isolation valve before a system relief valve

We just finished replacing the chilled gylcol system here at the WIPP site. The question I have is this…. The system relief valve, I installed an isolation valve before the relief valve for maintenance and calibration purposes. This was done so that the system would not have to be recovered [drained] [35% gylcol solution] to preform maintenance on the relief valve. As long as the valve is locked open with an approved locking system is this againist code?