It is definite that equipment expires at some point but the components might not have the same condition at a time. This is common to boilers because its tubes degrade at a much faster rate because of outside factors such as extreme stress and high temperature. It is important to detect early signs of aging in boilers and the right knowledge in dealing with boiler corrosion will help in preventing failure.
In case of an excellent water chemistry control, the economizers are known to last longer in comparison to reheaters or the superheaters. The components are more likely to degrade because of the high temperature which is necessary for the system to operate within the creep range.
The temperature of each stub tube will determine the damage known as thermal fatigue or creep fatigue. To know the reason for the damage, the cracks must be analyzed in a microstructural level. The average steam temperature might not be enough to trigger tubes in the header to operate.
Along with the microstructural changes, there are also reduction in ductility, hardness and strength. There also changes such as the formation of sigma phase, carbon and ferritic steel undergoing graphitization and stainless steels are more sensitize.
If there is a differential expansion present between the roof and the header, it is inevitable to see damage in the stub which is located from tube to header. The source of the stresses can be determined using a simple beam theory, conditions present on the actual fabrication and stresses present on the weld alloys during operation.
It is essential to know where to inspect for any symptoms of damage due to ageing. This can be the reason for failure to occur especially when the steam generators have already reached the age of 25 years or more. The cracks can be discovered easily through careful inspection accomplished by cleaning. This process alone takes a lot of time. There are different inspection techniques that can be utilized including replication, liquid penetrant and magnetic particle. It is important to know what to do when dealing with boiler corrosion because it can lead to total damage if unnoticed.