A welded pipe joint for pipes which are internally lined for carrying corrosive fluids is formed by an internally lined insert extending into the belled end sections of the pipes to be joined and engaging the belled end sections with a mechanical interference fit. The insert, which is provided with a heat shield to retard the transfer of heat during a subsequent welding operation, is held in coaxial alignment with the pipes while the adjacent ends of the pipes are brought together. The adjacent ends of the pipes are finally welded to complete the joint.

A double containment pipe joint assembly is provided with an inner pipe and an outer or containment pipe secured to the joint assembly in concentric relation. The pipe joint assembly includes a first and second fitting coupled together to present end surfaces which can be secured to a length of a primary (inner) and containment (outer) pipe at intervals along the pipeline wherein sections of the pipeline can be removed and repaired without the necessity of removing the whole pipeline, while anchoring the pipes together at spaced locations along the pipeline. The arrangement further allows the pipes to be formed from different materials compatible with the pipe fittings and precludes the necessity of providing flanges on the inner and containment pipes so they can be secured in concentric relationship, lessening the chance for failure. One of the inner and outer fittings has two sections (either separate or cast in one piece) which are secured in mirror-image relation to a ring on the other section. One of the pipe fittings has a tubular section forming a bore therethrough for the passage of fluid from the primary or inner pipe. The other fitting either has tabs or a ring for receiving tabs coupling the fittings together to present end surfaces for securement to the inner and containment (outer) pipes.

A concentric insulating tubular conduit member for use in forming a conduit string such as a tubing string in a subterranean oil or gas well, is disclosed. Each individual conduit comprises concentric inner and outer members rigidly attached at each end. Both the inner and outer tubular members are welded to an intermediate bushing. At least one of the inner and outer members is upset to prevent weakening of the tubular joint at the welded connection. Adjacent tubular conduits can be interconnected by couplings having an outer surface flush with the outer periphery of the two interconnected joints.

An improved insulated tubing string with insulated coupling formed of concentric tubing members insulated from each other to prevent heat from the inner tubing from being conducted to and through the outer tubing. The coupling joins the outer tubing of successive tubing assemblies to provide additional strength to the string and the inner tubing is insulated within the coupling to prevent heat loss at the coupling. The inner tubing is elongated during fabrication and joined to the outer tubing when elongated to reduce heat stress on the string when in use.

A coupling assembly includes a first coupling member, a second coupling member, and a coupling nut disposed over a portion of the second coupling member and threadingly engaging the first coupling member to retain the first and second coupling members together. An insulation blanket encloses the coupling nut, and a retention strip having a first end attached to an inner surface of the insulation blanket and a second end attached to the coupling nut is provided to prevent loosening of the coupling nut.