Stainless Steel Coil Tube for High-Pressure Steam Superheater Applications — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (盘管, Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered, continuous-coiled tubular product specifically designed for high-pressure steam superheater systems in power generation, petrochemical, and industrial process heating applications. Unlike conventional straight-length tubes that require field welding and joint fabrication, coil tubes are produced in continuous helical configurations, eliminating intermediate butt joints and thereby significantly reducing the risk of stress concentration, fatigue failure, and thermal deformation at weld points.
This product line is particularly distinguished by its application in high-pressure steam superheater (高压蒸汽过热) environments, where operating temperatures routinely exceed 550°C and pressures surpass 10 MPa. Extensive field experience and failure analysis studies — including systematic investigations into coil tube deformation mechanisms (变形原因分析) — have informed the design, material selection, and manufacturing tolerances of this product, ensuring long-term structural integrity under extreme thermal cycling and mechanical loading conditions.
Key unique selling points include:
- Jointless continuous coil geometry — eliminates weld-induced stress risers and reduces failure probability by up to 60% compared to field-welded assemblies
- Engineered for high-pressure steam superheater duty — validated through documented deformation analysis and countermeasure protocols
- Multi-grade stainless steel availability — covering austenitic, ferritic, and austenitic-ferritic (duplex) microstructures to suit diverse service conditions
- Consistent coil diameter and pitch control — CNC-guided forming ensures geometric uniformity critical for heat transfer optimization
- Comprehensive traceability — full material certification and manufacturing documentation per international standards
2. Material & Properties
2.1 Available Grades
The coil tube product line is offered in multiple stainless steel grades selected for superior resistance to oxidation, creep deformation, and thermal fatigue at elevated temperatures:
| Grade Designation | UNS Designation | Microstructure | Key Alloying Elements | Maximum Service Temperature (°C) | Typical Application |
|---|---|---|---|---|---|
| 304 / 06Cr19Ni10 | S30400 | Austenitic | 18–20% Cr, 8–10% Ni | 870 | General high-temperature service, moderate corrosion |
| 316 / 06Cr17Ni12Mo2 | S31600 | Austenitic | 16–18% Cr, 10–14% Ni, 2–3% Mo | 870 | Chloride-containing superheater environments |
| 310S / 06Cr25Ni20 | S31008 | Austenitic (high Cr-Ni) | 24–26% Cr, 19–22% Ni | 1150 | Ultra-high-temperature superheater zones |
| 321 / 06Cr18Ni11Ti | S32100 | Austenitic (Ti-stabilized) | 17–19% Cr, 9–12% Ni, 0.08–0.20% Ti | 900 | Intergranular corrosion-resistant superheater duty |
| 430 / 06Cr13 | S43000 | Ferritic | 11.5–14.5% Cr | 870 | Cost-effective superheater with moderate oxidation resistance |
| 2205 / S31803 | S31803 | duplex (Austenitic-Ferritic) | 21–23% Cr, 4.5–6.5% Ni, 0.1–0.3% N | 425 | High-strength, chloride-resistant superheater applications |
2.2 Mechanical Properties (Representative Values)
| Property | Grade 304 | Grade 316 | Grade 310S | Grade 321 | Grade 430 | Grade 2205 |
|---|---|---|---|---|---|---|
| Tensile Strength (Rm, MPa) — Room Temperature | ≥ 520 | ≥ 515 | ≥ 515 | ≥ 515 | ≥ 450 | ≥ 550 |
| Yield Strength (Rp0.2, MPa) — Room Temperature | ≥ 205 | ≥ 205 | ≥ 205 | ≥ 205 | ≥ 205 | ≥ 450 |
| Elongation (A5, %) — Room Temperature | ≥ 40 | ≥ 40 | ≥ 40 | ≥ 40 | ≥ 22 | ≥ 25 |
| Creep Strength (100 h, 1% strain, MPa) — 700°C | ~100 | ~105 | ~220 | ~110 | ~85 | ~180 |
| Thermal Expansion Coefficient (20–800°C, ×10⁻⁶/°C) | 16.5 | 16.5 | 18.0 | 16.5 | 10.5 | 14.0 |
| Thermal Conductivity (W/m·K) — 100°C | 16.3 | 16.3 | 24.7 | 16.3 | 26.2 | 14.0 |
2.3 Key Material Characteristics for Superheater Service
- High-temperature oxidation resistance (高温抗氧化性): Chromium content ≥ 18% ensures formation of a stable Cr₂O₃ passive oxide scale, providing protective barriers against oxidative degradation at temperatures up to 1150°C (Grade 310S).
- Creep resistance (抗蠕变性): Alloying elements such as Ti (Grade 321), Nb (Grade 347), and high Cr-Ni ratios (Grade 310S) enhance dislocation pinning and grain boundary stability, mitigating time-dependent plastic deformation under sustained high-temperature loading.
- Thermal fatigue resistance (抗热疲劳性): The austenitic grades exhibit superior ductility and thermal shock tolerance, accommodating repeated thermal cycling without crack initiation at stress-concentrated coil bends.
- Intergranular corrosion resistance (抗晶间腐蚀性): Ti-stabilized grades (321) and Mo-bearing grades (316) prevent chromium carbide precipitation at grain boundaries, maintaining microstructural integrity in chloride-rich environments.
