Stainless Steel Coil Tube — Heater Coil Tube for Industrial Furnace Applications
Product Overview
The Stainless Steel Coil Tube (Product Code: 1001) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled tubular product specifically designed for use in industrial heating furnaces, radiant tubes, and high-temperature process heating systems. Unlike straight seamless tubes, coil tubes are produced in a continuous coiled configuration, offering significant advantages in installation efficiency, material utilization, and on-site flexibility for complex furnace geometries.
This product line encompasses both new manufacturing and advanced repair welding solutions for heater coil tubes, addressing the critical need for reliable, long-lasting performance in demanding thermal environments. The coil tube is formed through cold or hot coiling processes that maintain metallurgical integrity throughout the bending radius, ensuring uniform wall thickness and consistent mechanical properties along the entire coil length.
Material & Properties
Stainless steel coil tubes for furnace applications are predominantly fabricated from austenitic and austenitic-ferritic alloy grades that provide exceptional resistance to oxidation, scaling, and thermal fatigue at elevated operating temperatures.
Common Material Grades
- 310S (UNS S31008) — High-temperature austenitic stainless steel with excellent resistance to oxidation and scaling up to 1150°C (2100°F); ideal for furnace radiant tubes and heating elements.
- 309S (UNS S30908) — Enhanced weldability variant of 309; suitable for repair welding applications and structural furnace components.
- 316L (UNS S31603) — Low-carbon austenitic grade with superior resistance to intergranular corrosion; used in process heating coils exposed to corrosive environments.
- 321H (UNS S32109) — Stabilized with titanium; offers outstanding resistance to thermal fatigue and stress corrosion cracking in cyclic heating applications.
- HP-Nb (UNS S31815) — High-purity niobium-stabilized grade providing superior thermal stability for high-temperature furnace coil tubes.
Key Mechanical Properties
- Operating Temperature Range: -40°C to 1150°C (-40°F to 2100°F), depending on grade selection
- Tensile Strength: 520–700 MPa (75,000–101,500 psi) at room temperature
- Yield Strength: 205–310 MPa (29,700–44,950 psi)
- Elongation: ≥ 40% (minimum)
- Thermal Conductivity: 15–30 W/(m·K) at operating temperatures
- Corrosion Resistance: Excellent resistance to oxidation, scaling, and sulfidation in air and reducing atmospheres
Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 12.7 mm – 219.1 mm (0.5" – 8.625") | ASTM A213 / A318 |
| Wall Thickness | 1.0 mm – 19.0 mm (0.040" – 0.750") | ASTM A213 / EN 10216 |
| Coil Length (Single Coil) | 50 m – 300 m (164 ft – 984 ft), customizable | Manufacturer Specification |
| Bending Radius (Minimum) | 3D (3× Outer Diameter) for cold bending; 5D for hot forming | ASME B31.3 |
| Surface Finish | Pickle & Passivate (PP), 2B, or No. 4 Brushed | ASTM A478 |
| End Condition | Plain, Beveled (37.5°), or Threaded (NPT/BSP) | ASME B31.3 |
| Tolerance (OD) | ±0.5% to ±1.5% of nominal (per ASTM A213) | ASTM A213 |
| Tolerance (Wall Thickness) | ±10% of nominal | ASTM A213 |
| Heat Treatment | Solution Annealed (1050°C – 1150°C) followed by water or air quench | ASTM A213 |
| Repair Welding Standard | ASME Section IX / EN ISO 15614 / AWS D10.6 | ASME BPVC Section IX |
Manufacturing Process
The production of stainless steel coil tubes for furnace applications involves a multi-stage manufacturing workflow that ensures dimensional accuracy, metallurgical quality, and long-term service reliability.
1. Raw Material Procurement & Inspection
High-purity austenitic stainless steel slabs or ingots are sourced from certified mills. Incoming material undergoes rigorous chemical composition analysis via Optical Emission Spectroscopy (OES) and Positive Material Identification (PMI) to verify grade compliance.
2. Seamless Tube Formation
- Piercing & Elongation: Billets are heated to 1100°C–1200°C and pierced through a mandrel to form a hollow shell.
- Pilger Milling or Cross-Rolling: The hollow shell is rolled to achieve precise outer diameter and wall thickness dimensions.
- Stretch Reducing: Further dimensional refinement is achieved through multi-stand stretch reduction.
3. Heat Treatment (Solution Annealing)
Tubes are heated to 1050°C–1150°C in a controlled atmosphere furnace to dissolve carbides and restore full austenitic microstructure. Quenching is performed in water (for cold-worked grades) or air (for solution-annealed grades) to achieve the required mechanical properties.
4. Surface Treatment & Passivation
- Pickling: Removal of oxide scale and surface contaminants using mixed acid solutions (HNO₃/HF).
