High-Efficiency Internally Threaded Stainless Steel Coil Tube (Coiltube)
Product Overview
The High-Efficiency Internally Threaded Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd., designed for applications demanding superior heat transfer performance, energy efficiency, and long-term corrosion resistance. This product represents a significant advancement in the metallurgical and materials engineering domain, combining the inherent advantages of stainless steel with internally threaded surface enhancement technology to achieve remarkable improvements in thermal exchange efficiency.
The internally threaded (helically ribbed) inner surface of the Coiltube dramatically increases the effective heat transfer area and promotes turbulent flow within the tube bore, thereby reducing the thermal resistance of the boundary layer. This design philosophy is rooted in fundamental principles of heat transfer and fluid dynamics, where surface roughness elements are strategically engineered to disrupt laminar flow and enhance convective heat transfer coefficients.
Material and Properties
Base Material
The Coiltube is manufactured from high-grade stainless steel, primarily utilizing the following austenitic and duplex stainless steel grades:
- Austenitic Stainless Steel (e.g., AISI 304 / UNS S30400, AISI 316 / UNS S31600, AISI 321 / UNS S32100)
- Duplex Stainless Steel (e.g., UNS S31803 / S32205)
- Super Duplex Stainless Steel (e.g., UNS S32750 / S32760)
Mechanical Properties
- Tensile Strength (Ultimate Tensile Strength, UTS): 515–720 MPa (depending on grade)
- Yield Strength (0.2% Proof Stress): 205–450 MPa
- Elongation (at Break): ≥35% (minimum)
- Hardness (Brinell, HBW): 130–250
- Impact Strength (Charpy V-Notch at -40°C): ≥47 J (for duplex grades)
Corrosion Resistance
- Pitting Resistance Equivalent Number (PREN): 19–40 (grade-dependent)
- Corrosion Resistance: Excellent resistance to pitting, crevice corrosion, and intergranular corrosion (IGC) in chloride-containing environments
- Temperature Range: -196°C to +870°C (continuous service)
Thermal Properties
- Thermal Conductivity (at 20°C): 14.5–16.5 W/(m·K)
- Thermal Expansion Coefficient: 16–18 × 10⁻⁶ /K
- Enhanced Heat Transfer Coefficient: 25%–45% improvement over smooth-wall equivalent due to internal threading
Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm – 50.8 mm (¼" – 2") | ASTM A213 / EN 10216 |
| Wall Thickness | 0.50 mm – 3.00 mm | ASTM A269 / ASME SA-213 |
| Coil Diameter | 50 mm – 300 mm (standard); custom available | Manufacturer Specification |
| Coil Length (per roll) | 50 m – 500 m | Manufacturer Specification |
| Internal Thread Pitch | 1.5 mm – 4.0 mm (helical) | Manufacturer Specification |
| Internal Thread Height | 0.2 mm – 0.8 mm | Manufacturer Specification |
| Surface Finish (Internal) | Threading-Enhanced; Ra ≤ 1.6 μm (base surface) | ASTM A213 |
| Surface Finish (External) | Polished / Pickled / Bright Annealed; Ra ≤ 0.8 μm | ASTM A269 |
| Winding Tolerance | ±0.5% on OD; ±10% on coil diameter | ISO 1307 |
| Pressure Rating | Up to 25 MPa (grade and dimension dependent) | ASME B31.3 / EN 13480 |
| Operating Temperature | -196°C to +870°C | AISI Grade-Specific |
| Heat Transfer Enhancement | 25% – 45% over smooth tube equivalent | Manufacturer Test Data |
Manufacturing Process
Process Flow Overview
- Raw Material Selection and Inspection: Ingot or slab procurement from certified stainless steel mills, with full chemical composition verification via Optical Emission Spectrometry (OES) and Positive Material Identification (PMI).
- Hot Rolling / Billet Extrusion: Production of seamless tube blanks via rotary piercing or extrusion methods, achieving precise dimensional control of the parent tube.
- Intermediate Annealing and Pickling: Removal of scale and stress relief through acid pickling (HNO₃/HF blend) or electrolytic descaling to achieve a clean, oxide-free surface.
- Cold Drawing / Cold Winding: Precision reduction of tube diameter and wall thickness through multi-pass cold drawing, followed by controlled coil winding on precision mandrels to achieve the target coil geometry.
- Internal Threading (Helical Ribbing): Application of proprietary internal threading technology using rotating thread-forming tools or laser-induced surface texturing to create uniform helical ridges on the inner tube surface. This step is critical for heat transfer enhancement.
- Solution Annealing: High-temperature annealing (1050°C–1150°C, grade-dependent) in a controlled atmosphere (vacuum or argon) followed by rapid quenching to restore full solution-strengthened condition and maximize corrosion resistance.
- Pickling and Passivation: Final acid pickling and passivation treatment to remove any residual scale and establish a stable, protective chromium oxide (Cr₂O₃) passive film on the surface.
- Final Quality Control and Testing: Comprehensive dimensional inspection, hydrostatic pressure testing, non-destructive testing (NDT), and performance validation.
- Packaging and Dispatch: Protective packaging with desiccant and moisture barrier materials for international shipment compliance.
