Unlike PSV the rupture discs are inline with the flow. PSV flows take 90 degree turn from inlet to outlet. The effect of reaction force on piping while the PSV relieves is much more than that while a rupture disc bursts. Probably this is the reason why we are not calculating reaction force for rupture disc installation.
There is a commonly used equation for rupture disc force that dated back to an article in Hydrocarbon Processing years ago, by a guy named Driscoll. The force is calculated as: F = 0.63 x DAF x (kc+0.2) x carrier area x pressure, in consistent units.
Why there is a 0.63 factor and kc+0.2 I am not sure. It does not fit any fluid dynamics that I am aware of. I was interested in whether there are any manufacturer guidelines perhaps related back to test results ?
API 520 Pt II reaction force guidance and equations are for all type of relief devices. Note that the API terminology (PRD) means pressure relief devices, which includes disks and PSVs.
Of course, the flowrate through the disk is continuously changing, so you'll want to calculate the reaction force based on the initial flowrate and not the required relief flowrate. The initial flow is usually much higher, thus it creates a much higher reaction force.
