Wellhead Control Systems – Fail-Safe Design

Two types of failure modes are described in Section 1300, “Process Alarm and Shutdown Systems.” One mode is de-energized-to-trip and the other energized-totrip. All wellhead control systems and components must use the de-energized-to-trip design, which means that the system will be a fail-safe design.

As previously mentioned, the fail-safe design is accomplished by maintaining a pneumatic pressure holding circuit on all the components of the control system located at the surface of the wellhead and a hydraulic pressure on the SCSSV during normal operation.

A typical simplified pneumatic circuit for a wellhead control of an SSV is shown in Figure 1700-6.

Simplified Wellhead Control for SSV

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