Valves need to guarantee workplace safety without leaking money
30 May 2018
Pressure Relief Valves perform an essential role in ensuring safety in the workplace but leakage is an issue that needs addressing in order to control unwanted expense, explains Roger Bours.
In industrial processes, often working under pressure, safety is generally handled through the use of Pressure Relief Valves (PRVs).
The use of these devices is preferred as they ensure the safe operation of processes as they reclose after the incidental overpressure has been handled. Being essential safety devices the optimal performance of these critical PRVs is paramount.
The pressure relief valve is designed to contain the pressurised media within the sealed system, however, the reality is that most PRVs will demonstrate some leakage.
API 576 is the only industry standard currently available defining acceptable levels of leakage through conventional PRVs. Where the main objective of the PRV is to protect the installation against unacceptable overpressure, leakage – even when slight – can lead to additional costs and production downtime.
Where critical components of the PRV may be suffering from damage, created by ongoing exposure to corrosion or erosion, important investments will need to be made to have spare parts readily available.
Where pressure relief valves discharge into a common header system, the collective and continuous leakage of media from all connected PRVs may result in a base load on the emergency handling system or equipment which will increase the need for maintenance. With the base load increase resulting from leakage, there is a need to consider capacity increase of the emergency handling system. Last but not least increasingly stringent emission restrictions with related penalties are driving the industry to reduce the ongoing leakage of all devices, including PRVs.
These issues can be easily resolved by introducing by isolating the valve with a rupture disc (Fike’s ValveGuard is one example): the use of an upstream rupture disc device will eliminate any leakage and the resulting risk for corrosion or erosion on the critical PRV components.
The rupture disc creates a leak tight seal which will burst when the specified overpressure is reached, allowing the PRV to discharge. Due to the fact that the PRV is not continuously exposed to process media, major reductions in initial investments can be achieved through the selection of less costly materials of construction for the PRVs.
The rupture disc, made from suitable corrosion resistant material, will isolate the PRV from such exposure. By adding a rupture disc to the PRV outlet the occasional back pressure can be kept away from the PRV valve internals, allowing for the balanced bellows to be avoided.
By doing this to isolate the valve, the typical PRV leakage of media is reduced dramatically, the base load on the downstream material handling system (flare, knock out drum, neutralizer, etc.) is also reduced which then avoids unnecessary investments and penalties for emissions. It will reduce downtime, emissions, corrosion, capital investments, maintenance costs and spare parts inventory while the reliability of the safety system is kept at the highest level.
Simply put, it can help to keep the cost of ownership of the process pressure safety system under your control.
Roger Bours is director, pressure relief at Fike Corporation
