What is ESDV (Emergency shutdown Valve)?
ESD valves are used to isolate the facilities in emergency situations. An ESD (emergency shutdown) valve is a valve fitted with a spring return actuator, allowing the valve to be closed by the actuator spring when the actuator pressure signal is released.
Shutdown valves (SDV) are widely used to reduce the escalation of hazardous from one system to another in the oil and gas production process for safe and proper isolation purposes. General shutdown valve is controlled by a high integrity Emergency Shutdown System (ESDS).
ESD valves are usually quarter turned ball valves, but they can also be sliding stem gate valves or other types, although less common.
Main features of ESD valves:
Tie Shut Off:
Zero / minimum leakage is required as a shutdown valve for a system. The seat leakage check per API 508 and/or ISO 5208 shall generally be passed by a shutdown valve seat leakage.
Firesafe:
It is expected that the shutdown valve will operate promptly even if it exposes to external fire attacks. The shutdown valve body is therefore known as API 607 fire for soft seated valves or API 6FA for API 6A & API 6D valves or BS 6755 Part 2 fire valves.
Fast action:
A shutdown valve should act quickly to reduce risk escalation. In particular, the excellent system in rapid action is a quarter ball valve.
As a rule of thumb, the shutdown valve should start the shutdown within 10 seconds of activation and the time taken from Full Open to Full Close is within 1-2 seconds per inch of the shutdown valve size.
Fail-safe:
A pneumatic / hydraulic fail-safe spring-return form is required for a shutdown valve actuator. It was usually not possible to close a shutdown valve (FC). There shall be no use of electrical powered type.
Minimum disturbance:
This function was designed to minimize excessive loss of energy. Reduced ball valve (RB) with hole in the middle will mitigate changes in flow path and turbulence. Practically like a tube, the Full Bore (FB) ball valve significantly minimizes the energy lost.
Position switches:
Position switches on the shutdown valve for simple positioning and the status of a shutdown valve for the control room.
Accumulator:
Some shutdown valve may be equipped with accumulator to facilitate valve stroking and /or reopen in the event maloperation.
Physical indicator:
For clear positioning and status of a shutdown valve, the shutdown valve shall be fitted with visible external valve location indicators.
How does ESDV Works?
Full Open Position – Normal Operation
When the valve is in full open position, the ESDV offers limited pressure differential. The full bore ball valve is essentially a tube that reduces the liquid friction of the system.
Full Closed Position – Emergency Situation:
The setpoint pressure was surpassed and the ESDV was completely closed, providing its double-seated model with a bubble-tightened shut-off.
Unlocking Assured by Position Indicator:
The ESDV comes with an easy-to-read location indicator on the actuator, which helps to ensure that the valve is positioned in the open position.
An ESDV must act quickly to minimize the effect of a state of dangerous activity. The development of the quarter-turn ball valve offers a swift operation inherently. In addition, with its equal percentage flow characteristic (high gain), it can not only close easily, but can also greatly reduce the amount of process fluid that passes through.
It is essential to know that the valve is capable of providing the necessary level of safety quality and that the valve can work on demand for shutdown valves used in safety instrumented systems.
Installation location of ESD valves
The ESD valves should be placed near the pipeline riser on larger plants, with a gap of 15 meters between the ESD valves and the nearest system building.
The idea is to create an ESD “boundary” whereby all piping and vessels on the “facility side” of the ESD valves would be depressured in an emergency situation and the ESD valve is positioned far enough away from possible fire areas to ensure that the valve is not enveloped in the blaze.
Based on the tube configuration, if the idealized design can not be accomplished, it may be desirable to clad the exposed pressurized pipe with fireproof insulation to mitigate the risk to this tube in an ESD situation.
