Stainless Steel Coil Tube (Coiltube) for Low-Pressure Steam Condensate Tank Systems
Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Product Serial No. 243) is a precision-engineered tubular component designed for integration into low-pressure steam condensate tanks (Low-Pressure Steam Condensate Tanks, LP-SCT) employing dual internal and external coil tube configurations for efficient heat exchange and condensate cooling. This product represents a specialized application of stainless steel tubing technology within thermal management systems, where the coiltube serves as the primary heat transfer medium facilitating rapid condensation of low-pressure steam and subsequent cooling of the resulting condensate.
The dual coil tube arrangement—comprising both an internal coil tube (Internal Coil Tube, ICT) and an external coil tube (External Coil Tube, ECT)—enables a cascaded cooling approach that maximizes thermal efficiency while minimizing energy consumption in industrial steam systems. This design philosophy addresses the engineering challenge of achieving optimal condensate recovery temperatures under varying operational loads.
Material & Properties
Base Material Composition
- Primary Alloy: Austenitic Stainless Steel, Grade 304 (UNS S30400) or Grade 316L (UNS S31603), selected based on the corrosive environment of the condensate medium.
- Chromium Content (Cr): 18–20% (Grade 304) or 16–18% (Grade 316L), providing superior passive film stability.
- Nickel Content (Ni): 8–10.5% (Grade 304) or 10–14% (Grade 316L), ensuring excellent ductility and corrosion resistance.
- Molybdenum Content (Mo): 2.0–3.0% (Grade 316L only), enhancing resistance to pitting and crevice corrosion in chloride-containing condensate.
- Carbon Content (C): ≤0.08% (Grade 304) or ≤0.03% (Grade 316L), minimizing intergranular corrosion susceptibility.
Mechanical Properties
| Property | Grade 304 | Grade 316L | Test Standard |
|---|---|---|---|
| Tensile Strength (抗拉强度) | ≥515 MPa | ≥485 MPa | ASTM A270 / GB/T 12451 |
| Yield Strength (屈服强度, 0.2% offset) | ≥205 MPa | ≥170 MPa | ASTM A270 / GB/T 12451 |
| Elongation (延伸率) | ≥40% | ≥40% | ASTM A270 |
| Hardness (硬度) | ≤217 HB | ≤217 HB | ASTM E10 |
| Density (密度) | 8.0 g/cm³ | 8.0 g/cm³ | — |
Thermal Properties
- Thermal Conductivity (热导率): 16.3 W/(m·K) at 300 K, ensuring efficient heat transfer between the steam/condensate and the cooling medium.
- Specific Heat Capacity (比热容): 502 J/(kg·K) at 300 K.
- Thermal Expansion Coefficient (热膨胀系数): 17.3 × 10⁻⁶ /K (20–100°C), requiring careful engineering consideration for thermal stress management in coiled configurations.
- Maximum Operating Temperature (最高使用温度): 870°C (oxidation limit in non-cyclic conditions); recommended service temperature for condensate applications: ≤250°C.
Corrosion Resistance
- Excellent resistance to atmospheric corrosion, condensate water, and dilute organic/inorganic acids.
- Grade 316L variant provides superior resistance to chloride-induced pitting corrosion (临界点蚀温度, Critical Pitting Temperature, CPT ≥40°C in 3.5% NaCl solution).
- Passive chromium oxide film (Cr₂O₃) self-healing mechanism ensures long-term integrity in steam condensate environments.
Specifications
Geometric Dimensions
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (外径, OD) | Φ12 mm – Φ50 mm (customizable) | ASTM A270 / GB/T 12451 |
| Wall Thickness (壁厚, WT) | 0.5 mm – 3.0 mm | ASTM A270 |
| Coil Mean Diameter (盘管平均直径) | Φ200 mm – Φ1200 mm | Custom / Project-specific |
| Coil Pitch (盘管节距) | 10 mm – 50 mm (adjustable per thermal design) | Custom |
| Number of Turns (圈数) | 5 – 50 turns per coil section | Custom |
| Overall Length (总长) | 10 m – 100 m (continuous coiling) | Custom |
| Surface Finish (表面状态) | Pickled & Passivated (酸洗钝化), Ra ≤ 0.8 μm | ASTM A967 |
| End Condition (端部状态) | Plain end, flanged, or threaded (per drawing) | Project specification |
Pressure & Temperature Ratings
| Operating Parameter | Internal Coil Tube (ICT) | External Coil Tube (ECT) |
|---|---|---|
| Design Pressure (设计压力) | ≤1.6 MPa (gauge) | ≤1.0 MPa (gauge) |
| Operating Pressure (工作压力) | 0.05 – 0.8 MPa (gauge) | 0.02 – 0.6 MPa (gauge) |
| Steam Temperature (蒸汽温度) | 80°C – 180°C (low-pressure steam) | Ambient +10°C to +80°C (cooling medium) |
| Condensate Outlet Temperature (凝液出口温度) | 40°C – 60°C (target) | — |
Manufacturing Process
Process Flow
- Raw Material Procurement & Inspection (原材料采购与检验): Stainless steel tubing procured from certified mill suppliers with full Chemical Composition Analysis (化学成分分析, CCA) and Mechanical Test Reports (力学试验报告) per ASTM A270 or GB/T 12451.
- Dimensional Inspection & Segmentation (尺寸检验与定尺): Incoming tubing undergoes ultrasonic testing (超声波检测, UT) for wall thickness uniformity and visual inspection for surface defects. Segmented to required coil lengths with precision cutting.
