an apparatus and a method for inhibiting metal dusting corrosion of a tubesheet inside a shell - and - tube heat exchanger having at least one exit nozzle for transmitting at least one process fluid from the shell - and - tube heat exchanger include and use : an isolation baffle disposed inside the shell - and - tube heat exchanger at a location between a first exit nozzle and the tubesheet , whereby an isolated space exists between the tubesheet and the isolation baffle ; and a means for purging the isolated space with a purging fluid .