Constant Temperature Variable Frequency Stainless Steel Coil Tube — Coiltube (Model No. 513)
1. Product Overview
The Constant Temperature Variable Frequency Stainless Steel Coil Tube (Model No. 513), manufactured by Wenzhou Jixing Metal Materials Co., Ltd, is a precision-engineered coil tube designed for thermal management systems requiring stable temperature regulation under variable operating loads. This product represents an advanced integration of stainless steel metallurgy with variable frequency drive (VFD) compatible thermal transfer architecture, enabling energy-efficient and highly responsive heat exchange applications.
Unlike conventional coil tubes that operate at fixed thermal output, this product incorporates design features optimized for compatibility with variable frequency control systems, allowing dynamic adjustment of fluid flow rates and heat transfer capacity in response to real-time demand fluctuations. The coil geometry maximizes surface area within a compact footprint, making it ideal for space-constrained industrial and commercial installations.
2. Material & Properties
2.1 Base Material
- Primary Alloy: Austenitic stainless steel conforming to ASTM A269 / ASTM A213 standards
- Standard Grades: 304 (UNS S30400), 316 (UNS S31600), and 316L (UNS S31603) depending on application requirements
- Carbon Content: ≤ 0.08% (304/316) or ≤ 0.03% (316L, low-carbon variant for weld sensitization resistance)
- Chromium (Cr): 18–20% — provides passive oxide layer and general corrosion resistance
- Nickel (Ni): 8–12% — stabilizes austenitic microstructure and enhances ductility
- Molybdenum (Mo): 2–3% (316/316L grades) — improves pitting and crevice corrosion resistance in chloride environments
2.2 Key Physical Properties
- Density: 7.93 g/cm³ (304) / 8.00 g/cm³ (316)
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (304) / 16.3 W/(m·K) at 20°C (316)
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C (20–100°C)
- Melting Range: 1400–1450°C
- Maximum Service Temperature: 870°C (oxidation limit in continuous air exposure)
- Magnetic Susceptibility: Non-magnetic (austenitic structure)
2.3 Mechanical Properties (Annealed Condition)
- Tensile Strength (UTS): ≥ 515 MPa (304) / ≥ 515 MPa (316)
- Yield Strength (0.2% offset): ≥ 205 MPa
- Elongation at Break: ≥ 40% (2 inches gauge length)
- Hardness (HB): ≤ 217
3. Specifications
| Parameter | Specification / Range | Standard / Reference |
|---|---|---|
| Product Model | Coiltube No. 513 | — |
| Outer Diameter (OD) | 6.0 mm – 38.1 mm (¼" – 1½") | ASTM A269 |
| Wall Thickness | 0.5 mm – 3.0 mm | ASTM A269 / ASME B36.19M |
| Coil Pitch (Center-to-Center) | 10 mm – 50 mm (customizable) | — |
| Coil Diameter | 50 mm – 600 mm | — |
| Tube Length (Coiled) | Up to 300 m per coil | — |
| Surface Finish | No. 1 (hot-rolled), 2B, BA (Bright Annealed), or Electropolished (Ra ≤ 0.4 μm) | ASTM A478 / ASTM A479 |
| Operating Temperature | -196°C to +870°C | — |
| Operating Pressure | Up to 25 MPa (3625 psi) | ASME B31.3 |
| Variable Frequency Compatibility | Compatible with 0–50 Hz VFD control; supports PWM modulation for constant-temperature operation | — |
| End Form | Plain end, Beveled end, or Threaded (BSPP/BSPT/NPT) | — |
| Tolerance on OD | ±0.05 mm (precision) / ±0.1 mm (standard) | — |
| Tolerance on Wall Thickness | ±10% of nominal | ASTM A269 |
| Corrosion Resistance | Pitting Resistance Equivalent Number (PREN): 19 (304) / 24–26 (316/316L) | — |
| Welding Suitability | Excellent — TIG (GTAW), MIG (GMAW), orbital welding | ASME IX |
4. Manufacturing Process
4.1 Process Flow
- Slab Casting & Hot Rolling: Primary steelmaking via Basic Oxygen Furnace (BOF) or Electric Arc Furnace (EAF), followed by hot rolling to produce seamless tube billet or perforated plate for ERW/ODW processes.
