One is Static Equivalence method, to apply force as concentrate force and apply DLF of 1.5-2,
second is dynamic method ( Spectrum and Time History), you have to develop your spectrum curve based on information you have, tutorial has very good example,
you should know what kind of condition of downstream of PSV before PSV openning,
If PSV downstream pipe is empty, the speed of pressure is flow velocity,
if PSV downstrean pipe is fully filled, the speed of pressure is sound velocity (about 1200m/s),
if PSV downstream pipe is partially filled, this will become slug flow, you have to use your engineering judgement to calculate reaction force + slug force,

Hope this will help you,