Heating
The primary validated application stems from experimental research demonstrating the effectiveness of spiral coil tubes in maintaining optimal fermentation temperatures within anaerobic biogas digesters. The Coiltube is immersed in the digestate slurry, with hot water or thermal oil circulated through the tube to maintain temperatures of 35–55°C (mesophilic) or 55–70°C (thermophilic), thereby maximizing methane yield. The stainless steel construction ensures resistance to the highly corrosive hydrogen sulfide (H₂S) and organic acid environment present in digesters.
5.2 Geothermal & Solar Thermal Energy Systems
Coiltubes are deployed as heat collection elements in closed-loop geothermal heat exchangers and solar thermal storage tanks. The helical geometry enhances the logarithmic mean temperature difference (LMTD) and increases the overall heat transfer coefficient (U-value) by 30–50% compared to equivalent straight-pipe configurations.
5.3 Industrial Process Heating & Cooling
- Waste heat recovery in chemical processing plants
- Reactor jacket heating in pharmaceutical manufacturing
- Evaporator and condenser elements in food and beverage processing
- Chiller coils in industrial refrigeration systems
5.4 HVAC & District Heating
Used as immersion heaters in commercial water heating systems, district heating buffer tanks, and radiant floor heating manifolds where compact heat exchange surfaces are required.
5.5 Marine & Offshore Applications
Grade 316L Coiltubes are employed in shipboard heating systems, ballast water heat exchangers, and offshore platform thermal management systems, leveraging superior resistance to chloride-induced pitting and crevice corrosion.
6. Quality Certifications & Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification ensuring consistent product quality and process control throughout manufacturing. |
| ISO 14001:2015 | Environmental Management System certification demonstrating commitment to sustainable manufacturing practices. |
| CE Marking | Conformity with European Union directives for pressure equipment (PED 2014/68/EU) where applicable. |
| ASTM / ASME Compliance | Material and manufacturing compliance with ASTM A213 and ASME SA-213 seamless stainless steel tube standards. |
| EN 10217 | European standard for seamless stainless steel tubes for general applications. |
| GB/T 12771 | Chinese national standard for stainless steel seamless tubes for general use. |
| 3.1 MTC (EN 10204) | Mill Test Certificate providing full chemical and mechanical property documentation for each production batch. |
7. Unique Selling Points
- Research-Validated Performance: Product design informed by peer-reviewed experimental data on spiral coil heat transfer in enclosed thermal systems, ensuring optimized coil geometry for maximum thermal efficiency.
- Superior Corrosion Durability: Austenitic stainless steel grades provide decades of service life in aggressive chemical environments without degradation of heat transfer performance.
- High Surface-Area-to-Volume Ratio: Helical configuration delivers 30–50% higher heat transfer rates compared to conventional straight-pipe heat exchangers of equivalent volume.
- Full Customization Capability: Coil diameter, pitch, tube dimensions, surface finish, and end preparations are tailored to customer-specific engineering drawings and application requirements.
- End-to-End Quality Assurance: From incoming material verification through final dimensional and pressure testing, every production stage is governed by documented quality procedures.
- Multi-Grade Availability: Broad selection of stainless steel grades accommodates diverse operating conditions, from cryogenic to high-temperature applications.
- Compact Footprint: High thermal density enables integration into space-constrained installations such as biogas digesters, marine vessels, and modular industrial units.
Technical Note: The spiral coil geometry promotes secondary flow (Dean vortices) within the tube, which disrupts the thermal boundary layer and sustains turbulent flow even at relatively low Reynolds numbers. This phenomenon, validated through experimental heat transfer studies in biogas digester applications, is a critical performance differentiator over conventional straight-pipe heat exchange designs.