In liquefied gas operations, what does the term "rollover" describe?

The term "rollover" refers to the phenomenon that occurs when there is a sudden mixing of stratified layers of different density LNG within a storage tank. In a scenario where a tank is partially filled with LNG, variations in composition and temperature can lead to the formation of two or more distinct layers that have differing densities. Over time, if these layers remain undisturbed, they can become stable; however, if an external factor or agitation leads to mixing, a rapid and often violent transition can occur, resulting in the lighter gas rising and the denser liquid sinking. This mixing can release a significant quantity of vapor quickly, which poses safety risks and operational challenges.

Understanding rollover is critical for safely managing LNG operations, as proper measures must be in place to monitor and mitigate the risks associated with this phenomenon. This understanding helps ensure that LNG is handled safely during storage and transfer processes, thereby protecting personnel, equipment, and the environment.