Semi-membrane tanks are non-self supporting tanks in the loaded condition and consist of a layer, parts of which are supported through insulation by the adjacent hull structure, whereas the rounded parts of this layer connecting the above mentioned supported parts are designed also to accommodate the thermal and other expansion or contraction.
The design vapour pressure P0 is not normally to 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, P0 may be increased to a higher value but less than 0,7 bar.
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