Vent headers must be provided with adequate slope for proper drainage and to element low points or pockets. API 521 188.8.131.52.7 recommends 1/4″ per 10 feet.
In addition to above recommendation following also needs to be considered:
- Flare system route
- Total elevation change from 1st discharge location to flare drum
- PSV located higher than the Flare header
- Piping support interval