Installing a Delta Valves in 2009 & would like feedback on Delta Valves operation without steam purge & its associated leakage to atmosphere (if any). The thought is if the leakage is considerble that we should deploy a N2 back-up system to prevent hydrocarbon release to atmosphere….however very few companies todate have which would suggest that leakage is negligible.
The steam purge is to prevent the resid from entering the valve cavity. If there is a steam pressure loss, leakage can occur, and it will enter the cavity (bonnet).
As with switch & overhead vapor valves, you need steam pressure to prevent the cavity from getting full of resid.
At an extra heavy crude upgrader I worked a few years ago, they do not have any leakage through their bottom delta valve (installed 2005). They did have leakage, through the bolted transition spool. A welded transition spool is recommended.