Large-Scale Stainless Steel Spiral Coil Tube — Medium-Frequency Induction Heating Push-Forming Technology
1. Product Overview
The Large-Scale Stainless Steel Spiral Coil Tube (hereinafter referred to as "Coil Tube") is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. using advanced medium-frequency induction heating push-forming technology. This product is designed to meet the demanding requirements of high-temperature, high-pressure, and corrosive environments encountered in the petrochemical, energy, and advanced manufacturing industries.
Unlike conventional coil tubes produced through cold bending or hydraulic forming, the medium-frequency induction heating push-forming method enables the production of large-diameter spiral coil tubes with superior dimensional accuracy, uniform wall thickness, and enhanced metallurgical integrity. The process combines electromagnetic induction heating with controlled mechanical push-forming to achieve precise helical geometry without introducing residual stress concentrations or microstructural degradation.
Product Catalogue Reference: Item No. 1497 | Classification: Technical Literature & Process Learning
2. Material & Properties
2.1 Base Material Grades
The coil tube is fabricated from austenitic and duplex stainless steel grades, selected based on service environment requirements:
- Austenitic Grades: SUS304 (UNS S30400), SUS316L (UNS S31603), SUS321 (UNS S32100), SUS310S (UNS S31008)
- Duplex Grades: SUS31803 (UNS S31803 / 2205), SUS32750 (UNS S32750 / 2507 Super Duplex)
- Heat-Resistant Grades: SUS309S (UNS S30908), SUS310 (UNS S31000)
2.2 Key Mechanical Properties
| Property | Grade 304 (UNS S30400) | Grade 316L (UNS S31603) | Grade 2205 (UNS S31803) |
|---|---|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa | ≥ 480 MPa | ≥ 550 MPa |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ≥ 170 MPa | ≥ 450 MPa |
| Elongation (A50) | ≥ 40% | ≥ 40% | ≥ 25% |
| Density (ρ) | 8.00 g/cm³ | 8.03 g/cm³ | 7.80 g/cm³ |
| Thermal Expansion Coefficient (α, 20–800°C) | 17.3 × 10⁻⁶ /K | 17.4 × 10⁻⁶ /K | 13.5 × 10⁻⁶ /K |
| Maximum Service Temperature | 870°C | 870°C | 350°C (continuous) |
2.3 Corrosion Resistance
All grades exhibit exceptional resistance to intergranular corrosion (IGC), pitting corrosion (measured by Critical Pitting Temperature, CPT), and stress corrosion cracking (SCC). Grade 316L demonstrates a CPT exceeding 25°C in 3.5% NaCl solution, while duplex grade 2205 achieves a CPT above 40°C, making it suitable for aggressive chloride-containing environments.
3. Product Specifications
| Parameter | Specification Range | Applicable Standard |
|---|---|---|
| Outer Diameter (OD) | φ15 mm – φ325 mm | ASTM A312 / ASME SA-312 |
| Wall Thickness | 0.5 mm – 12.0 mm | ASTM A312 / EN 10216-5 |
| Spiral Pitch (P) | 20 mm – 500 mm | Custom / Customer Drawing |
| Coil Diameter (CD) | φ200 mm – φ6,000 mm | Customer Specification |
| Coil Length (per turn) | 1.0 m – 50.0 m | Customer Specification |
| Total Developed Length | Up to 500 m (continuous) | — |
| Dimensional Tolerance (OD) | ± 0.05 mm to ± 0.5 mm | ASTM A312 / EN 10216-5 |
| Dimensional Tolerance (Wall) | ± 10% of nominal | ASTM A312 |
| Surface Finish | 2B Annealed / No. 4 Brushed / Mirror (Ra ≤ 0.4 μm) | ASTM A480 / Custom |
| End Treatment | Beveled / Square Cut / Threaded | ASME B1.20.1 / Custom |
| Heat Treatment | Solution Annealed (1050°C – 1150°C) + Water Quenched | ASTM A312 |
4. Manufacturing Process
4.1 Medium-Frequency Induction Heating Push-Forming Method
The core differentiating technology employed by Wenzhou Jixing Metal Materials Co., Ltd. is the Medium-Frequency Induction Heating Push-Forming Process (中频加热推制法), which represents a significant advancement over traditional cold-bending and hydraulic push-forming methods for large-diameter coil tube production.
4.2 Process Flow
- Raw Material Inspection & Cutting: Seamless stainless steel pipe blanks are received, subjected to visual inspection, dimensional verification, and ultrasonic testing (UT). Blanks are cut to required lengths using precision plasma or laser cutting to ensure square ends with burr-free edges.
