•   Since the outer casing of an Externally Pressurized Metal Expansion Joint (EPMEJ) absorbs the full internal pressure thrust during an anchor failure event, what specialized hydrostatic testing procedures are implemented to ensure the structural soundness and weld integrity of this critical secondary pressure boundary?

     The outer casing of an Externally ressurized Metal Expansion Joint plays a vital safety role in system integrity. Under normal operating conditions, the casing serves primarily as a pressure balance housing. However, during a catastrophic anchor failure, the entire internal pressure thrust is instantaneously transferred to the casing and its restraining structure. This converts the casing into a secondary containment pressure vessel. To address this critical gap, a dedicated Casing Containment Test (CCT) protocol is implemented. During this specialized hydrostatic test, the outer casing of the Steel Expansion Bellow assembly is isolated and pressurized independently, typically to 1.5 times the system design pressure ($P_d$). This ensures that the casing structure, weld seams, and end connections can safely sustain emergency loading conditions without structural compromise. By validating the casing as an independent pressure boundary, the CCT provides an essential layer of safety assurance beyond traditional fatigue testing of the bellows.

•   How does an Externally Pressurized Metal Expansion Joint (EPMEJ) inherently prevent bellows column squirm?

     Bellows column squirm is a form of lateral instability where the bellows centerline bends or buckles under internal pressure. The Externally Pressurized Metal Expansion Joint (EPMEJ) overcomes this limitation by reversing the pressure application. Instead of acting on the internal surface of the Metal Expansion Bellow, the process media pressure is redirected to the exterior of the bellows convolutions. This creates a hydrostatic pressure jacket that uniformly supports the bellows from the outside. This external pressurization provides a powerful stabilizing effect, dramatically improving the bellows’ resistance to buckling and squirm. As a result, the Steel Expansion Bellow can safely accommodate long axial movements while maintaining full structural integrity.

•   Why is a drain coupling essential on an Externally Pressurized Metal Expansion Joint?

     While the internal Metal Expansion Bellow of an Externally Pressurized Metal Expansion Joint (EPMEJ) is typically self-draining, the outer pressure casing that surrounds it can accumulate condensate or trapped fluid over time. This retained liquid may lead to corrosion of the casing, or even create conditions for water hammer or flash-steam erosion when transitioning between hot and cold operation. To eliminate these risks, a drain coupling is installed on the outer casing. This simple yet critical feature allows any accumulated fluid to be safely drained, ensuring that the interstitial space between the casing and the Steel Expansion Bellow remains dry. By keeping the casing free of condensate, the drain coupling protects against corrosion, prevents sudden hydraulic shock, and significantly extends the service life of the Metal Expansion Joint.