0Cr25Ni20 Heat-Resistant Superheated Steam Coil Tube (Coiltube) — Technical Specification
1. Product Overview
The 0Cr25Ni20 Heat-Resistant Superheated Steam Coil Tube (Catalogue No. 1279) is a high-temperature austenitic stainless steel coil tube manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is specifically engineered for superheated steam service environments where extreme thermal cycling, oxidative degradation, and mechanical fatigue present significant challenges. The coil tube configuration enables efficient heat transfer surface area in compact geometries, making it an indispensable component in power generation, petrochemical processing, and industrial thermal systems.
Unlike conventional straight-section tubing, coil tubes are formed into helical or serpentine geometries during manufacturing, providing superior thermal performance in superheater and reheater sections of boilers. The 0Cr25Ni20 grade offers exceptional hot strength, scale resistance, and thermal stability at operating temperatures exceeding 1100°C (2012°F), making it the preferred alloy for the most demanding superheated steam applications.
2. Material & Properties
2.1 Chemical Composition (0Cr25Ni20 / SUS310 / UNS S31008)
The base material conforms to GB/T 20878 (Chinese National Standard for Stainless Steel and Heat-Resistant Steel) and is equivalent to ASTM A213 TP310, EN 1.4845 (X15CrNiSi25-21), and ISO 3506 (SUS310).
| Element | Minimum (%) | Maximum (%) |
|---|---|---|
| Carbon (C) | — | 0.08 |
| Chromium (Cr) | 24.00 | 26.00 |
| Nickel (Ni) | 19.00 | 22.00 |
| Manganese (Mn) | — | 2.00 |
| Silicon (Si) | — | 1.50 |
| Sulfur (S) | — | 0.030 |
| Phosphorus (P) | — | 0.045 |
| Iron (Fe) | Balance | — |
2.2 Mechanical Properties (Annealed Condition)
| Property | Specification | Test Temperature |
|---|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa (75.4 ksi) | Room Temperature (20°C) |
| Yield Strength (Rp0.2) | ≥ 205 MPa (29.7 ksi) | Room Temperature (20°C) |
| Elongation (A50mm) | ≥ 40% | Room Temperature (20°C) |
| Reduction of Area (Z) | ≥ 50% | Room Temperature (20°C) |
| Hot Tensile Strength | ≥ 220 MPa | 1000°C (1832°F) |
| Hot Tensile Strength | ≥ 150 MPa | 1100°C (2012°F) |
2.3 Physical Properties
- Density: 7.94 g/cm³ (0.287 lb/in³)
- Thermal Conductivity: 21.6 W/(m·K) at 100°C; 33.8 W/(m·K) at 500°C
- Specific Heat: 0.50 J/(g·K) at 100°C; 0.60 J/(g·K) at 500°C
- Coefficient of Thermal Expansion: 17.1 × 10⁻⁶ /K (20–1000°C)
- Electrical Resistivity: 750 μΩ·cm at 20°C
- Melting Range: 1400–1450°C (2552–2642°F)
2.4 Heat Resistance & Oxidation Resistance
- Maximum Continuous Service Temperature: 1150°C (2092°F)
- Intermittent Service Temperature: Up to 1200°C (2192°F)
- Scale Formation Rate: < 1.5 mg/(dm²·h) at 1000°C in air (ASTM G93)
- Creep Strength (1% total elongation, 10,000 h): ~170 MPa at 1000°C; ~120 MPa at 1100°C
- Sintering Temperature: 1300°C (2372°F) — onset of grain boundary sintering
3. Specifications
3.1 Dimensional Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 14.0 – 159.0 mm (0.55 – 6.26 in) | GB/T 14976 / ASTM A213 |
| Wall Thickness | 1.0 – 6.0 mm (0.039 – 0.236 in) | GB/T 14976 |
| Coil Diameter (Center-to-Center) | 150 – 3000 mm (5.9 – 118.1 in) | Project-Specific |
| Coil Pitch (Turn-to-Turn) | 50 – 500 mm (2.0 – 19.7 in) | Project-Specific |
| Tube Length (Uncoiled) | 6.0 – 12.0 m (20 – 40 ft) per section | ASTM A213 |
| OD Tolerance | ±0.10 mm for OD ≤ 50 mm; ±0.05% for OD > 50 mm | GB/T 14976 |
| Wall Thickness Tolerance | ±10% (minimum ±0.10 mm) | GB/T 14976 |
| Roundness | ≤ 0.5% of OD | GB/T 14976 |
3.2 Material Grade Designations
| Standard | Grade Designation | Equivalent |
|---|---|---|
| GB (China) | 0Cr25Ni20 | — |
| ASTM (USA) | TP310 / TP310S | UNS S31008 / S31009 |
| EN (Europe) | 1.4845 (X15CrNiSi25-21) | — |
| JIS (Japan) | SUS310 / SUS310S | — |
| BS (UK) | 310S | — |
4. Manufacturing Process
4.1 Production Workflow
- Raw Material Procurement: High-purity 0Cr25Ni20 stainless steel billets or strip, sourced from certified mills with full heat number traceability and mill test certificates (MTC) conforming to EN 10204 Type 3.1.
