The present invention relates to an assembly comprising a duct, preferably a turbine duct, and at least one segment formed of at least two rigid shells, each shell comprising at least one fixing orifice for fixing to the duct and at least one fixing element at least one boss per shell which boss is fixed to the duct and against which boss the shell rests, such that at least one orifice and one boss face one another, and that the fixing element passes through the orifice facing the boss and is fixed to the boss.