- Passivation: Application of nitric acid or citric acid to enrich the chromium oxide passive film, enhancing corrosion resistance.
5. Coil Forming & Bending
Finished straight tubes are formed into coils using precision bending equipment. Cold bending is performed at room temperature for smaller diameters (≤ 76 mm), while hot bending (at 800°C–1000°C) is employed for larger diameters to prevent work hardening and cracking. The coiling process maintains dimensional tolerances within ±1.5% of nominal.
6. Repair Welding for Heater Coil Tubes
A specialized repair welding process has been developed and validated for heater coil tubes that sustain damage during furnace operation. Key aspects include:
- Damage Assessment: Visual inspection, Ultrasonic Testing (UT), and Radiographic Testing (RT) to evaluate crack depth, wall thinning, and corrosion extent.
- Welding Procedure Specification (WPS): Developed per ASME Section IX, specifying electrode type (e.g., E309L, E310L), preheat temperature (50°C–150°C), interpass temperature (≤ 250°C), and post-weld heat treatment (PWHT) parameters.
- Weld Execution: Multi-pass welding using Shielded Metal Arc Welding (SMAW) or Gas Tungsten Arc Welding (GTAW) with appropriate filler metals matched to base metal composition.
- Post-Weld Inspection: Dye Penetrant Testing (PT) for surface defects and Ultrasonic Testing (UT) for volumetric integrity verification.
- Post-Weld Heat Treatment: Solution annealing at 1050°C–1100°C for 1 hour followed by controlled cooling to restore mechanical properties in the Heat-Affected Zone (HAZ).
7. Final Inspection & Packaging
Each coil undergoes 100% visual inspection, dimensional verification, and sample destructive testing (tensile, hardness, impact). Coils are packaged with moisture-absorbing desiccants and protected with VCI (Volatile Corrosion Inhibitor) films for shipment.
Applications
Stainless steel coil tubes from Wenzhou Jixing Metal Materials Co., Ltd. are deployed across a broad spectrum of industrial heating and process applications:
- Industrial Heating Furnaces: Radiant tubes, flue tubes, and heating coils in continuous annealing furnaces, heat treatment furnaces, and carburizing furnaces in the steel and metal processing industries.
- Petrochemical & Refinery: Process heating coils, reformer tubes, and heat exchanger tubes in cracking furnaces and vaporizer units.
- Ceramic & Glass Manufacturing: Tunnel kiln heating elements and combustion air distribution coils requiring high-temperature oxidation resistance.
- Food & Pharmaceutical Processing: Sanitary-grade process heating coils for pasteurization, sterilization, and CIP (Clean-in-Place) systems.
- Power Generation: Boiler economizer tubes and superheater coils in waste heat recovery systems.
- Aerospace & Defense: High-temperature exhaust system components and thermal management coils.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system aligned with international standards:
- ISO 9001:2015 — Quality Management Systems certification ensuring consistent product quality and process control.
- ISO 14001:2015 — Environmental Management Systems certification demonstrating commitment to sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management Systems certification.
- ASME "S" Stamp / "U" Stamp — Authorization for the manufacture of pressure vessels and piping components per ASME Boiler and Pressure Vessel Code.
- EN 10204 Type 3.1 Certificates — Third-party inspected material test certificates provided with each shipment.
- API Monogram — American Petroleum Institute certification for oil and gas industry applications.
- ASME Section IX Welding Qualification — Qualified welding procedures and certified welders for repair and fabrication work.
Unique Selling Points
- Specialized Repair Welding Expertise: Proprietary repair welding procedures for heater coil tubes, validated through extensive field testing, enabling cost-effective restoration of damaged furnace components with verified service life.
- Custom Coil Configuration: Ability to produce coils with variable bending radii, custom coil diameters, and tailored end preparations to match specific furnace designs.
- Full Traceability: Each coil is serialized and traceable to its mill heat number, ensuring complete material lineage from raw stock to finished product.
- Wide Grade Selection: Availability of over 15 stainless steel grades, including specialty high-temperature alloys (HP, HP-Nb, 310S), to address diverse application requirements.
- Integrated Supply Chain: In-house capabilities spanning tube manufacturing, heat treatment, surface finishing, coil forming, and welding repair — reducing lead times and ensuring consistent quality control.
Technical Note: For heater coil tube repair welding applications, it is critical that the welding procedure specification (WPS) is qualified specifically for the base metal grade, thickness range, and service conditions of the application. Wenzhou Jixing Metal Materials Co., Ltd. provides fully documented WPS and Procedure Qualification Records (PQR) per ASME Section IX for all repair welding operations, ensuring regulatory compliance and long-term structural integrity.