Sometimes the corrosive resistance of AISI 316 acid resistant steel is challenged by highly aggressive chemicals (e.g. hydrochloric acid HCl). Then it is necessary to use either very expensive couplings made of special nickel-based alloys (e.g. Hastelloy) or less expensive couplings lined with ECTFE. The last couplings are made of AISI316 steel however all inner surfaces in contact with the medium are powder coated with ECTFE lining.
ECTFE, a copolymer of ethylene and chlorotrifluoroethylene, known under its brand name Halar®. It has excellent chemical resistance in a wide range of temperatures (approximately from -40°C to +130°C). Resistant to the impact of all acids, lye and other aggressive substances (pH range from 1 to 14). Its mechanical properties, hardness and abrasion resistance in particular, are very high as for fluoropolymers. ECTFE lining features outstanding surface smoothness. The lining is usually 0,5 ÷ 0,6 mm thick. A conductive lining version (R < 106 Ω) and the one compliant with FDA requirements for food application are also available.
There are many types of couplings available with ECTFE lining: