Stainless Steel Coil Tube for Organic Heat Carrier (Thermal Oil) Furnaces
Product Overview
The Stainless Steel Coil Tube (Product Code No. 772) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular component specifically designed for use in Organic Heat Carrier Furnaces (also known as Thermal Oil Heaters or Thermic Fluid Heaters). These coil tubes serve as the primary heat exchange elements within industrial thermal oil systems, where they transfer heat from a combustion source to a circulating organic heat transfer fluid (typically synthetic or mineral-based thermal oils), enabling efficient and uniform heat delivery to downstream process equipment.
Coil tubes in organic heat carrier systems are subject to extreme thermal cycling, high operating temperatures (commonly 300°C to 400°C), and continuous mechanical stress from fluid flow and thermal expansion. Consequently, the design, material selection, and manufacturing quality of these tubes are critical to system reliability, safety, and energy efficiency. This product line addresses the well-documented challenges of coil tube deformation — including ovalization, buckling, sagging, and creep — through optimized metallurgical properties, advanced fabrication techniques, and rigorous quality control protocols.
Material & Properties
Coil tubes for organic heat carrier furnaces must exhibit exceptional oxidation resistance, creep resistance, thermal fatigue resistance, and dimensional stability under prolonged high-temperature exposure. The following material grades are typically employed:
Primary Material Grades
- AISI 304 (UNS S30408 / 1.4301) — Austenitic stainless steel with excellent general corrosion resistance and moderate high-temperature strength. Suitable for thermal oil systems operating up to approximately 350°C.
- AISI 321 (UNS S32108 / 1.4541) — Titanium-stabilized austenitic stainless steel offering superior resistance to intergranular corrosion and enhanced high-temperature strength. Preferred for systems operating at 350°C to 400°C.
- AISI 310S (UNS S31008 / 1.4845) — High-chromium, high-nickel austenitic stainless steel providing outstanding oxidation resistance and creep strength at elevated temperatures. Recommended for demanding applications exceeding 400°C.
- AISI 316L (UNS S31603 / 1.4404) — Low-carbon molybdenum-bearing austenitic stainless steel offering enhanced pitting and crevice corrosion resistance. Selected when thermal oils contain halogenated contaminants or chloride impurities.
Key Mechanical and Physical Properties (AISI 321 Representative)
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (0.2% Yield) | ≥ 205 MPa (at 20°C); ≥ 150 MPa (at 400°C) | ASTM A213 / A269 |
| Elongation | ≥ 40% | ASTM A213 / A269 |
| Thermal Expansion Coefficient | 17.3 × 10⁻⁶ /°C (20–300°C) | ASTM E228 |
| Thermal Conductivity | 16.3 W/(m·K) (at 100°C) | ASTM E1461 |
| Critical Creep Temperature | ~600°C (10⁵ hours) | ASTM E139 |
| Maximum Recommended Operating Temperature | 400°C (continuous thermal oil service) | ISO 15927 |
| Carburization Resistance | Excellent (Ti-stabilized microstructure) | ASTM A999 |
Specifications
| Parameter | Specification / Range |
|---|---|
| Product Designation | Coil Tube (Coiltube) — Product No. 772 |
| Outer Diameter (OD) | 12 mm – 51 mm (custom sizes available) |
| Wall Thickness | 1.5 mm – 4.0 mm |
| Coil Mean Diameter | 200 mm – 1,500 mm |
| Tube Length (per coil) | 5 m – 50 m (adjustable per furnace design) |
| Material Grade | AISI 304 / 321 / 310S / 316L (per customer requirement) |
| Surface Finish | Pickled & Passivated (Ra ≤ 1.6 μm); Mirror Polish available |
| Tolerance — OD | ±0.10 mm (precision drawn); ±0.15 mm (cold drawn) |
| Tolerance — Wall Thickness | ±10% (minimum wall thickness guaranteed) |
| Operating Pressure | Up to 1.6 MPa (thermal oil system typical) |
| Operating Temperature Range | 25°C – 400°C (continuous); 420°C (intermittent) |
| Heat Treatment | Solution Annealed (1050°C – 1150°C, water quenched) |
| Coil Winding Tension | Controlled to minimize residual stress and ovalization |
| End Preparation | Plain, beveled (37.5°), or threaded per customer specification |
Manufacturing Process
The production of high-quality coil tubes for organic heat carrier furnaces follows a multi-stage process designed to ensure dimensional accuracy, metallurgical integrity, and resistance to thermal deformation:
- Raw Material Selection and Inspection — Certified stainless steel seamless tube blanks (per ASTM A213 or ASTM A269) are sourced from reputable mills. Each batch undergoes spectrographic analysis (OES) and mechanical testing to verify chemical composition and tensile properties.
