Stainless Steel Coil Tube — Nuclear Primary Pump High-Pressure Cooler
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd (Wenzhou Jixing) | Product No.: 359
Flow-Induced Vibration (FIV) Analysis-Informed Design
This product line represents a specialized class of stainless steel coil tubes engineered for deployment in the high-pressure cooling circuits of nuclear reactor primary pumps. The design and manufacturing parameters are informed by rigorous Flow-Induced Vibration (FIV) analysis methodologies, ensuring that the coil tubes maintain structural integrity under the extreme hydrodynamic loads encountered in primary coolant loops. The following technical specification provides a comprehensive overview of the product's material composition, dimensional specifications, manufacturing processes, applicable operating conditions, and quality assurance framework.
1. Product Overview
The stainless steel coil tube is a continuously wound, seamless or welded tubular component designed to serve as the primary heat-exchange element within nuclear reactor primary pump high-pressure coolers. Unlike straight-tube configurations, the coil geometry offers a significantly higher surface-area-to-volume ratio within a compact envelope, enabling efficient heat rejection from the primary coolant stream while minimizing the spatial footprint of the cooling assembly.
The coil tube is subjected to sustained high-pressure, high-temperature, and high-velocity coolant flow. Under these conditions, Flow-Induced Vibration — encompassing both Flow-Induced Oscillation (FIO) and Flow-Induced Response (FIR) — becomes a critical design consideration. The coil's inherent flexibility, while advantageous for thermal expansion accommodation, introduces susceptibility to Fluidelastic Instability (FEI) and Fluidelastic Damping (FED) phenomena. The product is therefore engineered with specific geometric tolerances, wall thicknesses, and material selections that mitigate FIV risk to levels acceptable under nuclear-grade safety standards.
Wenzhou Jixing Metal Materials Co., Ltd produces these coil tubes using precision cold-forming and hot-winding techniques, followed by thorough non-destructive examination (NDE) and pressure testing protocols to ensure zero-defect delivery.
2. Material & Properties
2.1 Base Alloy Selection
The coil tube is manufactured from austenitic stainless steel grades specifically qualified for nuclear service. The primary alloy options include:
- SUS304 / ASTM A213 TP304 (UNS S30400) — General-purpose austenitic stainless steel with excellent corrosion resistance and formability.
- SUS316L / ASTM A213 TP316L (UNS S31603) — Low-carbon variant with added molybdenum (Mo 2.0–2.5%) for enhanced resistance to pitting and crevice corrosion in chloride-containing coolant environments.
- SUS321 / ASTM A213 TP321 (UNS S32100) — Titanium-stabilized grade for applications requiring resistance to intergranular corrosion at elevated temperatures.
2.2 Mechanical Properties
| Property | SUS304 (Typical) | SUS316L (Typical) | Test Standard |
|---|---|---|---|
| Tensile Strength (Rm) | 515 – 720 MPa | 485 – 720 MPa | ASTM A370 / ISO 6892 |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ≥ 170 MPa | ASTM A370 / ISO 6892 |
| Elongation (A50) | ≥ 40% | ≥ 40% | ASTM A370 |
| Density | 7.93 g/cm³ | 7.99 g/cm³ | — |
| Thermal Conductivity (at 20°C) | 16.3 W/(m·K) | 14.6 W/(m·K) | ASTM E1461 |
| Thermal Expansion Coefficient (20–100°C) | 16.0 × 10⁻⁶ /K | 16.0 × 10⁻⁶ /K | ASTM E228 |
| Maximum Operating Temperature | 870°C (oxidizing) | 870°C (oxidizing) | — |
| Minimum Operating Temperature | −196°C (cryogenic) | −196°C (cryogenic) | — |
2.3 Chemical Composition (Wt%)
| Element | C | Si | Mn | P | S | Cr | Ni | Mo | Ti |
|---|---|---|---|---|---|---|---|---|---|
| SUS304 | ≤ 0.08 | ≤ 1.00 | ≤ 2.00 | ≤ 0.045 | ≤ 0.030 | 18.0 – 20.0 | 8.0 – 10.5 | — | — |
| SUS316L | ≤ 0.030 | ≤ 1.00 | ≤ 2.00 | ≤ 0.045 | ≤ 0.030 | 16.0 – 18.0 | 10.0 – 14.0 | 2.0 – 2.5 | — |
| SUS321 | ≤ 0.08 | ≤ 1.00 | ≤ 2.00 | ≤ 0.045 | ≤ 0.030 | 17.0 – 19.0 | 9.0 – 12.0 | — | 5 × (C+N) – 0.70 |
2.4 Material Characterization for FIV Mitigation
The elastic modulus (Young's Modulus) of austenitic stainless steel (approximately 193 GPa for SUS304 and 195 GPa for SUS316L) is relatively low compared to carbon steels, which influences the natural frequency of the coil tube under fluid excitation. The product design accounts for this by optimizing the coil diameter, pitch, and wall thickness to ensure that the structural natural frequency remains well separated from the dominant Strouhal Frequency of the cross-flow, thereby avoiding Vortex-Induced Vibration (VIV) resonance.
