Patent ID: 7908732

Claim:
A method of joining plastic-lined conduits comprising the following steps, not necessarily in the following order: providing a first conduit and a second conduit, each conduit comprising a wall of metal defining a bore having an open end for connection and being substantially lined by a plastic liner, the liner ending within the bore to leave a short unlined section at the open end of the conduit; arranging said first and second conduits with their ends abutting; welding said ends together to form a longer conduit; providing a tubular bridging member of corrosion-resistant material dimensioned to fit inside the lined conduits, the bridging member having a first sealing portion toward one end thereof and a second sealing portion toward the second end, said sealing portions being interconnected by an intermediate portion, the length of said intermediate portion being sufficient to bridge the unlined portions of the abutting first and second conduits while the first and second sealing portions overlap said liners within the first and second conduits respectively; with the first sealing portion of the bridging member located within the first conduit and overlapping the liner, expanding said first sealing portion radially so as to press the first sealing portion against the liner to form a first seal between the liner and the bridging member; and with the second sealing portion of the bridging member located within the second conduit and overlapping the liner of the second conduit, expanding said second sealing portion radially so as to press the second sealing portion against the liner to form a second seal between the liner and the bridging member, whereby the liners, the first and second seals and the bridging member form a continuous barrier between the interior bore of the lined conduits and the metal of the conduit walls, wherein the dimensions of the bridging member and the sequence of the method steps are such as to insure that there is space between the material of the bridging member and the inside of the abutting ends of the conduits during at least an initial pass of said welding step; and at a time after said initial pass of said welding step, after introducing the bridging member at the location of the abutting ends but before expanding at least one of the first and second sealing portions, expanding said intermediate portion of the bridging member radially so as to substantially eliminate any gap between the bridging member and the inside of the abutting ends of the conduits; whereby there is produced a plastic-lined conduit for use in offshore oil and gas operations capable of withstanding corrosion and elevated temperatures and pressure.