Emergency shut down system
Emergency shut down system
The emergency shutdown system (ESD) controls the flowline valve
actuator and, if necessary, an additional surface safety valve
located upstream of the choke. Additional push-button stations can
be located, for example, at the steam heat exchanger, separator,
gauge tank and burner pedestals.
The ESD system can be complemented by high or low level
alarms.
The pilots initiate well closure when the pressure rises above a
high level threshold (perhaps due to choke plugging) or falls below
a low level threshold (due to flowline leakage).
The ESD system consists of an ESD control skid that includes a
pump, hydraulic tank, air reservoir and three hose reels. The first
hose reel contains 20 meters of high pressure hose for a shutdown
valve actuator. The other two reels each contain 90 meters of low
pressure hose for connecting the push button stations.
The ESD actuator system is designed for use with any
single-action, fail-safe actuator, provided required hydraulic
pressure does not exceed 6000 psi.
Emergency shutdown system
The well test emergency shut down allows remote closing of a
flowline valve should quick closure be necessary due to pipe leak
or burst, separator malfunction, fire, etc.
The system is suitable for connection to the actuated flowhead
valve or any other single action, failsafe, hydraulic actuated
valve.
The equipment consists of a pneumatic console which pressurizes
the various pneumatic and hydraulic circuits, push-pull shutdown
stations and in some instances, hi-lo pressure pilots.
In an emergency, either the pressure pilots or the manual ESD
stations release the air pressure in the system. The hydraulic
circuit is then bed off by the interface valve in the console and
the failsafe valve closes.
Equipment to be RITE maintained as per the ESD maintenance
manual M 834455 are the following :
Pressure pilots
Hi pilot
If the pilot senses the flowline pressure is below the preset
value (fixed by the adjustable spring force) air supply pressure is
retained between the pilot and the interface valve in the console.
Hydraulic pressure from the pump is allowed to go to the hydraulic
actuator keeping the shutdown valve open.
When the flowline pressure rises above the preset spring value,
air is bled off at the pilot, the interface valve vents the
hydraulic pressure from the actuator, and the shutdown valve
closes.
Lo pilotIf the pilot senses the flowline pressure is above the
preset value (fixed by the adjustable spring force) air supply
pressure is retained between the pilot and the interface valve in
the console. Hydraulic pressure from the pump is allowed to go to
the hydraulic actuator keeping the shutdown valve open.
When the flowline pressure falls below the preset spring value,
air is bled off at the pilot, the interface valve vents the
hydraulic pressure from the actuator, and the shutdown valve
closes.
Check of ESD equipment
Coming standard with the ESD console are normally 4 remore ESD
stations. The client may have some specific safety requirement, but
these are typically placed on the rig in the follwing locations
:
-Drillers dog house
-Well test area
-Main deck
-Safe exit from the drill floor.
Lines are run back to the console which is usually located on
the rig floor.The type and specifications of the equipment rigged
up for the well test will dictate the number and type of pressure
pilots required.
Lo pressure pilots
Generally, in a simple flowhead-choke manifold-separator setup,
a lo pressure pilot would be located upstream of the choke manifold
which would be activated in the event of a rupture in the flowline
connecting the choke manifold and the flowhead. Another lo pressure
pilot would be located upstream of the separator which would be
activated in the event of a rupture in the flowline connecting the
separator and the choke manifold.
With all pilots isolated, set the ESD system so the flowhead
safety valve remains open and close off the segment to be checked.
Downstream there should be an open path for pressure to vent to the
burner.
Pressure up the line segment slowly, above the setting pressure
of the lo pilot, and switch the pilot on line.
Bleed off the pressure slowly and observe the pilot trip, the
ESD activate and the SSD close.
Hi pressure pilot
In the same simple testing setup, a high pressure pilot would be
located upstream of the separator which would be activated in the
event of a plug in the flowline connecting the separator and the
choke manifold or a blockage of the separator outlet.
With all pilots isolated, set the ESD system so the flowhead
safety valve remains open and close off the segment to be checked.
Downstream there should be an open path for pressure to vent to the
burner.
Switch the hi pressure pilot on line, pressure up the line
segment slowly and observe the pilot trip, the ESD activate and the
SSD close.
Testing of the pilots is complete.
