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I am currently working on an LNG job and a question had come up as to the the minimum volume of blocked-in pipework (between 2 isolation valves) that require the addition of a Thermal PSV.
I have some very small inventories (of the order of 5 litres) on the LNG piping; the LNG will vaporise when blocked in - operating temp is about -165 Deg.C!!.
Does anyone have an idea when I should apply a TSV (inventory?), or should ALL sections on the piping system that can be blocked in have a TSV.
To get an idea of the pressure developed on heating a packed liquid you may divide the absolute values of the cubic thermal expansion of the fluid
α = (1/ V)(∂ V/∂T)p
by its isothermal compressibility
κ = -(1/ V) (∂ V/∂ p)T
for the envisaged temperature range.
α and κ can be estimated from tables; α from the density changes, and κ from the sound speed in the liquid.
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