Abstract: A pipe coupling assembly of threaded and coupled (T and C) type for forming well strings by operably connecting lengths of pipe or tubes in a coaxially aligned relationship. The interior longitudinal bore of the pipes are preferably lined or coated with a corrosion resistant material. A plastic corrosion barrier seal ring is operably positioned in a recess in the longitudinal bore of the coupling member to protect the metal-to-metal seals, torque shoulders and engaged threads of the coupling assembly and pipes from contact with corrosive fluids. The plastic seal ring prior to thread make up is substantially rectangular in cross-section with a radial dimension between the outside and inside diameter or width equal to a greater than 1.5 times the axial or longitudinal height.