Stainless Steel Coil Tube for Heating Furnace Applications
Product Overview
The Stainless Steel Coil Tube (盘管) is a specialized heat-exchange tube product engineered for continuous service in industrial heating furnaces, boilers, and high-temperature process systems. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd, this coil tube is formed into helical, spiral, or serpentine configurations to maximize heat transfer surface area within compact furnace volumes. The product is specifically designed to withstand aggressive thermal environments, cyclic temperature fluctuations, and corrosive media commonly encountered in metallurgical, petrochemical, and power generation processes.
Unlike conventional straight tube sections, coil tubes exploit their inherent geometric curvature to enhance convective heat transfer coefficients and improve structural resilience against thermal stress. The product line addresses the critical engineering challenge of corrosion and protection (腐蚀与防护) in heating furnace environments, where oxidizing atmospheres, sulfidation, ash deposition, and thermal fatigue collectively degrade tube integrity over extended service cycles.
Material & Properties
The coil tubes are fabricated from a range of austenitic and super-austenitic stainless steel grades, selected according to the specific operating conditions of the furnace environment:
- Grade 304 (UNS S30400 / 06Cr19Ni10): General-purpose austenitic stainless steel with excellent corrosion resistance in oxidizing environments. Suitable for furnace temperatures up to approximately 870 °C. Contains 18–20% Chromium (Cr) and 8–10.5% Nickel (Ni).
- Grade 316 / 316L (UNS S31600 / UNS S31603): Molybdenum-bearing austenitic stainless steel offering superior resistance to pitting and crevice corrosion. The addition of 2–3% Molybdenum (Mo) enhances performance in chloride-containing and sulfidation-prone furnace atmospheres. Operating temperature range up to approximately 925 °C.
- Grade 310S (UNS S31008 / 06Cr25Ni20): High-temperature austenitic stainless steel with elevated Chromium (24–26%) and Nickel (19–22%) content. Provides outstanding resistance to thermal oxidation and thermal cycling. Suitable for continuous furnace service up to 1150 °C, making it the preferred grade for regenerative furnace burners and high-temperature heater tubes.
- Grade 321 (UNS S32100 / 06Cr18Ni11Ti): Titanium-stabilized austenitic stainless steel. The titanium addition (5× the carbon content, minimum 0.40%) prevents intergranular corrosion during welding and high-temperature exposure. Suitable for furnace applications up to approximately 900 °C.
- Grade 347 (UNS S34700 / 06Cr17Ni12Mo2Ti): Titanium-stabilized variant with enhanced resistance to intergranular corrosion in welded assemblies exposed to furnace environments.
Mechanical Properties (Typical Values at Room Temperature)
| Property | Grade 304 | Grade 316 | Grade 310S | Grade 321 |
|---|---|---|---|---|
| Tensile Strength (Rm, MPa) | ≥ 520 | ≥ 515 | ≥ 515 | ≥ 520 |
| Yield Strength (Rp0.2, MPa) | ≥ 205 | ≥ 205 | ≥ 205 | ≥ 205 |
| Elongation (A50, %) | ≥ 40 | ≥ 40 | ≥ 35 | ≥ 40 |
| Density (g/cm³) | 7.93 | 8.00 | 8.02 | 7.93 |
| Thermal Conductivity at 100 °C (W/m·K) | 16.3 | 16.3 | 15.1 | 16.3 |
| Maximum Continuous Service Temperature (°C) | 870 | 925 | 1150 | 900 |
Corrosion Resistance Characteristics
The corrosion performance of coil tubes in heating furnace environments is governed by several interrelated degradation mechanisms:
- Thermal Oxidation (高温氧化): At elevated temperatures, a protective chromium oxide (Cr₂O₃) scale forms on the tube surface. The stability and adherence of this oxide layer depend on the Chromium content and the presence of alloying elements such as Silicon (Si) and Titanium (Ti). Grade 310S, with its high Chromium content, forms a particularly robust and self-healing oxide scale.
- Sulfidation (硫化): In reducing atmospheres containing sulfur compounds (H₂S, SO₂), the protective oxide layer can be broken down. Molybdenum-bearing grades (316/316L) and high-Chromium grades (310S) exhibit enhanced sulfidation resistance.
