Stainless Steel Coil Tube — Intermittent Duty Heat Exchanger Series
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered coiled tubular product specifically designed for intermittent-duty heat exchanger applications. This product category represents a specialized segment within the coil tube manufacturing domain, where the tube is formed into a continuous helical or spiral configuration to maximize heat transfer surface area within a compact footprint. The coil tube is engineered to withstand cyclic thermal loading conditions inherent in intermittent operation, where the heat exchanger alternates between active heating/cooling phases and standby periods.
Based on the parametric analysis of intermittent working coil-type heat exchangers, this product line addresses the critical engineering challenges of thermal fatigue, cyclic expansion-contraction stresses, and fluid distribution uniformity that arise during repeated start-stop operational cycles. The design philosophy integrates material selection, geometric configuration, and manufacturing tolerances to ensure long-term reliability under non-steady-state thermal conditions.
Material & Properties
Base Alloy Composition
The coil tube is fabricated from austenitic stainless steel grades selected for superior resistance to thermal cycling, corrosion, and mechanical fatigue. The primary grades employed include:
- SAE 304 (UNS S30400) — General-purpose austenitic stainless steel with balanced corrosion resistance and formability. Chromium content 18–20%, Nickel content 8–10.5%.
- SAE 316 (UNS S31600) — Enhanced corrosion resistance grade with 2–3% Molybdenum addition, suitable for aggressive chemical and marine environments.
- SAE 321 (UNS S32100) — Stabilized grade with Titanium addition for improved resistance to sensitization at elevated temperatures (up to 870°C).
- SAE 316L (UNS S31603) — Low-carbon variant of 316 for superior weldability and reduced risk of intergranular corrosion.
Key Mechanical Properties
| Property | SAE 304 | SAE 316 | SAE 321 |
|---|---|---|---|
| Tensile Strength (MPa, min) | 515 | 515 | 515 |
| Yield Strength (MPa, min) | 205 | 205 | 205 |
| Elongation (%) | ≥40 | ≥40 | ≥40 |
| Thermal Expansion Coefficient (×10⁻⁶/K, 20–100°C) | 17.3 | 17.3 | 17.3 |
| Thermal Conductivity (W/m·K, 100°C) | 16.3 | 14.6 | 16.3 |
| Maximum Service Temperature (°C) | 870 | 870 | 925 |
| Density (g/cm³) | 8.0 | 8.0 | 8.0 |
Corrosion Resistance Characteristics
The austenitic microstructure provides inherent resistance to oxidation and pitting corrosion. The passive chromium oxide film (Cr₂O₃) self-repairs in the presence of oxygen, maintaining surface integrity during intermittent thermal cycling. The Molybdenum-bearing grades (316/316L) exhibit Point Defect Resistance Index (PDI) values exceeding 220, providing enhanced resistance to chloride-induced pitting and crevice corrosion in industrial process environments.
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) — Intermittent Duty Heat Exchanger Series |
| Product Code | No. 1329 |
| Outer Diameter (OD) | φ6.0 mm – φ50.8 mm (customizable) |
| Wall Thickness | 0.5 mm – 3.0 mm |
| Coil Diameter | 100 mm – 2000 mm (configurable per heat exchanger design) |
| Coil Pitch | 10 mm – 150 mm (optimized for fluid dynamics) |
| Tube Length per Coil | 5 m – 500 m (continuous coil) |
| Surface Finish | Ba < 0.5 μm (electropolished) or Ba < 1.6 μm (pickled & passivated) |
| Dimensional Tolerance | OD: ±0.05 mm; Wall thickness: ±0.03 mm; Coil diameter: ±0.5% |
| Operating Pressure | Up to 2.5 MPa (PN25), test pressure 3.75 MPa |
| Operating Temperature Range | −196°C to +450°C (continuous); intermittent peaks to 870°C |
| Applicable Standards | ASTM A213/A213M, EN 10216-5, GB/T 12771 |
| Available Grades | 304, 304L, 316, 316L, 321, 321H, 310S, 904L |
Manufacturing Process
The production of the intermittent-duty coil tube follows a rigorous multi-stage manufacturing sequence optimized for dimensional accuracy and metallurgical integrity:
- Raw Material Preparation — Ingot casting via Vacuum Induction Melting (VIM) or Argon Oxygen Decarburization (AOD) processes, ensuring ultra-low sulfur and nitrogen content. Billet annealing at 1100°C followed by controlled cooling to achieve uniform austenitic grain structure (ASTM grain size 5–8).
- Hot Rolling — Billet hot rolling to initial tube blank dimensions with controlled reduction ratios (≤70% per pass) to prevent centerline segregation and maintain material homogeneity.
- Cold Drawing & Precision Sizing — Multi-stage cold drawing through calibrated dies to achieve final OD and wall thickness tolerances. Drawing lubricants are food-grade or pharmaceutical-grade per application requirements. Post-drawing annealing at 1050°C in argon atmosphere to relieve cold work stresses and restore full ductility.
- Coiling (Spiral Forming) — Precision coiling using CNC-controlled mandrel systems. The coil is formed at a controlled bending rate with minimum bend radius ≥5×OD to prevent ovalization and wall thinning. Springback compensation algorithms ensure dimensional accuracy after release from the mandrel.
- Heat Treatment (Solution Annealing) — Final solution annealing at 1050–1150°C with rapid water quenching to dissolve carbides and maximize corrosion resistance. For stabilized grades (321/347), precipitation heat treatment at 870–900°C promotes TiC/NbC formation at grain boundaries.
