Stainless Steel Coil Tube for Oilfield Phase Change Heater — Technical Specification
1. Product Overview
The Coil Tube (盘管) manufactured by Wenzhou Jixing Metal Materials Co., Ltd (Product No. 659) is a precision-engineered stainless steel heat exchange element specifically designed for use in Oilfield Phase Change Heaters (油田相变加热炉). Phase change heaters are critical thermal management devices employed in upstream petroleum operations to maintain the flow temperature of crude oil, thereby reducing viscosity and ensuring efficient pipeline transport in cold or sub-zero environments.
Unlike conventional tubular heat exchangers, coil tubes leverage the inherent advantages of coiled geometry — including compact volumetric footprint, high surface-area-to-volume ratio, and superior turbulent flow characteristics — to achieve efficient heat transfer through a phase-change working medium (typically paraffin or salt hydrate). The coil tube serves as the primary heat exchange surface where the thermal energy stored in the latent heat material is transferred to the flowing crude oil.
This product represents a specialized engineering solution developed through rigorous research into coil tube heat exchange calculation methodologies (盘管换热计算方法), incorporating advanced thermal-fluid modeling to optimize heat transfer efficiency, pressure drop characteristics, and long-term operational reliability under demanding oilfield conditions.
2. Material & Properties
2.1 Base Material Grades
The coil tube is fabricated from high-grade austenitic and duplex stainless steels selected for their exceptional corrosion resistance, thermal conductivity, and mechanical integrity under cyclic thermal loading:
- Austenitic Stainless Steel (奥氏体不锈钢): SUS304 (UNS S30408), SUS316 (UNS S31608), and SUS321 (UNS S32108) — offering outstanding resistance to pitting, crevice corrosion, and stress corrosion cracking in chloride-containing oilfield environments.
- Duplex Stainless Steel (双相不锈钢): SUS31803 / UNS S31803 (2205 equivalent) — providing superior mechanical strength (yield strength ≥ 450 MPa) and enhanced resistance to sulfide stress cracking in sour service conditions.
- Super Duplex Stainless Steel (超级双相不锈钢): UNS S32750 (2507 equivalent) — for extreme corrosion environments with high chloride concentrations and elevated temperatures.
2.2 Key Material Properties
| Property (性能参数) | SUS304 | SUS316 | UNS S31803 (2205) |
|---|---|---|---|
| Tensile Strength (抗拉强度), MPa | ≥ 520 | ≥ 515 | ≥ 550 |
| Yield Strength (屈服强度), MPa | ≥ 205 | ≥ 170 | ≥ 450 |
| Thermal Conductivity (导热系数), W/(m·K) @ 100°C | 16.3 | 14.6 | 18.0 |
| Thermal Expansion Coefficient (热膨胀系数), 10⁻⁶/K | 17.3 | 16.0 | 13.0 |
| PREN (Pitting Resistance Equivalent Number) | 19 | 26 | 35 |
| Maximum Service Temperature (最高使用温度), °C | 870 | 870 | 320 |
| Corrosion Resistance to H₂S (耐硫化氢性能) | Moderate | Good | Excellent |
2.3 Surface Finish
The inner and outer surfaces of the coil tube are finished to a precision electropolished (电解抛光) or mechanically polished (机械抛光) condition, achieving a surface roughness of Ra ≤ 0.4 μm. This ensures minimal frictional resistance to crude oil flow and prevents the accumulation of wax deposits and corrosion products on the heat exchange surface, thereby maintaining long-term thermal efficiency.
