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Well Control Surface Equipment 153

Figure 4.9 Choke damage.
Downstream pressure 5 1500 psi.

6500 2 1500
5 0:77:
6500
In this example, damage is likely to occur.

4.6 GATE VALVES

Gate valves are designed to create a seal, shutting off flow through a
line by means of a gate moving within the body of the valve. They are
the preferred type of valve for surface well control installations, since they
can hold high differential pressure, and are generally reliable, easy to
maintain, and simple to use. Gate valves are on/off valves and should
never be used to choke or regulate flow; doing so risks damage to the
gate, seat, and valve body and can lead to a loss of containment.
The many gate valves that are used with well control surface equip-
ment are mostly manually operated. For surface installations, the API 5C
does not make any recommendations concerning the use of actuated
valves in the choke line or choke manifold. It does, however, recommend
the use of an actuated valve in the kill line for pressure above 5000 psi.
Many drilling contractors and operating companies will use more that the