The different tank types are:
Independent tank means a cargo containment envelope, which is not contiguous with or part of the hull structure. An independent tank is not essential to the structural completeness of the ship’s hull.
Integral tank means a cargo containment envelope which forms part of the ship’s hull and which may be stressed in the same manner and by the same loads which stress the contiguous hull structure. An integral tank is normally essential to the structural completeness of the ship’s hull.
Gravity tank means a tank having a design pressure not greater than 0.07 MPa gauge at the top of the tank. A gravity tank may be independent or integral. A gravity tank must be constructed and tested according to recognised standards, taking account of the temperature and the relative density of cargoes carried.
Pressure tank means a tank having a design pressure greater than 0.07 MPa gauge. A pressure tank must be an independent tank and of a configuration permitting the application of pressure vessel design criteria according to recognised standards.