Base Tube Material: ASME SA213 T22

Standard: ASME SA213 covers seamless ferritic and austenitic alloy-steel boiler, superheater, and heat-exchanger tubes.

Grade T22 (UNS K21590): A low-alloy steel containing approximately 2.25% Chromium and 1% Molybdenum.

Key Properties:

High-Temperature Strength: Excellent creep resistance and tensile strength at elevated temperatures (typically up to ~1100°F / 595°C).

Oxidation & Corrosion Resistance: Good resistance to oxidation and corrosion in steam and flue gas environments, superior to carbon steel.

Weldability: Readily weldable with appropriate procedures (often requires post-weld heat treatment - PWHT).

Typical Applications: Boiler superheater/reheater tubes, heat recovery steam generators (HRSGs), process heaters, and other high-pressure/high-temperature heat exchangers in power plants, refineries, and petrochemical plants.

Fin Type: Serrated Fins

Structure: Solid fins are mechanically formed or welded onto the outer surface of the base tube. "Serrated" means each fin has small, regular notches or cuts perpendicular to the fin height, creating a segmented or "serrated" edge profile along the fin's length.

Purpose & Advantages:

Dramatically Enhanced Heat Transfer: The serrations disrupt the thermal boundary layer on the fin surface and create turbulence in the gas/fluid flow outside the tube. This significantly improves the heat transfer coefficient compared to smooth or plain fins (often by 25-45% or more).

Increased Surface Area: Provides more effective surface area per unit length than a plain tube, further boosting heat transfer.

Mitigated Fin Efficiency Reduction: While fins improve heat transfer, they also introduce a temperature gradient along their height, reducing their effectiveness ("fin efficiency"). Serrated fins can have slightly higher fin efficiency than solid fins of the same height because the notches effectively shorten the conductive path for heat in the fin material locally.

Considerations:

Higher Pressure Drop: The increased turbulence also leads to a higher pressure drop on the fin-side (gas/fluid side) compared to plain or solid fins. This requires more fan/pump power.

Potential Fouling: The serrations can trap particulate matter more easily than smooth fins, potentially leading to faster fouling in dirty gas streams (e.g., flue gas with ash). Regular soot blowing or cleaning might be necessary.

Mechanical Strength: Serrated fins are generally slightly less robust than solid fins during handling and cleaning operations.

Combination: SA213 T22 Serrated Fin Tube

Purpose: This combination is specifically engineered for high-efficiency heat transfer in high-temperature, high-pressure, and corrosive environments.

Applications:

• HRSGs (Heat Recovery Steam Generators): Economizer, evaporator, superheater, and reheater sections recovering heat from gas turbine exhaust.
• Boilers: Superheaters and reheaters in coal-fired, biomass-fired, or waste-to-energy plants.
• Process Heaters/Fired Heaters: In refineries and petrochemical plants.
• Waste Heat Recovery Units: Where exhaust gases are hot and potentially corrosive.

Key Benefits:

High Thermal Efficiency: Serrated fins maximize heat recovery from the gas stream.

Material Suitability: T22 alloy withstands the high metal temperatures and corrosive flue gas components (sulfur, vanadium) encountered in these applications.

Pressure Containment: The seamless SA213 tube reliably contains high-pressure steam/water inside.

Fin Attachment: Fins are typically helical and can be attached by:

Embedded / Extruded: The fin is formed from the base tube material (less common for alloy steels like T22 due to hardness).

Welded (GTAW/Laser): A separate fin strip (often also T22 or a compatible alloy like SS409) is resistance welded, high-frequency welded, or laser welded to the base tube. This is the most common method for T22 finned tubes.