Stainless Steel Coil Tube for Steam Superheater Applications
1. Product Overview
The Stainless Steel Coil Tube is a precision-engineered heat exchange component manufactured by Wenzhou Jixing Metal Materials Co., Ltd., specifically designed for use in steam superheater systems, boiler assemblies, and industrial heat transfer applications. These coil tubes are formed from high-grade stainless steel strip or seamless pipe through advanced coil forming processes, providing superior thermal efficiency, corrosion resistance, and mechanical durability under extreme operating conditions.
Coil tubes are widely employed in steam superheater (蒸汽过热) systems where hot flue gases transfer thermal energy to process steam, raising its temperature beyond saturation. The continuous helical geometry maximizes heat transfer surface area while minimizing pressure drop, making these components critical in power generation, petrochemical processing, and industrial steam systems.
2. Material & Properties
2.1 Commonly Used Stainless Steel Grades
- 304 (UNS S30400 / 06Cr19Ni10) — General-purpose austenitic grade with excellent corrosion resistance and formability; suitable for moderate-temperature superheater applications.
- 321 (UNS S32100 / 06Cr18Ni11Ti) — Titanium-stabilized austenitic grade offering superior resistance to intergranular corrosion and high-temperature scaling; preferred for steam superheater coil tubes operating above 600°C.
- 310S (UNS S31008 / 06Cr25Ni20) — High-chromium, high-nickel austenitic grade with exceptional oxidation resistance up to 1150°C; used in ultra-high-temperature superheater zones.
- 347 (UNS S34700 / 06Cr18Ni11Nb) — Niobium-stabilized variant providing enhanced creep strength and resistance to sensitization at elevated temperatures.
2.2 Key Mechanical Properties (Typical Values for Grade 321)
- Tensile Strength (抗拉强度): ≥ 520 MPa at room temperature
- Yield Strength (屈服强度): ≥ 205 MPa (0.2% offset)
- Elongation (延伸率): ≥ 40% (minimum 2 inches gauge length)
- Hardness (硬度): ≤ 201 HB (annealed condition)
- Thermal Conductivity (导热系数): 16.3 W/(m·K) at 100°C
- Thermal Expansion Coefficient (热膨胀系数): 17.3 × 10⁻⁶ /°C (20–100°C)
- Maximum Operating Temperature (最高使用温度): 870°C (continuous service)
2.3 Corrosion Resistance Characteristics
Stainless steel coil tubes exhibit outstanding resistance to a wide range of corrosive media encountered in steam superheater environments, including:
- Resistance to sulfuric acid (硫酸) and sulfurous acid at moderate concentrations
- Resistance to nitric acid (硝酸) and organic acids
- Resistance to oxidation (氧化) and scaling (结垢) at elevated temperatures
- Resistance to chlorides (氯化物) — limited for standard 304; use 316L for chloride-rich environments
3. Specifications
| Parameter | Specification / Range | Unit | Standard Reference |
|---|---|---|---|
| Outer Diameter (外径) | φ19.05, φ21.34, φ25.4, φ31.75, φ38.1, φ44.45, φ50.8, φ57.15, φ60.3, φ76.2, φ88.9, φ101.6, φ114.3, φ159.0 | mm | ASTM A312 / GB/T 12771 |
| Wall Thickness (壁厚) | 0.50 – 6.00 | mm | ASTM A312 / ASME B36.19M |
| Coil Bend Radius (盘管弯曲半径) | 100 – 2000 | mm | Custom per application |
| Coil Length (盘管长度) | Up to 50,000 | mm | Custom per application |
| Spiral Pitch (螺旋节距) | 20 – 500 | mm | Custom per application |
| Surface Finish (表面光洁度) | 2B (mill finish) or No. 4 brushed; Ra ≤ 0.8 μm for polished | — | ASTM A478 |
| End Condition (端部状态) | Plain cut, beveled, threaded, or socket welded | — | Per customer drawing |
| Tolerance — OD (外径公差) | ±0.10 mm (for OD ≤ φ32); ±0.15 mm (for OD > φ32) | mm | ASTM A312 |
| Tolerance — Wall Thickness (壁厚公差) | ±10% of nominal | — | ASTM A312 |
| Operating Pressure (工作压力) | Up to 35 | MPa | ASME BPVC Section I |
| Operating Temperature (工作温度) | −196 to 870 | °C | Material-dependent |
| Coil Forming Method (成型方式) | Hot bending, cold bending, or roll forming | — | Per design specification |
| Heat Treatment (热处理) | Solution annealing (固溶处理) at 1010–1150°C followed by air/water quench | — | ASTM A312 |
4. Manufacturing Process
4.1 Raw Material Preparation
High-purity stainless steel ingots or strip are sourced from certified mills. Incoming materials undergo strict inspection for chemical composition (via Spectroscopic Analysis 光谱分析), grain structure, and mechanical properties before entering the production line.
4.2 Seamless Pipe Production
- Auting (穿孔): Billet is heated to 1100–1200°C and pierced through a mandrel to form a hollow shell.
