Class 2 (2nd Engineer) SC&S 📅 Dec 2022

Exam Question

With reference to membrane tank for the carriage of liquified gas at very low temperture

(a) Describe with the aid of a sketch, ONE method of building up the insulation

(b) State with reasons the alloy, which is used for the membrane

(i) Longitudinally

(ii) Transversly.

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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