Vapor-tight tanks are horizontal vessels that can usually hold up to 14.7 pounds per square inch (gauge) (1.01 bar(g)).
Connection to a flare allows these systems to be operated in situations with a high hydrogen sulfide content.
In fact, their original intended use was sour crude oil production.
Vapor-tight tanks are frequently packaged with an integral separator, flare stack, and other equipment to form a complete single-well battery.
Because of their small size and portability, they are mostly used in temporary production of oil wells.