Problem: A major polymer processing plant in Texas uses trichloroacetyl chloride solution with pH less that 1.0 in its process. The acid had been handled in PVDF piping in a shielded area, but a process modification made it necessary to pump it from ground level to its point of use on the fifth floor, over ninety feet up. The PVDF pipe required routine replacement of fittings because of the chemical attack and leakage at the threaded sections.
When the process modification was in the planning stage, the plant engineering and safety departments carefully considered the implications of pumping this hazardous and toxic chemical ninety feet overhead. Only a system that could be relied on to be leak free and impervious to attack by the corrosive acid could be used. Stainless pipe was considered but ruled out because it would be subject to stress corrosion cracking when exposed to the chlorinated acid.
A piping company was called in to evaluate the problem. Because of its good chemical resistnce, mechanical properties and ease of installation, they recommended ECTFE-lined steel pipe and fittings be used for the installation. The ECTFE resists permeation, so there wqas no requirement for weep holes in the steel pipe which would have been required with pipe lined with other fluoropolymers. ECTFE resists a wide variety of acids, bases, and solvents in a temperature range from sub-zero to 300°F. Extruded liners in the straight sections and molded liners in the fittings have integral flange faces. The liners are fusion bonded and locked in to prevent stress cracking and cold flow. The ECTFE lined pipe is available in schedules 10 through 80 carbon steel pipe with liner thicknesses to 0.190". Standard pipe sizes from 1" to 8" are available with various standard and special configurations.
The acid process line has been trouble-free since it bagan service more than two years ago. Because of the corrosive nature of the trichloroacetic acid each fitting is inspected routinely for signs of failure that might lead to leakage. None has been found so far.