NOVELTY - The joint (14) has a first structure (10) fastened to a second structure (12) at a joint unit submerged in water (16). A flexible membrane (30) is fixed over the joint unit and provided with two ends (32, 34) connected to the two structures. The membrane defines an enclosed space (36) surrounding the joint unit. The membrane is exposed to the enclosed space at exterior pressure, where pressure inside an enclosed space of the membrane is equal to exterior pressure outside the membrane. Protective liquid (38) is filled within the enclosed space in an amount sufficient to cover the joint unit.    USE - Protected submerged pipe joint e.g. flanged joint, threaded joint and welded joint (all claimed), for use in an ocean thermal energy conversion system, an offshore oil and gas system, a naval vessel and a submarine for connecting elements such as two pipes or pipe and valve, submerged in water e.g. sea water. Can also be used for a pressure vessel joint, a pump joint, a heat exchanger joint, an instrumentation joint and a filter joint.    ADVANTAGE - The joint ensures that the fluid protecting the joint can remain in prolonged exposure with the joint to extend life of the joint compared to direct submersion of the joint in the corrosive fluid to be used. The portion or majority of the enclosure can be made from non-flexible materials with the remaining portion being made from flexible material to sufficiently deflect to equalize pressure from inside to outside so as to allow the potential for loose tolerances and easier manufacture and installation. The joint utilizes a bladder to ensure that the pressure inside the enclosed space is equal to the outside pressure.    DETAILED DESCRIPTION - The protective liquid is non-electrically conductive liquid such as dielectric liquid, grease or fresh water. The flexible membrane is made of polymeric material, elastomeric material or water impermeable fabric. An INDEPENDENT CLAIM is also included for a method for protecting a joint between a first structure and a second structure.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of a protected submerged pipe joint.    Structures (10, 12)    Protected submerged pipe joint (14)    Water (16)    Flexible membrane (30)    Ends of flexible membrane (32, 34)    Enclosed space (36)    Protective liquid (38)