Large-Diameter Spiral Coil Tube — Medium-Frequency Push-Formed Stainless Steel Coil Pipe
Product Overview
The Large-Diameter Spiral Coil Tube (hereinafter referred to as "Coil Tube") is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. using an advanced Medium-Frequency Induction Heating Push Forming (MF-PF) process. This technology enables the production of seamless, large-diameter spiral coil tubes with exceptional dimensional accuracy, uniform wall thickness, and superior mechanical integrity. Unlike conventional cold-bending or hot-rolling coil tube manufacturing methods, the MF-PF process eliminates cold-work hardening, reduces residual stresses, and significantly improves the formability and fatigue resistance of the final product.
Coil tubes are widely deployed in heat exchanger systems, chemical processing plants, power generation facilities, and petrochemical industries where long, continuously curved piping configurations are required to maximize heat transfer surface area within compact installation footprints.
Material & Properties
Coil tubes are fabricated from a range of austenitic and duplex stainless steel grades, selected to meet specific service conditions involving corrosion resistance, temperature endurance, and mechanical strength requirements.
Available Steel Grades
- SUS304 / AISI 304 (UNS S30400) — General-purpose corrosion resistance; suitable for food-grade and chemical applications
- SUS316L / AISI 316L (UNS S31603) — Enhanced pitting and crevice corrosion resistance due to molybdenum addition; ideal for marine and pharmaceutical environments
- SUS321 / AISI 321 (UNS S32100) — Titanium-stabilized austenitic grade with excellent resistance to intergranular corrosion at elevated temperatures
- SUS310S / AISI 310S (UNS S31008) — High-temperature oxidation resistance; suitable for furnace and furnace tube applications
- SAF 2205 / UNS S32205 — Duplex austenitic-ferritic stainless steel with approximately twice the yield strength of 304/316L grades
- SUS304L / AISI 304L (UNS S30403) — Low-carbon variant with superior weldability and resistance to sensitization
Mechanical Properties (Typical — SUS304, Annealed Condition)
| Property | Specification |
|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa (75,400 psi) |
| Yield Strength (Rp0.2) | ≥ 205 MPa (29,700 psi) |
| Elongation (A50) | ≥ 40% |
| Hardness | ≤ 217 HBW (Brinell) |
| Operating Temperature Range | -196 °C to +870 °C (ASTM A270) |
Corrosion Resistance
- Pitting Resistance Equivalent Number (PREN): 19 (SUS304) / 24 (SUS316L) / 24.5 (SAF 2205)
- Excellent resistance to atmospheric, acidic, and alkaline environments
- Immune to stress corrosion cracking (SCC) in most chloride-containing solutions (duplex grades)
- Non-magnetic or weakly magnetic in annealed condition (austenitic grades)
Specifications
| Parameter | Specification Range |
|---|---|
| Outer Diameter (OD) | φ20 mm – φ150 mm (custom sizes available) |
| Wall Thickness (WT) | 0.5 mm – 6.0 mm |
| Coil Diameter (CD) | φ500 mm – φ5,000 mm |
| Tube Length per Coil | 10 m – 500 m (continuous) |
| Surface Finish | No. 1 (Pickled), 2B, BA (Bright Annealed), No. 4 (Brushed), Mirror (8K) |
| End Treatment | Plain, Beveled, Threaded, Flanged, or Weld-Prepped |
| Dimensional Tolerance (OD) | ±0.10 mm (precision grade) / ±0.30 mm (standard grade) |
| Dimensional Tolerance (WT) | ±0.05 mm (precision grade) / ±0.15 mm (standard grade) |
| Coil Straightness Deviation | ≤ 1.5 mm per meter |
| Applicable Standards | ASTM A213, ASTM A269, ASTM A270, GB/T 12771, GB/T 21832, EN 10216-5, JIS G3459 |
| Material Form | Seamless (from seamless tube stock) or Welded (from precision strip) |
| Heat Treatment Condition | Annealed (Solution Annealed at 1050–1150 °C, Water Quenched) |
Manufacturing Process — Medium-Frequency Induction Heating Push Forming (MF-PF)
The MF-PF process represents a significant advancement in large-diameter coil tube fabrication. This method combines Medium-Frequency Induction Heating with a Push Forming (PF) die system to produce spiral coil tubes with superior quality characteristics.
Process Flow
- Material Preparation: Seamless stainless steel tubes or precision-welded tubes are inspected, cut to length, and straightened to ensure uniform feed stock. Surface contaminants are removed through chemical pickling and passivation.
- Medium-Frequency Induction Heating: The tube blank is fed into an induction heating coil operating at a frequency of 1–10 kHz. The tube is selectively heated to a controlled forging temperature of 950–1100 °C (austenite range for austenitic grades), achieving rapid and uniform heating with minimal oxidation scale formation.
- Push Forming Operation: The heated tube is pushed through a precision die set designed to impart the desired spiral curvature. The push force is applied axially through a hydraulic or mechanical pusher mechanism, while the die geometry progressively bends the tube into the target coil radius.
- Continuous Coiling: As the tube exits the die, it is wound onto a large-diameter reel at a controlled speed, maintaining consistent coil diameter and pitch throughout the production run.
- Post-Forming Annealing (if required): Depending on the grade and application, the coiled tube may undergo a controlled solution annealing cycle (1050–1150 °C, water quench) to restore full austenitic microstructure and eliminate any residual stress introduced during forming.
