Stainless Steel Coil Tube for Coke Oven Waste Gas Heat Exchangers
1. Product Overview
The stainless steel coil tube (Coiltube) produced by Wenzhou Jixing Metal Materials Co., Ltd. is a specialized heat exchange component engineered for coil-type coke oven waste gas heat exchangers. These heat exchangers are critical units in coking industry processes, designed to recover thermal energy from high-temperature waste gas (荒煤气, Blast Furnace Waste Gas) generated during the coke-making process. The coil tube serves as the primary heat transfer element, facilitating efficient energy exchange between the hot waste gas and the working fluid (typically water or process steam).
Unlike conventional straight-tube heat exchangers, coil tube configurations offer a significantly higher surface-area-to-volume ratio, enabling compact heat exchange units with superior thermal performance. The serpentine coil geometry also promotes turbulent flow within the tube, enhancing the convective heat transfer coefficient and reducing fouling tendencies on the inner tube surface.
2. Material & Properties
Given the demanding operating environment of coke oven waste gas — characterized by high temperatures (typically 700–1100°C), corrosive flue gas components (including H₂S, SO₂, HCN, NH₃, and phenolic compounds), and particulate matter — the coil tube is fabricated from austenitic stainless steel grades selected for exceptional thermal stability, corrosion resistance, and mechanical strength at elevated temperatures.
2.1 Primary Material Grades
- 304 (UNS S30408 / 06Cr19Ni10): General-purpose austenitic stainless steel with excellent corrosion resistance and formability. Suitable for moderate-temperature waste gas applications (up to 870°C continuous).
- 316L (UNS S31603 / 022Cr17Ni12Mo2): Low-carbon variant with molybdenum addition providing superior resistance to pitting and crevice corrosion from sulfide-containing waste gas. Recommended for aggressive coke oven gas environments.
- 321 (UNS S32100 / 06Cr18Ni11Ti): Titanium-stabilized austenitic steel with enhanced resistance to intergranular corrosion and thermal cycling fatigue. Ideal for applications involving repeated heating and cooling cycles.
- 310S (UNS S31008 / 06Cr25Ni20): High-temperature austenitic steel with excellent oxidation resistance up to 1150°C. Deployed in zones with peak waste gas temperatures.
2.2 Key Material Properties
| Property | 304 Grade | 316L Grade | 321 Grade | 310S Grade |
|---|---|---|---|---|
| Chromium (Cr) Content | 18–20% | 16–18% | 17–19% | 24–26% |
| Nickel (Ni) Content | 8–10.5% | 10–14% | 9–13% | 19–22% |
| Molybdenum (Mo) Content | — | 2–3% | — | — | Maximum Continuous Service Temperature | 870°C | 870°C | 900°C | 1150°C |
| Tensile Strength (RT, annealed) | ≥515 MPa | ≥485 MPa | ≥515 MPa | ≥515 MPa |
| Thermal Conductivity (RT) | 16.3 W/(m·K) | 16.3 W/(m·K) | 16.3 W/(m·K) | 16.3 W/(m·K) |
| Linear Expansion Coefficient (20–100°C) | 17.3 × 10⁻⁶ /K | 17.3 × 10⁻⁶ /K | 17.3 × 10⁻⁶ /K | 17.3 × 10⁻⁶ /K |
3. Specifications
| Parameter | Specification |
|---|---|
| Product Model | Coiltube No. 523 |
| Tube Outer Diameter (OD) | Φ14 mm – Φ51 mm (customizable) |
| Tube Wall Thickness | 0.5 mm – 3.0 mm |
| Coil Mean Diameter | Φ500 mm – Φ2000 mm |
| Coil Length (Unwound) | Up to 120 m per continuous coil |
| Surface Finish | No. 4 Brushed / 2B Annealed / Electropolished (Ra ≤ 0.4 μm) |
| Tolerance on OD | ±0.1 mm (Grade A); ±0.2 mm (Grade B) |
| Tolerance on Wall Thickness | ±10% of nominal |
| Coil Pitch Tolerance | ±0.5 mm |
| End Preparation | Flat cut / Beveled (30°–45°) / Threaded |
| Operating Temperature Range | −20°C to 1100°C (depending on grade) |
| Operating Pressure | Up to 2.5 MPa (working pressure) |
| Standard Reference | ASTM A213 / GB/T 14976 / EN 10216-5 |
| Packaging | Coiled on wooden spools with protective wrapping; seaworthy export packing available |
4. Manufacturing Process
The production of high-quality stainless steel coil tubes for heat exchanger applications follows a rigorous multi-stage manufacturing workflow:
- Raw Material Selection: Cold-rolled stainless steel strip is procured from certified mill sources with full chemical composition analysis and mechanical property verification. Incoming material undergoes 100% visual inspection and dimensional checking.
- Coil Forming (Tube Milling): The strip is fed through a series of progressively reducing roll stations in a precision tube mill, forming the strip into a seamless circular cross-section. The forming process is controlled to maintain uniform wall thickness and minimize residual stresses.
- Welding (if applicable): For welded coil tubes, the longitudinal seam is joined using submerged arc welding (SAW) or gas tungsten arc welding (GTAW / TIG), followed by inline ultrasonic seam inspection to detect any discontinuities or porosity.