- Seamless Tube Production: Hot-rolled seamless tube (HRS) produced via Mannesmann piercing or capillary piercing methods; cold-drawn seamless tube (CDT) produced via rotary piercing followed by multi-pass cold drawing.
- Heat Treatment (Solution Annealing): Tubes are solution-annealed at 1040–1120°C followed by rapid water quenching to dissolve carbides, restore full austenitic structure, and maximize corrosion resistance.
- Coil Forming: Precision CNC-controlled coiling machines wind the annealed tube into the specified coil geometry with controlled pitch, diameter, and tensile stress distribution. Tension-controlled feeding ensures uniform coil density and prevents permanent set or kinking.
- Pickling & Passivation: Acid pickling (mixed HNO₃/HF solution) removes mill scale and heat treatment oxides; subsequent passivation treatment (HNO₃-based) regenerates the chromium-rich passive film to achieve corrosion resistance.
- Surface Finishing (Optional): Bright annealing in a protective atmosphere (H₂/N₂ or vacuum) for BA finish; mechanical polishing and/or electropolishing for mirror or sanitary-grade surfaces.
- End Preparation: Mechanical cutting, beveling, or thread machining to specification.
- Quality Inspection: Hydrostatic testing, dimensional inspection, surface defect detection (eddy current / magnetic particle), and chemical/spectral analysis.
- Packaging & Marking: Protective wrapping, moisture barrier packaging, and traceability labeling per ISO 9001 requirements.
4.2 Variable Frequency Optimization
The coil tube geometry is specifically designed to maintain consistent thermal performance across the full variable frequency operating range. The uniform coil pitch and precise wall thickness tolerances ensure that fluid flow distribution remains stable regardless of pump speed modulation (0–50 Hz). The smooth internal surface finish (Ra ≤ 0.4 μm when electropolished) minimizes friction losses and prevents flow turbulence at low flow rates, which is critical for maintaining constant temperature control at reduced energy inputs.
5. Applications
5.1 Primary Application Domains
- Industrial Process Heating & Cooling: Constant-temperature heat transfer loops in chemical processing, pharmaceutical manufacturing, and food-grade thermal systems where variable load demands require precise temperature regulation.
- HVAC & Chiller Systems: Integration with variable frequency drive (VFD) water pumps in commercial air conditioning systems, district cooling networks, and heat recovery ventilation units.
- Refrigeration & Cold Chain: Evaporator and condenser coils in industrial refrigeration plants, cold storage facilities, and transport refrigeration units requiring energy-efficient operation across variable ambient conditions.
- Power Generation: Condenser tubes and heat exchanger coils in combined-cycle power plants, solar thermal systems, and nuclear cooling loops where corrosion resistance and long service life are paramount.
- Marine & Offshore: Seawater heat exchanger coils, ballast water cooling systems, and offshore platform thermal management where chloride-induced pitting resistance is essential.
- Biomedical & Laboratory: Constant-temperature circulators, autoclave heating coils, and analytical instrument cooling systems requiring biocompatible, corrosion-free stainless steel contact surfaces.
- Food & Beverage Processing: Pasteurization heat exchangers, CIP (Clean-in-Place) system coils, and beverage conditioning loops requiring sanitary-grade (3-A / EHEDG) stainless steel construction.
5.2 Variable Frequency System Integration
This product is engineered for seamless integration with modern variable frequency drive (VFD) control architectures. The constant-temperature operation is achieved by modulating the pump motor speed via PWM (Pulse Width Modulation) control, which adjusts fluid velocity through the coil in response to thermal load changes. This approach eliminates the need for throttling valves, reduces hydraulic energy losses by up to 60%, and extends the operational life of associated pump systems by eliminating constant high-speed operation.
