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 |
|---|---|---|
| D | 0.110 | 71 |
| E | 0.196 | 126 |
| F | 0.307 | 198 |
| G | 0.503 | 325 |
| H | 0.785 | 506 |
| J | 1.287 | 830 |
| K | 1.838 | 1,186 |
| L | 2.853 | 1,841 |
| M | 3.60 | 2,323 |
| N | 4.34 | 2,800 |
| P | 6.38 | 4,116 |
| Q | 11.05 | 7,129 |
| R | 16.00 | 10,323 |
| T | 26.00 | 16,774 |
Note: Values are reported as inches in the standard, above they have been converted to millimeters with a precision of 1.
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