Stainless Steel Coil Tube for Floating Roof Tank Heating Systems (Coiltube)
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product specifically designed for thermal management applications in floating roof tank systems. This product line represents a specialized segment of stainless steel coil tubing engineered to withstand the demanding conditions of hydrocarbon storage environments, where it serves as a critical heat transfer medium for maintaining optimal fluid viscosity in crude oil, fuel oil, and other viscous petroleum products stored in atmospheric and low-pressure tanks.
Based on extensive research into the numerical simulation of floating roof tank coil heating processes, this product has been optimized for uniform heat distribution, thermal cycling resistance, and long-term structural integrity under continuous operational stress. The coil tube geometry enables maximum surface-area-to-volume ratios, facilitating efficient heat exchange while minimizing thermal gradients across the tank bottom and sidewall.
Material & Properties
Primary Material Grades
- Austenitic Stainless Steels: AISI 304 (UNS S30408), AISI 316L (UNS S31603), and AISI 321 (UNS S32100) — selected for superior corrosion resistance in hydrocarbon-rich environments
- Super-Austenitic Grades: 904L (UNS N08904) and 254 SMO (UNS S31254) — for aggressive sulfuric acid and chloride-containing service conditions
- Stabilized Austenitic Grades: AISI 347 (UNS S34700) — for elevated temperature applications where carbide precipitation must be controlled
Key Mechanical Properties
- Tensile Strength: 520–720 MPa (depending on grade and condition)
- Yield Strength: ≥205 MPa (0.2% offset)
- Elongation at Break: ≥35% (minimum)
- Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C
- Coefficient of Thermal Expansion: 16–18 × 10⁻⁶ /°C (20–100°C range)
- Maximum Operating Temperature: 870°C (304/321), 1150°C (316L in oxidizing atmosphere)
Corrosion Resistance Characteristics
- Excellent resistance to atmospheric corrosion, dilute acids, and organic compounds
- High resistance to pitting and crevice corrosion (particularly 316L and super-austenitic grades)
- Resistance to intergranular corrosion following sensitization at 450–850°C
- Outstanding performance in reducing and oxidizing acid environments
Technical Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Tube Outer Diameter (OD) | 10.0 mm – 114.3 mm (1/2" – 4") | ASTM A213 / ASTM A269 |
| Wall Thickness | 0.5 mm – 6.35 mm (0.020" – 0.250") | ASTM A213 / EN 10216-5 |
| Coil Inner Diameter | 150 mm – 1200 mm (adjustable per application) | Manufacturer's Specification |
| Coil Length per Spool | 50 m – 2000 m (continuous coil) | ASTM A213 |
| Surface Finish | Mill finish, pickled & passivated, or polished (Ra ≤ 0.4 μm) | ASTM A967 / EN 10307 |
| Manufacturing Method | Seamless (hot/cold drawn) or welded (ERW, TIG) | ASTM A213 / ASTM A269 |
| Heat Treatment Condition | Solution annealed (1050–1150°C, water/quench cooled) | ASTM A213 |
| Pressure Rating | Up to 16 MPa (design dependent) | ASME B31.3 |
| Temperature Range | -196°C to +870°C (grade dependent) | ASTM A213 |
| Acceptable Deviations | ±0.1 mm OD; ±10% wall thickness | ASTM A213 / EN 10216-5 |
| Coating Options | Passivation, PTFE inner coating, ceramic coating (for anti-scaling) | ASTM A967 / Manufacturer's Specification |
Manufacturing Process
Process Flow
- Raw Material Selection: Virgin stainless steel billets or strip are sourced from certified mills, with full chemical composition verification per ASTM A240/A276 requirements.
- Hot Rolling / Extrusion: Billets are heated to 1100–1200°C and formed into seamless tube blanks or flat strip for welded tube production.
- Piercing & Elongation: (Seamless route) The tube blank is pierced and elongated through multiple passes to achieve the target OD and wall thickness.
- Pipe Milling / Forming: (Welded route) Flat strip is cold-formed into tube shape with precise dimensional control, followed by longitudinal welding (ERW or TIG).
- Solution Annealing: Tubes are heated to 1050–1150°C in a controlled atmosphere furnace and rapidly quenched to dissolve carbides and restore full austenitic microstructure.
- Pickling & Passivation: Acid pickling removes oxide scale; passivation treatment establishes a protective chromium oxide film (Cr₂O₃) on the surface.
- Cold Drawing / Sizing: Precision cold working refines dimensions, surface finish, and mechanical properties to meet tight tolerances.
- Coiling: Finished tubes are wound into coils of specified inner diameter using controlled tension systems to prevent deformation or kinking.
- Quality Inspection: Comprehensive non-destructive testing (NDT) including hydrostatic testing, eddy current inspection, and visual examination.
- Coiling & Packaging: Final coils are wrapped in protective film, secured with steel straps, and packaged for shipment.
