Stainless Steel Coil Tube for Organic Heat Carrier Furnace Systems

Product Overview

The stainless steel coil tube (盘管) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered heat transfer component designed specifically for organic heat carrier furnace systems (有机热载体炉). This product series is distinguished by its optimized hydraulic geometry, which enables reliable thermal performance while maintaining operational safety through controlled fluid dynamics within the coil circuit. The coil tube serves as the primary heat exchange medium in indirect heating systems where organic heat transfer fluids circulate through serpentine tube arrangements to absorb and distribute thermal energy efficiently.

Unlike conventional straight-tube heat exchangers, the coil configuration provides a significantly larger surface-area-to-volume ratio, enhancing convective heat transfer coefficients and enabling compact furnace designs. The theoretical foundation governing the operational safety of these coil-type systems is rooted in Reynolds number (Re) analysis, which characterizes the flow regime—laminar versus turbulent—within the coil passages and directly influences heat transfer efficiency, pressure drop, and fouling susceptibility.

Material & Properties

The coil tubes are fabricated from high-grade austenitic and duplex stainless steels selected for their superior resistance to thermal cycling, corrosion under organic heat transfer media, and mechanical integrity at elevated operating temperatures.

Primary Grades: AISI 304 (UNS S30408), AISI 316L (UNS S31603), AISI 321 (UNS S32100), and AISI 347 (UNS S34700)
High-Temperature Grades: 310S (UNS S31008) for extreme thermal duty applications exceeding 900°C
Chemical Composition: Chromium (Cr) 18–25%, Nickel (Ni) 8–35%, with controlled carbon (C ≤ 0.08%) to prevent intergranular corrosion during prolonged thermal exposure
Mechanical Properties: Yield strength ≥ 205 MPa at 20°C; Tensile strength ≥ 515 MPa; Elongation ≥ 40%
Thermal Conductivity: 14.9–16.3 W/(m·K) at 100°C, providing adequate heat conduction through the tube wall while maintaining structural stability
Corrosion Resistance: Excellent resistance to non-oxidizing organic heat transfer fluids including Therminol VP-1, Dowtherm A, and Yitong YD series media
Maximum Operating Temperature: Up to 870°C (310S grade); Up to 800°C (321/347 grade); Up to 750°C (304/316L grade)

Specifications

Parameter	Specification	Standard Reference
Outer Diameter (OD)	Φ19 mm – Φ108 mm (customizable)	ASTM A213 / GB/T 14976
Wall Thickness	1.0 mm – 6.0 mm	ASTM A213 / GB/T 14976
Coil Mean Diameter (CMD)	150 mm – 2,000 mm	Enterprise Standard
Tube Length per Coil	3 m – 50 m (continuous coil)	Enterprise Standard
Number of Turns	3 – 80 turns	Enterprise Standard
Tightness (Pitch)	1.0× OD – 2.5× OD (adjustable)	Enterprise Standard
Surface Finish	Internal Ra ≤ 0.8 μm; External Ra ≤ 1.6 μm	ASTM A269
End Preparation	Beveled to 30°±2° or plain cut	ASME B1.20.1
Hydrostatic Test Pressure	1.5× working pressure (minimum 6.0 MPa)	GB/T 24511
Design Pressure	Up to 4.0 MPa (typical); Up to 10.0 MPa (high-pressure grade)	ASME BPV Section VIII
Reynolds Number Range (Design)	Re > 10,000 (turbulent flow regime for optimal heat transfer)	Dittus-Boelter / Sieder-Tate correlation
Maximum Flow Velocity	3.0 m/s (to prevent erosion-corrosion)	API 579 / Vendor guideline
Heat Transfer Coefficient (h)	≥ 800 W/(m²·K) (turbulent organic fluid flow)	Engineering calculation

Manufacturing Process

The production of coil tubes for organic heat carrier furnace applications follows a rigorous multi-stage manufacturing sequence ensuring dimensional accuracy, metallurgical integrity, and hydraulic performance:

Raw Material Selection & Incoming Inspection: Seamless stainless steel tubes conforming to ASTM A213 or GB/T 14976 are sourced from certified mills. Each batch undergoes spectrometric analysis (OES), mechanical testing, and non-destructive examination (eddy current per ASTM E709) prior to acceptance.
Tube Straightening & Annealing: Tubes are cold-straightened to eliminate residual curvature and subsequently annealed at 1,050°C ± 20°C with controlled furnace cooling to restore full solution-treated microstructure and relieve residual stresses.
Coil Forming (Cold Bending): Precision CNC coil-forming machines bend the straight tubes into the specified helical geometry. The bending process employs a mandrel-supported die system to prevent ovalization, ensuring that the cross-sectional distortion remains within ±3% of nominal dimensions. The bending radius is optimized to maintain the internal Reynolds number above the critical threshold (Re_crit ≈ 2,300) under design flow conditions, guaranteeing turbulent flow and maximizing heat transfer coefficients.
Post-Forming Stress Relief: After coiling, assemblies undergo stress-relief annealing at 650°C – 750°C for 2 hours per 25 mm of wall thickness to eliminate residual bending stresses that could compromise fatigue life or promote stress-corrosion cracking.
Internal Cleaning & Passivation: Coils are cleaned using chemical pickling (HNO₃/HF blend) followed by passivation treatment to establish a protective chromium oxide film. Internal surfaces are inspected via borescope to confirm cleanliness and absence of oxide inclusions.
End Finishing & Welding: Tube ends are prepared for welding to header manifolds or furnace inlet/outlet connections. Where welded joints are required, GTAW (Gas Tungsten Arc Welding) is employed with inert gas backing (argon) to ensure penetration and surface quality per ASME Section IX qualification.
Hydrostatic & Pressure Testing: Each coil assembly is hydrostatically tested at 1.5× the maximum design pressure with a hold time of 30 minutes. Pneumatic testing at 1.1× design pressure follows to verify leak-tightness under operating conditions.
Reynolds Number Verification: A hydraulic performance test is conducted by circulating water at design flow rates and measuring the pressure drop across the coil. The measured ΔP is used to back-calculate the actual Reynolds number, confirming that the design Re > 10,000 criterion is met for turbulent flow operation.

