Stainless Steel Coil Tube (Coiltube) — External Welded Semi-Disk Heating Structure
Product Overview
The Stainless Steel Coil Tube (Coiltube), manufactured by Wenzhou Jixing Metal Materials Co., Ltd, is a precision-engineered heat exchanger component designed for industrial heating and thermal transfer applications. This product category encompasses externally welded semi-disk coil tubes, which integrate a helically wound tubular core with semi-circular disk headers to form a compact, high-efficiency heating assembly. The design eliminates the need for internal threading, reduces pressure drop, and maximizes heat transfer surface area within a constrained footprint.
Coiltubes are widely deployed in chemical processing, petrochemical refining, power generation, pharmaceutical manufacturing, and HVAC systems where reliable thermal management is critical. The external welding configuration provides superior mechanical integrity at connection points while maintaining the flexibility and thermal conductivity inherent to coiled geometries.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its exceptional corrosion resistance, high-temperature performance, and long service life under demanding industrial conditions.
- Primary Materials: Austenitic Stainless Steel grades including 304 (UNS S30400), 316 (UNS S31600), 316L (UNS S31603), and 321 (UNS S32100)
- Alternative Alloys: Duplex stainless steel grades such as 2205 (UNS S32205) for elevated chloride environments
- Key Properties:
- Corrosion resistance in acidic, alkaline, and chloride-containing media
- High-temperature oxidation resistance up to 870°C (1600°F) for Grade 321
- Thermal conductivity of 16.3 W/(m·K) for Grade 304 at 20°C
- Non-magnetic in the annealed condition
- Excellent formability and weldability without preheating
- Surface Finish: Available in standard mill finish, electropolished (Ra ≤ 0.4 μm), or passivated surface
Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Tube Outer Diameter (OD) | Φ6 mm – Φ50 mm | ASTM A269 / GB/T 12771 |
| Wall Thickness | 0.5 mm – 3.0 mm | ASTM A269 / GB/T 12771 |
| Coil Winding Diameter | 50 mm – 500 mm | Custom design |
| Coil Length (Developed) | 1 m – 120 m | Custom design |
| Number of Turns | 5 – 500 turns | Custom design |
| Turn-to-Turn Spacing | 2 mm – 25 mm | Custom design |
| Welding Method (External) | TIG (GTAW) / Orbital TIG | ASME Section IX / AWS D10.6 |
| Design Pressure | Up to 25 MPa (3,625 psi) | ASME BPV Code Section VIII |
| Operating Temperature | −196°C to +600°C (−320°F to +1112°F) | Material grade dependent |
| End Connection Type | Semi-disk header with external weld | Custom / ASME B31.3 |
| Tolerance (OD) | ±0.15 mm (standard); ±0.05 mm (precision) | ASTM A269 |
| Tolerance (Wall Thickness) | ±10% of nominal | ASTM A269 |
Manufacturing Process
The production of externally welded semi-disk coil tubes follows a rigorous multi-stage manufacturing workflow:
- Material Selection & Inspection: Raw stainless steel strip or seamless tube stock is procured per ASTM A269/A270 specifications. Incoming material undergoes spectroscopic analysis (PMI — Positive Material Identification) and mechanical property verification.
- Coil Forming (Cold Bending): Continuous stainless steel tube is cold-bent into helical coil geometry using CNC-controlled coiling machinery. The bending process is executed below the yield point to prevent work hardening and microstructural distortion. Turn-to-turn spacing is precisely controlled via programmable tooling.
- Semi-Disk Header Fabrication: Semi-circular disk headers are precision-cut and formed from the same stainless steel grade as the coil tube. These headers serve as the inlet/outlet manifolds and structural anchoring points.
- External Welding Assembly: The coil tube ends are welded to the semi-disk headers using Gas Tungsten Arc Welding (GTAW/TIG) with argon shielding. Orbital TIG welding may be employed for circumferential welds to ensure uniform penetration and bead geometry. Weld parameters are optimized based on ASME Section IX qualification procedures.
- Weld Inspection & NDT: Completed welds undergo 100% visual inspection, followed by dye penetrant testing (DPT) or magnetic particle testing (MT) for surface defect detection. Radiographic testing (RT) is performed on critical welds to verify internal fusion and absence of voids or inclusions.
