Causes of super heater tubes
Causes of super heater tubes failure :
Failure in super heater tubes is rarely caused by corrosion except the condition of steam boiler is being maintaining or stands by in long term. Failure in super heater tubes is often occurs because of overheating either “short term overheating” or “long term overheating”.
Overheating is caused by attached deposit in internal tubes which is carried over by flow of bad quality steam which bring suspended solid or dissolved solid (hardness). The hardness can be carried over with steam because separation process of steam-water mixture can not executed perfectly in steam drum.
Deposit can be removed by adding chemical injection (phosphate) in steam drum to make hardness be soluble then the next step is discharge it through blowdown process.
Failure in super heater tubes may also occur during bad start up process. If combustion temperature is increased rapidly without doing water and steam balance flow, the super heater will feel overheating in short term because there is not steam flow which has function as cooler. Steam flow through super heater tubes act as cooler because temperature of steam is lower than temperature radiant combustion. So start up procedure shall be established to perform good combustion.