PSV Metric Units

[Sharik]

Does anyone know if there are 'official' ASME SI units for PSV set pressures and capacities? We've seen set pressures in: kPag, kg/cm2, BARG and capacities (for air) in: NCM/HR, kg/hr and NCM/MIN.

Or is is like the vessel nameplates, data reports, etc. where any SI unit can be used as long as it is consistant between all the documents and nameplates ? (UG 115(b)


Thanks

 

[Sharik]

That is what I thought. Makes things a little confusing when the MAWP on the vessel nameplate is in kPag and the set pressure on the PSV nameplate is in kg/cm2.

I realize the conversions are simple enough but they shouldn't be required.

 

[zdas04]

The plethora of pressure units in "SI" is a very good indication of the impracticality of the "standard" pressure unit (is it "Pa" or "kPa"?). As a user I would insist that every nameplate on a vessel (including PSV's) be couched in the same units. Either Barg or MPa seem to make some sort of sense, but the rest are just noise.

Bottom line in the code is that you have to use units in your calcs that demonstrate that the vessel meets or exceeds both strength and over pressure protection requirements. The units must be constitent within a given calculation, but need not be consistent from calc to calc, just documented.

David

 

[Sharik]

This brings up another point, if a PSV Data Sheet was develooped using kg/cm2 for pressure and kg/hr for capacity (air), is it acceptable for the PSV nameplate to have the set pressure in kPag and the capacity in cm/hr? Or must the PSV nameplate exactly match the Data Sheet for units?