3. Specifications
3.1 Geometric Dimensions
| Parameter (参数) | Specification / Range (规格/范围) | Standard Reference (标准参照) |
|---|---|---|
| Outer Diameter (外径, OD) | Φ 6.0 mm – Φ 38.0 mm (customizable) | ASTM A213 / GB/T 12771 |
| Wall Thickness (壁厚) | 0.5 mm – 3.0 mm | ASME B36.19M |
| Coil Pitch (盘管节距) | 15 mm – 80 mm (optimized per thermal model) | Custom Engineering |
| Coil Diameter (盘管直径) | Φ 200 mm – Φ 1,200 mm | Custom Engineering |
| Tube Length per Coil (单圈管长) | 1.0 m – 15.0 m (continuous coil) | — |
| Total Developed Length (展开总长) | Up to 200 m per coil assembly | — |
| End Preparation (端部处理) | Beveled / Flat / Threaded / Socket-weld (per customer spec) | ASME B1.20.1 / GB/T 12716 |
| Dimensional Tolerance (尺寸公差) | OD: ±0.1 mm; Wall: ±0.05 mm | ASTM A213 |
3.2 Thermal Performance Parameters
| Thermal Parameter (热工参数) | Typical Value (典型值) | Test/Calculation Method (测试/计算方法) |
|---|---|---|
| Overall Heat Transfer Coefficient (总传热系数), U | 180 – 350 W/(m²·K) | Numerical simulation (CFD) + empirical correlation |
| Heat Transfer Area per Unit Volume (单位体积换热面积) | 120 – 280 m²/m³ | Geometric calculation |
| Pressure Drop (压降), ΔP | 0.02 – 0.15 MPa (at design flow rate) | Darcy-Weisbach equation with coil correction factor |
| Maximum Design Temperature (最高设计温度) | 120°C – 180°C (depending on PCM type) | Phase change material compatibility |
| Design Pressure (设计压力) | 1.6 MPa – 6.4 MPa | ASME VIII Div.1 / GB/T 150 |
| Thermal Efficiency (热效率) | ≥ 85% (NTU-ε method) | Effectiveness-NTU analysis |
3.3 Applicable Standards
- ASTM A213 / A213M — Standard Specification for Seamless Austenitic Stainless Steel Tubing for High-Temperature Service
- ASME B31.3 — Process Piping
- GB/T 12771 — Welded Stainless Steel Tubing for Fluid Transport
- GB/T 24511 — Pressure Vessel and Heat Exchanger Design
- API 5CT — Casing and Tubing (for oilfield compatibility)
- NACE MR0175 / ISO 15156 — Materials for Use in H₂S Environments
4. Manufacturing Process
4.1 Process Flow
- Material Selection & Heat Treatment Verification (材料选择与热处理验证): Incoming stainless steel bar stock or seamless tube billets are verified for chemical composition (per ASTM A29/A29M) and mechanical properties. Heat treatment condition (annealed / solution-treated at 1050–1150°C followed by rapid cooling) is confirmed to ensure full austenitic or duplex microstructure.
- Precision Forming / Cold Coiling (精密成型/冷盘绕): Seamless stainless steel tubing is cold-coiled into the specified helical geometry using CNC-controlled coiling equipment. The forming process is carefully controlled to prevent work hardening beyond acceptable limits, maintaining ductility for subsequent installation. Coil pitch and diameter tolerances are monitored in real-time.
- Welding & Seam Repair (焊接与焊缝修复): Where continuous length requires joining, orbital GTAW (Gas Tungsten Arc Welding, 钨极氩弧焊) is employed with full penetration welds. Back-purging with high-purity argon (O₂ < 20 ppm) ensures a clean, oxide-free weld interior. Weld seams undergo 100% visual inspection and radiographic testing (RT) per ASME Section V.
- Surface Treatment & Passivation (表面处理与钝化): The coil tube undergoes mechanical polishing or electropolishing to achieve the target surface roughness. Chemical passivation (per ASTM A967, using nitric acid or citric acid solution) removes free iron and establishes a stable chromium oxide passive film, enhancing corrosion resistance.
- Hydrostatic Testing (水压试验): Each coil assembly is subjected to hydrostatic pressure testing at 1.5× the design pressure for a minimum dwell time of 30 minutes, with zero leakage permitted. Testing is conducted in accordance with ASTM A213 and ASME B31.3 requirements.
