Stainless Steel Coil Tube (盘管) — Biogas Tank Heating Heat Exchanger Series
Product Overview
The Stainless Steel Coil Tube (盘管 / Coil Tube), manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered helical heat exchange element designed primarily for immersion-type heating applications within biogas engineering digesters and anaerobic digestion tanks. This product series serves as a critical component in thermal management systems where efficient heat transfer is required to maintain optimal fermentation temperatures (typically 35°C–55°C for mesophilic and thermophilic anaerobic digestion processes) while withstanding aggressive chemical environments including hydrogen sulfide (H₂S), ammonia (NH₃), and organic acids present in biogas slurry.
The coil tube design maximizes the heat transfer surface area per unit volume, enabling rapid thermal equilibration within large-volume digesters. The helical geometry promotes natural convection currents within the coil channels, enhancing both internal heat transfer coefficients and external fluid mixing, thereby improving overall thermal efficiency. This product is categorized under industrial heat exchange components and is engineered in accordance with rigorous metallurgical and mechanical standards.
Material & Properties
Primary Material Grades
- SUS304 (ASTM A269 TP304): The standard grade for biogas heating applications, offering excellent corrosion resistance in mildly aggressive environments, good formability, and cost-effectiveness. Contains 18% chromium (Cr) and 8% nickel (Ni).
- SUS316L (ASTM A269 TP316L): Enhanced grade with 2%–3% molybdenum (Mo) addition for superior resistance to pitting and crevice corrosion in high-chloride or sulfide-containing biogas environments.
- SUS321 (ASTM A269 TP321): Titanium-stabilized grade (Ti ≥ 5×C) for applications requiring resistance to intergranular corrosion at elevated temperatures.
Mechanical Properties (SUS304 Reference)
| Property | Value | Test Standard |
|---|---|---|
| Tensile Strength (抗拉强度) | ≥ 520 MPa | ASTM A269 / GB/T 12771 |
| Yield Strength (屈服强度) | ≥ 205 MPa | ASTM A269 |
| Elongation (延伸率) | ≥ 40% | ASTM A269 |
| Thermal Conductivity (热导率) | 16.3 W/(m·K) @ 100°C | — |
| Density (密度) | 7.93 g/cm³ | — |
| Operating Temperature Range (工作温度范围) | -196°C to +870°C | — |
Corrosion Resistance Characteristics
- Corrosion rate in biogas slurry (pH 6.5–7.5, TDS < 3000 ppm): < 0.05 mm/year for SUS316L
- Pitting Resistance Equivalent Number (PREN): ≥ 24 for SUS316L (PREN = %Cr + 3.3×%Mo + 16×%N)
- Crevice corrosion resistance validated per ASTM G48 Method A
Specifications
| Parameter | Specification | Unit |
|---|---|---|
| Outer Diameter (OD) | Φ12 – Φ51 | mm |
| Wall Thickness (WT) | 1.0 – 3.0 | mm |
| Coil Pitch (螺旋间距) | 15 – 80 (adjustable) | mm |
| Coil Diameter (盘管外径) | Φ200 – Φ2000 | mm |
| Coil Length (总展开长度) | 3 – 50 | m |
| Surface Finish | 2B / No.4 / Electropolished (Ra ≤ 0.4 μm) | — |
| End Connection | Threaded (NPT/BSP), Flanged, or Butt-welded | — |
| Maximum Working Pressure (最大工作压力) | ≤ 1.6 MPa (typical) | MPa |
| Heat Transfer Fluid | Hot water, thermal oil, or steam | — |
| Applicable Standard | ASTM A269 / GB/T 12771 / EN 10216-5 | — |
Manufacturing Process
- Raw Material Selection & Inspection: Seamless stainless steel tubes conforming to ASTM A269 are procured from certified mills. Incoming material undergoes spectroscopic analysis (PMI), hydrostatic pressure testing, and dimensional verification.
- Heat Treatment (Solution Annealing): Tubes are annealed at 1050°C–1100°C followed by water quenching to achieve a fully austenitic microstructure, ensuring maximum ductility and corrosion resistance.
- Precision Coiling (螺旋成型): CNC-controlled coiling machines form the tube into a precise helical geometry. The coiling process is performed at ambient temperature with controlled bending forces to prevent work hardening and ovalization (ovality ≤ 2% of OD).
