Stainless Steel Coil Tube (Coiltube) — Waste Heat Recovery System Application
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Code: 264
Category: Literature Study & Technical Reference
Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered continuous-length tubular product designed specifically for high-temperature heat exchange and waste heat recovery applications. This product is manufactured by Wenzhou Jixing Metal Materials Co., Ltd., a leading supplier of specialty stainless steel products in East China. The coil tube is supplied in continuous coil form, enabling seamless integration into complex heat exchanger geometries without the need for butt-welded joints, thereby minimizing leak points and maximizing system reliability.
This technical specification is informed by the academic study titled "Simulation and Optimization of Coil-Type Coke Oven Rising Pipe Waste Heat Recovery System", which validates the thermodynamic performance, structural integrity, and operational efficiency of coil tubes deployed in coke oven rising pipe (COP) waste heat recovery environments. The research demonstrates that coiled stainless steel tubing achieves superior heat transfer coefficients compared to straight-tube alternatives, owing to the inherent turbulence enhancement generated by the helical geometry.
Unique Selling Points
- Continuous Coil Configuration: Eliminates longitudinal weld seams, reducing failure points by up to 85% compared to straight-tube assemblies.
- Enhanced Heat Transfer Efficiency: Helical curvature induces secondary flow patterns (Dean vortices), increasing the Nusselt number by 20–40% over equivalent straight tubes.
- Corrosion Resistance: Superior performance in sulfuric acid, sulfur dioxide, and flue gas environments typical of coke oven operations.
- Compact Installation Footprint: Coiled geometry reduces required installation area by 30–50% versus conventional tube banks.
- Thermal Stress Mitigation: Continuous coil form accommodates thermal expansion and contraction without additional expansion joints.
Material & Properties
Material Grades
The coil tube is available in multiple austenitic and austenitic-ferritic stainless steel grades, selected based on the specific thermal and corrosive environment of the application:
- 304 (UNS S30408 / 1.4301): General-purpose grade with excellent corrosion resistance and formability; suitable for moderate-temperature waste heat recovery.
- 304L (UNS S30403 / 1.4307): Low-carbon variant offering enhanced resistance to intergranular corrosion after welding.
- 316 (UNS S31608 / 1.4401): Molybdenum-bearing grade providing superior resistance to pitting and crevice corrosion in chloride-containing environments.
- 316L (UNS S31603 / 1.4404): Low-carbon 316 variant for demanding weldability requirements.
- 321 (UNS S32108 / 1.4541): Titanium-stabilized grade for sustained service above 425 °C, preventing sensitization.
- 310S (UNS S31008 / 1.4845): High-temperature grade for extreme heat duty above 800 °C.
Mechanical Properties (Annealed Condition)
| Property | Grade 304/304L | Grade 316/316L | Grade 321 | Grade 310S |
|---|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 520 | ≥ 520 | ≥ 520 |
| Yield Strength (MPa) | ≥ 205 | ≥ 205 | ≥ 205 | ≥ 205 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 40 | ≥ 35 |
| Density (g/cm³) | 8.00 | 8.03 | 8.00 | 8.03 |
| Thermal Conductivity (W/m·K) at 100 °C | 16.3 | 16.3 | 16.3 | 21.5 |
| Maximum Continuous Service Temperature (°C) | 870 | 870 | 900 | 1150 |
Chemical Composition (Typical)
| Element | 304/304L | 316/316L | 321 | 310S |
|---|---|---|---|---|
| C (% max) | 0.08 / 0.03 | 0.08 / 0.03 | 0.08 | 0.08 |
| Cr (%) | 18.0–20.0 | 16.0–18.0 | 17.0–19.0 | 24.0–26.0 |
| Ni (%) | 8.0–10.5 | 10.0–14.0 | 9.0–12.0 | 19.0–22.0 |
| Mo (%) | — | 2.0–3.0 | — | — |
| Si (%) | ≤ 0.75 | ≤ 0.75 | ≤ 0.75 | ≤ 1.50 |
| Mn (%) | ≤ 2.00 | ≤ 2.00 | ≤ 2.00 | ≤ 2.00 |
| Other | — | — | Ti: 5×C–0.70 | — |
Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (custom sizes available) |
| Wall Thickness (WT) | 0.5 mm – 3.0 mm |
| Coil Inner Diameter (CID) | 300 mm – 1200 mm |
| Coil Length per Spool | 50 m – 200 m (continuous) |
| Tolerance on OD | ± 0.05 mm (precision) / ± 0.10 mm (standard) |
| Tolerance on WT | ± 10% (standard) / ± 5% (precision) |
| Surface Finish | 2B (cold rolled & annealed), No. 1 (hot rolled), BA (bright annealed), Pickled & Passivated |
| Surface Roughness (Ra) | ≤ 0.8 µm (2B) / ≤ 0.4 µm (BA) |
| Coiling Tolerance | Concentricity ≤ 3 mm |
| Delivery Form | Coiled (on wooden reel or steel drum) |
| Standard References | ASTM A213 / A269, EN 10216-5, GB/T 12771, GB/T 13296 |
Manufacturing Process
The production of stainless steel coil tubes follows a rigorous multi-stage manufacturing process, ensuring dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection: High-purity stainless steel strip or rod stock is sourced from certified mills (e.g., Outokumpu, POSCO, Taigang), with mill test certificates (MTC) verifying chemical composition per ASTM/EN/GB standards.
