How to identify the cause of Tube Sheet failure in a Firetube Boiler?

 A firetube boiler consists of many parts, which can be classified as pressure parts and non-pressure parts. The most important and fundamental part is the firetube and the tube sheet.  The tube and the tube sheet when constructed together give a shape to the boiler, we can simply say that this is the skeleton of the boiler. During the life cycle of a firetube boiler, there can be an unprecedented occurrence of a tube sheet getting failed over a period of time, or in some cases, it can be a premature failure too.  The below chart can be helpful to analyze and identify the cause of a Tube to Tube sheet joint failure in a Firetube Boiler.