Stainless Steel Coil Tube (Coil Tube) for Thermal Exchange Applications

1. Product Overview

The Stainless Steel Coil Tube (盘管, Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered heat transfer component designed for demanding industrial applications involving thermal management, fluid circulation, and heat exchange. Unlike conventional straight tubing, coil tubes are formed into helical or spiral geometries that maximize surface area within a compact footprint, offering superior heat transfer efficiency and hydraulic performance.

This product line is particularly notable for its application in floating roof tank (FRT) systems, where coil assemblies are deployed to facilitate the melting and flow enhancement of waxy crude oil under sub-ambient storage conditions. Research studies have demonstrated that the inclination angle of coil assemblies within floating roof tanks significantly influences the melting kinetics and thermal distribution of high-pour-point crude oils, making geometric precision and material integrity critical design parameters.

2. Material & Properties

Coil tubes are fabricated from high-grade austenitic stainless steel grades selected for their exceptional combination of corrosion resistance, mechanical strength, and thermal conductivity under elevated temperature differentials.

• Primary Grades: AISI 304 (UNS S30400), AISI 316 (UNS S31600), and AISI 321 (UNS S32100)
• Corrosion Resistance: Excellent resistance to pitting, crevice corrosion, and intergranular corrosion in both aqueous and hydrocarbon environments
• Mechanical Properties: Yield strength (R_p0.2) of 205–310 MPa; ultimate tensile strength (R_m) of 515–720 MPa depending on grade and temper condition
• Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C, with stable performance across operating ranges of −196°C to +870°C
• Surface Finish: Electropolished or mechanically polished to Ra ≤ 0.4 μm for applications requiring low-fouling characteristics
• Chemical Composition (AISI 316L): C ≤ 0.03%, Cr 17.0–18.5%, Ni 12.0–14.0%, Mo 2.0–3.0%, Si ≤ 1.0%, Mn ≤ 2.0%

3. Specifications

Parameter	Specification	Standard Reference
Outer Diameter (OD)	12.7 mm – 168.3 mm (0.5" – 6.625")	ASTM A213 / ASME SA-213
Wall Thickness	0.5 mm – 6.35 mm (0.020" – 0.250")	ASTM A213
Coil Pitch	15 mm – 150 mm (adjustable per design)	Manufacturer specification
Coil Diameter	100 mm – 2000 mm	Project-specific
Tube Length (Per Coil)	1 m – 50 m	—
Operating Temperature Range	−196°C to +870°C	ASME BPVC Section VIII
Maximum Operating Pressure	Up to 40 MPa (5,800 psi)	ASME BPVC
Inclination Angle (Assembly)	0° – 90° (configurable for thermal optimization)	Engineering design basis
End Preparation	Beveled, threaded, grooved, or plain per ASTM A249	ASTM A249 / ASME B1.20.1
Tolerance on OD	±0.05 mm (±0.002")	ASTM A213
Tolerance on Wall Thickness	±10% of nominal	ASTM A213
Material Certification	Mill Test Certificate (MTC) EN 10204 Type 3.1	EN 10204

4. Manufacturing Process

The production of high-quality stainless steel coil tubes involves a rigorous multi-stage manufacturing sequence ensuring dimensional accuracy, metallurgical integrity, and surface quality:

1. Raw Material Procurement: Seamless stainless steel tubes are sourced from certified mills conforming to ASTM A213 or ASME SA-213 specifications. Incoming material undergoes spectroscopic verification (PMI testing) for chemical composition compliance.
2. Heat Treatment (Solution Annealing): Tubes are solution-annealed at 1040–1120°C followed by rapid water quenching to achieve full austenitic microstructure, relieve cold-work stresses, and maximize corrosion resistance.
3. Precision Cutting: Tubes are cut to specified lengths using CNC-controlled sawing equipment to ensure square ends within ±0.1 mm tolerance.
4. Coil Forming: Tubes are cold-formed into helical coil geometry using CNC coil-winding machines. The forming process is carefully controlled to avoid excessive work hardening and to maintain uniform springback characteristics. The inclination angle of the final assembly is programmatically set based on thermal hydraulic design requirements.
5. Welding (If Applicable): Butt-welded joints, where required, are performed using Gas Tungsten Arc Welding (GTAW/TIG) with argon gas shielding to prevent oxidation. Welds are inspected for full penetration.
6. Pickling & Passivation: Post-welding or post-forming, coils undergo acid pickling (HNO₃/H₂SO₄ solution) to remove heat-affected scale, followed by passivation treatment to restore the protective chromium oxide layer.
7. Non-Destructive Testing (NDT): Hydrostatic pressure testing (at 1.5× maximum working pressure), dye penetrant inspection (DPI) for surface defects, and radiographic testing (RT) for weld integrity.
8. Final Inspection & Packaging: Dimensional verification, surface quality assessment, and protective packaging with desiccant to prevent corrosion during storage and transit.

