Stainless Steel Coil Tube for Process Air Preheating Systems
Product Overview
The Stainless Steel Coil Tube (盘管/Coil Tube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered heat exchange component designed for demanding industrial applications, particularly in process air preheating systems within first-stage converter furnaces (一段转化炉工艺空气预热系统). These coil tubes are fabricated to withstand extreme thermal environments, providing efficient heat transfer while maintaining structural integrity under prolonged exposure to high-temperature process gases and air streams.
Coil tubes represent a critical component in petrochemical, refining, and energy conversion industries where process air preheating is essential for improving thermal efficiency and reducing fuel consumption. The design and material selection of these coils directly impact system reliability, operational safety, and overall plant productivity.
Material & Properties
Wenzhou Jixing Metal Materials Co., Ltd. offers coil tubes in a range of stainless steel grades optimized for high-temperature service conditions:
- Austenitic Stainless Steels: Grades 304 (UNS S30408), 304L (UNS S30403), 316 (UNS S31608), and 316L (UNS S31603) — providing excellent corrosion resistance and formability.
- Heat-Resistant Stainless Steels: Grades 310 (UNS S31008), 310S (UNS S31008), and 347 (UNS S34700) — engineered for sustained service temperatures exceeding 1100°C (2012°F).
- Super-Austenitic Grades: Custom compositions with enhanced chromium (Cr) and nickel (Ni) content for exceptional oxidation resistance in aggressive sulfur-containing atmospheres.
Key material properties include:
- High-temperature strength retention up to 1150°C (2102°F) for 310S grade
- Superior resistance to thermal fatigue cycling
- Outstanding resistance to sulfidation, carburization, and scaling
- Low thermal expansion coefficients minimizing stress accumulation
- Weldability suitable for field fabrication and repair
Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 12 mm – 219 mm (0.5" – 8.6") |
| Wall Thickness | 0.5 mm – 12 mm (0.020" – 0.472") |
| Minimum Bend Radius | 2D – 5D (D = tube OD) |
| Coil Winding Diameter | 500 mm – 6000 mm (customizable) |
| Material Grades | 304, 304L, 316, 316L, 310, 310S, 347, 321, Custom Alloys |
| Surface Finish | Pickled & Passivated (P&P), 2B, No. 4 Brushed, Mirror Polish |
| Maximum Service Temperature | 1150°C (2102°F) — Grade Dependent |
| Design Pressure | Up to 6.0 MPa (870 psi) |
| Manufacturing Standards | ASTM A213, ASTM A269, ASME B36.19M, EN 10216-5, GB/T 12771 |
| Applicable Codes | ASME Section VIII Div.1, TEMA, PED 2014/68/EU |
Manufacturing Process
1. Raw Material Selection and Verification
Only certified stainless steel wire rod or strip from accredited mills is used. Each batch undergoes spectroscopic analysis (OES) to verify chemical composition within specified tolerances. Heat number traceability is maintained throughout production.
2. Cold Drawing / Seamless Forming
For small-diameter coil tubes, precision cold drawing through hardened die sets ensures dimensional accuracy (±0.1 mm tolerance) and surface quality. For larger diameters, seamless tube stock is used as the base material.
3. Heat Treatment (Solution Annealing)
Tubes are solution annealed at 1050°C–1150°C followed by controlled water quenching to achieve full austenitic microstructure, ensuring maximum ductility, corrosion resistance, and freedom from sensitization.
4. Coil Forming (Bending)
Coil tubes are formed using CNC-controlled bending machines with mandrel-assisted tooling to prevent ovality, wrinkling, or wall thinning at bends. The minimum bend radius is maintained to avoid excessive stress concentration. Post-bending stress relief is performed at 850°C–950°C for heat-resistant grades.
5. Pickling and Passivation
All coil tubes receive a final pickling and passivation treatment to remove surface oxides, scale, and contaminants, establishing a protective chromium oxide passive film essential for long-term corrosion resistance in service.
6. Non-Destructive Testing (NDT)
Quality assurance includes:
- Visual inspection of all bends and weld joints
- Eddy current testing for surface and near-surface defects
- Hydrostatic pressure testing at 1.5× design pressure
- Dimensional verification per ASME tolerance tables
Applications
- Petrochemical Process Air Preheating: First-stage converter furnace (一段转化炉) air preheater coils in natural gas reforming and steam methane reforming (SMR) units.
- Hydrogen Production Plants: Coil tubes in water-gas shift reactors and reformer preheating systems.
- Oil Refining: Catalytic cracker regeneration coils and furnace tube bundles.
- Power Generation: Waste heat recovery systems and economizer coil assemblies.
- Ammonia and Methanol Synthesis: Process gas preheating and heat integration loops.
- Specialty Chemical Manufacturing: High-temperature reaction vessels and heat exchanger coils.
Over-Temperature Analysis and Design Countermeasures
Based on field experience documented in industry case studies (《一段转化炉工艺空气预热盘管超温原因分析及对策》), coil tube over-temperature events in first-stage converter furnace air preheating systems are typically caused by:
- Flow Maldistribution: Uneven gas or air flow across the coil bundle leads to localized hot spots exceeding design limits.
- Scale and Coking Buildup: Internal fouling increases thermal resistance, causing metal temperature to rise above the coolant-side temperature.
- Material Degradation: Prolonged exposure to temperatures exceeding the grade's maximum continuous service temperature accelerates grain growth, intergranular oxidation, and loss of creep strength.
- Thermal Cycling Fatigue: Repeated startup/shutdown cycles induce fatigue cracking at weld joints and bend regions.
Design Countermeasures implemented by Wenzhou Jixing Metal Materials Co., Ltd.:
- Optimized coil geometry to ensure uniform flow distribution (ΔP balanced within ±5%)
- Selection of 310S or custom super-alloys for zones exceeding 1000°C (1832°F)
- Increased wall thickness at high-temperature zones (minimum 3 mm for OD < 32 mm)
- Smooth internal surface finish (Ra ≤ 0.8 μm) to minimize fouling accumulation
- Thick-wall design with generous corrosion allowance (minimum 0.5 mm)
- Weld joint optimization using full-penetration butt welds with post-weld heat treatment (PWHT)
Quality Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health and Safety Management
- ASME "S" Stamp — Authorized Manufacturer for Seamless & Welded Boiler Tubes
- EN 10204 3.1 — Material Test Reports per European Standard
- CE Marking (PED 2014/68/EU) — Pressure Equipment Directive Compliance
- API Q1 — Quality Management System for Petroleum, Petrochemical, and Natural Gas Industry
Unique Selling Points
- Field-Proven Design: Engineering solutions derived from documented over-temperature failure analysis in converter furnace applications, ensuring reliability under worst-case operating conditions.
- Custom Alloy Development: Capability to develop proprietary super-austenitic compositions tailored to specific thermal and chemical environments.
- End-to-End Traceability: Complete heat number tracking from raw material through final shipment, enabling rapid root-cause analysis in the event of field issues.
- Extended Service Life: Coil tubes designed for minimum 10-year continuous service or 50+ thermal cycles before major maintenance intervention.
- Comprehensive Testing: Every coil assembly undergoes full NDT, hydrostatic testing, and dimensional verification prior to dispatch.