I am trying to make a sheet metal part.

the part i am making is an API 650 type repad for a  tank.

Consists of 2 concentric circles, ID of 24.25" and OD of 50"

I need a flat pattern and one that shows the bent radius of the tank.

I have tried fold and unfold, and convert to sheet metal. the problem seems to be there is no linear face on this part

so it cannot be folded or unfolded.

I've watched all the tutorials i could find on the subject but none of the techniques seem to work,

Any ideas?

regards,

Derek