FCCU expansion joints usually incorporate 2-ply testable bellows and each ply endures the design conditions.
The two ply testable bellows will serve as a warning of an urgent problem. A pressure device in the outer ply alerts about the inner ply failure.
The two ply testable bellows also allows inspectors to pressure test during shutdowns.
To prevent an unscheduled shutdown and create a predictable environment, a two-ply testable bellows expansion joint should be installed.
A two-ply testable bellows expansion joint contains a bellows capable of allowing the flow of fluid between the two plies to be monitored by either a gauge or pop-up device.
Wire mesh may be placed between the two plies of bellows material to ensure a flow path between two plies. Two test ports are attached at opposite ends, 180 degrees apart.
Unlike a common multiply bellows, each ply of the two-ply testable bellows can withstand the designed line pressure.
If the inner ply fails, the outer ply shall compensate and endure the designed condition until the planned repair or replacement.