Our FCCU is an orthoflow and modified for external risers. The reactor gases go to the main fractionator. From the top after condensation the gases go to the compressor. In the event of a compressor failure, there are two valves (one redundant from another) that relieve gases to the flare. These valves are not the anti-surge valve of the compressor. Today the failure mode of these valves is a stationary failure and the other failure closes. We want to transform the failure closes to failure opens. What are the problems for the process? What is the typical failure mode for these valves?