1) TANK performs the stiffener calculations as detailed in API-650 Section 5.9. If the thank needs stiffeners the software will tell you what the required section modulus is. You cannot specify existing stiffeners and have the software rate their acceptability.
2) The database supplied with the software contains the material properties as defined in API-650. You are free to add additional materials to this database, but this is the only database supplied.
_________________________
Regards,
Richard Ay - Consultant