Karan Sotoodeh - A Practical Guide to Piping and Valves for the Oil and Gas Industry

Ball valves; Design; Testing; Packing and preservation; Oil and gas industry

Ball valves are usually selected for process and aggressive services containing hydrocarbon oil and gas. A ball valve (see ) is used for on/off purposes and not throttling (flow control).

Fig. 1.1 Ball valve.

Injection lines that inject seawater into the reservoirs for enhanced oil recovery in high-pressure classes are mixed with hydrocarbon services. Ball valves are the best valves for on/off purposes in this type of application. Alternative choices such as butterfly and wedge gate valves are not as robust as ball valves in process services.

Ball valves for water injection lines in the offshore industry are manufactured in exotic materials such as 25 chromium super duplex, in medium to large sizes such as 12, 14, and 16, and in high-pressure classes such as class 1500. Although a butterfly valve is cheaper than a ball valve, it is not recommended for a seawater injection line since the fluid is aggressive, contains hydrocarbon, and flows at high pressure. Butterfly valves may not be robust enough for high-pressure and aggressive process services containing hydrocarbons.

Wedge-type gate valves (see ) are also not recommended for this application, for several reasons.

• Wedge gate valves that are 12 tall or taller may interfere with operator access to the handwheel.
• Actuation of wedge gate valves must be done accurately to avoid seat and wedge overtorqueing and resulting damages. Overtorqueing a wedge gate valve increases the risk of stem bending.
• Small-size ball valves that are 2, 1, or smaller, can be less expensive than wedge gate valves in the same size and pressure class due to less material usage and weight.
• Wedge gate valves can be heavier and more costly due to their taller height and yoke arrangement.
• 1 or ball valves can be used instead of wedge gate valves for vent-and-drain purposes.
• Quarter-turn ball valves can be operated faster and more easily than gate valves. These valves allow a 90-degree turn of the stem and ball, providing for full opening to full closing position, and vice versa.

Fig. 1.2 Wedge gate valve.

Actuated ball valves with emergency shutdown (ESD) functions are used for blowdown purposes to release overpressure piping or equipment to the flare (see ).

Fig. 1.3 Blowdown valve.

When compared to through conduit gate (TCG) valves, ball valves have the advantage of being more compact vertically. TCG valves occupy more space vertically, especially if they are actuated due to vertically mounted actuation.

Although ball valves may be more expensive than TCG valves in smaller sizes, TCG valves in larger sizes such as 30 and 38 are usually more expensive than ball valves. discusses the selection of a ball valve instead of a TCG valve for the inlet of a 24-class 1500 separator.

Ball valves are not recommended for fast-opening applications. Generally, it is possible to reduce the opening time of a fail-open actuated valve through installation of a quick exhaust valve on the control panel to release the instrument air from the pneumatic actuator in the fail mode quickly. However, ball-valve seats and disks are in contact during the opening and closing, which can jeopardize the fast opening characteristic. In addition, moving the relatively large and heavy ball requires higher stem torque, a larger actuator, and perhaps a longer opening time. A ball-valve manufacturer was asked about using a soft-seat ball valve for this application, but the manufacturer believed that the fast opening of a soft-seat ball valve in 2 s could result in damage to the soft seat because of rapid contact with the ball.