- Surface Treatment — Acid pickling (HNO₃/HF mixture) followed by passivation to establish protective chromium oxide film. Electropolishing available for ultra-clean surface finish (Ra < 0.25 μm) in pharmaceutical and food-grade applications.
- Quality Inspection — Comprehensive testing including hydrostatic pressure testing, dimensional verification, spectroscopic composition analysis, and (where applicable) eddy current flaw detection.
Intermittent Duty Design Considerations
The parametric analysis of intermittent working coil-type heat exchangers identifies several critical design parameters that influence coil tube performance:
- Cyclic Thermal Stress — Calculated using the formula: σ_cyclic = α × ΔT × E, where α is the thermal expansion coefficient, ΔT is the temperature swing per cycle, and E is Young's modulus. The coil geometry inherently accommodates thermal expansion through helical flexibility, reducing stress concentration factors (Kt) to values below 1.5.
- Thermal Fatigue Life — Estimated using the Coffin-Manson relationship: N_f = C × (Δε_p)^(-m), where Δε_p is the plastic strain amplitude per cycle. The austenitic stainless steel grades selected provide fatigue life exceeding 10⁵ cycles under typical intermittent duty conditions.
- Flow Distribution Uniformity — Coil pitch and diameter are optimized to ensure uniform fluid distribution across all turns, minimizing dead zones and thermal stratification during intermittent operation.
Applications
The Intermittent Duty Coil Tube is specifically engineered for applications requiring cyclic thermal operation:
Primary Applications
- Intermittent Heat Exchangers — Batch processing systems in chemical, pharmaceutical, and food industries where heating/cooling cycles alternate with standby periods.
- Cooling Coils for Air Handling Units — HVAC systems with variable operating schedules requiring repeated thermal cycling.
- Industrial Process Cooling — Heat recovery systems in intermittent manufacturing processes (e.g., batch reactors, kiln preheating systems).
- Refrigeration Evaporator Coils — Cryogenic and industrial refrigeration systems with cyclic compressor operation.
- Solar Thermal Collectors — Flat-plate and evacuated tube solar collectors with intermittent irradiation cycles.
Industry-Specific Applications
| Industry | Application | Recommended Grade |
|---|---|---|
| Pharmaceutical | CIP (Clean-in-Place) heat exchangers, autoclave coils | 316L (Electropolished) |
| Food & Beverage | Pasteurization coils, milk processing heat exchangers | 304/316L (Food-grade finish) |
| Chemical Processing | Batch reactor cooling coils, evaporator bundles | 316/904L |
| Power Generation | Condenser coils, steam recovery systems | 321H/310S |
| Marine & Offshore | Ballast water cooling, marine HVAC systems | 316/2205 |
Unique Selling Points
- Cyclic Thermal Fatigue Optimized — Material selection and coil geometry specifically engineered for intermittent duty cycling, with validated fatigue life exceeding 10⁵ thermal cycles.
- Parametric Design Validation — Product development informed by rigorous parametric analysis of intermittent heat exchanger performance, ensuring optimal thermal-hydraulic efficiency across operating cycles.
- Precision Dimensional Control — CNC coiling with springback compensation delivers coil diameter accuracy within ±0.5%, critical for proper fit in heat exchanger housings.
- Multi-Grade Availability — Extensive alloy range from standard 304/316 to high-performance 904L and 310S grades, enabling application-specific material optimization.
- Custom Configuration Capability — Fully customizable OD, wall thickness, coil diameter, and pitch to match specific heat exchanger design requirements.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains the following quality management certifications and product compliance standards:
Management System Certifications
- ISO 9001:2015 — Quality Management Systems
- ISO 14001:2015 — Environmental Management Systems
- ISO 45001:2018 — Occupational Health & Safety Management Systems
- ISO/IEC 17025 — Testing & Calibration Laboratory Competence
Product Compliance Standards
- ASTM A213/A213M — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for High Temperature Service
- EN 10216-5 — Non-ferrous metallic tubes for heat exchangers and heat sinks — Part 5: Technical delivery conditions for austenitic stainless steel tubes
- GB/T 12771 — Chinese National Standard for Stainless Steel Seamless Tubes for General Purposes
- ASME BPV Section VIII — Pressure Vessel Code (where applicable for pressure-containing heat exchangers)
- EHEDG Guidelines — European Hygienic Engineering Design Group standards for food/pharmaceutical applications
- 3-A Sanitary Standards — American Dairy Association standards for dairy equipment components
Testing & Inspection Protocols
- Hydrostatic pressure testing at 1.5× working pressure with minimum hold time of 30 seconds
- Spectroscopic analysis (OES) for chemical composition verification per batch
- Hardness testing (HV30) to confirm annealing condition
- Intergranular corrosion testing (ASTM A262 Practice E) for stabilized grades
- Pitting resistance testing (ASTM G48) for chloride-containing environments
- Dimensional inspection with laser micrometry and coordinate measuring machines (CMM)
- Visual inspection of coil surface for defects, discoloration, or mechanical damage
Technical Support & Customization
Wenzhou Jixing Metal Materials Co., Ltd provides comprehensive technical support including:
- Thermal-hydraulic performance modeling for specific intermittent duty cycles
- Material selection guidance based on fluid chemistry, temperature range, and cycling frequency
- Custom coil geometry design and finite element analysis (FEA) for thermal stress validation
- Welding procedure specification (WPS) development for heat exchanger assembly
- Full traceability documentation from raw material mill certificate to final product test report