Pressure Vessel Hydro Testing

I have always considered the use of two pressure relief valves to be a decided advantage. Firstly for redundancy in the event of failure of one valve, and secondly because it allows the vessel to safely remain in operation while a faulty relief valve is replaced, provided of course that you have lockable stop cocks between the vessel and the valves. If using a gate valve, make sure it is mounted such that the operating wheel is lowermost, otherwise a stem failure may cause the valve to fail closed, globe valves must have the pressure side under the seat for the same reason).

Although the regulations allow for an aggregation of relief valve capacities, each valve should be able to relieve any excess pressure by itself, otherwise you may have to shut the system down for repairs. An added advantage here is that the extra valve capacity can provide a greater volume release in the event of a major overload.

As for the safe work practices, I'm sure that a Google search would provide plenty of information on the subject, study it well as this can be a dangerous game

Not sure where you are but here in the USA pressure vessel relief is determined by vessel size and ANSI rating.

ASME Section 8 contains very specific language pertaining to the pressure vessel and size requirements for relief valves.

For instance; A 30,000 Gallon ANSI 150 Class air storage tank is required to have two each relief valves with one valve sized large enough to relieve at 100% of the capacity and the second relief valve sized large enough to relieve at 50% capacity.

I suggest you contract with a reputable pressure vessel testing facility to perform the test and closely observe their procedure before attempting hydro testing on your own.

You're in the wrong business. Quit NOW.

Remotely!

Good Luck, Old Salt