I agree with the remarks from Bruce. One more thing to pay attention to is the dry out procedure and making sure the relevant hold temperatures take place. I have seen many times were operations get to excited on putting feed in the unit and from the start of the run the refractory can be compromise. Also, slow the amount of catalyst circulation if you can. If you have too much blast steam at the bottom of the Y that can be a problem too. Try to use lift gas and back out steam, as the velocities with steam can damage the refractory.