Stainless Steel Coil Tube (Coiltube) — Semi-Circular Floating Coil for Heat Exchangers
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered, semi-circular cross-section tubing product specifically designed for use in Floating Coil Heat Exchangers (FCHE). Unlike conventional circular-section coil tubes, the semi-circular (D-shaped or flat-bottom) geometry provides superior heat transfer surface utilization, enhanced fluid dynamics characteristics, and improved mechanical stability within the heat exchanger shell. This product represents a significant advancement in thermal exchange technology, combining high-performance material properties with innovative geometric design to deliver exceptional thermal efficiency, corrosion resistance, and long-term operational reliability.
The semi-circular coil tube is coiled into a compact spiral configuration that allows for maximum heat exchange area within a minimized footprint. The floating design permits independent thermal expansion and contraction of the coil relative to the shell, eliminating thermal stress accumulation and enabling continuous maintenance access without system shutdown.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its outstanding combination of corrosion resistance, mechanical strength, and thermal conductivity. The primary material grades include:
- ASTM A270 / AISI 304 (06Cr19Ni10) — General-purpose corrosion resistance with excellent weldability
- ASTM A270 / AISI 316L (022Cr17Ni12Mo2) — Enhanced resistance to pitting and crevice corrosion due to molybdenum addition
- ASTM A270 / AISI 321 (06Cr18Ni11Ti) — Stabilized grade suitable for elevated-temperature service
Key Material Properties (AISI 316L Reference):
- Density: 8.0 g/cm³
- Thermal conductivity: 14.6 W/(m·K) at 20°C
- Maximum operating temperature: 870°C (non-oxidizing atmosphere)
- Tensile strength: ≥ 485 MPa
- Yield strength: ≥ 205 MPa
- Corrosion resistance: Excellent against dilute acids, alkalis, chlorides, and atmospheric environments
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Semi-Circular Coil Tube (Coiltube) |
| Cross-Section Geometry | Semi-circular / D-shaped / Flat-bottom profile |
| Outer Diameter (OD) | 8 mm – 25 mm (customizable) |
| Wall Thickness | 0.5 mm – 1.5 mm |
| Coil Winding Diameter | 30 mm – 150 mm (adjustable per design) |
| Coil Length | Up to 60 m per continuous coil (custom lengths available) |
| Material Grade | ASTM A270 Type 304, 316L, 321, 310S |
| Surface Finish | Bright annealed / Polished (Ra ≤ 0.4 μm available) |
| Manufacturing Standard | ASTM A270 / ASTM A269 / GB/T 12771 / EN 10217 |
| End Treatment | Plain ends / Beveled ends / Threaded / Flanged |
| Operating Pressure | Up to 1.6 MPa (design-dependent) |
| Operating Temperature Range | -196°C to +870°C |
| Heat Treatment | Solution annealing at 1050°C – 1150°C followed by water quench |
| Packaging | Wooden crate / Export-standard pallet with moisture-proof wrapping |
Manufacturing Process
The production of semi-circular coil tubes follows a rigorous, multi-stage manufacturing workflow to ensure dimensional accuracy, mechanical integrity, and surface quality:
- Raw Material Selection & Inspection: Hot-rolled stainless steel strip or wire is sourced from certified mills and subjected to spectroscopic analysis (PMI) to verify chemical composition compliance with the specified ASTM/GB grade.
- Cold Forming (Cross-Section Shaping): The raw strip is passed through a multi-stand roll-forming mill to progressively shape the circular cross-section into the required semi-circular (D-shaped) profile. This process maintains metallurgical integrity while achieving precise dimensional tolerances (±0.1 mm).
- Welding & Seaming: The formed strip is continuously welded along the longitudinal seam using high-frequency induction welding or orbital TIG welding, followed by internal and external seam grinding to achieve a smooth, uniform wall thickness.
- Solution Annealing & Pickling: The formed tube is annealed in a protective atmosphere furnace at 1050°C–1150°C to relieve residual stresses, restore full austenitic structure, and achieve maximum ductility. Subsequent pickling and passivation remove scale and form a protective chromium oxide layer.
- Coiling (Spiral Winding): The annealed semi-circular tube is precisely coiled onto a mandrel using CNC-controlled coiling equipment, maintaining uniform winding pitch and diameter to ensure consistent fluid flow distribution within the heat exchanger.
- Heat Treatment (Post-Coiling): A final annealing cycle relieves any residual stresses introduced during the coiling process.
- Quality Inspection & Testing: Each coil undergoes hydrostatic pressure testing, dimensional verification (laser measurement), visual inspection, and eddy current testing to detect subsurface defects.
Applications
The semi-circular floating coil tube finds extensive application across multiple industrial sectors:
- Chemical Processing: Floating coil heat exchangers for evaporators, condensers, and reboilers handling aggressive chemical media including acids, alkalis, and organic solvents.
- Pharmaceutical Industry: Sterile heat exchange systems where hygiene standards demand smooth, corrosion-resistant, and easily cleanable surfaces.
- Food & Beverage Processing: Pasteurization, sterilization, and thermal processing equipment requiring high purity and compliance with food-grade standards.
- Petrochemical & Oil Refining: Heat recovery systems, condensers, and exchangers in refinery units processing hydrocarbons and sour gases.
- Power Generation: Waste heat recovery systems and feedwater preheating in thermal power plants.
- Textile & Dyeing Industry: Dye liquor heating and cooling systems where continuous operation and resistance to dye chemical attack are critical.
- Marine & Offshore: Seawater cooling systems and marine heat exchangers requiring exceptional resistance to chloride-induced corrosion.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems and holds the following certifications:
- ISO 9001:2015 — Quality Management System
- ISO 14001 — Environmental Management System
- CE Marking — European Conformity for pressure equipment and machinery
- EN 10204 3.1 — Material Test Certification
- NSF/ANSI 61 — Drinking Water System Components (where applicable)
- Pressure Vessel Compliance — GB/T 150 / ASME Section VIII (as applicable)
Every production batch is accompanied by a Mill Test Certificate (MTC) documenting chemical composition, mechanical properties, and heat treatment records, traceable to the specific heat number of the raw material.
Unique Selling Points
- Enhanced Heat Transfer Efficiency: The semi-circular cross-section provides a larger surface-to-volume ratio compared to conventional round tubes, increasing heat transfer coefficients by up to 15–20%.
- Floating Design Advantage: The independent coil structure accommodates thermal expansion without imposing stress on the shell, enabling extended service life and online maintenance.
- Compact Footprint: High coil density maximizes heat exchange capacity within minimal equipment volume, reducing capital expenditure and installation space.
- Superior Corrosion Resistance: Austenitic stainless steel with solution-annealed finish provides decades of reliable service in aggressive chemical environments.
- Customizable Engineering: Full customization of tube dimensions, coil geometry, material grade, and end treatments to match specific process requirements.
- Cost-Effective Lifecycle: Reduced fouling tendency, ease of cleaning, and low maintenance requirements deliver significant total cost of ownership (TCO) advantages.
Technical Note: The application of semi-circular tubes in floating coil heat exchangers represents a paradigm shift in thermal engineering. The flat-bottom geometry promotes laminar-to-turbulent transition at lower Reynolds numbers, significantly enhancing convective heat transfer while the floating mechanism ensures mechanical resilience under cyclic thermal loading. This combination of geometric optimization and material science positions the product as a premier solution for demanding industrial heat exchange applications.