- Heat Treatment (if required): For high-stress or high-temperature applications, the assembly may undergo solution annealing (1050°C – 1150°C with water quench) or stress-relief annealing (870°C – 900°C with air cool) to restore full corrosion resistance and relieve residual welding stresses.
- Passivation & Surface Treatment: The final product receives acid pickling and passivation treatment to remove free iron contamination and establish a protective chromium oxide film on all exposed surfaces, including weld zones.
- Pressure Testing & Final QA: Each coil tube assembly undergoes hydrostatic pressure testing at 1.5× the design pressure for a minimum of 30 minutes. Dimensional verification is performed against the engineering drawing using coordinate measuring machines (CMM) or laser scanning.
Applications
Externally welded semi-disk coil tubes are employed in a broad spectrum of industrial thermal systems:
- Chemical Processing: Reactor cooling coils, heat exchangers for acid concentration, and process fluid preheating in polyethylene and PVC production
- Petrochemical & Refining: Crude oil preheating, fractionation column internals, and heat recovery systems in distillation units
- Power Generation: Steam generator coil tubes, economizers, and condensate recovery systems in thermal and nuclear power plants
- Pharmaceutical & Food Processing: Pasteurization coils, CIP (Clean-in-Place) compatible heat exchangers, and sterile fluid handling systems
- Marine & Offshore: Seawater heat exchangers, ballast water treatment systems, and platform heating coils resistant to chloride-induced pitting
- Automotive & Aerospace: Intercoolers, exhaust gas recirculation (EGR) cooling, and thermal management of fuel cells
- HVAC & Refrigeration: Compact evaporator and condenser coils for commercial refrigeration and industrial air handling units
Quality Certifications & Standards
Wenzhou Jixing Metal Materials Co., Ltd maintains comprehensive quality management systems and product certifications to ensure global compliance:
- Quality Management: ISO 9001:2015 Certified
- Product Standards: ASTM A269 (Welded and Seamless Austenitic Stainless Steel Tubing), ASTM A270, GB/T 12771, EN 10217-7
- Welding Qualification: ASME Section IX, AWS D10.6 (Welding of Nickel and Nickel-Alloy Base Materials — applicable to austenitic stainless steel)
- Pressure Vessel Compliance: ASME BPV Code Section VIII Division 1 (where applicable)
- NDT Certification: ASNT Level II/III qualified personnel for all non-destructive testing operations
- Environmental & Safety: ISO 14001:2015 (Environmental Management), ISO 45001:2018 (Occupational Health & Safety)
- Material Traceability: Full heat-number traceability from raw material mill certificate through final product dispatch
- Third-Party Inspection: Available upon request — Lloyd's Register, DNV, Bureau Veritas, SGS, or TÜV inspection services
Unique Selling Points
- External Weld Semi-Disk Configuration: Eliminates internal thread connections that create flow turbulence and erosion points, resulting in reduced pressure drop and extended service intervals.
- Precision Engineering & Calculation: Each coil tube assembly is designed using validated thermal-hydraulic calculation models, ensuring optimal heat transfer coefficient (U-value) and pressure drop performance tailored to specific operating conditions.
- Compact Footprint: The helical coil geometry delivers high heat transfer area per unit volume, enabling space-efficient installations in constrained industrial environments.
- Superior Corrosion Resistance: Austenitic stainless steel construction provides reliable performance in aggressive chemical environments without the need for internal coatings or linings.
- Full Traceability & Compliance: End-to-end material traceability and adherence to international standards ensure regulatory compliance across global markets.
- Customization Capability: Flexible design parameters (diameter, wall thickness, coil geometry, header configuration) allow tailored solutions for unique process requirements.
Note: The design and calculation methodology for externally welded semi-disk coil tube heating structures follows established thermal engineering principles, including Dittus-Boelter and Sieder-Tate correlations for convective heat transfer coefficients, combined with Ergun equation-based pressure drop calculations. All designs are validated through finite element analysis (FEA) for structural integrity and thermal stress evaluation prior to fabrication.