In our present Project we have a scenario where we have a emergency depressurization system through an RO. During peak flow the upstream pressure is 21 barg. As critical pressure ratio is 0.55 the downstream pressure is 21*0.55 = 11.55 barg. As such choked flow through orifice happens.
Now the downstream goes to Flare the design pressure of this header is 3.5 barg. Now how to protect this 3.5 barg header and what will happen to this excess pressure .
Back calculation from flare to the downstream of RO predicts only 1.5 barg at this peak flow.