Stainless Steel Coil Tube for Biogas Engineering Tank Heating Systems
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Product Code: #820 | Category: Stainless Steel Coil Tube (盘管 / Coil Tube)
1. Product Overview
The stainless steel coil tube product from Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered heat exchange element specifically designed for installation within biogas engineering digesters and storage tanks. This coiled tube configuration serves as an integral heating medium, facilitating thermal transfer to maintain optimal operating temperatures within anaerobic digestion systems. The product is manufactured to withstand the corrosive, high-moisture, and chemically aggressive environments inherent in biogas production facilities.
The coil tube geometry maximizes surface area within a confined volume, thereby enhancing heat transfer efficiency (传热效率) and enabling uniform temperature distribution throughout the tank contents. This design principle is critical for maintaining the thermophilic or mesophilic temperature ranges required for efficient anaerobic digestion and biogas generation.
2. Material & Properties
2.1 Base Material
- Grade: Austenitic stainless steel conforming to ASTM A213 / GB/T 14976 standards
- Common Alloy Specifications:
- 304 (0Cr18Ni9): Chromium (Cr) 18–20%, Nickel (Ni) 8–10.5% — suitable for general biogas environments with moderate sulfur content
- 316L (00Cr17Ni12Mo2): Chromium 16.5–18.5%, Nickel 10–14%, Molybdenum (Mo) 2–3% — recommended for environments with elevated hydrogen sulfide (H₂S) or chloride ion concentrations
- 321 (0Cr18Ni11Ti): Titanium-stabilized variant for elevated temperature service above 450°C
2.2 Key Mechanical & Physical Properties
| Property | Specification (Grade 304) | Specification (Grade 316L) |
|---|---|---|
| Tensile Strength (抗拉强度) | ≥ 515 MPa | ≥ 485 MPa |
| Yield Strength (屈服强度) | ≥ 205 MPa | ≥ 170 MPa |
| Elongation (延伸率) | ≥ 40% | ≥ 45% |
| Thermal Conductivity (导热系数) | 16.3 W/(m·K) @ 100°C | 14.6 W/(m·K) @ 100°C |
| Corrosion Resistance (耐腐蚀性) | Excellent against organic acids, moderate H₂S | Superior against chlorides, H₂S, and acidic biogas condensates |
| Operating Temperature Range | -196°C to +870°C | -196°C to +870°C |
| Surface Finish (表面光洁度) | Polished or passivated, Ra ≤ 0.8 μm | Polished or passivated, Ra ≤ 0.8 μm |
2.3 Corrosion Resistance in Biogas Environments
Biogas typically contains 50–70% methane (CH₄), 25–40% carbon dioxide (CO₂), and trace amounts of hydrogen sulfide (H₂S), ammonia (NH₃), and water vapor. The CO₂ and H₂S components, when dissolved in condensate water, form carbonic acid (H₂CO₃) and hydrosulfuric acid (H₂S(aq)), creating a highly corrosive environment. The austenitic stainless steel matrix, with its high chromium content forming a self-healing passive oxide layer (Cr₂O₃), provides robust protection against pitting corrosion (点蚀), crevice corrosion (缝隙腐蚀), and uniform corrosion (均匀腐蚀) under these conditions.
3. Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (外径) | Φ19 mm, Φ25 mm, Φ32 mm, Φ38 mm, Φ51 mm (customizable) |
| Wall Thickness (壁厚) | 1.5 mm – 4.0 mm |
| Coil Pitch (盘管间距) | 50 mm – 200 mm (adjustable per tank geometry) |
| Coil Diameter (盘管直径) | Customized to match digester/tank internal dimensions |
| Overall Length (总长度) | Up to 50 m per continuous coil assembly |
| Heating Medium | Hot water (60–80°C), thermal oil (up to 200°C), or steam |
| Design Pressure (设计压力) | 0.6 MPa – 1.6 MPa (depending on heating medium) |
| Test Pressure (试验压力) | 1.5 × Design Pressure (hydrostatic test) |
| Connection Type (连接方式) | Flanged (法兰连接), threaded (螺纹连接), or welded (焊接) end fittings |
| Surface Treatment (表面处理) | Acid pickling and passivation (酸洗钝化) |
| Applicable Standards (适用标准) | GB/T 14976, ASTM A213, EN 10216-5, ASME B36.19M |
4. Manufacturing Process
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Raw Material Selection & Inspection (原材料选型与检验):
Virgin stainless steel seamless tubes are sourced from certified mills. Incoming material undergoes spectroscopic analysis (光谱分析) to verify chemical composition, mechanical property testing (力学性能测试), and hydrostatic pressure testing (水压试验) in accordance with ASTM A213 requirements.
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Tube Cutting & Deburring (管材切割与去毛刺):
Tubes are cut to the required segment lengths using precision plasma or saw cutting methods. All cut ends are deburred and chamfered to ensure uniform flow characteristics and facilitate welding operations.
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Coil Forming (盘管成型):
The straight tube segments are cold-formed into the specified coil geometry using CNC-controlled tube bending machinery. The bending process is carefully controlled to prevent ovalization (椭圆化) and to maintain wall thickness uniformity. The coil pitch, diameter, and total length are precisely matched to the tank installation drawings.
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Welding & Joining (焊接与连接):
End connections and any required mid-coil splices are performed using Gas Tungsten Arc Welding (GTAW / TIG welding, 钨极氩弧焊) or Automatic Orbital Welding (自动环焊). Weld parameters are optimized to minimize heat-affected zone (HAZ) sensitization and to ensure full penetration. All welds are 100% inspected via visual examination (VT) and, where required, dye penetrant testing (PT, 渗透检测).
