API 598 is the principle testing standard utilize by API for its valve standard, the allowable leakage and a couple key notes are put together for quick references purposes. The following table is for the allowable closure leak value testing with water at 1.1 times rated pressure and gas at low pressure (about 80 psig) or high pressure if specified by customer.
For Check valve allowable leakage rate, please see API 598 Check Valve Allowable Leakage Rate.
API 598 Leakage Rate
| Size (NPS) | Liquid (drops/min) | Liquid (ml/min) | Gas (bub/min) | Gas (ml/min) |
|---|---|---|---|---|
| 2 | 0 | 0 | 0 | 0 |
| 2.5 | 5 | 0.3125 | 10 | 0.1 |
| 3 | 6 | 0.375 | 12 | 0.12 |
| 4 | 8 | 0.5 | 16 | 0.16 |
| 5 | 10 | 0.625 | 20 | 0.2 |
| 6 | 12 | 0.75 | 24 | 0.24 |
| 8 | 16 | 1 | 32 | 0.32 |
| 10 | 20 | 1.25 | 40 | 0.4 |
| 12 | 24 | 1.5 | 48 | 0.48 |
| 14 | 28 | 1.75 | 56 | 0.56 |
| 16 | 32 | 2 | 64 | 0.64 |
| 18 | 36 | 2.25 | 72 | 0.72 |
| 20 | 40 | 2.5 | 80 | 0.8 |
| 24 | 48 | 3 | 96 | 0.96 |
| 26 | 52 | 3.25 | 104 | 1.04 |
| 28 | 56 | 3.5 | 112 | 1.12 |
| 30 | 60 | 3.75 | 120 | 1.2 |
| 32 | 64 | 4 | 128 | 1.28 |
| 36 | 72 | 4.5 | 144 | 1.44 |
| 40 | 80 | 5 | 160 | 1.6 |
| 42 | 84 | 5.25 | 168 | 1.68 |
| 48 | 96 | 6 | 192 | 1.92 |
| 52 | 104 | 6.5 | 208 | 2.08 |
| 56 | 112 | 7 | 224 | 2.24 |
| 60 | 120 | 7.5 | 240 | 2.4 |
| 64 | 128 | 8 | 256 | 2.56 |
| 68 | 136 | 8.5 | 272 | 2.72 |
| 72 | 144 | 9 | 288 | 2.88 |
| 76 | 152 | 9.5 | 304 | 3.04 |
| 80 | 160 | 10 | 320 | 3.2 |
For resilient seated valves, such as slab gate valve with ptfe seating surfaces, there are no allowable visible leakage through the seating surface. The millilitre volume have been converted using note 1 from API 598 Table.
For help with conversion between NPS vs DN, please check this table.
For reduced bore valves, such as a 12×10 NPS trunnion ball valve, the valve shall be tested according to 12 NPS values unless otherwise agreed.
For counting bubbles/minutes, 0 bubbles mean that during the test duration, there are less than 1 bubble per minute.
Finally, if direct visual identification is not possible, a tube with an ID of 2 to 4 mm can be connected to the proper area of the valve and submerge 3 to 6 mm into water for observation for bubble count.
API 598 Test Duration
| NPS | Shell (s) | Backseat (s) | Check Valve Closure (s) | Other Valves Closure (s) |
|---|---|---|---|---|
| ≤2 | 15 | 15 | 60 | 15 |
| 2.5 to 6 | 60 | 60 | 60 | 60 |
| 8 to 12 | 120 | 60 | 120 | 120 |
| ≥14 | 600 | 60 | 120 | 120 |
For a summary of API 598, please see the summary page.
For access to API 598 standard, please check. IHS | Techstreet |
For information on additional valve standards please see Standards Summaries.