- Formation of layer of scales on the furnace wall at the water side can cause overheating and bulging defect on the furnace shell.
- Bulging in water tube is due to calcium scale deposition on tube walls which cause improper heat transfer.
- In smoke tube due to carbon deposits bulging is caused.
- Low water level in boiler.
- Misalignment of burner can cause overheating which will further cause bulging.
Any opening in a pressure vessel is kept to a minimum and for a man entry an elliptical hole is lesser in size than the corresponding circular hole. More over it is prime concern to have a smoothed generous radius at the corners to eliminate stress concentration. Hence other geometrical shapes like rectangle and square are ruled out. To compensate for the loss of material in the shell due to opening, a doubler ring has to be provided around the opening. The thickness of the ring depends on the axis length along the dirrection in which the stresses are maximum and the thickness of the shell. It is important to align the minor axis along the length of the vessel, as the stress in this direction is maximum. Longitudinal stress: Pd/2t where P= pressure inside the vessel, d= diameter of the arc, t= thickness of the shell plating Circumferential stress: Pd/4t More over a considerable material and weight saving is achieved as minor is along the direction of maximum stress.