design&test pressure of nitrogen evaporator 1

[Jens12]

I'm a mechanical engineer and have to check data sheets for a nitrogen evaporator. The operating pressure of the nitrogen system itself is about 5 barg, the max. op. pressure of the evaporator is indicated with 35.1 barg and the test pressure is 38.61 barg.
Why is the max. op. pressure so high and, in case this is right, why is the test pressure not 1.5 times the max. op. pressure ?
Many thanks for reply and best regards,
Jens

 

[rzrbk]

Just guessing: the max pressure looks about right to contain nitrogen up past its critical pressure, and the 1.1x pressure test may mean that a pneumatic test is required in lieu of a hydro to reduce the chance of water being left inside the evaporator.

Need to check with the process guy who spec'ed it out to confirm his reasoning.

 

[rzrbk]

I would like to recall the statement about critical pressure, as I'm not sure what good it would do.

But there should be some scenario the Process group thinks could cause high pressure, and the given max pressure will probably be set to eliminate or reduce the need for overpressure protection such as a PSV.