- Tube Straightening and Cutting — Seamless tubes are straightened using hydraulic straightening machines to achieve flatness within ±0.5 mm/m. Tubes are cut to specified lengths with controlled burr-free ends.
- Precision Cold Drawing — Tubes are cold-drawn through calibrated tungsten carbide dies to achieve exact OD and wall thickness tolerances. This process work-hardens the material, enhancing yield strength and fatigue resistance.
- Coil Winding — Straightened and drawn tubes are wound into coils using CNC-controlled coiling machines. Winding tension, coil diameter, and pitch are precisely controlled to minimize residual stresses and prevent ovalization during service. The coil winding process is a critical step, as improper winding tension is a primary contributor to post-installation deformation.
- Solution Annealing — Coils are subjected to solution annealing at 1050°C–1150°C followed by rapid water quenching. This eliminates residual stresses from cold working, restores full ductility, and ensures a uniform austenitic microstructure with dissolved carbides (particularly in Ti-stabilized grades like 321).
- Pickling and Passivation — Annealed coils are immersed in a hydrofluoric/nitric acid pickling solution to remove oxide scales, followed by passivation in a citric or nitric acid bath to restore the protective chromium oxide passive film. Surface roughness is verified to meet Ra ≤ 1.6 μm.
- Hydrostatic Testing — Each coil undergoes hydrostatic pressure testing at 1.5× the maximum operating pressure (typically 2.4 MPa) for a minimum of 30 seconds to verify weld integrity and absence of wall defects.
- Dimensional Inspection and Final QC — Comprehensive inspection includes OD/wall thickness measurement (ultrasonic and caliper), ovalization measurement (≤ 1% of nominal OD), straightness verification, and surface defect inspection (visual and magnetic particle testing per ASTM E165).
- Packaging and Dispatch — Coils are wrapped in protective polyethylene film and crated on wooden pallets with desiccant to prevent corrosion during transit. Each shipment is accompanied by a Mill Test Certificate (MTC) and Quality Inspection Report.
Applications
Stainless steel coil tubes for organic heat carrier furnaces are integral components in industrial thermal oil heating systems across multiple sectors:
- Petrochemical and Refining Industries — Process heating in distillation columns, reactors, and heat exchangers where precise temperature control is essential. Coil tubes carry thermal oil through fired heater sections.
- Polymer and Plastics Manufacturing — Heating of extruders, injection molding machines, and reactors for polymerization processes requiring uniform heat distribution at 250°C–350°C.
- Textile and Rubber Processing — Calender heating, vulcanization presses, and textile drying ovens utilizing thermal oil as a clean, non-toxic heat transfer medium.
- Food and Beverage Processing — Heating of cooking equipment, pasteurizers, and drying systems where food-grade stainless steel (304/316L) is mandated.
- Wood and Paper Industries — Kiln drying, paper calender heating, and board pressing operations requiring consistent thermal profiles.
- Pharmaceutical Manufacturing — Process heating in reactors and distillation units where high-purity thermal oil systems are employed.
