A spigot (22) and socket (20) are welded together by inducing a current in an induction member (12) embedded in the weld region. The temperature of the induction member (12) rises until it reaches its Curie temperature, at this point the temperature ceases to rise. The induction member (12) may be embedded in one or both of the spigot (22) and socket (20) or in a separate collar (10) interposed between the two. A welding appliance (30) for inducing current in the induction member may be in the form of a clamp for simultaneously inducing current and clamping the socket (20) onto the spigot (22). A method of forming a socket (20) makes use of extrusion, and includes steps of expanding a tube end, and retracting it over a collar (10) including an induction member (12).