Stainless Steel Coil Tube for Large-Diameter Once-Through Steam Generators
Product Code: 1144 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
1. Product Overview
The Stainless Steel Coil Tube (盘管 / Coil Tube) is a precision-engineered tubular component specifically designed for use in Large-Diameter Once-Through Steam Generators (OTSG, Once-Through Steam Generator). These steam generators are critical heat exchange components found predominantly in Pressurized Water Reactor (PWR) nuclear power plants and advanced fossil-fuel power generation systems, where feedwater flows through the coil tube in a single pass without recirculation, converting directly into superheated steam.
The coil tube product line from Wenzhou Jixing Metal Materials Co., Ltd. is manufactured to meet the demanding thermal-hydraulic, mechanical, and corrosion resistance requirements imposed by high-pressure, high-temperature steam generation environments. The product incorporates advanced metallurgical design principles and rigorous manufacturing protocols to ensure reliable performance over extended service lives exceeding 40 years in nuclear-grade applications.
The thermal analysis framework underlying the design of large-diameter coil tubes encompasses steam-side heat transfer (蒸汽侧传热), water-side heat transfer (水侧传热), wall temperature distribution (管壁温度分布), dryout (干烧) and departure from nucleate boiling (DNB, Departure from Nucleate Boiling) analysis, and critical heat flux (CHF, Critical Heat Flux) evaluation. These thermal-hydraulic considerations directly inform the material selection, wall thickness design, and manufacturing tolerances of the coil tube.
2. Material & Properties
2.1 Base Material Specification
The coil tube is fabricated from austenitic stainless steel (奥氏体不锈钢) grades that provide an optimal combination of high-temperature strength, oxidation resistance, and corrosion resistance under the extreme operating conditions of once-through steam generators. The primary material grades include:
- S31603 / 316L (UNS S31603): Low-carbon austenitic stainless steel with molybdenum addition, offering superior resistance to chloride pitting corrosion and stress corrosion cracking (SCC, Stress Corrosion Cracking). Carbon content ≤ 0.03% (mass).
- S30408 / 304L (UNS S30408): Low-carbon austenitic stainless steel with excellent general corrosion resistance and formability. Carbon content ≤ 0.03% (mass).
- S32168 / 321H (UNS S32168): Titanium-stabilized austenitic stainless steel designed for high-temperature service, with enhanced resistance to intergranular corrosion (IGC, Intergranular Corrosion).
2.2 Key Mechanical Properties (Typical Values at Room Temperature)
| Property | Grade 316L | Grade 304L | Grade 321H | Test Standard |
|---|---|---|---|---|
| Tensile Strength (Rm, MPa) | ≥ 485 | ≥ 485 | ≥ 520 | ASTM A213 / GB/T 213 |
| Yield Strength (Rp0.2, MPa) | ≥ 170 | ≥ 170 | ≥ 205 | ASTM A213 / GB/T 213 |
| Elongation (A, %) | ≥ 40 | ≥ 40 | ≥ 35 | ASTM A213 / GB/T 213 |
| Hardness (HBW) | ≤ 220 | ≤ 220 | ≤ 230 | ASTM A213 |
| Density (g/cm³) | ~7.98 | ~7.93 | ~7.98 | — |
2.3 Thermal Properties
| Property | Value (Typical) | Temperature Range |
|---|---|---|
| Thermal Conductivity (W/(m·K)) | 14–16 | 25–600 °C |
| Specific Heat Capacity (J/(kg·K)) | 470–550 | 25–600 °C |
| Coefficient of Thermal Expansion (×10⁻⁶/K) | 16–18 | 25–600 °C |
| Maximum Service Temperature (°C) | 870 (316L) / 870 (304L) / 925 (321H) | Continuous service |
2.4 Chemical Composition (Typical, mass %)
| Element | 316L | 304L | 321H |
|---|---|---|---|
| C (Carbon) | ≤ 0.030 | ≤ 0.030 | 0.04–0.10 |
| Mn (Manganese) | ≤ 2.00 | ≤ 2.00 | ≤ 2.00 |
| P (Phosphorus) | ≤ 0.045 | ≤ 0.045 | ≤ 0.045 |
| S (Sulfur) | ≤ 0.030 | ≤ 0.030 | ≤ 0.030 |
| Si (Silicon) | ≤ 1.00 | ≤ 1.00 | 0.50–1.50 |
| Ni (Nickel) | 10.0–14.0 | 8.0–10.5 | 9.0–12.0 |
| Cr (Chromium) | 16.0–18.0 | 18.0–20.0 | 17.0–19.0 |
| Mo (Molybdenum) | 2.0–3.0 | — | — |
| Ti (Titanium) | — | — | 5×C – 0.70 |
2.5 Corrosion Resistance
The austenitic stainless steel coil tube exhibits excellent resistance to:
- General corrosion (均匀腐蚀) in high-purity steam and feedwater environments
- Pitting and crevice corrosion (点蚀与缝隙腐蚀) due to molybdenum addition (316L grade)
- Intergranular corrosion (晶间腐蚀) due to low carbon content or titanium stabilization
