ASTM A312 TP304H Serrated Fin Tube For Steam Boilers and Economizers

ASTM A312 TP304H Serrated Fin Tube For Steam Boilers and Economizers

1. Deconstructing the Name

• ASTM A312: This is the standard specification for "Seamless, Welded, and Heavily Cold Worked Austenitic Stainless Steel Pipes" from ASTM International. It governs the dimensions, mechanical properties, chemical composition, and testing requirements for the base tube.

• TP304H: This is the specific grade of stainless steel.

  • TP304: The base austenitic stainless steel grade, known for excellent corrosion resistance and formability. Its key alloying elements are Chromium (18-20%) and Nickel (8-10.5%).

  • H: This suffix denotes a high-carbon variant. The carbon content for 304H is restricted to a range of 0.04-0.10%. This higher carbon content provides improved high-temperature strength (creep strength) compared to standard 304/304L. It is specifically designed for service temperatures above 525°C (1000°F).

• Serrated Fin Tube: This describes the extended surface attached to the outside of the base tube. "Serrated" means the fins are not continuous; they are cut at regular intervals, creating gaps.

2. Key Features and Advantages of the Serrated Fin Design

The serrated fin is a key differentiator that offers significant thermal and mechanical advantages over solid (continuous) fins.

• Dramatically Enhanced Heat Transfer: The serrations (gaps) disrupt the boundary layer of gas or fluid flowing over the fins. This creates turbulence, which is far more effective at transferring heat than laminar flow. This results in a much higher overall heat transfer coefficient.

• Reduced Fouling: The gaps between the fin segments prevent the easy buildup of soot, ash, or other particulates. Debris has a harder time bridging across the fins, making the tube easier to clean and maintain, especially in flue gas applications.

• Optimal Balance of Strength and Efficiency: The fin base provides a strong, continuous attachment to the base tube, while the serrated tips maximize heat transfer. This design also offers some flexibility, reducing the risk of fin damage during handling and operation.

• Lighter Weight: For the same overall length and fin density, a serrated fin tube can be lighter than a solid fin tube, as material is removed to create the serrations.

3. Manufacturing Process

These tubes are typically manufactured using a resistance welding process:

1. A continuous strip of stainless steel (typically 304H to match the base tube's thermal expansion) is fed into a high-frequency electric resistance welder.

2. The strip is wound helically around the cleaned ASTM A312 TP304H base tube.

3. As the fin strip is pressed against the tube, an electrical current is passed through the point of contact, creating intense localized heat.

4. Pressure is simultaneously applied, fusing the fin root to the tube's outer wall without the use of filler metal, creating a metallurgical bond with high strength and excellent thermal conductivity.

5. A serrating tool immediately cuts the continuous fin at predetermined intervals to create the distinctive serrated pattern.

4. Typical Technical Specifications

5. Chemical Composition (ASTM A312 TP304H)

6. Primary Applications

This tube is specifically designed for demanding, high-temperature service in:

• Heat Recovery Steam Generators (HRSGs): Recovering waste heat from gas turbine exhaust.

• Economizers & Air Heaters: In coal-fired, biomass, and waste-to-energy boilers to preheat feedwater or combustion air.

• Fired Heaters & Process Furnaces: In petrochemical and refining industries.

• Waste Incineration Boilers: Where corrosion and fouling are significant concerns.

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