When inspecting your piping in vessels do you emphasize size changes in elbows after catalyst beds? My experience has shown that a momentum change happens to your process flow and a lot of erosion can occur in the post catalyst bed beads. The issue comes from bed beating, normally a silicone or ceramic structure, that is highly erosive and similar to sandpaper. These points of change of momentum, which are the changes in flow patterns such as expansion or direction, encourage your catalyst beads to impact the surface. This happened to me and I have used this thought to increase the inspection areas consistently throughout operations.