4.2.5.1 Internal insulation
tanks are non-self-supporting and consist of thermal insulation materials
which contribute to the cargo containment and are supported by the
structure of the adjacent inner hull or of an independent tank. The
inner surface of the insulation is exposed to the cargo.
4.2.5.2 The two categories
of internal insulation tanks are:
-
.1 Type 1 tanks which are
tanks in which the insulation or a combination of the insulation and
one or more liners functions only as the primary barrier. The inner
hull or an independent tank structure should function as the secondary
barrier when required.
-
.2 Type 2 tanks which are
tanks in which the insulation or a combination of the insulation and
one or more liners functions as both the primary and the secondary
barrier and where these barriers are clearly distinguishable.
The term “liner” means a thin, non-self-supporting,
metallic, nonmetallic or composite material which forms part of an
internal insulation tank in order to enhance its fracture resistance
or other mechanical properties. A liner differs from a membrane in
that it is not intended to function alone as a liquid barrier.
4.2.5.3 Internal insulation
tanks should be of suitable materials enabling the cargo containment
system to be designed using model tests and refined analytical methods
as required in 4.4.7.
4.2.5.4 The design vapour
pressure P
o should not normally exceed 0.25
bar. If, however, the cargo containment system is designed for a higher
vapour pressure, P
o may be increased to such
higher value, but not exceeding 0.7 bar if the internal insulation
tanks are supported by the inner hull structure. However, a design
vapour pressure of more than 0.7 bar may be accepted by the Administration
provided the internal insulation tanks are supported by suitable independent
tank structures.