When scale, sludge or oil stops water from cooling a patch of metal, the steel overheats, loses strength and bulges toward the fire side under boiler pressure. Inspectors measure the size and depth of a bag and decide whether it can be heated and pushed back, patched or must be cut out. A bag is a warning that water treatment has failed.
Inspector found a bag on the furnace about the size of a dinner plate, right over the burner, the boiler's down till it's repaired.
Also heard as
- bulge
Related terms
Scale
A hard mineral crust that forms on boiler heat transfer surfaces from calcium, magnesium and silica in the water.
Furnace
The part of a boiler where the fuel actually burns, such as the big flame tube of a firetube or the water-walled box of a watertube.
Dry fire
To run the burner on a boiler that has lost its water, overheating and often destroying the heating surfaces.
Watertube boiler
A boiler in which water and steam circulate inside tubes while the fire and hot gases pass around the outside.