Emerson’s Adam Attig & Ricardo Garcia presented Eliminating Unseen Threats: Innovation in Bellows Leak Detection for PRVs at the 2024 4C Health, Safety & Environmental Conference.
They opened their presentation by defining the concept of back pressure. Back pressure is pressure present at the outlet of the pressure relief valve (PRV). There are two main categories of back pressure: built-up and superimposed. Back pressure can affect the valve’s operation, so it is paramount to have back pressure information when sizing and selecting a PRV.
Common Sources of back pressure include:
- Flare Header System
- Discharge piping
- Vapor recovery
- Common Header
- Secondary Containment system
- Recovery System
Flowing back pressure will build up in the body bowl and the bonnet area where the spring chamber is located. This superimposed back pressure can be constant or variable. Constant superimposed back pressure is when the pressure at the outlet of the PRV does not change. This type of backpressure can be accounted for when setting the valve’s set pressure—cold differential test pressure (CDTP).
Variable superimposed back pressure at the outlet of the PRV is a changing pressure. This type of backpressure cannot be accounted for when setting the valve, as the set pressure would become unpredictable. A balanced valve is needed in this instance.
Balanced Pressure Relief Valve
Balanced pressure relief valves all have technologies designed to mitigate the effects of back pressure.
These leaks create safety and environmental compliance issues through fugitive emissions. Since most PRVs have no diagnostics associated with them, they are often not spotted until routine rounds with sniffers notice the leak.
The Crosby™ Bellows Leak Detection solution is designed to detect bellows damage when it occurs is based on two proven technologies—a Crosby back pressure balancing piston and Rosemount pressure transmitter. The intelligence provided by the pressure transmitter provides instant notification of a bellows rupture.
The pressure transmitter is plumbed into the piston bellow chamber to detect the pressure buildup in the chamber upon a bellows rupture. The pressure measurement enables volumetric calculations of emissions going to the atmosphere through the bonnet vent.
Because these events are timestamped, improved root cause failure analysis can be performed by correlating with other system information.
This bellows leak detection solution helps enable safer operations, using the backup piston to ensure balanced operation after a bellows rupture. Instant notification of a rupture enhances reliability and reduces fugitive emissions, enabling faster repair operations.
Learn more about this innovative bellows leak detection solution.
