Class 2 (2nd Engineer) SC&S 📅 Apr 2023

Exam Question

With reference to membrane tanks for the carriage of liquefied gas at very low temperatures.

(a) Describe with a sketch one method of building up the insulation. (6)

(b) State which alloy is used for the membrane and the reason (6)

(i) Longitudinally

(ii) Transversely

Reference Answer

(a) Membrane tanks for liquefied gas carriage are built with a double hull throughout the cargo length. The insulation system includes the following:
Primary Barrier: A thin membrane made of INVAR (36% Nickel, 64% Iron) with a thickness of 0.5 to 1.2 mm, forming the primary containment layer for the liquefied gas.
Primary Insulation box: A 200 mm thick layer of granulated Perlite insulation packed in plywood boxes, surrounding the primary barrier. Perlite is siliconised to make it impervious to moisture.
Secondary Barrier: A secondary membrane made of the same INVAR material is installed to prevent cargo leakage in case of primary barrier failure.

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