For many years, copper and black iron have been the overwhelming favorite for plumbing compressed-air systems. However, recent advances in materials technology have made thermoplastic pipe a safe and economical alternative to traditional materials. A big advantage of metal pipe, tubing, and fittings is that installers are familiar with them and the techniques for joining them. While black iron is inexpensive, installation is time consuming and labor intensive. Moreover, threaded joints often serve as a source of leakage. This leads to higher operating costs because compressors must operate overtime to compensate for the leakage. Although connections between copper pipe and fittings are less prone to leakage, copper components are more expensive, and installation, again, is labor intensive especially when large diameters are involved.
But these aren’t the only drawbacks to metal piping systems. Interior corrosion can cause scaling and pitting on inside surfaces. As the corrosion products combine with moisture and other contaminants, they accumulate on the inner surfaces of the pipe and fittings, increasing their roughness. As the internal diameter becomes rougher, pressure drop though the system increases. Again, this ends up costing money by reducing efficiency of the compressed air system. Perhaps more importantly, particles can dislodge and clog or damage end-of-line equipment.
Because of the drawbacks, compressed air system users have been seeking alternatives to traditional metal pipe and tubing. Over the past ten years, industrial plastics have been developed that present an attractive alternative to metal piping.
PVC piping is relatively inexpensive, easy to install, lightweight, and corrosion resistant. However, PVC has one major drawback, it is brittle. An inadvertent impact could cause the piping to shatter, endangering surrounding personnel. Most PVC pipe manufacturers warn against using PVC for compressed air service due to potential liability from such failures. The Plastic Piping Institute, in their Recommendation B, states that plastic piping used for compressed air transport in above-ground systems should be protected in shatter-proof encasements, unless otherwise recommended by the manufacturer.
In many states, the Occupational Health and Safety Administration (OSHA) has stepped in and regulated against using brittle plastics such as PVC in these applications, and additional states are following suit.
The strictest standard in the country has been issued by California’s OSHA. It includes five tests, as well as a requirement for comprehensive marking of the pipe and fittings. These tests include long-term hydrostatic, short-term burst, and three specialized impact tests — all to ensure the safety and ductility of the system. The impact tests include striking frozen, pressurized pipe with both blunt and sharp strikers, using various forces, and striking a frozen pipe with a hemispherical striker, using various forces. Manufacturers are required to present the results of these tests for review upon request. When specifying a thermoplastic system, for safety’s sake it is important that your supplier meets Cal-OSHA regulations, regardless of the state in which the system will be installed.