- Heat Treatment (Solution Annealing): Formed tubes are solution annealed at 1050–1150°C followed by rapid water quenching to restore full austenitic microstructure, relieve forming stresses, and ensure maximum corrosion resistance. This step is critical for achieving the required mechanical properties and preventing stress corrosion cracking.
- Coil Bending: Annealed tubes are cold-bent into the specified serpentine coil geometry using CNC-controlled coil bending machines. The bending radius is carefully controlled to prevent wall thinning (typically limited to ≤5% reduction at the bend outer fiber) and ovality distortion (limited to ≤3% of nominal OD).
- Punching & Forming of Headers: Coil ends are prepared for welding to header plates or manifolds. End preparation includes beveling, cleaning, and dimensional verification.
- Surface Finishing: Tubes may undergo electropolishing or pickling and passivation to remove any surface contaminants, oxide scale, and achieve a smooth, corrosion-resistant passive film.
- Non-Destructive Testing (NDT): Final coils undergo ultrasonic testing (UT) for wall thickness verification, dye penetrant testing (PT) for surface defect detection, and hydrostatic pressure testing at 1.5× working pressure for leak integrity.
5. Applications
The coil-type coke oven waste gas heat exchanger, utilizing Wenzhou Jixing's stainless steel coil tubes, finds extensive application across multiple industrial sectors:
- Coke Oven Waste Gas Heat Recovery: Primary application — recovering thermal energy from 700–1100°C waste gas to generate high-pressure steam (typically 3.5–4.0 MPa, 450–500°C) for power generation or process heating. A single heat exchanger unit can recover 20–30 GJ/h of thermal energy, significantly improving the overall energy efficiency of the coking plant.
- Industrial Waste Heat Recovery Systems: Adapted for waste gas heat recovery in metallurgical furnaces, glass manufacturing, cement kilns, and chemical processing plants where high-temperature flue gas energy recovery is economically beneficial.
- Process Heating in Chemical Industries: Coil tubes serve as heat exchange elements in reactor cooling systems, distillation columns, and process heating loops in petrochemical and specialty chemical manufacturing.
- Power Generation Support Systems: Utilized in boiler feedwater preheating, economizer sections, and auxiliary heat exchange units in coal-fired and biomass power plants.
- Food and Pharmaceutical Processing: In sanitary-grade configurations (electropolished, 316L), coil tubes are employed in pasteurization systems, CIP (Clean-in-Place) circuits, and process heat exchange where hygiene and corrosion resistance are paramount.
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring product conformance to international and national standards:
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and process control.
- ISO 14001:2015 — Environmental Management System certification for sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management System certification.
- CE Marking (EU) — Conformity with European Directive requirements for pressure equipment and mechanical components.
- ASME Certification — Manufacturing compliance with American Society of Mechanical Engineers standards for pressure-containing components (where applicable).
- GB/T 14976 — Chinese national standard for seamless stainless steel tubes for fluid transport.
- ASTM A213 / A269 — American standards for austenitic stainless steel tubes for heat exchangers and boiler heat transfer applications.
- EN 10216-5 — European standard for austenitic stainless steel tubes for heat exchangers and similar heat transfer apparatus.
- Mill Test Certificates (MTC) — Full traceability documentation including chemical analysis (EN 10204 3.1), mechanical test reports, and NDT records provided with each shipment.
7. Unique Selling Points
- Superior Thermal Efficiency: The serpentine coil geometry maximizes heat transfer surface area within a compact footprint, achieving overall heat exchanger thermal efficiency exceeding 85%.
- Corrosion Resistant in Aggressive Environments: Molybdenum-enhanced austenitic grades provide outstanding resistance to sulfide-induced pitting and stress corrosion cracking in coke oven waste gas, extending service life to 10–15 years with minimal maintenance.
- Seamless Continuous Coil: Eliminates longitudinal welds that would be susceptible to corrosion attack, ensuring uniform wall integrity and leak-free performance throughout the coil length.
- Thermal Fatigue Resistance: Titanium-stabilized and high-temperature grades withstand repeated thermal cycling without intergranular cracking, maintaining structural integrity over extended operational life.
- Customization Capability: Flexible manufacturing capability allows customization of tube diameter, wall thickness, coil geometry, and material grade to meet specific project requirements and operating conditions.
- Energy Conservation Contribution: By enabling efficient waste heat recovery, these coil tubes directly contribute to reducing fossil fuel consumption and CO₂ emissions, supporting industrial sustainability and carbon neutrality goals.
Technical Note: The coil-type coke oven waste gas heat exchanger represents a mature and proven technology in the coking industry. Its structural advantages — including self-supporting coil configuration, reduced support structures, compact design, and inherent resistance to thermal stress — make it the preferred choice over plate and shell-and-tube heat exchangers for high-temperature waste gas applications exceeding 700°C. Wenzhou Jixing Metal Materials Co., Ltd. leverages advanced manufacturing capabilities and rigorous quality controls to deliver coil tubes that meet the most demanding performance and reliability requirements of modern industrial heat recovery systems.