Process Optimization Based on Numerical Simulation
Advanced finite element analysis (FEA) and computational fluid dynamics (CFD) modeling have been applied to optimize the manufacturing parameters. Numerical simulations of the floating roof tank coil heating process have revealed critical insights regarding:
- Thermal stress distribution within coiled tube geometries during heating and cooling cycles
- Optimal coil pitch and layer arrangement for uniform heat transfer efficiency
- Residual stress patterns developed during cold coiling and their impact on fatigue life
- Thermal expansion constraints and their effect on tube-to-tube contact forces in multi-layer coil configurations
Applications
Primary Application: Floating Roof Tank Heating
The principal application domain for this coil tube product is the heating of viscous petroleum products stored in floating roof tanks (FRTs). In this configuration:
- Coil tubes are laid in serpentine or spiral patterns on the tank bottom or along tank walls
- Hot water, steam, or thermal oil circulates through the coil tubes to maintain product temperature
- Typical operating temperature range: 40°C – 150°C (depending on product viscosity requirements)
- Heat flux design: 500 – 3000 W/m²
Additional Applications
- Heat Exchanger Coils: Shell-and-coil heat exchangers in petrochemical processing
- Boiler Tube Systems: Fire-tube and water-tube boiler components
- Refrigeration Coils: Evaporator and condenser coils in industrial refrigeration systems
- Chemical Processing: Reaction vessel heating/cooling jackets and internal coils
- Food & Pharmaceutical Industry: Sanitary-grade heat transfer coils (316L with electropolished finish)
- Power Generation: Condenser tube bundles and feedwater heaters
- Marine Engineering: Bilge heating systems and fuel oil preheating coils
- Automotive Industry: Exhaust system components and turbocharger cooling circuits
Unique Selling Points
- Simulation-Validated Design: Product specifications are informed by rigorous numerical simulation of the floating roof tank heating process, ensuring optimal thermal performance and structural reliability under actual operating conditions.
- Customizable Coil Geometry: Coil inner diameter, tube length, and pitch are customizable to fit specific tank dimensions and thermal load requirements.
- Wide Grade Selection: From standard 304 to super-austenitic 904L and 254 SMO, covering the full spectrum of corrosion resistance requirements.
- Consistent Mechanical Properties: Solution annealing and controlled cold working ensure uniform properties throughout the coil length, critical for fatigue performance under thermal cycling.
- Surface Integrity: Pickled and passivated surfaces provide immediate corrosion protection and facilitate fluid flow with minimal fouling.
- Traceability: Full heat number traceability from raw material to finished product, supporting quality assurance and regulatory compliance.
Quality Certifications & Standards Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification for consistent product quality |
| ISO 14001:2015 | Environmental Management System certification |
| ISO 45001:2018 | Occupational Health and Safety Management System |
| ASTM A213 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for High Temperature Service |
| ASTM A269 | Standard Specification for Welded Austenitic Stainless Steel Tubing |
| EN 10216-5 | European standard for welded stainless steel tubes for pressure purposes |
| GB/T 12771 | Chinese National Standard for welded stainless steel tubes for general purposes |
| GB/T 13296 | Chinese National Standard for seamless stainless steel tubes for pressure purposes |
| ASME SA-213 | Boiler and Heat Exchanger Tube specification (American Society of Mechanical Engineers) |
| API 5CT (where applicable) | |
| Mill Test Certificates (MTC) | EN 10204 Type 3.1 certification with full chemical and mechanical test data |
| NACE MR0175 / ISO 15156 | Resistance to sulfide stress cracking in sour service (select grades) |
Testing & Inspection Protocol
- Chemical Analysis: Spectrometric verification of Cr, Ni, Mo, C, Mn, Si, S, P content per grade specifications
- Mechanical Testing: Tensile testing, hardness testing (Rockwell B/C), and impact testing (Charpy V-notch at -40°C where specified)
- Hydrostatic Testing: 100% pressure testing at 1.5× design pressure with minimum dwell time of 5 seconds
- Eddy Current Testing: 100% coverage for wall thickness verification and surface defect detection
- Dimensional Inspection: OD, wall thickness, straightness, and coil geometry verification
- Visual Inspection: Surface quality, weld integrity, and absence of defects per ASTM E1012
- Corrosion Testing: Intergranular corrosion test (ASTM A262 Practice E), pitting resistance (ASTM G48), and stress corrosion cracking evaluation where applicable
- Thermal Cycling Test: Simulated operational cycling to validate fatigue resistance for floating roof tank service
Thermal Performance Considerations for Floating Roof Tank Service
Numerical simulation studies of the floating roof tank coil heating process have established the following design parameters for optimal coil tube performance:
- Heat Transfer Coefficient: Typical values of 2000–4000 W/(m²·K) for forced convection of hot water/steam through the coil tubes
- Temperature Uniformity: Design targets maintain tank bottom temperature variation within ±5°C across the heated area
- Thermal Cycling Life: Minimum 10,000 cycles at ΔT = 100°C before fatigue failure (based on Coffin-Manson relationship)
- Heat Loss Factor: Maximum 15% heat loss to ambient through tank walls and insulation
- Flow Velocity: Recommended 1.0–3.0 m/s within coil tubes to prevent laminar flow and ensure efficient heat transfer