Using plastic for compressed air piping
Contaminant-free compressed air piping systems continue to become increasingly important with the advent of industrial automation. This article discusses the benefits to using plastic piping, the limitations of certain plastics, the do's and don'ts of installation, joint drying times for 100 percent pressure testing, provides a sizing guide for main air lines and more.
| Plant Engineering – January 2001
Feature article : Using plastic for compressed air piping
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“Plastics,” the famous one-word line from the 1967 film “The Graduate,” was said to be the key to the future. That prediction was never truer than today as it relates to compressed air piping systems. The technology for using plastic for compressed air systems ( Fig. 1 ) has been around for a number of years in Europe. Today, the use of plastic for clean compressed air systems has become widespread in the United States.
Contaminant-free compressed air systems have continued to become increasingly important with the advent of industrial automation. Assembly robots, packaging equipment, paint spraying, and pharmaceutical processing are just a few of the many applications that require clean compressed air.
Black iron or galvanized steel pipe commonly used for compressed air systems typically generates rust, corrosion, and other debris that can cause manufacturing problems. These contaminants are minimized or eliminated by using stainless steel or copper pipe. However, metal piping systems, particularly threaded systems, are still prone to leakage, which forces the use of larger, more expensive compressors. Also, stainless steel and copper, on an installed-cost basis, can be prohibitively expensive.
Low operating costs are possible with plastic in compressed air systems. Even if only a small percentage of threaded joints in a plant are leaking, this loss can amount to thousands of dollars per year, not counting any major leaks that may go unrepaired for long periods of time. The end result is lower efficiency and waste of valuable energy, which plastic piping can reduce.
Other thermoplastic piping materials, such as PVC and CPVC, are recommended for liquid service, but should never be used to convey compressed air. The use of PVC and CPVC in a compressed air system could result in a failure that would cause the rapidly decompressing air to fling sharp fragments of plastic through the air.