- Stress corrosion cracking (应力腐蚀开裂, SCC) in chloride-containing environments
- Oxidation (氧化) at elevated temperatures up to 870–925 °C
3. Specifications
3.1 Dimensional Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD, 外径) | Φ25.4 mm – Φ114.3 mm (1" – 4.5") | ASTM A213 / GB/T 213 |
| Wall Thickness (壁厚) | 1.0 mm – 6.0 mm | ASTM A213 / GB/T 213 |
| Length (长度) | Coil length: 5 m – 200 m (customizable) | Manufacturer specification |
| Coil Inner Diameter (盘管内径) | Φ200 mm – Φ2000 mm (customizable) | Manufacturer specification |
| OD Tolerance (外径公差) | ±0.05 mm (precision grade); ±0.10 mm (standard grade) | ASTM A213 |
| Wall Thickness Tolerance (壁厚公差) | ±5% (precision grade); ±10% (standard grade) | ASTM A213 |
| Roundness (圆度) | ≤ 0.1% of nominal OD | ASTM A213 |
| Straightness (直线度) | ≤ 1.5 mm/m (on straightened sections) | ASTM A213 |
| End Condition (端部状态) | Plain ends, beveled ends, or threaded ends (as specified) | Customer specification |
3.2 Performance Specifications
| Parameter | Specification |
|---|---|
| Design Pressure (设计压力) | Up to 20 MPa (200 bar) |
| Design Temperature (设计温度) | Up to 350 °C (steam side); Up to 330 °C (water side) |
| Maximum Wall Temperature (最高壁温) | ≤ 550 °C (with adequate steam-side heat transfer) |
| Heat Flux Capacity (热流密度) | Up to 1.5 × 10⁶ W/m² (below critical heat flux) |
| Service Life (使用寿命) | ≥ 40 years (nuclear-grade application) |
| Minimum Bend Radius (最小弯曲半径) | ≥ 3D (D = outer diameter) |
3.3 Surface Finish
| Surface Condition | Specification |
|---|---|
| Outer Surface (外表面) | Pickled and passivated (酸洗钝化); Ra ≤ 0.8 μm (polished option available) |
| Inner Surface (内表面) | Pickled and passivated; Ra ≤ 0.8 μm (standard); Ra ≤ 0.4 μm (precision) |
| Surface Defects (表面缺陷) | No cracks, laps, seams, or rolled-in scale permitted |
4. Manufacturing Process
The manufacturing of stainless steel coil tubes for large-diameter once-through steam generators follows a rigorous multi-stage process chain, with each step subject to strict quality control:
- Raw Material Procurement (原材料采购): Sourcing of certified stainless steel strip or rod from approved mills with full chemical and mechanical property documentation. Material traceability is maintained throughout the production chain.
- Hot Rolling / Seamless Tube Production (热轧/无缝管生产): The base tube is produced via seamless tube manufacturing processes including:
- Piercing (穿孔): Heating of steel billets to 1150–1250 °C, followed by piercing to produce a hollow shell.
- Elongation (延伸): Sequential rolling to achieve approximate dimensions.
- Pilot Mill Rolling (定径轧制): Final rolling to achieve precise outer diameter and wall thickness tolerances.
- Heat Treatment (热处理): Solution annealing (固溶处理) at 1050–1150 °C followed by rapid water quenching to achieve a fully austenitic microstructure with dissolved carbides. This eliminates residual stresses and ensures uniform mechanical properties. For stabilized grades (321H), a stabilization anneal (稳定化处理) at 870–900 °C is performed to precipitate titanium carbides (TiC) and prevent chromium carbide formation at grain boundaries.
- Cold Working / Cold Drawing (冷加工/冷拔): Cold drawing or cold rolling to achieve final dimensional tolerances, improved surface finish, and enhanced mechanical properties through work hardening. Intermediate annealing (中间退火) may be performed for tubes requiring significant dimensional reduction.
- Pickling and Passivation (酸洗钝化): Removal of surface scale and oxide films via controlled acid pickling (typically HNO₃/HF blend or citric acid solution), followed by passivation to form a protective chromium oxide layer. This step is critical for ensuring corrosion resistance in the service environment.
- Coiling (盘卷): The finished tube is wound into coils of specified inner diameter using precision coiling equipment with controlled tension to prevent deformation, kinking, or surface damage. Protective wraps and banding are applied to secure the coil during storage and transport.
- Non-Destructive Testing (无损检测, NDT): Comprehensive inspection including:
- Eddy Current Testing (涡流检测): 100% inspection of the entire tube length for detection of internal and external surface defects.
- Hydrostatic Testing (水压试验): Pressure testing at 1.5–2.0× design pressure to verify pressure integrity.