Stainless Steel Coil Tube for Organic Heat Carrier Systems — Coiltube Series
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered continuous coil pipe designed for high-temperature thermal fluid circulation systems. This product is specifically developed for use in oil-fired organic heat carrier furnaces (organic heat transfer fluid heaters), where it serves as the primary heat exchange element responsible for transferring thermal energy from combustion gases to the circulating thermal oil. The coil tube is supplied in continuous helical coil form, enabling efficient integration into boiler heat exchanger bundles and minimizing the number of weld joints required during system assembly.
The design philosophy of this coil tube product is rooted in the safety-critical nature of organic heat carrier systems. As identified in industry safety analyses, the integrity of the coil tube is paramount to preventing thermal oil leakage, overheating, and potential fire hazards. Wenzhou Jixing addresses these safety concerns through rigorous material selection, precise dimensional tolerances, and comprehensive quality control protocols.
Material & Properties
The coil tube is fabricated from austenitic stainless steel grades selected for superior resistance to thermal fatigue, oxidation, and corrosion under prolonged high-temperature service conditions. The primary material grades employed include:
- SUS310S (UNS S31008) — Chromium-nickel austenitic stainless steel with excellent resistance to scaling and oxidation at temperatures up to 1150°C. Ideal for high-temperature radiant tube applications.
- SUS304 (UNS S30408) — General-purpose austenitic stainless steel offering a balanced combination of corrosion resistance, formability, and cost-effectiveness for moderate temperature service.
- SUS316 (UNS S31608) — Molybdenum-enhanced austenitic stainless steel providing superior resistance to pitting and crevice corrosion, suitable for environments where chloride exposure is a concern.
- TP347H (UNS S34709) — Stabilized austenitic stainless steel with niobium stabilization, engineered to resist intergranular corrosion during sensitization temperatures (450–850°C), making it highly suitable for thermal oil heater applications.
Key metallurgical properties include:
- Maximum Service Temperature: 800–1150°C (depending on grade)
- Thermal Conductivity: 16–31 W/(m·K) at 100°C
- Coefficient of Thermal Expansion: 16–18 × 10⁻⁶ /°C
- Yield Strength: 205–310 MPa (as-annealed condition)
- Corrosion Resistance: Excellent resistance to oxidation in air up to 800°C; good resistance to most organic thermal fluids
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) |
| Material Grades | SUS310S, SUS304, SUS316, TP347H |
| Outer Diameter (OD) | Φ19 mm – Φ89 mm (custom sizes available) |
| Wall Thickness (WT) | 1.5 mm – 6.0 mm |
| Coil Diameter | 500 mm – 2000 mm (adjustable per application) |
| Coil Length | 10 m – 100 m per coil (continuous) |
| Surface Finish | Mirror polished, satin finish, or mill finish |
| Manufacturing Standard | ASTM A213 / ASTM A269 / GB/T 12771 |
| Pressure Rating | Up to 6.4 MPa (design pressure, depending on dimensions) |
| Temperature Range | -40°C to 1150°C |
| Application | Organic heat carrier furnaces, thermal oil heaters, industrial process heating |
Manufacturing Process
The production of stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd. follows a multi-stage precision manufacturing process designed to ensure dimensional accuracy, metallurgical integrity, and long-term service reliability:
- Raw Material Selection: Certified stainless steel wire rod or strip is sourced from approved mills with full material traceability documentation (Mill Test Certificates per EN 10204 Type 3.1).
- Hot Rolling / Seamless Tube Forming: The base tube is produced via hot-rolling or seamless piercing processes to achieve the required outer diameter and wall thickness without longitudinal weld seams.
- Precision Annealing: Solution annealing in a controlled atmosphere furnace (1050–1150°C followed by controlled cooling) to restore full austenitic microstructure, relieve internal stresses, and achieve required mechanical properties.
- Pickling & Passivation: Chemical cleaning using mixed acid solutions (nitric-hydrofluoric acid blend) followed by passivation to remove scale, restore chromium oxide surface film, and enhance corrosion resistance.
- Coil Forming (Cold Bending): The straight tube is cold-formed into a continuous helical coil using CNC-controlled coiling machinery. The forming process is carefully controlled to prevent excessive work hardening, distortion, or wall thinning at the coil bends. Minimum bend radius is maintained at 3× the tube outer diameter.
