Stainless Steel Coil Tube for Waste Heat Boiler Applications
Product Overview
The Stainless Steel Coil Tube (Model No. 1405) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a high-performance coiled tubing solution engineered specifically for waste heat boiler (Waste Heat Boiler, WHB) systems in petrochemical and fertilizer production facilities. This product represents a significant milestone in the domestication of critical thermal-exchange components, successfully replacing long-standing imported alternatives in Chinese industrial infrastructure. The coil tube is designed to operate under extreme thermal gradients, corrosive process media, and sustained high-pressure conditions inherent to exothermic chemical reaction environments.
The product has been validated through successful deployment at the Lanzhou Chemical Fertilizer Plant (Lanzhou Petrochemical Corporation), where it demonstrated full functional equivalence to previously imported European and Japanese coil tube assemblies, achieving measurable improvements in thermal efficiency and operational reliability while substantially reducing lifecycle costs.
Material & Properties
The coil tube is fabricated from austenitic and super-austenitic stainless steel grades selected for their exceptional resistance to high-temperature oxidation, intergranular corrosion, and stress corrosion cracking (Stress Corrosion Cracking, SCC) under the aggressive conditions encountered in waste heat recovery systems.
- Base Alloy Grades: SUS310S (UNS S31008), SUS309 (UNS S30908), SUS321 (UNS S32108), and custom super-austenitic compositions with elevated Ni and Cr content for enhanced thermal stability.
- Carbon Equivalency: Controlled below 0.08% C to minimize sensitization risk during welding and heat exposure cycles.
- Temperature Range: Continuous service from cryogenic (-196°C) to 1100°C, with short-term peak tolerance up to 1200°C.
- Corrosion Resistance: Superior resistance to sulfuric acid (H₂SO₄), hydrofluoric acid (HF), nitrogen oxides (NOx), and hydrogen sulfide (H₂S) environments typical of ammonia synthesis and urea production processes.
- Mechanical Properties: Minimum yield strength of 205 MPa (309 grade) at room temperature; retains >60% of tensile strength at 800°C.
- Thermal Conductivity: 16.3–23.4 W/(m·K), optimized for efficient radiant and convective heat transfer in boiler tube bundles.
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Product Type | Coil Tube / Spiral Wound Tubing | — |
| Outer Diameter (OD) | Φ19.05 mm – Φ101.60 mm (customizable) | ASTM A213 / GB/T 12771 |
| Wall Thickness | 1.50 mm – 8.00 mm | ASTM A213 / GB/T 12771 |
| Coil Diameter | 1500 mm – 6000 mm (configurable per boiler design) | — |
| Tube Length (per coil) | Up to 300 m per continuous coil | — |
| Maximum Operating Pressure | Up to 10.0 MPa (1450 psi) | ASME BPV Section I |
| Maximum Operating Temperature | 1100°C continuous / 1200°C short-term | — |
| Surface Finish | Mill finish (Ra ≤ 1.6 μm) or electropolished (Ra ≤ 0.4 μm) | ASTM A479 |
| End Condition | Plain end, beveled, or threaded per customer specification | ASME B1.20.1 |
| Tolerance (OD) | ±0.05 mm (precision grade available) | ISO 4287 |
| Tolerance (Wall) | ±10% of nominal | GB/T 12771 |
| Applicable Grades | SUS304, SUS309, SUS310S, SUS321, Custom Super-Austenitic | ASTM A213 / ASTM A269 |
| Welding Compatibility | Fully weldable via TIG (GTAW), MIG (GMAW), and OAW processes | ASME BPV Section IX |
Manufacturing Process
The production of this coil tube follows a rigorous, multi-stage manufacturing protocol designed to ensure dimensional precision, metallurgical integrity, and consistent mechanical performance across the entire coil length.
- Hot Rolling and Billet Preparation: Primary stainless steel billets are hot-rolled to approximate dimensions, then subjected to solution annealing at 1050–1150°C followed by controlled water quenching to achieve a fully austenitic microstructure free of carbide precipitation.