- Welding & Forming of End Connections: End fittings are fabricated via TIG (Tungsten Inert Gas) welding using argon shielding (Ar ≥ 99.99% purity) to prevent oxidation. Weld quality is verified through visual inspection and, where required, radiographic testing (RT) per ASTM E94.
- Surface Treatment: Electropolishing or pickling and passivation (per ASTM A967) removes surface contaminants and establishes a stable chromium oxide passive film (Cr₂O₃) for enhanced corrosion resistance.
- Pressure Testing & Final Inspection: Each coil assembly undergoes hydrostatic pressure testing at 1.5× the maximum working pressure for a minimum dwell time of 30 minutes. Dimensional accuracy, surface finish, and weld integrity are documented.
Applications
- Biogas Engineering (沼气工程): Immersion heating of anaerobic digesters to maintain optimal thermophilic (50–60°C) or mesophilic (35–45°C) digestion temperatures for efficient methane (CH₄) production.
- Industrial Wastewater Treatment: Thermal pretreatment of sludge prior to anaerobic digestion or aerobic bioremediation.
- Agricultural Biogas Systems: Heating of small-to-medium scale biogas reactors for rural and farm-scale renewable energy generation.
- Chemical Processing: Heating of corrosive process fluids in reactors and storage tanks where carbon steel heat exchangers are unsuitable.
- Food & Beverage Industry: Sanitary-grade heating coils for CIP (Clean-in-Place) systems and process tanks.
- Pharmaceutical & Laboratory: Precision temperature control in reaction vessels and fermentation bioreactors.
Quality Certifications & Compliance
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 14001:2015 | Environmental Management System |
| CE Marking (EU) | Pressure Equipment Directive (PED 2014/68/EU) where applicable |
| GB/T 12771-2019 | Chinese National Standard for Seamless Stainless Steel Tubes |
| ASTM A269/A269M | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubes |
| EN 10216-5 | European Standard for Seamless Tubes for Technical Use — Austenitic Steels |
| GB/T 20878-2007 | Chinese Standard for Classification and Designation of Stainless Steels |
| NB License (中国特种设备制造许可证) | Pressure Vessel and Piping Manufacturing Qualification (where applicable) |
Unique Selling Points
- Optimized Helical Geometry: The coil pitch and diameter are engineered to maximize the overall heat transfer coefficient (U-value) while minimizing flow resistance, achieving thermal efficiencies exceeding 85% in biogas digester applications.
- Corrosion-Resistant Alloy Selection: Material grade is matched to the specific chemical composition of the process fluid, ensuring a design life exceeding 15 years in aggressive biogas environments.
- Customizable Configuration: Full customization of OD, wall thickness, coil dimensions, total length, and end connections to meet project-specific thermal load requirements and spatial constraints.
- Sanitary-Grade Surface Finish: Electropolished surfaces (Ra ≤ 0.4 μm) minimize biofilm adhesion, reducing maintenance frequency and ensuring consistent heat transfer performance over time.
- Full Traceability: Each coil tube carries a heat number traceability record linking back to mill certificates, ensuring complete material provenance documentation.
- Field-Proven Performance: Validated through thermal analysis modeling and field deployment in biogas engineering projects, demonstrating reliable performance under continuous-duty conditions.
Technical Note: The heat transfer performance of immersion coil tubes in biogas digesters is governed by the combined internal convective coefficient (hᵢ), tube wall conductance (k/w), and external convective coefficient (hₒ). The overall heat transfer coefficient is calculated as: 1/U = 1/hᵢ + w/k + 1/hₒ. For typical biogas slurry conditions, the external coefficient is often the rate-limiting factor, and the helical geometry enhances hₒ through induced secondary flow patterns within the coil channels.
Manufacturer Information
Wenzhou Jixing Metal Materials Co., Ltd. (温州市吉兴金属材料有限公司) is a specialized manufacturer of stainless steel seamless tubes, welded pipes, and precision-formed components including coil tubes, heat exchanger elements, and process piping systems. The company maintains a vertically integrated production facility in Wenzhou, Zhejiang Province, China, with in-house capabilities spanning material procurement, precision forming, welding, surface treatment, and non-destructive testing (NDT).