Applications

Stainless steel coil tubes are integral components in a wide range of industrial heating systems where organic heat transfer fluids provide indirect process heating:

Chemical & Petrochemical Industry: Heat transfer coils in organic heat carrier furnaces for exothermic reaction temperature control, distillation column reboilers, and polymerization reactors. The turbulent flow regime (high Re) ensures uniform heat distribution and prevents localized hot spots that could cause thermal degradation of organic media.
Pharmaceutical Manufacturing: Clean-in-place (CIP) compatible coil assemblies for solvent recovery systems, crystallization processes, and controlled thermal treatment under GMP conditions. The smooth internal surface (Ra ≤ 0.8 μm) minimizes fouling and supports effective cleaning cycles.
Food Processing: Heating coils for cooking, blanching, pasteurization, and drying operations where direct contact with food-grade organic media is required. Compliance with FDA 21 CFR Part 178 and EU Regulation EC 1935/2004 is ensured.
Textile Industry: Drying and curing ovens utilizing organic heat carrier systems for fiber treatment, dye fixation, and fabric finishing processes requiring precise temperature control up to 350°C.
Wood & Paper Industry: High-temperature drying kilns and press systems where coil furnaces provide consistent thermal output for board pressing and veneer drying at temperatures up to 250°C.
Power Generation (Auxiliary Systems): Oil heaters, transformer oil circulation systems, and auxiliary heating loops in power plants requiring reliable, corrosion-resistant heat transfer components.

Reynolds Number-Based Safety Analysis

The operational safety of coil-type organic heat carrier furnaces is fundamentally governed by the Reynolds number (Re = ρVD/μ), which determines the flow regime within the coil passages. Wenzhou Jixing Metal Materials Co., Ltd. applies rigorous theoretical analysis based on fluid dynamics principles to ensure safe and efficient furnace operation:

Laminar Flow Regime (Re < 2,300): Characterized by orderly fluid layers with minimal radial mixing. Heat transfer coefficients are low (h ≈ 200–500 W/(m²·K)), leading to potential hot spots on the tube inner wall where organic fluid may exceed its maximum film temperature, causing thermal decomposition and coking.
Transitional Flow (2,300 < Re < 10,000): Unstable flow with intermittent turbulence. Predictable heat transfer performance is difficult to achieve, posing risk of thermal runaway under variable load conditions.
Turbulent Flow Regime (Re > 10,000): Fully developed turbulence with intense radial mixing. Heat transfer coefficients reach 800–1,500 W/(m²·K), ensuring uniform wall temperature distribution, prevention of local overheating, and stable furnace operation. This is the mandatory design target for all coil tube products supplied by Wenzhou Jixing.

The coil geometry parameters—inner diameter (D), coil mean diameter (CMD), and pitch—are specifically optimized to maintain turbulent flow across the entire operating range (from minimum to maximum circulation pump capacity). The Dittus-Boelter correlation (Nu = 0.023 Re⁰·⁸ Pr⁰·⁴) and the enhanced heat transfer due to secondary Dean vortices in curved tubes (accounted for via a correction factor of 1.2–1.6) are incorporated into the design calculations to ensure adequate heat transfer margin.

Quality Certifications & Standards Compliance

Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management and product certification systems to assure customers of consistent product quality and regulatory compliance:

ISO 9001:2015 — Quality Management System certification covering the entire production chain from raw material procurement through final delivery
ISO 14001:2015 — Environmental Management System ensuring sustainable manufacturing practices
ASME "S" Stamp — Sectional certification for pressure vessels and components, applicable to coil assemblies used in pressure-retaining furnace systems
EN 10204 3.1 — Manufacturer's Test Report providing material certificates, dimensional inspection records, and test results traceable to accredited laboratories
CE Marking (PED 2014/68/EU) — Conformity with European Pressure Equipment Directive for furnaces classified as Category I or higher
GB/T 24511 — Chinese national standard for pressure vessel design, materials, manufacturing, inspection, and testing
ASTM A213 / A269 — Material specification compliance for austenitic stainless steel seamless tubes for high-temperature service
Third-Party Inspection: Available upon request through SGS, Bureau Veritas, or TÜV for on-site manufacturing surveillance and pre-shipment inspection

Unique Selling Points

Reynolds Number-Verified Design: Every coil tube product undergoes hydraulic verification to confirm turbulent flow operation (Re > 10,000), eliminating the risk of thermal decomposition of organic heat transfer media and ensuring long-term operational safety.
Customized Coil Geometry: Flexible customization of coil mean diameter, pitch, number of turns, and tube specifications to match specific furnace designs and thermal load requirements.
Extended Service Life: Solution-annealed austenitic stainless steel with controlled carbon content provides resistance to intergranular corrosion and thermal fatigue, ensuring coil assemblies remain leak-tight over thousands of thermal cycles.
Integrated Safety Analysis: Comprehensive theoretical documentation including Reynolds number calculations, Nusselt number correlations, pressure drop analysis, and thermal decomposition prevention criteria is provided with each product delivery.
Traceability: Full material traceability from mill certificate through heat number to final coil assembly, supporting lifecycle management and maintenance planning.

Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Product Code: JX-CT-1089 | Classification: Technical Literature & Engineering Application