- Pilger Rolling / Mannesmann Rolling (轧管): The hollow shell is rolled to reduce wall thickness and achieve near-final dimensions.
- Elongation (拉拔): The pipe is drawn through calibrated dies to achieve precise final dimensions and surface finish.
- Solution Annealing (固溶退火): The pipe is heated to 1010–1150°C and rapidly quenched to dissolve carbides and restore full austenitic microstructure.
4.3 Coil Forming (盘管成型)
- Cutting: Straight pipe segments are cut to required lengths using precision plasma or saw cutting.
- End Preparation: Tube ends are deburred, chamfered, or beveled as required.
- Bending:
- Cold Bending (冷弯): For bend radii ≥ 3D (D = pipe OD); performed at ambient temperature using hydraulic mandrel benders.
- Hot Bending (热弯): For tighter radii or larger diameters; pipe is locally heated to 800–950°C and formed over a mandrel.
- Roll Forming (滚压成型): Continuous spiral forming using rotating rollers for long, uniform coils.
- Spiral Assembly: Individual bent segments are joined by TIG (Tungsten Inert Gas 钨极氩弧焊) or Orbital Welding (自动环焊) to form the complete helical coil geometry.
- Post-Forming Heat Treatment: Stress-relief annealing at 500–650°C (for stabilized grades) to eliminate residual bending stresses without sensitization.
4.4 Surface Treatment & Finishing
- Pickling & Passivation (酸洗钝化): Removal of heat-affected scale followed by passivation to restore chromium oxide protective layer.
- Polishing (抛光): Available in 2B, No. 4, or mirror finish (Ra ≤ 0.2 μm) depending on application requirements.
- Protective Coating: Optional epoxy or polyurethane coating for transport protection.
5. Applications
5.1 Steam Superheater Systems (蒸汽过热器系统)
Coil tubes are the primary heat exchange element in convection superheaters (对流式过热器) and radiant superheaters (辐射式过热器) in:
- Power Generation Plants (火力发电厂): Coal-fired, oil-fired, and gas-fired boilers where steam must be superheated from saturation temperature (typically 300–350°C) to 540–620°C for turbine inlet.
- Boiler Coil Tube Replacement (锅炉盘管换管): Periodic replacement of oxidized or scaled superheater tubes to restore thermal efficiency and prevent tube rupture.
5.2 Petrochemical & Process Industries (石油化工与过程工业)
- Steam generators in catalytic cracking units (FCC)
- Reboilers and evaporators in distillation columns
- Process heaters in polymerization and refining operations
- Heat recovery steam generators (HRSG) in combined-cycle gas turbines
5.3 Marine & Offshore Applications (海洋与海上应用)
- Shipboard boiler superheaters
- Offshore platform heating systems
- Marine waste-heat recovery units
5.4 Food & Pharmaceutical Processing (食品与制药加工)
- Sterilization systems requiring sanitary-grade heat exchange
- Condenser and evaporator coils in pharmaceutical equipment
6. Quality Certifications & Standards Compliance
6.1 Applicable Standards (适用标准)
| Standard | Description |
|---|---|
| ASTM A312 / A312M | Standard Specification for Seamless, Welded, and Heavy-Walled Austenitic Stainless Steel Pipes and Tubes |
| ASME SA-213 | Boiler, Heat Exchanger, and Heat Transfer Equipment Tubes — Austenitic Steel |
| GB/T 12771 | Stainless Steel Seamless Tubes for General Purposes (Chinese National Standard) |
| EN 10216-5 | Non-alloy and Alloy Steel Tubes for Heat Exchangers and Similar Applications |
| ASME BPVC Section I | Rules for Construction of Power Boilers |
| API 5CT / 5L | For pressure-containing components in oil and gas industry |
| ISO 9001:2015 | Quality Management System Certification |
6.2 Quality Assurance Testing (质量保证检测)
- Chemical Composition Analysis (化学成分分析): Verified by optical emission spectroscopy (OES) and wet chemical analysis to confirm grade compliance (C, Cr, Ni, Ti/Nb, Mo, S, P limits).
- Mechanical Testing (力学性能测试): Tensile strength, yield strength, and elongation tested per ASTM A370 at representative sample intervals.
- Hydrostatic Testing (水压试验): 100% pressure test at 1.5× design pressure to verify weld integrity and absence of leaks.
- Dimensional Inspection (尺寸检测): OD, wall thickness, and length verified by ultrasonic thickness gauging and precision calipers.
- Non-Destructive Testing (无损检测, NDT):
- Eddy Current Testing (涡流检测): 100% inline inspection for surface and near-surface defects.
- Ultrasonic Testing (超声波检测, UT): For volumetric defect detection in thick-wall tubes.
- Magnetic Particle Inspection (磁粉检测, MPI): For ferromagnetic materials (if applicable).
- Visual Inspection (目视检测): All welds and coil geometry inspected for surface discontinuities.