3. Specifications
3.1 Dimensional Specifications
| Parameter | Specification | Tolerance | Applicable Standard |
|---|---|---|---|
| Outer Diameter (OD) | Φ9.5 mm – Φ114.3 mm | ±0.10 mm | ASTM A213 / GB/T 14976 |
| Wall Thickness (WT) | 0.50 mm – 6.00 mm | ±10% of nominal | ASTM A213 / GB/T 14976 |
| Coil Outer Diameter (C-OD) | Φ200 mm – Φ1,200 mm | ±2% of nominal | Manufacturer Specification |
| Coil Inner Diameter (C-ID) | Φ150 mm – Φ1,000 mm | ±2% of nominal | Manufacturer Specification |
| Coil Length (per coil) | 50 m – 300 m (continuous) | ±5% | Manufacturer Specification |
| Coil Pitch / Spacing | As per design requirement | ±0.5 mm | Customer Drawing |
| Bend Radius (minimum) | ≥ 3× OD | — | ASTM A213 |
| Surface Roughness (Ra) | ≤ 0.8 μm (inner); ≤ 1.6 μm (outer) | — | GB/T 1031 |
| End Condition | Plain cut, beveled, or threaded | Per customer spec | Customer Drawing |
3.2 Performance Specifications for High-Pressure Superheater Duty
| Performance Parameter | Design Value | Test Method |
|---|---|---|
| Maximum Operating Pressure | Up to 25 MPa (3,625 psi) | Hydrostatic Pressure Test (1.5× design pressure) |
| Maximum Operating Temperature | Up to 650°C (1,202°F) [Grade-dependent] | Thermal cycling test (10,000 cycles) |
| Design Service Life | ≥ 200,000 hours (continuous operation) | Creep rupture testing per ASTM E139 |
| Hydrostatic Test Pressure | 1.5× maximum operating pressure | ASTM A213 / ASME BPV Section I |
| Non-Destructive Testing (NDT) | 100% eddy current (ECT) + ultrasonic testing (UT) | ASTM E309 / ASTM E213 |
| Heat Treatment | Solution annealing + water quench (as required) | ASTM A213 / Manufacturer Spec |
4. Manufacturing Process
The production of stainless steel coil tubes for high-pressure steam superheater applications involves a rigorously controlled multi-stage manufacturing sequence, each step governed by defined process parameters to ensure dimensional accuracy, microstructural integrity, and mechanical performance:
4.1 Process Flow
- Raw Material Selection & Inspection (原材料选择与检验): Ingot or slab material is selected based on the target grade specification. Incoming material undergoes spectrographic analysis (OES), mechanical property verification, and visual inspection for surface defects. Each heat lot is assigned a unique traceability identifier.
- Hot Rolling / Seamless Tube Production (热轧/无缝管生产): The selected grade is processed via either hot-rolled or seamless piercing methods (e.g., Mannesmann piercing, PLC piercing) to produce round bar stock or seamless tube blanks with the target OD and WT dimensions. Hot rolling temperatures are controlled within the austenitization range (typically 1,100–1,200°C for austenitic grades) to achieve uniform grain structure.
- Pilot Mill & Cold Drawing (定径轧制与冷拔): The tube blank is passed through a series of precision pilot mills or cold-drawing dies to achieve the final OD and WT dimensions with tight tolerances. Cold working introduces controlled work hardening, improving yield strength while maintaining ductility.
- Solution Annealing (固溶处理): The drawn tube is heated to the solution treatment temperature (typically 1,010–1,150°C for austenitic grades) and rapidly quenched (air or water quench) to dissolve carbide precipitates, restore full austenitic microstructure, and achieve maximum corrosion resistance and ductility.
- Pickling & Passivation (酸洗钝化): The annealed tube surface is cleaned via controlled pickling (HNO₃/HF or citric acid solution) to remove scale and oxide films, followed by passivation treatment to establish a stable chromium oxide passive layer. Surface cleanliness is verified by visual inspection and acid droplet test.
- Coil Forming / Helical Bending (盘绕成型): The straight tube is fed through a CNC-controlled coil forming machine equipped with precision bending dies and guide rollers. The helical pitch, coil diameter, and bend radius are programmatically controlled to meet design specifications. Forming speed, die clearance, and lubrication parameters are optimized to prevent ovality, wrinkling, or thinning at the bend regions.
- Post-Forming Heat Treatment (成型后热处理): If required by the application specification, the formed coil may undergo stress-relief annealing to reduce residual stresses introduced during the bending process. This step is particularly critical for high-pressure superheater applications where residual stress can accelerate creep deformation.
- Non-Destructive Testing (NDT) (无损检测): Every coil tube undergoes 100% eddy current testing (ECT) for detection of internal and external surface defects, and ultrasonic testing (UT) for wall thickness verification and internal flaw detection. Additional testing methods (magnetic particle inspection, penetrant testing) may be applied as specified.
- Hydrostatic Pressure Testing (水压试验): Each coil tube is subjected to a hydrostatic pressure test at 1.5× the design operating pressure, held for a minimum duration to verify structural integrity and absence of leaks. Test results are recorded and documented.
- Final Inspection, Packaging & Shipping (