- Building Materials and Ceramics — Kiln preheating and curing processes requiring controlled temperature ramping.
Deformation Prevention — Key Design Considerations
Based on extensive field experience and technical analysis, the following measures are incorporated into the design and manufacturing of these coil tubes to prevent the common deformation modes observed in organic heat carrier furnace service:
- Ovalization Prevention — Optimized coil winding tension and post-winding stress-relief annealing reduce residual hoop stresses that contribute to ovalization under thermal cycling.
- Buckling Resistance — Adequate wall thickness selection based on thermal oil flow velocity and pressure, combined with proper support spacing recommendations (typically 1.5 m – 2.0 m between supports).
- Creep Mitigation — Material grades with elevated creep strength (321, 310S) are recommended for sustained operation above 350°C. Operating temperature limits are strictly defined to remain below the material's critical creep temperature.
- Thermal Expansion Accommodation — Coil geometry is designed with sufficient springback allowance to accommodate differential thermal expansion between tube and furnace shell, preventing stress-induced deformation.
- Flow-Induced Vibration Control — Tube diameter and support configuration are optimized to avoid resonance frequencies that could lead to fatigue failure or vibration-induced deformation.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework to ensure product conformity and traceability:
- ISO 9001:2015 — Quality Management System certification covering design, manufacturing, inspection, and delivery processes.
- ISO 14001:2015 — Environmental Management System certification ensuring environmentally responsible production practices.
- ISO 45001:2018 — Occupational Health and Safety Management System certification.
- EN 10204 Type 3.1 — Third-party inspection and testing certificates for all material batches.
- ASTM / ASME Compliance — Products manufactured and tested in accordance with ASTM A213 (welded and seamless austenitic stainless steel tubing for high-temperature service) and ASTM A269 (general requirements for austenitic stainless steel tubing).
- Mill Test Certificates (MTC) — Each shipment includes EN 10204 3.1 MTCs documenting chemical composition, mechanical properties, heat treatment records, and dimensional inspection results.
- Non-Destructive Testing (NDT) — Magnetic Particle Testing (MT) per ASTM E165 and Visual Inspection per ASTM E165 for surface defect detection. Hydrostatic testing per ASTM A530.
- CE Marking — Available for products intended for use in European Union industrial equipment per the Pressure Equipment Directive (PED 2014/68/EU), where applicable.
Unique Selling Points
- Application-Specific Engineering — Coil tubes are engineered specifically for organic heat carrier furnace service, incorporating lessons learned from deformation failure analyses to deliver enhanced service life and reliability.
- Multi-Grade Material Availability — Four premium stainless steel grades (304, 321, 310S, 316L) covering the full spectrum of thermal oil operating temperatures and corrosion environments.
- Precision Coil Winding Technology — CNC-controlled winding with optimized tension profiles minimizes residual stresses, reducing the risk of post-installation ovalization and deformation.
- Comprehensive Quality Traceability — Full traceability from raw steel mill certification through final product inspection, supported by EN 10204 3.1 MTCs and detailed inspection reports.
- Custom Configuration Capability — Flexible customization of OD, wall thickness, coil diameter, length, and end preparation to match specific furnace designs and OEM requirements.
- Deformation-Resistant Design Philosophy — Products are designed with explicit consideration of the five primary deformation modes (ovalization, buckling, sagging, creep, and vibration-induced fatigue) documented in organic heat carrier furnace failure analyses.
- Competitive Lead Times — In-stock standard configurations with rapid delivery; custom orders produced within 15–30 calendar days.
Note: This technical specification is based on industry-standard practices and the product knowledge documented under Product No. 772 by Wenzhou Jixing Metal Materials Co., Ltd. For project-specific requirements, customers are advised to consult with the manufacturer's engineering team to confirm material grade selection, dimensional tolerances, and design suitability for their specific organic heat carrier furnace application. All specifications are subject to mutual agreement between supplier and purchaser.