What reason to bulge boiler tubes?

Answer 1

This is caused by overheating of the shell plates and it affecsthe entire thickness of the plate. So, too much heat = weaker metal = thus bulge due to the weakend metal succombing to the boiler pressure. This is often due to deposit on the WATER side of tube. THe METAL gets too hot, thus the metal is weaker and bulges due to the pressure found inside the piping.. NOT the water gets too got. This is important to distinguish from a blister which is caused by a slag inclusion forming a lamination at the time the plate was rolled in the steel mill. Thus a blister is defect in the metal. Blisters may also be caused by a hydrogen environment. Blisters also are worsened by deposites which cause them to crack and release scale. This process repeats until it bursts. The bugle formation is similar in that it actually breaks away the scale that formed it upon its formation. This will allow water to absorb heat properly from the metal again and delay the progression of the bulge until the scale reforms. Small Bulges can be left in place if scale forming processes are removed. Blisters should be replaced eventually as they are thinner then is normally permitted by code.