Summary

This article lists the standard effective orifice areas for the orifice designations found in API RP 526 5th edition. These orifice designations set the minimum effective orifice area which a relief valve must have to meet the API 526 requirements and must be used with the sizing equations in API RP 520 Part I.



Effective Orifice Areas and Letter Designations

Orifice Designation
-
Effective Orifice Area
Inch2
Effective Orifice Area
mm2
D0.11071
E0.196126
F0.307198
G0.503325
H0.785506
J1.287830
K1.8381,186
L2.8531,841
M3.602,323
N4.342,800
P6.384,116
Q11.057,129
R16.0010,323
T26.0016,774
Note: Values are reported as inches in the standard, above they have been converted to millimeters with a precision of 1.