The valve backseat test is performed in the valve with backseat feature. The test shall be performed based on valve manufacturer approved test procedure. The requirement for the test is addressed in API Std. 598.
The backseat feature is a feature that allows valve packing being replaced while it is in the service.
The valve shall be mounted in test bench with fully opened position and valve ends closed. The packing gland shall be loose or packing not installed. The valve body shall be subjected to hydrostatic pressure, and no leak is permissible from packing and packing gland.
The test pressure shall not be less than 110% maximum allowable pressure at 38 °C (100 °F). For example, if you have a 900 Ib, 20 inch valve with A216 Gr. WCB material, your MAP will be 2252 psi (as per Table 2-1.1 ASME B16.34). The 110 % of this value will be 2477 psi. So your backseat test pressure will be 2477 psi.
The valve test duration depends on the valve size as per API Std 598. The test duration is 15 seconds for valve less than 2 inch, 60 seconds for valves greater than 2 inch
The valve packing gland shall be closely inspected while it is under backseat test pressure. Similar to valve shell test, no leak is acceptable for backseat test.
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