This configuration is seemingly becoming popular. A rupture plate upstream of a PSV protects against fouling, corrosion, and premature wear.
In a gas case, you would run your PSV analysis per usual, but include the load(s) between the burst plate and and relief valve.
I can't really envision a true liquid packed scenario. This would require placing inert liquid in the line.
A liquid line with a gas-filled cavity between the RD and RV would however be commonplace. How would you estimate loads upon piping?
In my mind, there's an instantaneous impulse applied to the piping at the bursting instance, but also when the fluid halts at the PSV, you'll also have fluid hammer.
As the RD is at a set point below the PSV setting, the PSV need not even fire, but if it does, you have another hammer event upstream the PSV, and then what happens downstream of the PSV is a function of size of pipe and superficial velocity, but the liquid could come out as a mist, one continuous liquid front, liquid slugs, or work as "open" channel flow.
What are your thoughts?