In Crude oil tankers and vessels carrying homogeneous cargo, We can use just one line for venting purpose as all the cargo is homogeneous(same). From all the cargo tanks venting pipelines lead to the Mast riser. The mast riser is fitted with a valve (called mast riser valve). Use of mast riser – While loading the pressure inside the cargo tank is released through the mast riser by opening the mast riser valve and also the cargo tank pressure is monitored and if required the mast riser valve is throttled to maintain the cargo tank pressure at certain level. During discharging cargo to avoid negative pressure in the tank, the inert gas is continuously supplied to the cargo tanks.
The exhaust of mast riser must be at least 6m above the deck.