I am trying to find a chart that gives me the sizes for amp frame & amp trip for heaters in industrial plant or offshore applications. Can anyone help me with this?

This will be found in the manufacturers liturature for the particular brand of switchgear that is installed, for example, GE, Square D, FPE, ABB, Siemens, and I am sure there are others I have missed.

What brand of switchgear do you have?

Ampere Trip is the limit to which if the current reached, CB will Trip. And Ampere Frame is actually the Size of Bus Bar of Penal Board and If in future we have to Replace it with some higher size of CB so we can. Ampere Frame is always higher than Ampere Trip.

AT is the value of current to be triped.
AF is the value of current to be carried without damage the unit of C.B.