Valve Pressure Testing as per API-598/API 6D

Valves are mechanical devices that control the flow and pressure within a system or process. They are essential components of a piping system that conveys liquids, gases, vapors, slurries etc..

All valves have the following basic parts.. the body, bonnet, trim (internal elements), actuator, and packing.

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The valve body, sometimes called the shell, is the primary boundary of a pressure valve.

The cover for the opening in the body is the bonnet, and it is the second most important boundary of a pressure valve

The removable and replaceable valve internal parts?that come in contact with the flow medium are collectively termed as?Valve trim. These parts include valve seat(s), disc, glands, spacers, guides, bushings, and internal springs.?

Disc?The disc is the part that allows, throttles, or stops the flow, depending on its position. In the case of a plug or a ball valve, the disc is called a plug or a ball. The disk is the third most important primary pressure boundary.

Seat(s)?The seat or seal rings provide the seating surface for the disk. A valve may have one or more seats. In the case of a globe or a swing-check valve, there is usually one seat, which forms a seal with the disc to stop the flow.

The valve stem provides the necessary movement to the disc, plug or the ball for opening or closing the valve, and is responsible for the proper positioning of the disk.

Pressure testing of Valves.

The following tests and examinations are specified in API-598,

a) shell test,

b) backseat test,

c) low-pressure closure test,

d) high-pressure closure test,

e) double block and bleed high-pressure closure test,

f) visual examination of castings,

g) high-pressure pneumatic shell test.

?backseat test, A pressure test used to verify leakage past the stem or shaft to bonnet seal (backseat).

shell test, A pressure test in excess of the cold working pressure (CWP) rating of the valve for the purpose of validating the soundness and strength of the valve pressure-containing structures.

The pneumatic shell test pressure shall be 110 % of the maximum allowable pressure at 38 °C (100 °F) or as specified in the purchase order. Visible leakage is not allowed

For the shell, high-pressure backseat, and high-pressure closure tests, the test fluid shall be air, inert gas, kerosene, water, or a noncorrosive liquid with a viscosity not higher than that of water.

For the liquid test, 1 mL is considered equivalent to 16 drops. For the gas test 1 mL is considered equivalent to 100 bubbles.

The shell test pressure shall be as listed in Table 2-API-598

Backseat and closure test pressures shall be as listed in Table 3-API-598

For each type of test, the required test pressure shall be maintained for at least the minimum time specified in Table 4-API-598