The Mobay Chemical Corporation Agricultural Chemicals Division plant in Kansas City, MO was experiencing corrosion problems with the fluoropolymer lined steel piping system for chlorine gas in the herbicide manufacturing unit. The polymer was not attacked by the chlorine, but the gas at about 30 psi was able to permeate and pass through the liner to the interior of the steel pipe and fittings. Small holes in the steel allowed the gas to escape to the atmosphere, eliminating possible build up of pressure that could collapse the liner.
The chlorine gas reacted with moisture in the air to produce hydrochloric and hypochlorous acids that corroded the steel. The approximately 1/16" holes drilled in the pipe wall gradually increased in diameter, and eventually reduced the structural integrity of the pipe. A different type of corrosion resistant pipe was needed to avoid the expense of periodically replacing corroded sections of the chlorine piping system.
In July, approximately 80' of steel pipe lined with ECTFE, a copolymer made of ethylene and chlorotrifluoroethylene, was installed on a trial basis in the chlorine piping system. ECTFE has excellent resistance to abrasion and is virtually unaffected by the most common corrosives including strong mineral and oxidizing acids, alkalis and essentially all organic solvents. It can also withstand continuous temperatures ranging from cryogenic to 300°F. The superior permeation resistance eliminates the need for weep holes in pipe and fittings where corrosion can weaken the metal.
The liner is locked in and fusion bonded to the pipe and fittings by an exclusive process that prevents stress cracking, joint creep or plastic flow. The schedule 10 through 80 carbon steel pipe and compatible fittings in standard and special configurations are available in 1" through 8" sizes. The lined pipe can be prefabricated to specification, or can be prepared at the job site with easy to use field fabrication tools available from Plastic Lined Piping Systems.
Mobay furnished engineering drawings to prefabricate spool pieces of schedule 40 pipe. There were also a few pieces of 1" pipe and 150 lb ductile iron flanges and fittings, including a number of 4 X 1, 4 X 2, and 6 X 2" reducers. Each piece was identified with a drawing to facilitate assembly into the existing piping system.
The test section of Halar (ECTFE) lined pipe and fittings was inspected after six months of service. There was no evidence of corrosion. Consequently, an additional 250 feet of prefabricated ECTFE lined piping and fittings will be installed to completely replace the balance of the original pipe.