- Non-Destructive Examination (无损检测, NDE): Comprehensive NDE includes 100% eddy current testing (ECT) for surface and near-surface defects, ultrasonic testing (UT) for internal wall thickness verification, and dye penetrant testing (PT) for end preparations and weld joints.
- Final Inspection & Packaging (最终检验与包装): Dimensional verification using coordinate measuring machines (CMM), surface finish measurement, and material certification (Mill Test Reports / 材质证明书) are compiled. Products are packaged in protective corrugated cartons with moisture-absorbing desiccants for export.
4.2 Thermal Design Methodology
The coil tube design incorporates advanced heat exchange calculation methodologies specifically developed for phase change heater applications. The design process integrates the following analytical and numerical approaches:
- Latent Heat Storage Modeling (潜热蓄热模型): The phase change material (PCM) surrounding the coil tube is modeled using the enthalpy-porosity method, accounting for the Stefan problem at the solid-liquid interface during melting and solidification cycles.
- Turbulent Flow Heat Transfer Correlation (湍流换热关联式): The Dittus-Boelter and Gnielinski correlations are modified with Dean number (De) corrections to account for secondary flow effects in the helical coil geometry, accurately predicting the Nusselt number and local heat transfer coefficient.
- Thermal Resistance Network Analysis (热阻网络分析): A comprehensive thermal resistance model is constructed, incorporating convective resistance on the oil side, conductive resistance through the tube wall, fouling resistance, and convective resistance on the PCM side.
- CFD Simulation (计算流体力学仿真): Three-dimensional computational fluid dynamics simulations (ANSYS Fluent / COMSOL Multiphysics) are performed to validate analytical results, optimize coil geometry, and predict thermal performance under transient operating conditions.
- Cyclic Thermal Fatigue Assessment (循环热疲劳评估): Given the repeated heating and cooling cycles inherent to phase change operation, thermal fatigue life is assessed using Coffin-Manson and Basquin relationships to ensure long-term structural integrity.
5. Applications
5.1 Primary Application: Oilfield Phase Change Heaters
The primary application of this coil tube product is within oilfield phase change heaters (油田相变加热炉), which are thermal management systems deployed at wellheads, gathering stations, and pipeline segments to maintain crude oil at a temperature sufficient for low-viscosity flow. These heaters operate by absorbing heat from a combustion source (or external thermal source) during the melting phase of the encapsulated PCM, and releasing this stored thermal energy to the crude oil during the solidification phase — enabling continuous, low-maintenance heating without the need for direct flame contact with the process fluid.
5.2 Detailed Application Scenarios
- Wellhead Heaters (井口加热): Maintaining production tubing temperature to prevent wax deposition and hydrate formation in subterranean or arctic production environments.
- Gathering Line Heaters (集输管线加热): Ensuring continuous flow of heavy or waxy crude oil through gathering pipelines in cold climates (e.g., Siberian, Canadian, and Arctic operations).
- Separators & Accumulators (分离器与储罐加热): Maintaining temperature in upstream processing equipment to facilitate oil-water-gas separation at optimal viscosity conditions.
- Subsea Production Systems (水下生产系统): Providing thermal management for subsea flowlines and manifolds where conventional electric tracing is impractical.
5.3 Extended Applications
- Chemical process heat exchangers requiring high-purity stainless steel contact surfaces
- Food and pharmaceutical industry heat exchange systems (hygienic grade)
- Geothermal energy extraction systems
- Marine and offshore platform thermal management
- Solar thermal energy storage systems
6. Quality Certifications & Compliance
6.1 International Certifications
- ISO 9001:2015 — Quality Management System certification covering the full manufacturing process from material procurement to final dispatch.
- ISO 14001:2015 — Environmental Management System certification, ensuring environmentally responsible manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management System.
- API Q1 (API Spec Q1) — Quality Management System for oil and gas industry, ensuring traceability and reliability for petroleum applications.
- CE Marking (EU) — Conformity with European Pressure Equipment Directive (PED 2014/68/EU) for pressure-rated applications.
- NACE MR0175 / ISO