- Hot Rolling / Seamless Tube Forming: Billet piercing followed by hot rolling on a Mannesmann mill or continuous tube mill to produce seamless round tubes of the required OD and wall thickness. Alternatively, hot-rolled strip is used for welded coil tube production via ERW (Electric Resistance Welding) or TIG (Tungsten Inert Gas) welding.
- Pickling and Descaling: Tubes are pickled in a mixed acid solution (HNO₃/HF) to remove mill scale and heat treatment oxides, followed by passivation to restore the passive chromium oxide layer.
- Heat Treatment (Solution Annealing): Tubes are solution-annealed at 1050–1150°C with rapid water quenching to dissolve carbides, eliminate sensitization, and achieve a uniform austenitic microstructure free of δ-ferrite.
- Coil Forming / Bending: Straight tubes are formed into helical or serpentine coil geometries using CNC-controlled cold coil bending machines or hot forming equipment. The bending process is carefully controlled to avoid cold work hardening and micro-cracking, with minimum bend radii of ≥ 3× OD for cold forming or ≥ 2× OD for hot forming.
- Post-Forming Annealing: Coiled tubes undergo stress-relief annealing at 1050°C to restore ductility and relieve residual stresses introduced during the bending process.
- Final Inspection and Testing: Comprehensive quality assurance including dimensional inspection, ultrasonic testing (UT), eddy current testing (ECT), hydrostatic testing, and chemical/spectral analysis.
4.2 Crack Repair Methodology for Superheated Steam Coil Tubes
A critical knowledge area associated with this product is the crack repair technique for 0Cr25Ni20 superheated steam coil tubes in operational service. Based on documented field experience, the following repair protocol has been established:
- Crack Detection and Assessment: Cracks are identified through visual inspection, dye penetrant testing (PT), or ultrasonic testing (UT). The crack depth, length, and location relative to the coil geometry are precisely mapped.
- Surface Preparation: The crack region is ground to a smooth, defect-free surface with a minimum 60° V-groove preparation. The area is cleaned with acetone to remove all contaminants.
- Preheating: The repair area is preheated to 200–300°C to reduce thermal gradients and prevent cold cracking during welding.
- Welding: TIG (GTAW) welding is performed using matching 0Cr25Ni20 or ER310 filler wire. Interpass temperature is maintained below 300°C. Multi-pass welding with root pass performed under high-purity argon shielding (99.999% Ar) is recommended.
- Post-Weld Heat Treatment: The repair area is solution-annealed at 1050–1100°C with air cooling or controlled water quenching to homogenize the weld zone and restore mechanical properties.
- Post-Repair Verification: The repaired section is subjected to 100% UT and PT inspection. Hydrostatic testing at 1.5× design pressure confirms leak tightness before return to service.
Key Learning Insight: The primary failure mode in 0Cr25Ni20 superheated steam coil tubes is high-temperature oxidation-induced surface cracking, typically initiated at the coil outer diameter where maximum thermal stress and scale accumulation occur. The combination of high chromium (24–26%) and nickel (19–22%) content provides excellent resistance to internal oxidation, but prolonged exposure above 1000°C can lead to chromia scale spallation and subsequent crack initiation. Regular inspection intervals of 12–24 months are recommended for coils operating above 900°C.
5. Applications
5.1 Primary Application Domains
- Power Generation: Superheater tubes and reheater tubes in subcritical, supercritical, and ultra-supercritical (USC) boilers operating at steam temperatures of 540–620°C (1004–1148°F). The coil tube configuration is particularly advantageous in compact superheater designs for biomass and waste-to-energy plants.
- Petrochemical Processing: Furnace tubes in ethylene crackers, reformers, and steam cracking coils where temperatures reach 900–1100°C. Used in radiating sections of process heaters and reformer tubes.
- Industrial Furnaces: Heat treatment furnace components, radiant tubes, and heating elements in steel annealing, glass manufacturing, and ceramic firing applications.
- Waste-to-Energy (WtE) Plants: Superheated steam generation coils in municipal solid waste incinerators where aggressive flue gas environments and thermal cycling are prevalent.
- Chemical Processing: High-temperature reactor coils, evaporators, and heat exchangers processing corrosive and high-temperature chemical streams.
- Aerospace: Turbine engine components, exhaust systems, and high-temperature structural elements requiring exceptional creep resistance.
5.2 Service Conditions
| Parameter | Typical Range |
|---|---|
| Operating Temperature | 800 – 1150°C (1472 – 2092°F) |
| Design Pressure | 1.0 – 10.0 MPa (145 – 1450 psi) |
| Medium | Superheated steam, combustion gases, hot air, inert atmospheres |
| Cyclic Loading | Up to 5000 thermal cycles (startup/shutdown) |
| Design Life | 20 – 30 years (with periodic inspection and repair) |