If the equipment is designed for full vacuum (as minimum design pressure).Do the instrumentation in the piping connected to the equipment (Piping is designed for full vacuum) is also designed for full vacuum.If not why?
Instrumentation tubing and other small diameter components designed for the range of industrial pressures commonly encountered are probably already protected for full vaccum by design.
For example: SS Instrument tubing of 1.00 inch and smaller and 0.065 wall thickness can sustain more than 14.7 pisd external pressure.
I think you have to go one step further and ask why is the piping or equipment designed for full vacuum? Can a vacuum be experienced during normal operating conditions? Or can a vacuum only be created during maintenance - for example, when steaming out. The answer to this question will determine whether or not the instrumentation should be specified for vacuum or not.