5. Applications

Stainless steel coil tubes from Wenzhou Jixing Metal Materials Co., Ltd. serve a diverse range of industrial applications:

• Petroleum & Energy Sector: Thermal management of waxy crude oil in floating roof storage tanks; heating coils for maintaining pour point; subsea pipeline heat tracing systems.
• Chemical Processing: Reactor cooling coils, heat exchanger bundles, condensate recovery systems, and corrosion-resistant fluid transfer lines.
• Food & Pharmaceutical Industry: CIP (Clean-In-Place) compatible heating and cooling circuits, pasteurization systems, and sanitary fluid handling.
• Power Generation: Steam generator tubes, condenser coils, and economizer elements in fossil-fuel and nuclear power plants.
• Marine & Offshore: Seawater-cooled heat exchangers, ballast water management systems, and cryogenic LNG storage vessel heating elements.
• HVAC & Refrigeration: Evaporator and condenser coils for industrial chillers, cryogenic applications, and process cooling systems.

6. Unique Selling Points

Thermally Optimized Inclination Design: Drawing from advanced research on floating roof tank thermal management, our coil assemblies can be fabricated with precise inclination angles (0°–90°) that are scientifically validated to maximize heat transfer efficiency during waxy crude oil melting processes. This geometric optimization reduces energy consumption and accelerates flow initiation in high-pour-point crude storage.

• Precision Engineering: CNC-controlled coil forming ensures repeatable geometry with ±0.5 mm dimensional tolerance on pitch and coil diameter.
• Full Traceability: Each coil assembly is accompanied by a complete quality dossier including material certificates, NDT reports, and dimensional inspection records.
• Custom Configurations: Tailored solutions accommodating non-standard diameters, special end preparations, and project-specific thermal performance targets.
• Extended Service Life: Superior corrosion resistance and fatigue performance eliminate the need for frequent replacement in aggressive chemical and marine environments.
• Energy Efficiency: The helical geometry provides 3–5× greater heat transfer surface area per unit volume compared to equivalent straight-tube configurations.

7. Quality Certifications

Wenzhou Jixing Metal Materials Co., Ltd. maintains the following quality management and product certifications:

• ISO 9001:2015 — Quality Management System
• ISO 14001:2015 — Environmental Management System
• ISO 45001:2018 — Occupational Health & Safety Management
• NADCAP — National Aerospace and Defense Contractors Accreditation Program (for aerospace-grade products)
• ASME "S" Stamp — Pressure Vessel and Pressure Piping certification
• EN 10204 Type 3.1 — Material Test Certification per European standard
• ASTM International — Compliance with ASTM A213, A269, A249, and A312 standards
• CRN (Canadian Registration Number) — For pressure equipment destined for Canadian markets
• TÜV / SGS Inspection — Third-party verification available upon request

8. Technical Notes on Inclination Angle Optimization

Research published under the study "The Effect of Coil Assembly Inclination Angle on the Melting Process of Waxy Crude Oil in Floating Roof Tanks" has established critical design guidelines for coil tube deployment in crude oil storage applications:

• Vertical Orientation (90°): Maximizes natural convection-driven heat transfer but requires greater vertical space within the tank envelope.
• Horizontal Orientation (0°): Facilitates uniform radial heat distribution but may exhibit thermal stratification in stagnant oil layers.
• Optimal Inclination (30°–60°): Provides a balanced configuration that enhances turbulent mixing while minimizing thermal short-circuiting, resulting in 15–25% faster melting rates compared to purely horizontal configurations.

Wenzhou Jixing Metal Materials Co., Ltd. offers engineering consultation services to determine the optimal coil inclination angle based on specific crude oil properties (API gravity, pour point, wax crystallization temperature) and tank geometry.