High-frequency Welded Fin Stainless Steel Tube

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High-Frequency Welded Fin Stainless Steel Tube for Heat Exchangers & Condenser Applications

Industrial extended-surface tubing formed by continuously resistance-welding a solid or serrated metal strip onto a stainless steel base pipe using high-frequency electrical energy. This thermal transfer component maximizes external surface area while maintaining a strong, continuous metallurgical bond at the fin-to-tube interface, ensuring sustained heat transfer efficiency under severe thermal cycling and high-temperature flue gas environments.

Product Types

Solid Fin Stainless Steel Tubes:

Features a continuous solid ribbon fin providing high mechanical strength and smooth airflow path, suited for clean gas environments and high-pressure air-cooled heat exchangers.

Serrated Fin Stainless Steel Tubes:

The fin strip is slit and notched at regular intervals to form segmented sections, interrupting boundary layers and enhancing convective heat transfer coefficients in turbulent gas flows.

Austenitic Stainless Steel Variants:

Manufactured using base pipes in grades 304, 304L, 316, and 316L for superior resistance to oxidation and aqueous corrosion.

Duplex Stainless Steel Variants:

Fabricated with UNS S32205 (Duplex 2205) or S32750 base tubes and matching alloy fins for high-chloride process streams and stress corrosion cracking resistance.

Technical Specifications

Parameter	Specification
Base Tube Outer Diameter (OD)	19.0 mm to 219.1 mm
Fin Height	1.5 mm to 10.0 mm
Fin Thickness	8.0 mm to 30.0 mm
Fin Pitch / Density	0.8 mm to 2.0 mm
Fin Pitch / Density	4 to 12 fins per inch (FPI) or custom spacing
Base Tube Alloy Grades	ASTM A213 / A269 / A312; TP304, TP304L, TP316, TP316L, UNS S32205
Fin Material Grades	Corresponding austenitic or duplex stainless steel strip matching base tube thermal expansion coefficients

Materials & Surface Finish

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Incoming Material Traceability:

Base carrier pipes and fin strips supplied with EN 10204 3.1 Mill Test Certificates verifying chemical composition, yield strength, and tensile properties.

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As-Welded Interface:

High-frequency electrical resistance melting creates a narrow, clean fusion zone without the addition of extraneous filler metal, preserving base alloy corrosion resistance.

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Post-Weld Cleaning:

Mechanical wire brushing and chemical degreasing remove surface scale, drawing compounds, and welding residue prior to final inspection.

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Optional Pickling and Passivation:

Acid bath immersion forms a uniform chromium-oxide passive film on stainless steel surfaces for enhanced resistance in corrosive chemical atmospheres.

Performance Features

01.

Continuous Metallurgical Bond:

Solid-state high-frequency resistance welding forms an atomic-level bond across the entire contact width, preventing thermal resistance buildup over extended operational lifecycles.

02.

High Thermal Cycling Tolerance:

Robust fin-to-tube joint withstands rapid temperature fluctuations and mechanical vibration without delamination or thermal contact degradation.

03.

Optimized Fin-to-Tube Ratio:

Extended external surface area increases overall heat transfer coefficients by 5 to 10 times compared to bare smooth tubes, reducing overall heat exchanger footprint.

04.

Low Flow Resistance:

Uniform fin geometries maintain stable pressure drop across shell-side or duct gas streams, minimizing blower energy consumption.

Applications and Selection

Selection Guide:

Choose solid fins for clean, non-fouling gas streams where minimum pressure drop is required; select serrated fins for dust-laden or fouling flue gas applications to disrupt boundary layers and promote self-cleaning airflow.

Petrochemical and Refining:

Air-cooled heat exchangers (fin-fan coolers), overhead condenser loops, and hydrocarbon stabilization reboilers.

Power Generation & Boiler Systems:

Waste heat recovery boilers (HRSG), flue gas economizers, and low-temperature superheater sections.

Chemical Processing:

Gas coolers, reactor intercoolers, and corrosive vapor condensers handling aggressive acidic gases.

Manufacturing & Quality Control

High-Frequency Welding Lines: Continuous automated induction welding mills maintain precise upset pressure, travel speed, and high-frequency power input (200 to 400 kHz) to ensure consistent weld zone depth.

Weld Peel Testing: Regular destructive peel tests performed at production startup and shift changes to verify that fin tearing occurs in the fin body rather than at the weld interface.

Eddy Current & Visual Inspection: 100 percent inline or visual inspection monitors weld continuity, alignment, and dimensional tolerances.

Pneumatic and Hydrostatic Testing: Base tubes undergo hydrostatic pressure testing prior to finning, with sample finished assemblies tested according to client design codes (ASME Section VIII).

Custom Tube Manufacturing

Custom Geometric Configurations:

Variable fin height, varied fin thickness, and localized un-finned ends (plain ends) customized for tube sheet expansion or welding into headers.

Bending and Coiling:

Tube bending into U-shapes, serpentine coils, or multi-row bundles according to specific heat exchanger layout drawings.

End Machining:

Square cutting, beveling, or counter-boring of tube ends to facilitate subsequent welding into heat exchanger manifolds.

Certifications

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FAQ

Q: How is the bonding integrity between the fin and the base tube verified during production?

A: Quality verification relies on destructive peel testing performed on test samples at the start of every production run. A mechanical force is applied to peel the fin away from the tube; a compliant weld results in tearing of the fin material itself while leaving the joint intact, proving the weld strength exceeds the tensile strength of the fin strip.

Q: What is the maximum operating temperature for high-frequency welded stainless steel finned tubes?

A: Operating limits depend primarily on the selected alloy grade. Austenitic grades (304L/316L) operate reliably up to 600 degrees Celsius, while specialized high-temperature stainless alloys or duplex grades accommodate specific thermal and mechanical stress limits defined in ASME standards.

Q: Can tubes be supplied with un-finned plain ends for header insertion?

A: Yes. Production lines can leave exact lengths of plain un-finned ends at one or both extremities (e.g., 50 mm to 200 mm plain ends) to accommodate tube-to-tubesheet rolling, welding, or plug header assembly.

Q: What is the minimum order quantity (MOQ) for custom stainless steel finned tubes?

A: MOQ is established based on material setup and production run requirements. For standard base tube dimensions, production runs typically start at 500 meters. Smaller quantities for prototyping can be evaluated based on existing raw material stock.

Q: Do you provide material test certificates with each shipment?

A: Every delivery includes complete documentation packages comprising EN 10204 3.1 Mill Test Certificates for both the base tubes and fin strips, covering chemical analysis, mechanical property test results, and dimensional inspection records.

Q: How do you prevent base tube wall thinning or distortion during the high-frequency welding process?

A: The induction welding process applies localized high-frequency current directly to the contact point for fractions of a second, restricting heat input to a microscopic interface zone. Combined with internal sizing plugs and controlled external clamping rolls, this prevents localized wall collapse or dimensional distortion of the base pipe.

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