WHCP installed near the wellhead incorporates all that components installed together in WHCP to do as a control function to operate the well. Wellhead control is used to monitor the flow conditions and to initiate a shutdown of the well.
Generally, four types of shutdown sensors are used to send signals to each wellhead control panel:
- Process and ESD shutdown pilot relays
- Fusible plugs on fire loop systems
- High- and low-pressure sensors from the flowline
- Sand probes in the flowline
Process Shutdown Relays:
The pneumatic wellhead control system must be pressurized in order to operate. Using a pilot relay, the system or device shutdown interface is accomplished. For a “pilot controlled, three-way valve or relay,” the pilot relay is short.
The relay comprises on the other side of a three-way block and bleeds valve as well as a pneumatic piston or a tension pilot. The relay is mounted within the control panel of the wellhead. This pilot relay must reset automatically if the process shutdown device is repressed or brought back to normal.
The three-way pilot valve allows free passage of the pneumatic holding tension with a signal transmitted from the remote device or platform shutdown system. The relay will switch, block the supply pressure, and vent all the downstream holding pressure when the remote signal is removed.
Manual Reset Relays:
A shutdown signal to the wellhead control system from a plant or platform ESD is usually caused by a possible dangerous or damaging condition that occurs downstream of the wellhead.
It is critical that a manual reset pilot relay is used to design the wellhead shutdown system. There is a knob on one end of the manual reset pilot relay as well as the tension pilot on the other side of a three-way valve. When the knob is pushed or the pilot is depressed, the three-way valve turns and shuts down the ground safety valve.
It means that the system must fly and stay shut down when the shutdown signal is triggered. Clearing the potentially hazardous or damaging situation will not reset the device automatically and will not open the surface safety valve.
High- and low-pressure sensors:
The flow line pressure of the well downstream of the choke is controlled by high and low-pressure sensors. Both the final flowline section and the downstream process equipment are covered by the high-pressure sensor. A leak or flowline breakup is observed using the low-pressure sensor. Pressure sensor criteria for offshore platforms are specified in API RP 14C Section A1.
Typically the pressure sensors are attached in tandem. The supply pressure of the holding circuit is connected to the pilot’s inlet. The pilot’s low-pressure connection is connected to the low-pressure pilot’s inlet connection.
Sand probes are used on flowlines where it is possible to experience erosion due to flowing conditions. Under these conditions, the sand passage will erode the probe and the sensor will be actuated.
The number of sand probe sensor failures may be useful in helping to assess the erosion wear on the flowline when properly placed in the flow line. It is therefore important to carefully record the number and date of occurrence of sand probe failures.
Sand probes should be inserted in a straight run of pipe at least ten feet downstream of the well choke or any other change in piping direction. The pipe downstream of the probe should also be straight for another four feet