Stainless Steel Coil Tube — Nuclear Main Pump Seal Pressure Reduction Coiltube
Product Code: 758 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Category: Nuclear-Grade Stainless Steel Coil Tube (盘管)
Product Overview
The stainless steel coil tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered helical tubing product designed primarily for nuclear power plant main pump seal systems. This product category encompasses pressure reduction coil tubes (减压盘管) that serve as critical flow-regulating and pressure-dissipating elements within the secondary containment loops of nuclear reactor coolant pumps. The coil geometry provides an exceptionally high surface-area-to-volume ratio, enabling efficient heat exchange while simultaneously offering controlled hydraulic resistance characteristics essential for maintaining seal integrity under extreme thermal-hydraulic conditions.
The product has been extensively studied in the context of hydraulic resistance (阻力特性) optimization, with particular attention to laminar and transitional flow regimes within helical geometries under high-pressure, high-temperature nuclear service environments. The research and development efforts reflected in the associated technical literature demonstrate a deep understanding of Dean number effects, secondary flow patterns, and pressure drop correlations specific to coiled configurations.
Material & Properties
Material Grades
- S30408 / 06Cr19Ni10 (304L equivalent): Low-carbon austenitic stainless steel with enhanced resistance to intergranular corrosion, suitable for primary coolant circuit applications.
- S31603 / 06Cr17Ni12Mo2 (316L equivalent): Molybdenum-bearing austenitic stainless steel offering superior resistance to pitting and crevice corrosion in chloride-containing nuclear environments.
- S32168 / 06Cr18Ni11Ti (321 equivalent): Titanium-stabilized austenitic stainless steel providing enhanced high-temperature strength and resistance to sensitization during welding operations.
- TP316H / TP304H: High-carbon austenitic grades with elevated temperature capability for heat exchanger and pressure boundary applications.
Mechanical Properties (Typical — Annealed Condition)
| Property | Grade 304L | Grade 316L | Grade 321 |
|---|---|---|---|
| Tensile Strength (Rm) | ≥ 485 MPa | ≥ 485 MPa | ≥ 515 MPa |
| Yield Strength (Rp0.2) | ≥ 175 MPa | ≥ 175 MPa | ≥ 205 MPa |
| Elongation (A5) | ≥ 40% | ≥ 40% | ≥ 40% |
| Impact Energy (20°C, Charpy V) | ≥ 270 J | ≥ 270 J | ≥ 270 J |
| Impact Energy (−196°C, Liquid N₂) | ≥ 180 J | ≥ 180 J | ≥ 180 J |
| Thermal Conductivity (300°C) | 16.3 W/(m·K) | 16.3 W/(m·K) | 16.3 W/(m·K) |
| Thermal Expansion (20–300°C) | 17.2 × 10⁻⁶ /K | 16.6 × 10⁻⁶ /K | 17.1 × 10⁻⁶ /K |
Chemical Composition (Maximum Limits, wt%)
| Element | C | Mn | P | S | Cr | Ni | Mo | Si |
|---|---|---|---|---|---|---|---|---|
| Grade 304L | 0.030 | 2.00 | 0.045 | 0.030 | 18.0–20.0 | 8.0–11.0 | — | 1.00 |
| Grade 316L | 0.030 | 2.00 | 0.045 | 0.030 | 16.0–18.0 | 10.0–14.0 | 2.0–3.0 | 1.00 |
Specifications
Dimensional Parameters
| Parameter | Specification | Tolerance | Reference Standard |
|---|---|---|---|
| Outer Diameter (OD) | Φ6.0 – Φ25.0 mm | ±0.10 mm | ASTM A269 / ASME SA-269 |
| Wall Thickness (WT) | 0.4 – 2.0 mm | ±10% of nominal | ASTM A269 / ASME SA-269 |
| Coil Pitch | 15.0 – 80.0 mm | ±0.5 mm | Custom specification |
| Coil Mean Diameter (CMD) | 50.0 – 500.0 mm | ±1.0 mm | Custom specification |
| Number of Turns | 5 – 200 turns | ±1 turn | Per design requirement |
| Tube Length (Developed) | 0.5 – 50.0 m | ±50 mm | Per design requirement |
| End Form | Plain / Beveled / Flanged | Per drawing | Per design requirement |
| Surface Finish | Electropolished / Ra ≤ 0.4 μm | — | ASTM A269 |
Performance Characteristics — Hydraulic Resistance
| Parameter | Specification | Test Condition |
|---|---|---|
| Flow Regime | Laminar to fully turbulent (Re: 100 – 100,000) | Water, 20°C |
| Pressure Drop Coefficient (f) | Calibrated per Dean number correlation | Per ASME PTC 10 |
| Maximum Operating Pressure | Up to 35.0 MPa (5000 psi) | Hydrostatic test: 1.5× operating pressure |
| Maximum Operating Temperature | −196°C to +650°C | Continuous service |
| Pressure Cycle Fatigue Life | ≥ 10⁶ cycles | Per RCC-MR / ASME BPV Section III |
| Corrosion Rate (BWR Primary Coolant Simulant) | < 0.005 mm/year | 288°C, pH 11.3, 2000 hours |
Manufacturing Process
The production of nuclear-grade stainless steel coil tubes follows a rigorously controlled multi-stage manufacturing sequence compliant with ASME BPV Section III, RCC-M (French Nuclear Code), and applicable IAEA safety standards.
