Armstrong Heat Exchangers Shell and Tube | Boiler Supplies

Materials:

• Standard: Copper (tubes), carbon steel (shell, tube sheet, baffles)
• Optional: Brass (tubes, tube sheets, baffles), bronze (heads), stainless steel (tubes, tube sheets, heads, shells, baffles), 90/10 Cu-Ni (tubes)

Shell Assembly:

The shell is typically made from steel pipe or rolled plate metal, although other metals or alloys may be used for extreme conditions. Using off-the-shelf pipe reduces costs and lead times. Maintaining shell roundness is crucial to minimize baffle spacing and enhance performance, achieved by expanding the shell around a mandrel or double rolling it after welding. In some cases, the shell is cast and then bored to the correct diameter. High fluid velocity at the nozzle requires an impingement plate to distribute fluid evenly, preventing erosion, vibration, and cavitation.

Tubes:

Heat exchangers use tubes made from materials like low carbon steel, copper, stainless steel, Hastelloy, and titanium, with diameters from 0.625 to 1.5 inches. Tubes can be seamless or welded, with high-quality electro resistance welded tubes offering good grain structure. Surface enhancements like fins improve heat transfer rates. Finned tubes are useful when the shell-side fluid has a lower heat transfer coefficient than the tube-side fluid. U-tube designs handle significant thermal differences to manage expansion, but are harder to clean and maintain.

Bonnets and End Channels:

Bonnets and end channels regulate fluid flow in the tube-side circuit and are mounted against the tube sheet with bolts and gaskets. Multi-pass designs may include pass ribs to direct flow through the tube bundle, ensuring consistent fluid velocity and pressure drop. Cast bonnets for smaller diameters are made from materials like iron, steel, bronze, Hastelloy, nickel-plated, or stainless steel, with various pipe connection types available.

Baffles:

Baffles guide tubes during assembly, prevent flow-induced vibration, and direct shell-side fluids to increase heat transfer. They must fit tightly within the shell to prevent fluid bypass. Baffles are stamped, punched, or machined, with material choices compatible with the shell-side fluid to prevent corrosion. Precise manufacturing of tube holes ensures easy assembly and maintenance. In liquid applications, baffles typically occupy 20-30% of the shell diameter, while in gas applications, they occupy 40-45%. Baffles are evenly spaced to reduce pressure drop and ensure even fluid velocity.