Hi CNSK,
I know this reply has been a long time since your post, but I want to put it here for others who are finding an experience operating a gas centrifugal compressor in choke, overload or stonewall region.
I've experienced a compressor had been running continuously within overload region for more than 2 months due to the unavailability of the parallel compressor. Overload region mentioned here means that the operating point of the compressor falls to the right of the stone wall line of the recommended operating map. The compressor delivered more than the design flow by 2MMscmd which was a significant increase in its capacity.
All compressor parameters including bearing vibration, lube oil temperature, bearing temperature were within their alarms. However, there was only a parameter, thrust bearing temperature, increased dramatically up to its alarm of over 100degC. The oil additives in lube oil has their limitation, and it is 90degC for our case. Normally, it is below 70degC. Consequently, the thrust bearing temperature was only the limit for our compressor at that time. Three years later, the compressor has been fine.
Of course, operating the compressor in overload region induces inaccurate aerodynamics prediction and impact on mechanical integrity. The tip Mach number of this condition shall be checked by the OEM, it was 0.45 for our case.
Hope it helps.