Abstract: A casing provides a hermetically sealed enclosure around a joint between two elongate substrates. The casing comprises two generally cylindrical members, each of which comprises a first open end section and second open end section. The first end section includes a heat-shrinkable sealing member which can be shrunk by heat to form a hermetic seal between the first end section and a substrate passing therethrough. The second open end section of each member can be hermetically sealed to the second open end section of the other member. There is a generally cylindrical flexible connecting section between the first and second end sections. This connecting section can be deformed to permit relative axial movement between the first and second open end sections to provide access to the joint.