Marine Installation Manual 2021-08 4-39
4 Ancillary Systems
4.4 Fuel gas system
X72DF
Figure 4-19 Section view of an integrated membrane tank
Free-standing –
Type A tank
As specified by the IGC Codes, the Type A tank must have a second barrier to
withhold leaks. Often the ship hull is used as this second layer, so to maximise
volume efficiency, the tank is designed in a prismatic shape to best fit inside the
vessels hull. Between the tank wall and secondary barrier is a solid insulation
layer and an air-gap layer. This reduces the thermal impact on the LNG from the
environment, therefore reducing the BOG. This gap also allows for a given ex-
pansion of the tank wall, which is a result of the Type A tank design. The tank
adjusts to the gas pressure due to its flexible structure. Therefore, it is very impor-
tant to control the pressure increase, which must remain within a very limited
pressure range (defined as non-pressurised tank), as otherwise structural dam-
ages would occur.
Figure 4-20 Section view of a free-standing Type A tank
SM-0740
Fuel tank
wall
Ship hull
Insulation
Fixtures
SM-0741
Primary
barrier
Secondary
barrier
Insulation
Bulkhead
Inspection
space
Support
To Next Page
Loading...
