Some instruments such as venture flow meters may need some length of straight pipe upstream or downstream to avoid flow turbulence and accurate measurement. However, a 20″ class 150 ball valve as per API 6D standard could have a bore that is approximately 8 mm smaller than the pipe. For example, a 24″ ball valve in duplex material and class 300 has about 2 mm less bore than the pipe. An API 6D FB ball valve in larger sizes such as 24″ and pressure classes 150–600 has a bore much closer to the pipe. The minimum bore in API 6D is usually larger than the ASME B16.34 standard for valves. Therefore, the valve bore should be equal to the pipe diameter when conducting PIG running for API 6D pipeline valves. API 6D bores are counted as full bore but they are not really full bore-which means that the bore of ball valves as per the API 6D standard is less than the pipeline (piping) bore. But the standard does not provide the minimum bore diameter for large size and high-pressure classes (maximum 20″ bore in CL2500 and 36″ bore in CL1500). But a metal seat has the disadvantage of possible leakage, unlike a soft seat, and it is a more costly solution than butterfly and axial control valves due to the valve and the large mounted actuator.ĪPI 6D, the standard for pipeline valves, gives a minimum bore diameter for rating 150–600 equally up to 60″ and separate minimum bore columns for CL900, CL1500, and CL2500 as shown in Table 1.1. On the other hand, the manufacturer stated that a 2-s opening time can be achieved with a metal seat ball valve.

The manufacturer believed that FO of the soft seat ball valve in 2 s could cause damage to the soft seat because of the very quick contact with the ball. The ball valve manufacturer was asked about the possibility of using a soft seat ball valve for this application. In addition, moving the relatively large and heavy ball requires a higher stem torque, a larger actuator, and perhaps a longer opening time. However, a ball valve’s seat and disk are in contact during the opening and closing, which can jeopardize FO. Generally, it is possible to reduce the opening time of the fail open actuated valve by installing a quick exhaust valve on the control panel to release the instrument air from the pneumatic actuator in the fail mode quickly. Karan Sotoodeh, in A Practical Guide to Piping and Valves for the Oil and Gas Industry, 2021 Ball valve selectionīall valves are not recommended for FO applications.

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