- Coil Forming / Bending (盘管成型/弯管): Cold bending (冷弯) process using CNC-controlled bending machinery (数控弯管机) to achieve precise coil geometry. Bend radius controlled to prevent wall thinning (壁厚减薄) below 85% of original wall thickness. Springback compensation (回弹补偿) algorithmically calculated for dimensional accuracy.
- Welding & Joining (焊接与连接): TIG (Tungsten Inert Gas) welding (钨极氩弧焊) or orbital welding for end connections and support bracket attachments. Weld parameters optimized to maintain austenitic microstructure and prevent sensitization (敏化).
- Heat Treatment (热处理): Solution annealing (固溶处理) at 1010–1150°C followed by rapid water quenching to restore full austenitic structure, eliminate residual stresses from cold forming, and maximize corrosion resistance.
- Pickling & Passivation (酸洗钝化): Immersion in nitric acid/hydrofluoric acid solution (硝酸/氢氟酸溶液) to remove oxide scale and iron contamination, followed by passivation treatment to establish protective chromium oxide film. Per ASTM A967.
- Final Quality Inspection (最终质量检验): Dimensional verification (尺寸验证), hydrostatic pressure testing (液压试验, 1.5× design pressure for 15 minutes), and surface quality assessment (表面质量评估).
- Packaging & Delivery (包装与交付): Individual coiltube units wrapped in moisture-proof protective film (防潮保护膜), secured on wooden pallets (木托盘), with accompanying quality documentation.
Process Quality Control Points
- Cold forming ratio (冷成型比) controlled to prevent excessive work hardening (加工硬化) that could compromise ductility.
- Interpass temperature (层间温度) during welding maintained below 150°C to avoid chromium carbide precipitation (碳化铬析出).
- Post-weld heat treatment (焊后热处理) performed when welding input exceeds sensitization threshold.
- Non-Destructive Testing (无损检测, NDT) including dye penetrant testing (渗透检测, PT) on all welds.
Applications
Primary Application: Low-Pressure Steam Condensate Tank Cooling (低压蒸汽凝液罐降温)
The dual internal-external coil tube configuration is specifically engineered for low-pressure steam condensate recovery systems where:
- Internal Coil Tube (ICT, 内部盘管): Receives low-pressure steam (低压蒸汽) and facilitates primary condensation. Steam flows through the ICT, condensing on the inner wall surface due to the temperature differential with the tank water/condensate environment. The latent heat of vaporization (汽化潜热) is released into the surrounding medium.
- External Coil Tube (ECT, 外部盘管): Circulates a secondary cooling medium (冷却介质)—typically circulating water (循环水) or refrigerant—to provide supplemental cooling. The ECT is positioned externally within the tank shell, absorbing residual heat from the condensate to achieve target outlet temperatures.
Secondary Applications
- Pharmaceutical Industry (制药行业): Condensate recovery in sterilization systems (灭菌系统) where sanitary-grade stainless steel (卫生级不锈钢) is mandatory.
- Food Processing Industry (食品加工行业): Steam condensate management in pasteurization (巴氏杀菌) and cooking equipment.
- Petrochemical Industry (石油化工行业): Heat recovery in distillation columns (蒸馏塔) and process steam systems.
- Power Generation (发电): Auxiliary steam condensate systems in cogeneration (热电联产) plants.
- Textile Industry (纺织行业): Steam condensate recovery in dyeing and finishing (染色与后整理) processes.
- Chemical Processing (化学加工): Condensate handling in reactors (反应器) and heat exchangers (换热器).
System Design Considerations
The dual coil tube arrangement in low-pressure steam condensate tanks represents an optimized thermal management strategy. The internal coil tube captures the primary latent heat load during steam condensation, while the external coil tube handles the sensible heat load for condensate cooling. This separation of thermal duties allows independent optimization of each heat transfer surface area (换热面积), resulting in a more compact and energy-efficient system design compared to single-coil configurations.
Quality Certifications
Product Standards Compliance
| Standard | Description | Scope |
|---|---|---|
| ASTM A270 / A270M | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing | Material & Tubing |
| GB/T 12451-2014 | Stainless Steel Seamless Tubes (中国国家标准) | Material & Tubing |
| ASTM A967 | Standard Practice for Chemical Cleaning and Passivation of Stainless Steel Parts | Surface Treatment |
| ASME BPVC Section VIII | Boiler and Pressure Vessel Code | Pressure Vessel Integration |
| ISO 3506-1 | Corrosion Resistance of Stainless Steels in Atmospheres | Corrosion Testing |
| EN 10216-5 | Heat Exchanger Tubes and Condenser Tubes — Stainless Steel | Heat Transfer Applications |
Manufacturing Certifications
- ISO 9001:2015 — Quality Management System Certification (质量管理体系认证)
- ISO 14001:2015 — Environmental Management System (环境管理体系)
- ASME "S" Stamp — Boiler and Pressure Vessel Manufacturer Certification (锅炉及压力容器制造认证)
- CE Marking — European Conformity for Pressure Equipment Directive (PED 2014/68/EU)
- NB Inspection — Notified Body Inspection for pressure equipment components
Testing & Inspection Protocols
- Hydrostatic Pressure Test (液压试验): 1.5 × Design Pressure, held for minimum 15 minutes with zero leakage tolerance.
- Dimensional Verification (尺寸验证): Coordinate Measuring Machine (坐标测量机, CMM) inspection of coil geometry, pitch accuracy, and dimensional tolerances (尺寸公差).
- Material Verification (材质验证): Spectroscopic analysis (光谱分析) confirming chemical composition within specified ranges.
- Corrosion Testing (腐蚀试验): Salt spray testing (盐雾试验) per ASTM B117 — minimum 500 hours without pitting.
- Weld Quality (焊缝质量): Dye Penetrant Testing (渗透检测,