- Surface Finishing: Final surface treatment (pickling, passivation, polishing, or brushing) is applied to achieve the specified surface finish class.
- Quality Inspection: Each coil undergoes dimensional verification, hydrostatic pressure testing, visual inspection, and (where required) non-destructive testing (NDT) including eddy current and ultrasonic examination.
Key Advantages of the MF-PF Process
- Elimination of Cold-Work Hardening: Unlike cold-bending methods, the hot-forming nature of MF-PF prevents work-hardening of the tube material, preserving ductility and fatigue life.
- Reduced Residual Stresses: The controlled heating and forming cycle minimizes residual stresses, reducing the risk of stress corrosion cracking (SCC) in service.
- Uniform Wall Thickness: The push-forming die system ensures consistent wall thickness throughout the coil, avoiding the thinning at the inner bend radius commonly seen in cold-formed coils.
- Large-Diameter Capability: The process is specifically suited for large-diameter coil tubes (OD > 50 mm) where conventional cold-forming equipment becomes impractical.
- Minimized Oxidation Scale: Medium-frequency induction heating provides rapid, controlled heating with a thin oxide scale layer that is easily removed during subsequent pickling.
- Energy Efficiency: Induction heating is a highly efficient energy delivery method, achieving thermal conversion efficiencies of 60–80% compared to 20–30% for resistance or furnace heating.
- Continuous Production: The push-forming method allows for continuous or semi-continuous production, enabling high throughput and consistent quality.
Applications
Power Generation
- Heat exchanger coil tubes in supercritical and ultra-supercritical (USC) boilers
- Steam generator tubes in nuclear power plants
- Condenser and feedwater preheater coils
Petrochemical & Chemical Processing
- Reboiler and condenser coil tubes in distillation columns
- Heat transfer coils in polymerization reactors
- Corrosive chemical storage and transfer systems (SUS316L, SAF 2205)
Food & Pharmaceutical
- Pasteurization and sterilization heat exchangers (SUS316L, food-grade finish)
- CIP (Clean-in-Place) compatible coil systems
- Bioreactor temperature control coils
Marine & Offshore
- Shipboard heat exchangers and condensers
- Offshore platform cooling systems
- Seawater desalination plant evaporator tubes
Automotive & HVAC
- Automotive radiator and intercooler coil assemblies
- Commercial HVAC air handling unit coils
- Refrigeration evaporator and condenser coils
Quality Certifications & Standards Compliance
Management System Certifications
- ISO 9001:2015 — Quality Management Systems
- ISO 14001:2015 — Environmental Management Systems
- ISO 45001:2018 — Occupational Health and Safety Management Systems
- ISO/TS 22163 — Automotive Production Part Approval Process (APQP) compliance (where applicable)
Product Certification & Inspection
- EN 10204 3.1 / 3.2 — Material Test Certificates (Manufacturer's Test Report / Third-Party Inspection)
- ASME Section IX — Welding qualification (for welded coil tube variants)
- API 5L / API 5CT — Compliance for oil and gas applications (where applicable)
- NORSOK M-650 — Offshore piping material certification (for marine/offshore applications)
- NSF/ANSI 61 — Drinking water system safety certification (for food/water applications)
- 3-A Sanitary Standards — Dairy and food processing equipment compliance
Testing & Inspection Protocol
| Test Method | Standard Reference | Acceptance Criteria |
|---|---|---|
| Hydrostatic Pressure Test | ASTM A270 / GB/T 21832 | No leakage at 2× working pressure for 10 seconds minimum |
| Chemical Composition Analysis | ASTM A240 / GB/T 20878 | Within specified grade limits (±0.05% for C, ±0.5% for major elements) |
| Mechanical Testing (Tensile, Elongation) | ASTM A370 / GB/T 228.1 | Meets minimum values per grade specification |
| Intergranular Corrosion Test | ASTM A262 Practice E / GB/T 4334 | Pass — no intergranular attack after 48-hour exposure |
| Dimensional Verification | ASTM A213 / EN 10216-5 | Within specified OD, WT, and coil diameter tolerances |
| Eddy Current Testing (ECT) | ASTM E709 / GB/T 28661 | No indications exceeding acceptance threshold |
| Surface Passivation Verification | ASTM A967 / ASTM A380 | Chromic acid dip test — no iron contamination detected |
Unique Selling Points
"Engineered for Extreme Curvature — Delivered with Seamless Precision"
- Pioneering MF-PF Technology: Wenzhou Jixing Metal Materials Co., Ltd. employs the Medium-Frequency Induction Heating Push Forming method, a cutting-edge approach that overcomes the fundamental limitations of traditional cold-forming processes for large-diameter coil tubes, delivering superior mechanical properties and dimensional accuracy.
- Full Customization Capability: From material grade selection to surface finish, coil diameter, tube length, and end treatment, every parameter can be tailored to meet specific engineering requirements and project specifications.
- End-to-End Traceability: Each coil tube is accompanied by a comprehensive material traceability package including mill certificates, heat number references, chemical analysis reports, mechanical test results, and dimensional inspection records, ensuring full supply chain transparency.
- Cost-Efficiency at Scale: The continuous nature of the MF-PF process enables high-volume production with reduced material waste, lower energy consumption per unit length, and competitive pricing for large-scale projects.
- Technical Support & Engineering Consultation: Wenzhou Jixing provides pre-sales engineering consultation, material selection guidance, and post-sales technical support to ensure optimal product selection and application performance.