Stainless Steel Coil Tube (Coiltube) — Large Diameter Once-Through Steam Generator Grade
1. Product Overview
The stainless steel coil tube (盘管 / Coil Tube) is a precision-formed tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is specifically engineered for high-performance thermal applications, particularly within once-through steam generator (OTSG) systems where large-diameter coiled configurations are required to maximize heat transfer surface area within compact geometries. The coil tube design eliminates the need for internal water circulation pumps by leveraging natural flow dynamics through continuously bent tubing, making it an ideal solution for high-efficiency energy conversion systems.
Based on experimental research into the thermal-hydraulic performance of large-diameter coil tubes in once-through steam generators, this product line has been optimized to deliver superior heat transfer coefficients, reduced pressure drops, and enhanced structural integrity under sustained high-temperature and high-pressure operating conditions.
2. Material & Properties
2.1 Base Material Composition
- Primary Alloy: Austenitic stainless steel conforming to ASTM A213/A213M and GB/T 14976 standards
- Typical Grades: TP304, TP316L, TP321, TP347H (heat-resistant variants)
- Key Alloying Elements: Chromium (Cr) 18–25%, Nickel (Ni) 8–22%, Molybdenum (Mo) 2–3% (for 316L), Titanium (Ti) and Niobium (Nb) stabilizers
- Carbon Equivalent (CE): ≤ 0.04% (low-carbon variants for weldability)
2.2 Mechanical Properties
- Tensile Strength: ≥ 515 MPa (annealed condition)
- Yield Strength: ≥ 205 MPa (0.2% offset)
- Elongation: ≥ 40% (minimum, 50 mm gauge length)
- Impact Toughness (Charpy V-Notch): ≥ 47 J at −40°C
- Creep Strength: Optimized for sustained service up to 650°C
2.3 Thermal & Corrosion Resistance
- Thermal Conductivity: 14–16 W/(m·K) at 20°C
- Operating Temperature Range: −196°C to +650°C (continuous)
- Oxidation Resistance: Excellent up to 870°C in intermittent service
- Corrosion Resistance: Superior resistance to pitting, crevice corrosion, and intergranular corrosion (IGC) in oxidizing and reducing environments
3. Technical Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 19 mm – 114 mm (custom ranges available) | ASTM A213 / GB/T 14976 |
| Wall Thickness | 0.8 mm – 6.0 mm | ASTM A213 / GB/T 14976 | Coil Diameter (Bending) | 300 mm – 3000 mm | Custom per application |
| Coil Length (per Spool) | 5 m – 120 m | Custom per application |
| Bend Radius (R/D Ratio) | ≥ 3D (minimum 5D recommended) | ASME B31.3 |
| Surface Finish | Pickled & Passivated (Ra ≤ 0.8 μm) | ASTM A380 / GB/T 19228 |
| Pressure Rating | Up to 40 MPa (design pressure, dependent on geometry) | ASME Section VIII |
| Welding Method | Orbital TIG (GTAW) / Pulse TIG | ASME Section IX |
| Non-Destructive Testing (NDT) | 100% Radiographic Testing (RT) + Eddy Current (ET) on welds | ASME V / GB/T 3323 |
| Packaging | Wooden crates with anti-condensation wrapping; spool coils on steel saddles | ISO 4180 |
4. Manufacturing Process
- Raw Material Selection & Verification: Mill-certified stainless steel seamless tubes or cold-drawn tubes are inspected for chemical composition (spectroscopic analysis), grain structure, and mechanical properties per ASTM A213 requirements.
- End Preparation: Tube ends are deburred, chamfered, and cleaned to ensure proper fit-up for subsequent welding operations.
- Precision Cold Bending: Using CNC-controlled rotary draw bending machines with internal mandrels and external wiper dies to maintain dimensional accuracy, prevent ovality (≤ 1.5% of OD), and avoid wall thinning at bend apexes. Bending is performed at controlled speeds to minimize strain-induced martensitic transformation.
- Coil Formation: Tubes are formed into helical or planar coil configurations on dedicated coiling mandrels, with continuous dimensional monitoring via laser measurement systems.
- Welding (if spliced): Orbital GTAW (Gas Tungsten Arc Welding) with internal helium backing gas to achieve full-penetration, single-pass welds with minimal heat-affected zone (HAZ). Weld parameters are qualified per ASME Section IX WPS/PQR.
- Heat Treatment: Solution annealing at 1050–1150°C followed by rapid water quenching to restore full austenitic microstructure and maximize corrosion resistance and ductility.
- Pickling & Passivation: Acid pickling (nitric-hydrofluoric acid blend) removes oxide scale and discoloration; subsequent passivation treatment forms a protective chromium oxide layer (Cr₂O₃) on the surface.
- Quality Assurance & Testing: Includes dimensional inspection (OD, wall thickness, coil diameter), hydrostatic pressure testing (1.5× design pressure), radiographic examination of all welds, and surface inspection for defects.
5. Applications
- Nuclear Power: Once-through steam generators in pressurized water reactors (PWRs) and advanced small modular reactors (SMRs)
- Power Generation: Supercritical and ultra-supercritical boiler evaporators and reheaters
- Marine Engineering: Shipboard waste heat recovery systems and marine steam turbines
- Petrochemical & Oil Refining: Process heat exchangers, reboilers, and distillation column internals
- Hydrogen Energy: High-temperature hydrogen production reactors and fuel cell heat management systems
- Industrial Process Heating: Organic rankine cycle (ORC) evaporators and thermal oil systems
6. Quality Certifications & Compliance
- ISO 9001:2015 — Quality Management System
- ISO 3834-2 — Quality Requirements for Welding of Metallic Materials
- ASME Section VIII Div. 1 — Pressure Vessel and Piping Components
- ASME BPV Code Section IV — Steam Generators
- GB/T 19228 — Chinese National Standard for Stainless Steel Tubular Products
- TÜV / DNV — Third-party inspection and certification (available upon request)
- Material Traceability: Full mill certificate (EN 10204 Type 3.1) with heat number traceability from raw material to finished coil
7. Unique Selling Points
Thermal Performance Optimization: Informed by rigorous experimental research on large-diameter coil tube once-through steam generator thermal-hydraulic performance, this product line achieves enhanced heat transfer coefficients through optimized coil geometry, surface roughness control, and material selection — resulting in measurable improvements in system efficiency and reduced fuel consumption.
- Large Diameter Capability: Specialized manufacturing infrastructure enables coil tubes up to 114 mm OD with consistent bending quality, addressing the specific demands of high-capacity once-through steam generator designs.
- Integrated Thermal-Hydraulic Design Support: Engineering team provides CFD (Computational Fluid Dynamics) modeling and thermal performance prediction services to optimize coil geometry for specific operating conditions.
- Extended Service Life: Stabilized austenitic grades with controlled intergranular corrosion resistance ensure reliable performance over extended operational cycles (10+ years) in demanding thermal environments.
- Customizable Configurations: Flexible manufacturing capability accommodates bespoke coil diameters, pitch configurations, support spacing, and end connections tailored to customer-specific system designs.
- End-to-End Quality Assurance: From raw material spectroscopic verification through final NDT and hydrostatic testing, every coil tube undergoes comprehensive quality control with full traceability documentation.