- Dimensional Inspection: Laser-based dimensional measurement of OD, wall thickness, coil diameter, pitch, and straightness. Non-destructive testing (NDT) including eddy current testing (ECT) and ultrasonic testing (UT) for wall thickness verification and defect detection.
- Final Surface Treatment: Electropolishing or mechanical polishing to achieve specified surface finish (Ra ≤ 0.4 μm for mirror finish applications).
- Hydrostatic Pressure Testing: Each coil is subjected to hydrostatic pressure testing at 1.5× the design pressure to verify weld integrity and structural soundness.
Applications
The stainless steel coil tube is engineered for demanding thermal processing applications, with primary use in the following sectors:
- Organic Heat Carrier Furnaces (Thermal Oil Heaters): Primary application as heat exchange coils in indirect-fired and direct-fired thermal oil boilers operating with synthetic thermal fluids (e.g., Therminol VP-1, Dowtherm A) at temperatures up to 350°C and pressures up to 6.4 MPa.
- Chemical Processing Industry: Reactor jacket heating coils, distillation column reboilers, and process heat exchangers requiring corrosion-resistant heat transfer elements.
- Petrochemical Industry: Crude oil preheating, product heating systems, and refinery process heating loops.
- Food & Pharmaceutical Industry: Steam generation systems, pasteurization equipment, and sterilization systems requiring sanitary-grade heat transfer.
- Textile Industry: Drying and calendering machines requiring uniform thermal oil heating.
- Wood Processing & Paper Industry: Continuous drying systems and press heating applications.
- Agricultural Drying: Large-scale grain drying systems utilizing thermal oil as the heat transfer medium.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems and holds the following certifications ensuring product compliance with international standards:
- ISO 9001:2015 — Quality Management System certification covering design, manufacturing, and supply of stainless steel pipe and tube products.
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management System certification.
- CE Marking — Conformity with European Union machinery and pressure equipment directives (PED 2014/68/EU) for pressure vessel applications.
- ASME Stamp Certification — Authorization for fabrication of pressure-containing components per ASME Boiler and Pressure Vessel Code (BPV Code) Section VIII.
- TÜV Inspection — Third-party inspection and certification for product quality and manufacturing process compliance.
- EN 10204 Type 3.1 Material Certificates — Independent inspection body-issued material test certificates for every production batch.
Unique Selling Points
The Coiltube product line from Wenzhou Jixing distinguishes itself through several critical technical advantages:
- Seamless Construction: Elimination of longitudinal weld seams significantly reduces the risk of thermal fatigue failure and thermal oil leakage at elevated operating temperatures, directly addressing the primary safety hazards identified in organic heat carrier furnace failure analyses.
- Continuous Coil Supply: Delivery in continuous helical coil form reduces field installation time by up to 60% compared to straight-length pipe with multiple welded joints, minimizing potential failure points in the system.
- Thermal Fatigue Resistance: The selection of niobium-stabilized (TP347H) and high-chromium (SUS310S) grades provides exceptional resistance to cyclic thermal stress, extending service life in applications with frequent start-stop cycles.
- Precision Dimensional Control: CNC-forming capabilities ensure coil diameter accuracy within ±5 mm tolerance and consistent pitch, facilitating seamless integration into existing boiler bundle designs.
- Comprehensive Safety Traceability: Full material traceability from mill certificate through final inspection report, enabling customers to maintain complete documentation for regulatory inspections and insurance requirements.
- Custom Engineering Support: Ability to design and manufacture coil tubes to customer-specific thermal load requirements, including variable OD/WT profiles along the coil length to optimize heat transfer efficiency.
Technical Notes on Safety Considerations
Based on industry safety analyses of oil-fired organic heat carrier furnaces, the following critical safety considerations are addressed in the design and manufacture of this coil tube product:
- Thermal Oil Coking Prevention: Surface finish requirements (Ra ≤ 0.8 μm) minimize thermal oil coking and fouling on the tube outer surface, maintaining heat transfer efficiency and preventing localized overheating.
- Over-Temperature Protection Compatibility: Material selection ensures that the coil tube maintains structural integrity even in over-temperature excursion scenarios, providing a safety margin before catastrophic failure.
- Thermal Expansion Accommodation: The continuous coil geometry inherently accommodates thermal expansion and contraction without requiring additional expansion joints, reducing system complexity and potential leak points.
- Corrosion Allowance: Wall thickness specifications include a corrosion allowance of 0.5 mm to account for long-term service degradation, ensuring minimum design life of 15 years under normal operating conditions.