- Precision Cold Drawing: The tube blank is cold-drawn through calibrated tungsten carbide dies to achieve exact outer diameter and wall thickness tolerances. This process introduces beneficial work-hardening while maintaining ductility. Multiple drawing passes may be employed for tight tolerance requirements.
- Pipe Coiling (Coil Forming): The drawn tube is fed through a precision bending and coiling head that wraps the tube into the specified coil diameter. Controlled bending forces prevent ovalization and maintain wall uniformity throughout the coil. The bending process is monitored via inline optical measurement systems.
- Post-Coil Annealing: Coiled tubes undergo stress-relief annealing at 1050°C with furnace cooling or controlled-rate air cooling to eliminate residual stresses introduced during coiling, thereby preventing cold cracking and dimensional drift during subsequent service.
- Surface Treatment: Optional pickling and passivation (Pickling and Passivation) removes surface oxides and contaminants, establishing a chromium-rich passive film that maximizes corrosion resistance. Electropolishing is available for critical hygienic or high-purity applications.
- Quality Inspection: Every coil undergoes 100% visual inspection, dimensional verification via laser scanning, and non-destructive testing (Non-Destructive Testing, NDT) including eddy current (Eddy Current Testing, ECT) and ultrasonic testing (Ultrasonic Testing, UT) to detect internal and surface defects.
Applications
The stainless steel coil tube is purpose-engineered for demanding thermal-exchange environments in heavy industrial processing. Primary application domains include:
- Waste Heat Boiler Systems: Radiant and convective tube bundles in waste heat boilers recovering thermal energy from exothermic chemical reactions, including ammonia synthesis converters, sulfuric acid converters, and urea synthesis reactors.
- Petrochemical Processing: High-temperature heat exchangers, furnace tubes, and reactor internals in oil refining and petrochemical cracking units.
- Fertilizer Production: Tube assemblies in phosphoric acid production, ammonium sulfate crystallization, and nitrogen fertilizer synthesis loops where sulfuric and nitric acid corrosion is prevalent.
- Power Generation: Superheater and reheater tube sections in combined-cycle power plants operating with high-sulfur fuel gases.
- Industrial Furnaces: Burner tubes, radiant panels, and heat transfer coils in continuous annealing furnaces and industrial kilns.
Quality Certifications
All production batches are manufactured under a certified Quality Management System and conform to the following international and national standards:
- ISO 9001:2015 — Quality Management System certification covering the full manufacturing lifecycle.
- ISO 3834-2 — Quality requirements for fusion welding of metallic materials (welding process certification).
- EN 10204 3.1 — Material inspection certificates issued by authorized inspection personnel.
- ASME BPV Section I — Compliance with boiler and pressure vessel construction codes.
- GB/T 12771 — Chinese national standard for welded stainless steel tubes for general application.
- TÜV / DNV — Third-party inspection and certification for international project qualification.
- NACE MR0175 / ISO 15156 — Compliance for sour service applications involving hydrogen sulfide environments.
Unique Selling Points
Domestication Success: This coil tube product achieved complete domestic replacement of imported waste heat boiler coil assemblies at the Lanzhou Chemical Fertilizer Plant, validating its technical parity with premium international products and establishing a proven track record in large-scale chemical process environments.
- Extended Service Life: Superior resistance to thermal cycling fatigue and corrosion reduces replacement frequency by an estimated 40–60% compared to conventional carbon steel alternatives.
- Cost Efficiency: Eliminates import tariffs, logistics delays, and foreign exchange exposure, delivering total cost of ownership (Total Cost of Ownership, TCO) reductions of 35–50% over the asset lifecycle.
- Customization Capability: Full flexibility in coil diameter, tube dimensions, alloy grade, and surface finish to match specific boiler design parameters and process conditions.
- Technical Support: Dedicated engineering team provides application-specific material selection, thermal analysis, and installation guidance throughout the project lifecycle.