Abstract: An improved insulating union is provided of the type designed to prevent electrolytic corrosion in flow lines. The tail sub is physically separated from both the threaded sub and nut by a plastic layer. An annular groove is conventionally provided in the threaded sub for an O-ring to seal between the plastic layer and the threaded sub. Another O-ring groove is provided in a tail sub for sealing between the tail sub and the plastic layer to prevent leakage of high pressure gas from the union. The O-ring is inserted in the tail sub groove, and the plastic insulating layer is thereafter molded over the end of the tail sub.