I have a cast fire pot in my forge,should I line it or will it be ok without it?

OK without if it's like a standard cast firepot.

Of all of the forges I have used with cast pots I have only seen the little cast rivet forges with liners. My vulcan fire pot is unlined with no problems.

any firepot over a 1/4" in thickness will not need lined unless you are going to be using it 8 to 12 hours a day on a daily basis. As a hobby smith or even part time smith it's not needed.