Damage of Air Preheater Pinion Gear

[powering2002]

Dear all,
We operate 2 x 100 MW Steam Power Plant. we have serious problem with our air preheater. Last recent months, The pinion gear of air preheater was often damaged. When it was damaged, we replace with new pinion gear. But, after few weeks, it was damaged again. For your information, the frequent damage of the pinion gear happens after we change the fuel supply from Residual Oil to Natural Gas. Also, when we used Natural Gas, we don't operate Steam Coil Air Preheater.
Could you help us to find out the cause of the damage of the air preaheater pinion gear? Thanks for your attention

 

[metengr]

First off, the air heater drive pinion gear should be sent to a metallurgical lab for a proper failure analysis. I have seen air heater pinion failures caused by improper fabrication - material, heat treatment - including improper case depth, a seized air heater caused by thermal mismatch.