The invention describes the use of compositions containing at least one thermoplastic polymer and an epoxy resin modified by at least one aromatic polyamine to coat surfaces, especially pipes through which oil is transported. The polymer compositions used contain at least one thermoplastic polymer which is preferably amorphous selected from the group formed by polysulphones, polyetherimides and polyphenylene esters and at least one epoxy resin modified by at least one aromatic polyamine containing at least two primary amine groups in its molecule. Different layers of polymers are deposited on different types of surface, more particularly as internal and external coatings for conduits. The invention also provides a surface coating comprising such compositions. Multi-layer coatings are also produced.