Multilayer structure for transporting or storing gas or for exploiting offshore oil deposits under the sea

A multilayer structure selected from a reservoir, a pipe or a tube for transporting or storing gas or for exploiting oil or gas deposits under the sea, comprising, from the inside to the outside, at least one sealing layer and at least one composite reinforcing layer,

• an innermost composite reinforcing layer being welded to an outermost adjacent sealing layer,
• said at least one sealing layer consisting of a composition predominantly comprising at least one semi-crystalline thermoplastic polymer P1i (i=1 to n, n being the number of sealing layers), the Tm of which, as measured according to ISO 11357-3:2013, is less than 280° C.,
• said at least one semi-crystalline thermoplastic polymer of each sealing layer may be the same or different, and
• at least one of said at least one composite reinforcing layer consisting of a fibrous material in the form of continuous fibers impregnated with a composition predominantly comprising at least one thermoplastic polymer P2j, (j=1 to m, m being the number of reinforcing layers), said thermoplastic polymer P2j having a Tg, as measured according to ISO 11357-3:2013, greater than the maximum temperature of use of said structure (Tu), with Tg ≥Tu+20° C., Tu being greater than 50° C.,
• hydrogen being excluded from said transporting or storing gas, and a multilayer structure selected from a reservoir, a pipe or a tube for transporting or storing hydrogen being excluded,
• wherein each polymer P1i of each sealing layer is partially or fully miscible with each polymer P1i of the adjacent layer(s), each polymer P2j of each reinforcing layer is partially or fully miscible with each polymer P2j of the adjacent layer(s), and the polymer P2j is partially or fully miscible with polymer P1i adjacent thereto,
• the total or partial miscibility of said polymers being defined by the difference in glass transition temperature of the two resins, in the mixture, relative to the difference in glass transition temperature of the two resins, before mixing, and the miscibility being total when said difference is equal to 0, and the miscibility being partial when said difference is different from 0 wherein said polymer P1i and said polymer P2j are polyamides.