Key Process Innovations
The internal threading process employed by Wenzhou Jixing Metal Materials Co., Ltd. utilizes a precision-controlled mechanical forming technique that ensures uniform thread geometry along the entire tube length. The helical thread parameters (pitch, height, and cross-sectional profile) are optimized through Computational Fluid Dynamics (CFD) simulations to achieve the optimal balance between heat transfer enhancement and pressure drop penalty.
Applications
Primary Application Domains
- Air Conditioning and Refrigeration (AC&R): Evaporators, condensers, and heat exchangers in commercial and industrial refrigeration systems, leveraging the enhanced heat transfer surface area for improved coefficient of performance (COP).
- Automotive Radiators and Intercoolers: Compact heat exchangers requiring high thermal efficiency in space-constrained environments.
- Process Heat Exchangers: Shell-and-tube heat exchangers in petrochemical, pharmaceutical, and food processing industries where fouling resistance and corrosion durability are critical.
- Power Generation: Feedwater heaters, economizers, and condenser tubes in fossil fuel and nuclear power plants.
- Marine and Offshore Systems: Seawater coolers and heat exchangers exposed to aggressive chloride environments.
- Cryogenic Applications: Liquefied natural gas (LNG) transfer lines and cryogenic heat exchangers requiring reliable performance at extremely low temperatures.
- Building Services: District heating/cooling systems, heat pump applications, and industrial water heating systems.
Unique Selling Points
- Superior Heat Transfer Performance: The internally threaded design delivers 25%–45% higher heat transfer rates compared to conventional smooth-wall stainless steel tubes of equivalent dimensions, directly translating to reduced equipment footprint and lower capital expenditure.
- Energy Efficiency: Enhanced thermal performance reduces pumping power requirements and improves overall system efficiency, contributing to lower operational carbon footprint and compliance with stringent energy regulations.
- Exceptional Corrosion Resistance: Stainless steel construction provides outstanding resistance to pitting, crevice, and stress corrosion cracking (SCC) in aggressive chemical environments, ensuring extended service life and reduced maintenance intervals.
- Fouling Mitigation: The helical thread geometry promotes turbulent flow, which inherently resists deposit accumulation and maintains heat transfer performance over extended operating periods.
- Cryogenic Capability: Full mechanical property retention at temperatures as low as -196°C, enabling reliable performance in cryogenic service without risk of brittle fracture.
- Customizable Geometry: Flexible manufacturing capability allowing customization of OD, wall thickness, coil diameter, coil length, and thread parameters to meet specific application requirements.
- Weldability: Excellent weldability with standard welding processes (TIG/GTAW, laser welding), facilitating on-site fabrication and integration into complex heat exchanger assemblies.
Quality Certifications and Compliance
Management System Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health and Safety Management System
- IATF 16949:2016 — Automotive Quality Management System (for automotive-grade applications)
Product Standards Compliance
- ASTM A213 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for High-Temperature and High-Pressure Boilers, Heaters, and Exchangers
- ASTM A269 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Similar Severities of Service
- ASME SA-213 / SA-249 — Boiler and Pressure Vessel Code, Section II, Part D
- EN 10216-5 — Tubes for Heat Exchangers and Similar Applications — Stainless Steel Tubes
- EN 10217-7 — Seamless Heat-Resistant Stainless Steel Tubes
- GB/T 12771 — Chinese National Standard for Stainless Steel Tubes for General Purposes
- JIS G3458 — Japanese Industrial Standard for Stainless Steel Tubes for Heat Exchangers
Testing and Inspection Protocols
- Hydrostatic Pressure Testing: Every coil subjected to pressure testing at 1.5× working pressure per ASTM A213 requirements.
- Eddy Current Testing (ECT): 100% non-destructive inspection for internal and external surface defects.
- Ultrasonic Testing (UT): Wall thickness verification and internal flaw detection.
- Chemical Analysis: Full spectral analysis (OES) of each heat lot with certified mill test reports (MTRs).
- Mechanical Testing: Tensile, hardness, and impact testing per applicable standards.
- Intergranular Corrosion Testing: ASTM A262 Practice E / Practice No. 1E verification for sensitization resistance.
- Heat Transfer Performance Testing: Bench-scale validation of thermal enhancement factors under controlled flow conditions.
Traceability and Documentation
Each Coiltube product is accompanied by comprehensive documentation including Mill Test Reports (MTRs), heat traceability records, dimensional inspection certificates, and non-destructive testing reports. Full batch traceability from raw material ingot through to final dispatch ensures complete supply chain accountability and facilitates regulatory compliance for critical applications.
Technical Summary
The High-Efficiency Internally Threaded Stainless Steel Coil Tube from Wenzhou Jixing Metal Materials Co., Ltd. exemplifies the convergence of advanced metallurgical engineering and precision manufacturing technology. By integrating proven stainless steel alloy chemistry with internally threaded surface enhancement technology, this product delivers a compelling combination of thermal efficiency, corrosion durability, and mechanical reliability. The product is particularly suited for demanding applications where energy efficiency, long service life, and resistance to aggressive environments are paramount design considerations. With full compliance to international standards and rigorous quality assurance protocols, this Coiltube represents a benchmark solution in the field of enhanced heat transfer tubing.