Stainless Steel Coil Tube for Waste Heat Boiler Systems
Product Code: WX-CT-1627 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd
1. Product Overview
The Stainless Steel Coil Tube (盘管 / Coil Tube) is a precision-engineered tubular component designed primarily for integration into waste heat boiler systems, process heating applications, and industrial thermal recovery installations. Unlike straight-length seamless or welded stainless steel pipes, coil tubes are supplied in continuous coiled configurations, enabling long-run installations with minimal field joints, reduced installation labor, and enhanced system integrity under thermal cycling conditions.
This product line draws upon advanced design methodologies established in waste heat boiler engineering, incorporating considerations for thermal expansion management, fluid dynamics optimization, and mechanical stress distribution under sustained high-temperature service. The coil form factor is particularly advantageous in applications requiring large heat transfer surface areas within compact spatial footprints, such as fired heater effluent recovery, waste gas incineration systems, and regenerative thermal oxidizers.
2. Material & Properties
2.1 Available Grades
- AISI 304 (UNS S30400): General-purpose austenitic stainless steel with excellent corrosion resistance and formability. Suitable for moderate-temperature waste heat recovery applications up to approximately 870°C in non-oxidizing environments.
- AISI 316 (UNS S31600): Molybdenum-enhanced austenitic grade offering superior resistance to pitting and crevice corrosion, particularly in chloride-containing waste gas streams.
- AISI 310S (UNS S31008): High-temperature austenitic grade with elevated chromium and nickel content, designed for sustained service temperatures exceeding 1100°C. Ideal for primary waste heat recovery from high-temperature process gases.
- AISI 321 (UNS S32100): Titanium-stabilized austenitic grade providing enhanced resistance to intergranular corrosion and thermal stress cracking at elevated temperatures.
- AISI 347 (UNS S34700): Niobium-stabilized variant offering comparable high-temperature performance to 321 with additional resistance to sensitization in the 650–850°C range.
2.2 Mechanical Properties (Typical Values)
| Property | 304 Grade | 316 Grade | 310S Grade | 321 Grade |
|---|---|---|---|---|
| Tensile Strength (MPa, min) | 515 | 515 | 515 | 515 |
| Yield Strength (MPa, min) | 205 | 205 | 205 | 205 |
| Elongation (% at Break, min) | 40 | 40 | 40 | 40 |
| Maximum Service Temperature (°C) | 870 | 870 | 1150 | 1095 |
| Density (g/cm³) | 8.00 | 8.00 | 8.00 | 8.00 |
| Thermal Conductivity at 100°C (W/m·K) | 16.3 | 16.3 | 31.6 | 26.2 |
2.3 Chemical Composition (wt%, Typical)
| Grade | C | Si | Mn | P | S | Cr | Ni | Mo | Ti/Nb |
|---|---|---|---|---|---|---|---|---|---|
| 304 | ≤0.08 | ≤1.00 | ≤2.00 | ≤0.045 | ≤0.030 | 18.0–20.0 | 8.0–10.5 | — | — |
| 316 | ≤0.08 | ≤1.00 | ≤2.00 | ≤0.045 | ≤0.030 | 16.0–18.0 | 10.0–14.0 | 2.0–3.0 | — |
| 310S | ≤0.08 | ≤1.50 | ≤2.00 | ≤0.045 | ≤0.030 | 24.0–26.0 | 19.0–22.0 | — | — |
| 321 | ≤0.08 | ≤1.00 | ≤2.00 | ≤0.045 | ≤0.030 | 17.0–19.0 | 9.0–12.0 | — | Ti ≥ 5×C |
3. Specifications
3.1 Dimensional Parameters
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 159.0 mm (custom sizes available) | ASTM A213 / GB/T 12771 |
| Wall Thickness | 0.5 mm – 6.0 mm | ASTM A269 / GB/T 13296 |
| Coil Winding Diameter | 500 mm – 3,000 mm (configurable per application) | Manufacturer Specification |
| Coil Length per Spool | 100 m – 3,000 m (continuous) | — |
| OD Tolerance | ±0.5 mm (OD ≤ 25 mm); ±0.8% (OD > 25 mm) | ASTM A213 |
| Wall Thickness Tolerance | ±10% of nominal | ASTM A269 |
| Straightness (per 1,000 mm) | ≤ 1.0 mm | ISO 1307 |
| End Condition | Plain end, beveled (37°), or threaded (per customer specification) | ASME B1.20.1 |
| Surface Finish | 2B, BA (Bright Annealed), No. 4 Brushed, or custom (Ra ≤ 0.4 μm available) | ASTM A480 |
| Heat Treatment | Solution annealed and water/quench cooled | ASTM A213 |
3.2 Performance Ratings
| Parameter | Specification |
|---|---|
| Maximum Operating Pressure | Up to 320 bar (dependent on OD, wall thickness, and grade) |
| Design Pressure (ASME VIII Div. 1) | Calculated per applicable code; typical range 5–250 bar |
| Maximum Design Temperature | Up to 1,100°C (grade-dependent) |
| Minimum Design Temperature | −196°C (cryogenic capability for 304/316 grades) |
| Corrosion Rate (10% H₂SO₄, 20°C) | < 0.05 mm/year (316L grade) |
| Corrosion Rate (3% NaCl, 20°C) | < 0.02 mm/year (316L grade) |
4. Manufacturing Process
4.1 Production Workflow
- Raw Material Procurement: Virgin stainless steel billets or strip are sourced from certified mills (e.g., Outokumpu, POSCO, ThyssenKrupp, Baosteel) with full mill test certificates (MTC) conforming to EN 10204 Type 3.1.