- Ash Deposition and Slagging (灰沉积与结渣): In coal-fired furnaces, molten ash deposits on tube surfaces can create concentration cells that accelerate localized corrosion. Surface finish and tube geometry influence ash adhesion.
- Thermal Fatigue (热疲劳): Cyclic temperature variations induce fatigue cracking, particularly at weld joints and geometric discontinuities. Proper material selection and post-weld heat treatment (PWHT) are critical mitigation strategies.
- Intergranular Corrosion (晶间腐蚀): Stabilized grades (321, 347) prevent chromium carbide precipitation at grain boundaries during welding and high-temperature exposure, maintaining uniform corrosion resistance throughout the microstructure.
Specifications
| Parameter | Specification / Range |
|---|---|
| Product Name | Stainless Steel Coil Tube (盘管) |
| Product Code | 1040 |
| Outer Diameter (OD) | Φ 6 mm – Φ 50.8 mm (1/4" – 2") |
| Wall Thickness (WT) | 0.5 mm – 3.0 mm |
| Coil Pitch | Customized, typically 20 mm – 150 mm |
| Coil Length | Customized per project requirements |
| Available Grades | 304, 304L, 316, 316L, 310S, 321, 347 |
| Surface Finish | 2B, BA (Bright Annealed), No. 4, No. 8, Mirror |
| Tolerance on OD | ± 0.05 mm to ± 0.10 mm (per ASTM A213 / A269) |
| Tolerance on WT | ± 10% (per ASTM A213 / A269) |
| Applicable Standards | ASTM A213, ASTM A269, ASME SA-213, ASME SA-269, GB/T 12771, EN 10216-5 |
| Maximum Operating Temperature | Up to 1150 °C (Grade 310S) |
| Maximum Operating Pressure | Up to 25 MPa (design-dependent) |
| Heat Treatment | Solution Annealing (固溶退火) + Water Quench |
Manufacturing Process
The production of high-quality stainless steel coil tubes involves a multi-stage manufacturing sequence, each step critically influencing the final product's dimensional accuracy, mechanical properties, and corrosion resistance:
- Material Selection and Incoming Inspection (来料检验): Raw stainless steel strip or seamless tube stock is procured from certified mills. Incoming material undergoes full chemical composition analysis (spectrographic testing) and mechanical property verification to ensure compliance with the specified grade requirements.
- Coil Forming / Bending (盘绕成型): Straight tube sections are formed into helical or serpentine coil configurations using precision coil forming machines. The forming process is carefully controlled to prevent excessive cold work, which could degrade the material's corrosion resistance and ductility. Forming parameters (die radius, tension, speed) are optimized for each tube diameter and wall thickness combination to achieve consistent coil geometry with minimal residual stress.
- Welding (焊接): Where coil tubes are assembled from straight sections, joints are fabricated using Automatic Submerged Arc Welding (SAW), Gas Metal Arc Welding (GMAW), or Orbital TIG Welding (GTAW) with inert gas (Argon, Ar) shielding to prevent oxidation of the weld zone. Weld parameters are qualified per ASME Section IX procedures.
- Solution Annealing (固溶退火): The coil tube assembly is subjected to solution annealing at temperatures between 1010 °C and 1150 °C (grade-dependent), followed by rapid water quenching. This process dissolves any precipitated chromium carbides, restores full austenitic microstructure, relieves residual stresses from forming and welding, and maximizes corrosion resistance. Annealing is conducted in a controlled atmosphere (vacuum or inert gas) to prevent surface scaling.
- Pickling and Passivation (酸洗钝化): After annealing, the tube surface is cleaned through acid pickling (typically using a mixture of hydrofluoric acid (HF) and nitric acid (HNO₃)) to remove oxide scale. Subsequent passivation with nitric acid or citric acid solutions establishes a stable, self-healing chromium oxide film that provides initial corrosion protection.
- Surface Finishing (表面处理): Depending on the application requirements, the coil tube may undergo additional surface treatments including electropolishing (to achieve a smooth, low-roughness surface that minimizes ash adhesion), grinding, or polishing to specified finish grades (2B, BA, No. 4, No. 8, or Mirror).