6. Quality Certifications & Compliance
6.1 International Standards & Certifications
- ISO 9001:2015 — Quality Management System certification for manufacturing processes
- ISO 14001:2015 — Environmental Management System certification
- ISO/IEC 17025 — Laboratory competence for testing and calibration facilities
- EN 10204 — Material Inspection Certificates (Type 3.1 mill test certificates available upon request)
- ASTM A269 / A213 — Standards for seamless and welded stainless steel tubing
- ASME BPV Code — Boiler and Pressure Vessel Code compliance (where applicable)
- ASME B31.3 — Process piping design compliance
- 3-A Sanitary Standards — For food-grade applications (optional)
- EHEDG — European Hygienic Engineering Design Group approval (optional)
- CE Marking — European Conformity for pressure equipment (PED Directive 2014/68/EU)
- NACE MR0175 / ISO 15156 — Resistance to sulfide stress cracking (for 316L grade in oil & gas service)
6.2 Testing & Inspection Protocol
- Hydrostatic Pressure Testing: 100% of production tested at 1.5× working pressure for minimum 5 seconds per tube length
- Eddy Current Testing (ECT): 100% inline inspection for internal and external surface defects
- Spectrographic Analysis: Optical emission spectrometry (OES) for chemical composition verification per ASTM E1933
- Dimensional Inspection: Ultrasonic wall thickness gauging, OD measurement, and straightness verification
- Corrosion Testing: Salt spray testing (ASTM B117, 1000 hours minimum for 316L) and intergranular corrosion testing (ASTM A262 Practice E)
- Traceability: Each coil is assigned a unique heat number and batch identifier for full production traceability
7. Unique Selling Points
Energy Efficiency: The VFD-compatible coil design reduces hydraulic energy consumption by up to 60% compared to fixed-speed systems through elimination of throttling losses and optimization of pump affinity laws.
Precision Thermal Control: Uniform coil geometry and tight manufacturing tolerances enable consistent heat transfer coefficients across the entire variable frequency operating range, achieving temperature stability within ±0.5°C.
Superior Corrosion Resistance: Austenitic stainless steel grades (304/316/316L) provide outstanding resistance to general corrosion, pitting, crevice corrosion, and stress corrosion cracking in aggressive chemical and marine environments.
Hygienic Design: Electropolished surfaces (Ra ≤ 0.4 μm) eliminate crevice contamination risks, comply with FDA 21 CFR and 3-A Sanitary Standards, and facilitate effective CIP/SIP cleaning protocols.
Customizability: Full customization of coil diameter, pitch, tube dimensions, surface finish, and end preparation to meet specific OEM and end-user requirements.
Long Service Life: Design life exceeding 25 years in continuous operation with minimal maintenance, supported by the inherent fatigue resistance and corrosion durability of austenitic stainless steel.
8. Technical Notes & Recommendations
- Storage: Store in a dry, well-ventilated area away from direct contact with carbon steel or other dissimilar metals to prevent galvanic corrosion and iron contamination.
- Handling: Use clean, non-abrasive handling equipment. Avoid dragging coils across rough surfaces to prevent surface damage.
- Welding: Use low-heat-input welding techniques (TIG preferred) with appropriate filler metals (ER308L for 304, ER316L for 316/316L). Post-weld solution annealing is recommended for critical corrosion applications.
- Variable Frequency Integration: Coordinate coil design parameters (pitch, OD, wall thickness) with system hydraulic calculations to ensure optimal Reynolds number (Re > 10,000 for turbulent flow) across the full VFD operating range.
- Anti-Vibration Mounting: Install vibration-damping supports at intervals not exceeding 3× the coil diameter to prevent fatigue-induced failure under variable flow conditions.