- Strip Processing: Cold-rolled strip is slit to precise width, inspected for surface defects via automated optical scanning, and leveled to ensure flatness within ±0.1 mm/m.
- Tubular Forming: The strip is fed through a progressive roll-forming die set to form the tubular seam. For diameters ≤ 50 mm, a rotary-drawing or cold-drawing process is employed; for larger diameters, a U-O or U-O-E (U-shape, O-shape, Elongation) method is utilized.
- Welding: A continuous longitudinal weld is produced via high-frequency induction welding (HFHW) or TIG welding (for larger diameters). Weld parameters are controlled to minimize heat-affected zone (HAZ) width, ensuring the weld metal achieves ≥ 95% of base metal tensile strength.
- Coil Winding: The formed tube is continuously wound onto a mandrel of specified diameter under controlled tension to prevent ovality and stress concentration. Winding tension is calibrated to ensure uniform curvature without plastic deformation.
- Solution Annealing: The coiled tube is heated to 1,050–1,150°C (grade-dependent) in a protective atmosphere (argon or dissociated ammonia) and rapidly quenched. This eliminates cold-work hardening, dissolves precipitated carbides, and restores full austenitic microstructure.
- Pickling & Passivation: Post-annealing, the coil undergoes acid pickling (HNO₃/HF mixture) to remove oxide scale, followed by nitric acid passivation to establish a protective chromium oxide film (Cr₂O₃) with minimum 200 nm thickness.
- Non-Destructive Testing (NDT): 100% inline eddy current testing (ECT) and magnetic particle inspection (MPI) for weld integrity. Radiographic testing (RT) per ASME Section V Article 2 for weld joint verification on sampled lengths.
- Dimensional Inspection: Automated laser-based diameter measurement, ultrasonic wall thickness gauging, and coil geometry verification against customer drawings.
- Packaging & Dispatch: Coils are wrapped in moisture-resistant polyethylene film, secured with steel strapping, and palletized for transport. Each coil is labeled with heat number, grade, dimensions, and certificate reference.
4.2 Process Advantages for Waste Heat Boiler Applications
The coil tube manufacturing methodology provides distinct advantages for waste heat boiler design:
- Minimized Field Joints: Continuous coil supply eliminates the need for numerous butt-welded joints in the field, significantly reducing potential leak points and improving system reliability.
- Thermal Stress Accommodation: The inherent flexibility of coiled tubing allows for natural thermal expansion and contraction without requiring extensive expansion loop provisions, simplifying mechanical design.
- Compact Heat Transfer Geometry: Coiled configurations maximize heat transfer surface area per unit volume, critical for space-constrained waste heat recovery installations.
- Uniform Wall Thickness: Cold-drawn coil tubes maintain consistent wall thickness throughout the coil length, ensuring uniform heat transfer coefficients and predictable thermal performance.
5. Applications
5.1 Primary Application Domains
- Waste Heat Boiler Systems (WHS): Primary and secondary heat transfer surfaces for recovering thermal energy from high-temperature process flue gases (400°C–1,200°C). Coil tubes serve as the heat exchange medium in radiant sections and convection banks.
- Regenerative Thermal Oxidizers (RTO): Heat recovery coils for capturing thermal energy from VOC (Volatile Organic Compound) destruction off-gases, preheating incoming process streams.
- Fired Heater