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Heat Treatment (热处理):
Post-weld solution annealing (固溶退火) is performed at 1050–1100°C followed by rapid water quenching to restore full austenitic microstructure and maximize corrosion resistance. Stress relief (去应力退火) may be applied for high-pressure applications.
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Surface Finishing & Passivation (表面处理与钝化):
The coil assembly undergoes acid pickling (酸洗) using a hydrofluoric-nitric acid solution (HF-HNO₃) to remove scale and contaminants, followed by passivation (钝化) with a citric acid or nitric acid solution to re-establish the protective chromium oxide passive film. Final surface roughness is verified to Ra ≤ 0.8 μm.
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Pressure Testing & Final Inspection (压力测试与最终检验):
Each coil assembly is subjected to hydrostatic pressure testing at 1.5 times the design pressure, held for a minimum of 15 minutes with no visible leakage or permanent deformation. Dimensional verification (尺寸验证), surface finish inspection, and material traceability documentation are completed prior to packaging and dispatch.
5. Applications
5.1 Biogas Engineering (沼气工程)
- Anaerobic Digester Heating (厌氧消化罐加热): The coil tube is the primary heat exchange element installed inside anaerobic digesters to maintain the slurry temperature within the optimal range for microbial activity (mesophilic: 35–40°C; thermophilic: 50–60°C). This is essential for achieving stable biogas production rates and ensuring efficient organic matter degradation.
- Biogas Storage Tank Thermal Management (沼气储罐热管理): Prevents condensation and freezing of water vapor within storage tanks during low-temperature ambient conditions, ensuring uninterrupted biogas supply.
- Sludge Preheating (污泥预热): Incoming raw sludge is preheated via coil tubes prior to entering the main digester, reducing thermal shock and accelerating microbial adaptation.
5.2 Additional Industrial Applications
- Liquid Waste Treatment Systems (液体废水处理系统): Heating of industrial effluents containing organic acids or sulfides.
- Chemical Process Heating (化工过程加热): Heat exchange in reactors and vessels handling corrosive chemical feedstocks.
- Agricultural Greenhouse Heating (农业温室加热): Integration into large-scale agricultural heating systems utilizing biogas as a renewable energy source.
- Food Processing Industry (食品加工行业): Sanitary-grade heating elements in food-grade processing tanks where hygienic standards are paramount.
6. Quality Certifications & Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System (质量管理体系) certification covering all manufacturing and inspection processes |
| ISO 14001:2015 | Environmental Management System (环境管理体系) certification for sustainable manufacturing practices |
| ASME / NB (National Board) | Pressure Vessel and Piping component certification for high-pressure applications |
| CE Marking (EN 10204) | European Conformity marking with Type 3.1 test certificate (第三方检验证书) for export to EU markets |
| GB/T 14976 | Chinese national standard for seamless stainless steel tubes — compliance verified through third-party laboratory testing |
| Material Traceability (材料可追溯性) | Full mill test certificates (MTC, 材质证明书) provided with each batch, including chemical composition, mechanical properties, and heat treatment records |
| NDE (Non-Destructive Examination, 无损检测) | 100% visual testing (VT), dye penetrant testing (PT), and ultrasonic testing (UT) for weld integrity verification |
7. Unique Selling Points
Engineered for Biogas-Specific Corrosion Environments: Unlike generic stainless steel coil tubes, Wenzhou Jixing's product line is specifically engineered and validated for the unique corrosive challenges of biogas systems — including hydrogen sulfide (H₂S) attack, carbonic acid corrosion, and chloride-induced pitting. The selection of appropriate alloy grades (304 vs. 316L) is guided by comprehensive environmental assessment of the specific installation.
- Optimized Heat Transfer Efficiency (传热效率优化): The coil geometry is computationally modeled to maximize the heat transfer coefficient (传热系数) within the tank volume. CFD (Computational Fluid Dynamics, 计算流体力学) analysis ensures uniform temperature distribution, eliminating cold spots that could inhibit microbial activity in anaerobic digesters.
- Customized Engineering (定制化工程设计): Each coil tube assembly is fabricated to precise customer specifications — including tank dimensions, heating medium parameters, and operating conditions. This bespoke approach ensures optimal performance and seamless integration into existing biogas plant infrastructure.
- Extended Service Life (延长使用寿命): Rigorous post-weld solution annealing and passivation processes ensure maximum corrosion resistance throughout the product lifecycle. Expected service life exceeds 15 years in typical biogas operating conditions, significantly reducing maintenance costs and system downtime.
- Full Traceability & Documentation (全生命周期可追溯与文档): Every coil tube assembly is accompanied by comprehensive documentation including material test certificates, weld records, NDE reports, pressure test results, and dimensional verification sheets — providing full quality traceability from raw material to final installation.
- Scalability (可扩展性): The modular coil design allows for incremental expansion of heating capacity as biogas plant throughput increases, protecting the customer's capital investment over the system's operational lifetime.
This product specification is based on technical data from Wenzhou Jixing Metal Materials Co., Ltd. (Product Code #820). All specifications are subject to the final engineering design agreement between the manufacturer and the end user. For detailed project-specific requirements, please contact Wenzhou Jixing Metal Materials Co., Ltd. directly for consultation and customized solutions.