Half Pipe Jacket Reliefs

We are evaluting relief devices for half pipe jackets on our tanks. The typical case of two phase flow of a liquid filled system results in a large device even though there is little actual quantity in the jacket.

We have adjusted for the insulation but still end up needing an "E" or "F" orifice depending on the set pressure. When we ignore jacket insulation, the size of the device becomes absurd considering the half pipe jacket is only a 3" or 3.5" OD.

Who else is struggling with high calculated values? The calculation methods only look at surface area and no account is made for the fact the jacket has very little volume and the coiled half pipe is more akin to a piping system than a "pressure vessel."

tia,

Tom