The Log-Damped Natural Frequency and Structural Damping Ratio of the coil assembly are validated through experimental modal analysis during the qualification testing phase. The target is to maintain a damping ratio sufficient to prevent the onset of Fluidelastic Instability at the maximum design coolant velocity.
3. Specifications
3.1 Dimensional Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 12 – 51 mm (customizable up to 76 mm) | ASTM A213 / EN 10216 |
| Wall Thickness (WT) | 0.8 – 4.0 mm | ASTM A213 / EN 10216 |
| Inner Diameter (ID) | Calculated: ID = OD − 2 × WT | — |
| Coil Winding Diameter | 200 – 1200 mm (typical) | Manufacturer specification |
| Coil Length (Uncoiled) | 10 – 300 m per coil (custom lengths available) | — |
| Coil Pitch (Center-to-Center) | 1.2 × OD – 2.5 × OD (design-dependent) | ASME BPV Section III |
| Winding Tolerance (Diameter) | ± 0.5% of nominal | ISO 8035 |
| Winding Tolerance (Pitch) | ± 1.0 mm | ISO 8035 |
| Roundness Tolerance | ≤ 0.5% of OD | ASTM A213 |
| Surface Finish (Ra) | ≤ 0.8 μm (electropolished option: ≤ 0.4 μm) | ASTM A240 / ISO 1302 |
| End Form | Plain, beveled, threaded, or welded to header | ASME B1.20.1 |
| Maximum Design Pressure | Up to 25 MPa (depending on geometry and grade) | ASME BPV Section III / NB-3200 |
| Design Temperature Range | −40°C to +350°C (nuclear primary loop) | — |
3.2 Performance Specifications
| Performance Parameter | Specification |
|---|---|
| Heat Transfer Coefficient (h) | 8,000 – 15,000 W/(m²·K) (turbulent flow, water) |
| Pressure Drop (per coil length) | ≤ 50 kPa per 10 m coil (design-dependent) |
| Flow Velocity (design) | 2.0 – 6.0 m/s |
| FIV Critical Velocity Margin | ≥ 1.5 × maximum design flow velocity |
| Seismic Design Category | SSS (Site-Specific Safety) per ASME BPV / IEC 60899 |
| Corrosion Allowance | ≥ 0.5 mm (included in wall thickness) |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Procurement & Inspection: Seamless stainless steel tubes conforming to ASTM A213, EN 10216-5, or GB/T 14976 are procured from certified suppliers. Each batch undergoes spectrographic chemical analysis (OES), mechanical property verification, and hydrostatic testing prior to acceptance.
- Pre-Forming & Straightening: Incoming tubes are straightened using a cold-draw or hydraulic straightening process to achieve a straightness tolerance of ≤ 1.0 mm/m. Surface contaminants, mill scale, and oxide layers are removed through mechanical brushing or chemical pickling.
- Coil Winding (Forming): The straightened tube is wound around a precision-machined mandrel using a CNC-controlled coil winding machine. The winding process maintains constant tension and controlled angular velocity to ensure uniform pitch and consistent coil diameter throughout the entire length. The winding is performed at ambient temperature for cold-formed coils or at elevated temperatures (400–600°C) for hot-wound configurations requiring higher dimensional accuracy.
- Welding & Joint Fabrication: Where continuous coil length is insufficient, butt-weld joints are fabricated using Gas Tungsten Arc Welding (GTAW / TIG) with argon shielding gas on both inside and outside of the joint. Weld parameters are optimized to achieve full penetration with minimal heat-affected zone (HAZ). Welded joints are subsequently ground flush and subjected to 100% volumetric NDE.
- Post-Forming Heat Treatment: For welded coil assemblies, a solution annealing treatment is performed at 1050–1100°C followed by rapid water quenching to restore full austenitic microstructure, eliminate sensitization, and relieve residual welding stresses.
- Pickling & Passivation: The coil is immersed in a mixed acid pickling bath (HNO₃/HF) to remove heat scale and surface contamination, followed by a passivation treatment in a dilute HNO₃ solution to form a uniform chromium oxide passive layer (≥ 100 nm thickness).
- Electropolishing (Optional): For applications requiring ultra-low surface roughness (Ra ≤ 0.4 μm) or removal of surface inclusions, the coil undergoes electropolishing in a phosphoric acid-based electrolyte at controlled current density and temperature.
- Non-Destructive Examination (NDE):
- 100% Visual Inspection (VT): Internal and external surfaces inspected under controlled lighting.
- 100% Eddy Current Testing (ECT): Inline eddy current probes detect surface and near-surface defects, wall thickness variations, and weld anomalies.
- 100% Ultrasonic Testing (UT): For wall thickness verification and volumetric defect detection, particularly at welded joints.
- 100% Radiographic Testing (RT) / Digital Radiography (DR): At all butt-weld joints and critical connections.
- Fluorescent Penetrant Testing (FPT): At weld joints and end connections for surface-breaking defect detection.
- Pressure Testing: Each coil assembly undergoes a pneumatic or hydraulic pressure test at 1.5 × the maximum design pressure, held for a minimum duration per ASME BPV Code Section III requirements. No leakage or visible distortion is permitted.
- Dimensional Verification: Final dimensional inspection includes coil diameter, pitch