- Raw Material Procurement & Inspection: Cold-rolled stainless steel strip (or seamless tube stock) is procured from certified mill sources with full material traceability documentation (Mill Test Report, MTR). Incoming material undergoes 100% chemical analysis verification via Optical Emission Spectroscopy (OES) and mechanical property confirmation.
- Pre-Forming Treatment: The base material undergoes stress-relief annealing at 1050–1100°C followed by controlled cooling to restore full solution-annealed microstructure and eliminate residual stresses from prior rolling operations.
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Coil Forming (Helical Bending): Precision CNC-controlled coil forming machines (螺旋成型机) bend the tube stock into the specified helical geometry. The forming process employs a combination of internal mandrel support and external die guidance to prevent ovality, wrinkling, or wall thinning. Critical process parameters include:
- Bending radius ratio (D/t) ≥ 20 to prevent excessive thinning
- Forming speed controlled to avoid adiabatic heating
- Real-time ovality monitoring (target: ≤ 2% of OD)
- Post-Forming Heat Treatment: Following coiling, the formed coil tubes undergo solution annealing (固溶处理) at 1050–1100°C in a protective atmosphere (vacuum or argon) followed by rapid water quenching. This restores full solution-annealed properties and eliminates work-hardening effects from the forming process.
- Precision Machining & End Preparation: Coil tube ends are cut to length using waterjet or abrasive saw methods to prevent heat-affected zones. End beveling, threading, or flange attachment is performed per design specifications using precision machining centers.
- Surface Treatment: Electropolishing (电解抛光) is performed to achieve a surface roughness of Ra ≤ 0.4 μm, removing surface contamination, residual grinding marks, and free iron. This is critical for nuclear service to minimize corrosion initiation sites and ensure biocompatibility in containment systems.
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Non-Destructive Testing (NDT):
- Eddy Current Testing (ECT): 100% coverage of coil tube surface for detection of surface and near-surface defects (ASTM E309 / E709)
- Helical Eddy Current (HEC): Automated inspection of internal and external surfaces
- Fluorescent Penetrant Inspection (FPI): Visual verification of weld integrity at formed joints (ASTM E165)
- Ultrasonic Testing (UT): Wall thickness verification and internal defect detection (ASTM E317)
- Pressure Testing & Hydraulic Characterization: Each coil tube assembly undergoes hydrostatic pressure testing at 1.5× the maximum operating pressure for a minimum hold time of 30 minutes. Additionally, the hydraulic resistance characteristics (阻力特性) are experimentally determined by measuring pressure drop (ΔP) across the coil at various flow rates to establish the flow resistance curve. The Dean number (De = Re·√(d/D)) is calculated for each test point to validate against theoretical correlations for helical flow.
- Dimensional Verification & Final Inspection: Coordinate Measuring Machine (CMM) scanning verifies coil geometry, pitch uniformity, and dimensional tolerances. Final visual inspection confirms surface quality, marking, and documentation completeness.
Applications
Primary Application — Nuclear Main Pump Seal Systems
The primary application of this coil tube product is as a pressure reduction coil tube (减压盘管) within the seal system of nuclear reactor main coolant pumps (Main Pumps / 核主泵). In this critical role, the coil tube functions as:
- Pressure Regulator: The inherent hydraulic resistance of the helical geometry provides precise, passive pressure reduction between the high-pressure primary coolant circuit and the lower-pressure seal support system. The resistance characteristics are carefully calibrated to maintain the optimal seal film pressure differential.
- Flow Limiter: Under transient or accident conditions (e.g., Loss of Coolant Accident, LOCA), the coil tube's resistance characteristics ensure controlled flow rates that prevent seal flooding or cavitation.
- Thermal Buffer: The extended surface area of the coiled configuration provides thermal mass and heat exchange capacity, moderating rapid temperature transients that could compromise seal integrity.
- Filter/Strainer Support: In some designs, the coil tube houses or supports in-line filtration elements that protect the mechanical seal from particulate contamination.
Additional Applications
- Nuclear Reactor Coolant Heat Exchangers: Helical coil bundles in steam generators, feed