Heat recoverable artiles comprising conductive polymer compositions

A method of joining, repairing or reinforcing substra­tes, particularly polymeric pipes for transporting fluids, e.g. natural gas and water. The method makes use of an article, preferably a heat-recoverable article, which comprises a conductive polymer composition and which is heated to its recovery temperature by passing electrical current through the conductive polymer. Preferably the article is a heat-shrinkable coupler (3). The coupler may make direct contat with and fuse to the pipes (1,2), or there may be an insert between the coupler and the pipes. The article pre­ferably comprises carbon black dispersed in either a sin­tered polymer, particularly ultra high molecular weight polyethylene or a very high molecular weight polymer, par­ticularly polyethylene having a molecular weight greater than 150,000.