- Dimensional Inspection and Testing (尺寸检验与测试): Final products undergo comprehensive quality verification including dimensional measurement (OD, WT, coil pitch, length), hydrostatic pressure testing (per ASTM A269), eddy current testing (ECT) for wall thickness and defect detection, and visual inspection of weld joints and surface condition.
- Packaging and Protection (包装与防护): Coil tubes are protected against mechanical damage and atmospheric corrosion during transport and storage. Protective measures include wrapping with moisture-absorbent desiccant paper, vacuum packaging, or application of temporary corrosion inhibitor coatings. Coil assemblies are secured on wooden or steel cradles to prevent deformation during handling.
Applications
Stainless steel coil tubes from Wenzhou Jixing Metal Materials Co., Ltd are deployed across a wide spectrum of industrial heating and heat-exchange applications:
- Industrial Heating Furnaces (工业加热炉): Primary application domain. Coil tubes serve as heating elements and heat-transfer surfaces in batch and continuous furnaces used for heat treatment, annealing, tempering, and carburizing of steel and other metals.
- Regenerative Furnace Burners (蓄热式炉燃烧器): Coil tubes are integral components of regenerative burners in glass manufacturing furnaces, steel reheating furnaces, and cement kilns, where they transfer combustion heat to process gases.
- Boiler Systems (锅炉系统): Coil tubes are used in water-tube boilers, superheaters, and economizers in power generation plants and industrial steam systems.
- Petrochemical Process Heaters (石油化工过程加热器): Fired heaters in refineries and petrochemical plants utilize stainless steel coil tubes for crude oil heating, reforming, and cracking processes.
- Heat Exchangers (热交换器): Spiral-wound and helical coil heat exchangers benefit from the high surface-area-to-volume ratio of coil tube geometry, providing compact and efficient heat exchange in chemical processing, food and beverage, and pharmaceutical industries.
- Marine and Offshore Applications (海洋与海上应用): Coil tubes in marine heating systems and offshore platform process heaters, where resistance to chloride-induced corrosion is paramount.
- Energy Recovery Systems (能量回收系统): Waste heat recovery units and combined heat and power (CHP) systems utilize coil tubes to capture and transfer thermal energy from exhaust streams.
Corrosion Protection Strategies
Given the critical nature of corrosion resistance in heating furnace applications, the following protection strategies are integrated into the product design and service guidance:
- Material Selection Optimization: Matching the stainless steel grade to the specific furnace atmosphere (oxidizing, reducing, sulfidizing) and temperature profile is the primary corrosion protection strategy. Higher-alloy grades (310S, 321, 347) are recommended for more aggressive environments.
- Post-Weld Heat Treatment: Mandatory solution annealing of welded assemblies ensures uniform microstructure and full corrosion resistance at weld joints, which are inherently more susceptible to intergranular corrosion.
- Surface Finish Specification: Smooth surface finishes (BA, electropolished) reduce ash adhesion and minimize the formation of crevice corrosion sites. Surface roughness (Ra) should be maintained below 0.4 µm for critical applications.
- Design Considerations: Coil geometry should avoid dead-legs and stagnant zones where corrosive deposits can accumulate. Adequate gas velocity across tube surfaces promotes self-cleaning and reduces localized corrosion.
- Inspection and Maintenance Protocols: Periodic inspection of tube wall thickness (ultrasonic testing), surface condition (visual and borescope inspection), and oxide scale integrity is recommended to detect early-stage degradation and plan preventive maintenance.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd maintains rigorous quality management systems and holds the following certifications and compliances:
- ISO 9001:2015 – Quality Management Systems certification, ensuring consistent product quality and process control throughout the manufacturing chain.
- ISO 14001:2015 – Environmental Management Systems certification, demonstrating commitment to environmentally responsible manufacturing practices.
- ISO 45001:2018 – Occupational Health and Safety Management Systems certification.
- CE Marking – Compliance with European Union directives for pressure equipment and industrial components.
- ASME (American Society of Mechanical Engineers) Stamp Certification – Where applicable