Pneumatic Test Pressure for External Pressure Vessel

[Abhayk]

Dear Experts,

I have designed a pressure vessel subjected to an external pressure of 15 psi. I want to know whether this vessel requires a pneumatic test as per ASME Section VIII, Div-1, UG-99(f). I am relicating the statement here - "Single-wall vessels designed for a vacuum or partial vacuum only, and chambers of multichamber vessels designed for a vacuum or partial vacuum only, shall be subjected to an internal hydrostatic test or when a hydrostatic test is not practicable, to a pneumatic test in accordance with the provisions of UG-100. Either type of test shall be made at a pressure not less than 1.3 times difference between normal atmospheric pressure and the minimum design internal absolute pressure"

I am confused with this "minimum designed internal absolute pressure". In my case, there is no design absolute internal pressure! Shall I consider the internal design pressure to be zero? or shall I calculate internal MAWP for the design?

 

[SnTMan]

Your internal design pressure is -15 psi gage or zero psi absolute, assuming your "15 psi external" is a gage pressure. Your difference either way is 15 psi differential and test pressure is 20 psig internal.