- Hot Rolling / Hot Extrusion: For larger OD tubes, seamless tubes are produced via hot rolling (穿孔轧制) or hot extrusion processes, yielding the initial blank tube.
- Pickle & Passivate: The hot-rolled tube undergoes acid pickling (typically HNO₃/HF or HNO₃/H₂SO₄ blend) to remove oxide scale, followed by passivation to establish a protective chromium oxide layer.
- Cold Drawing / Cold Rolling: The tube is drawn through precision tungsten carbide dies or cold-rolled between calibrated rolls to achieve final OD and WT dimensions with tight tolerances. This step also induces beneficial work hardening.
- Coiling: The drawn tube is continuously wound onto a coil former at controlled tension to produce the helical coil geometry. Coiling parameters (tension, speed, diameter) are optimized to prevent ovality, kinking, or inter-coil contact damage.
- Solution Annealing: The coiled tube is heat-treated at 1010–1150 °C (depending on grade) followed by controlled cooling to restore full annealed condition, eliminate residual stresses from cold working, and maximize corrosion resistance.
- Final Pickle & Passivate: Post-annealing oxide scale is removed, and a fresh passive film is established.
- Quality Inspection: Each coil undergoes dimensional measurement (OD, WT, coil diameter), visual surface inspection, hydrostatic pressure testing (typically 2–3× working pressure), and optionally spectroscopic chemical analysis (PMI — Positive Material Identification).
- Packaging: Coils are wrapped with moisture-proof film, secured with steel strapping, and mounted on wooden reels or steel drums for shipment.
Process Flow Diagram (Textual)
Raw Steel Strip/Rod → Hot Rolling/Extrusion → Pickle & Passivate → Cold Drawing/Rolling → Coiling → Solution Annealing → Final Pickle & Passivate → QC Inspection → Packaging & Shipment
Applications
Primary Application: Coke Oven Waste Heat Recovery
The coil tube is the core heat transfer element in coke oven rising pipe (COP) waste heat recovery systems. In this application, high-temperature coke oven gas (typically 700–900 °C) flows through the coiled tubes, transferring thermal energy to a working fluid (steam or heat transfer oil) on the shell side. The academic study "Simulation and Optimization of Coil-Type Coke Oven Rising Pipe Waste Heat Recovery System" confirms the following performance advantages:
- Waste heat recovery efficiency reaching 65–75% of available thermal energy
- Annual energy savings equivalent to 50,000–120,000 tons of standard coal per coke oven battery
- Reduction in CO₂ emissions by 150,000–300,000 tons per year per facility
- Service life exceeding 15 years with proper material selection and maintenance
Additional Applications
- Power Generation: Boiler water wall tubes, superheater coils, and economizer coils in fossil-fuel and biomass power plants.
- Chemical Processing: Reactor coil tubes, heat exchanger internals, and distillation column coils in petrochemical and pharmaceutical plants.
- Food & Beverage: Sanitary-grade heat exchangers for dairy pasteurization, beer brewing, and juice processing (grades 304L, 316L).
- Geothermal Energy: Borehole heat exchanger coils for ground-source heat pump systems.
- Marine & Offshore: Heat exchanger coils in ballast water treatment systems and oil platform process loops.
- Solar Thermal: Receiver coils in concentrated solar power (CSP) plants.
- Oil & Gas: Subsea heat exchanger coils, wellhead temperature control systems.
Quality Certifications & Standards Compliance
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 14001:2015 | Environmental Management System |
| ISO 45001:2018 | Occupational Health & Safety Management |
| ASTM A213 | Standard Specification for Seamless Ferritic/Austenitic Stainless Steel Boiler, Heat-Exchanger, and Heat-Treat Tubing |
| ASTM A269 | Standard Specification for Seamless and Welded Austenitic Chromium-Stainless Steel Tubing for Chemical and Heat-Transfer Purposes |
| EN 10216-5 | Non-alloy and Stainless Steel Tubes for Pressure Purposes — Part 5: Specifications for Austenitic Tubes |
| GB/T 12771 | Chinese National Standard for Stainless Steel Seamless Tubes for General Purposes |
| GB/T 13296 | Chinese National Standard for Cold-Rolled or Cold-Drawn Stainless Steel Tubes for Heat Exchangers and Heat Transfer |
| NACE MR0175 / ISO 15156 | Materials for Use in H₂S-Containing Environments (if applicable) |
| ASME Boiler & Pressure Vessel Code, Section I | Power Boiler Tubes (where applicable) |
| PED (EU 2014/68/EU) | Pressure Equipment Directive Compliance (for EU market) |