Regarding What is Orifice and its application, please refer to FLOW METER AND ORIFICE PLATE
Introduction of Erosion on Piping downstream around Orifice installation area:
Typical erosion in piping systems often occurs on the flow with the exclusion of turbulence, for example. Where the flow direction changes (elbow, tee) or downstream of the orifice in the pipe system. In addition, Flow is a two-phase (with solid or liquid particles) and has a higher speed of erosion.
In the Orifice installation area, the Flow Orifice (FO) is used to block the flow and reduce the pressure of Steam down to allow it to become condensate, but since Steam has passed from Orifice that cannot be fully condensed in this area, the turbulence of Flow will exist.