Manifold

A chamber for the collection and distribution of fluid to or from multiple parallel flow paths.

Louver of damper

A damper consisting of several blades called louvers each pivoted about its center and linked together for simultaneous operation.

Flue gas

The gaseous product of combustion including the excess air.

Bulging of a tube

      Bulging is generally an indication of overheating. Continuing under the same temperature and stress conditions will eventually lead to creep and stress rupture. The amount of bulging varies with the specific metal and the type of damage, creep or overstress. If the bulge is attributed to overstress (short-term overheating), and the temperature and stress have been returned to normal, typically the life of the tube has not been reduced. Creep life will be reduced, if the bulge is the result of creep damage (long-term overheating). Bulging is considered more serious than sagging or bowing.

Bowing of a tube

Excessive bowing is generally caused by uneven metal temperatures, which may be due to flame impingement or coke accumulation inside the tube. Heating on one side of the tube causes greater thermal expansion on the hotter side and bowing toward the heat source. Bowing may also be caused by binding of the tube in the tube sheets or improper suspension of the tube so that longitudinal expansion is restricted or by the use of improper tube lengths when individual tube replacements are made.

Sagging of a tube

Excessive sagging is usually because of a decrease in the structural strength of the tube caused by overheating. It may also be caused by improper spacing of hangers, uneven metal temperatures, or failure of one or more tube supports or hangers.