Design Pressure and Operating Pressure
The maximum operating pressure (Po), specified by process design engineers, is the maximum internal pressure that will occur under normal process conditions. The design pressure (Pd) is determined by adding a margin to the maximum operating pressure (Po) to allow for pressure surges above Po (without lifting the pressure safety relief valve).
Po should be increased by the following minimum margins to obtain Pd.
Po, psig Margin
0—170 25 psi
170—300 0.15 x Po
300—450 45 psi
450 + 0.10 x Po
These margins may have to be increased if the process designers anticipate higher pressure surges because of the characteristics of the process.
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