4.2.2.1 Membrane tanks are
non-self-supporting tanks which consist of a thin layer (membrane)
supported through insulation by the adjacent hull structure. The membrane
is designed in such a way that thermal and other expansion or contraction
is compensated for without undue stressing of the membrane.
4.2.2.2 The design vapour
pressure P
o should not normally exceed 0.25
bar. If, however, the hull scantlings are increased accordingly and
consideration is given, where appropriate, to the strength of the
supporting insulation, P
o may be increased
to a higher value but less than 0.7 bar.
4.2.2.3 The definition of
membrane tanks does not exclude designs such as those in which nonmetallic
membranes are used or in which membranes are included or incorporated
in insulation. Such designs require, however, special consideration
by the Administration. In any case the thickness of the membranes
should normally not exceed 10 mm.