- Pre-Forming Setup: The pipe blank is mounted on a specialized push-forming die assembly. The die geometry is designed with the target spiral pitch and coil diameter parameters. Fixtures ensure precise axial alignment.
-
Medium-Frequency Induction Heating: A medium-frequency (typically 1–10 kHz) induction heating coil surrounds the pipe section at the forming zone. Electromagnetic induction generates localized Joule heating, raising the forming zone temperature to the optimal plastic deformation range (800°C – 1,050°C for austenitic grades). This controlled heating:
- Reduces forming force by 60–80% compared to cold forming
- Prevents work hardening and microcrack initiation
- Enables uniform deformation across the pipe cross-section
- Minimizes residual stress accumulation
- Push-Forming Operation: A hydraulic pusher applies controlled axial force to the heated pipe section, driving it through the spiral die. The die progressively imparts helical curvature as the material deforms plastically at elevated temperature. The process is continuous and repeatable, producing uniform spiral geometry along the entire length.
- Controlled Cooling: Post-forming, the coil tube undergoes controlled cooling to prevent distortion. Cooling rates are managed to avoid martensitic transformation (for duplex grades) and to maintain solution-annealed microstructure.
- Solution Annealing: The formed coil tube is solution annealed in a vacuum or protective atmosphere furnace at 1,050°C – 1,150°C, followed by rapid quenching. This eliminates any precipitates (e.g., chromium carbides), restores full corrosion resistance, and relieves residual stresses.
- Surface Finishing: Depending on specification, the coil tube undergoes pickling and passivation (acid bath treatment), mechanical brushing, or electrolytic polishing to achieve the required surface quality.
- Quality Inspection & Testing: Comprehensive inspection including dimensional measurement, hydrostatic testing, radiographic testing (RT), eddy current testing (ECT), and hardness verification.
4.3 Technical Advantages of Medium-Frequency Heating Push-Forming
| Comparison Parameter | Cold Bending | Hydraulic Push-Forming | Medium-Frequency Heating Push-Forming |
|---|---|---|---|
| Maximum OD Capability | ≤ φ100 mm | ≤ φ200 mm | ≤ φ325 mm |
| Wall Thickness Ratio Control | ± 15–25% | ± 10–15% | ± 5–8% |
| Residual Stress Level | High | Medium | Low |
| Springback | Significant | Moderate | Minimal |
| Microstructural Integrity | Work-hardened zones | Localized deformation | Uniform, annealed |
| Production Speed | Slow | Moderate | High |
5. Applications
The Large-Scale Stainless Steel Spiral Coil Tube finds extensive application across multiple industrial sectors:
5.1 Petrochemical & Refining
- Heat exchanger coil bundles (air coolers, reboilers, condensers)
- Reactor internals and catalyst support structures
- High-pressure transfer lines in cracking units
- Hydrotreater and hydrocracker internals
5.2 Power Generation
- Supercritical and ultra-supercritical boiler tubes
- Heat recovery steam generator (HRSG) coil elements
- Gas turbine waste heat recovery systems
- Nuclear auxiliary heat exchanger components
5.3 Food & Pharmaceutical Processing
- Sanitary heat exchangers (UHT milk processing)
- Pharmaceutical sterilization coil systems
- Alcoholic beverage pasteurization equipment
- Bioreactor temperature control coils
5.4 Aerospace & Defense
- Engine heat exchangers (oil coolers, fuel coolers)
- Aircraft hydraulic accumulator coils
- Missile and rocket engine turbopump components
5.5 Energy & Environmental
- Geothermal heat exchanger coils
- Hydrogen fuel cell cooling systems
- Solar thermal collector absorber tubes
- Carbon capture and storage (CCS) heat exchange
6. Quality Certifications & Standards Compliance
6.1 Applicable Standards
| Standard | Scope |
|---|---|
| ASTM A312 / ASME SA-312 | Welded and seamless austenitic stainless steel tubes and pipes |
| ASTM A213 / ASME SA-213 | Heat exchanger and boiler tubing (austenitic) |
| EN 10216-5 | Non-ferrous metal tubes and pipes — stainless steel |
| ISO 15498 | Stainless steel tubes — pressure tube specifications |
| GB/T 12771 | Chinese national standard for stainless steel seamless tubes |
| JIS G3459 | Japanese Industrial Standard for stainless steel seamless tubes |
| ASME B31.3 | Process piping design requirements |