FOR YEARS, process plants have relied on non-metallic piping as a cost-effective alternative to stainless, alloy and other expensive metallic piping in applications posing high corrosion rates or requiring stringent cleanliness standards. Plastic piping affords excellent resistance to attack by many chemicals, including most acids, alkalis and salt solutions. Such piping comes in schedule-40, schedule-80 and other common sizes, with wall thickness usually corresponding to that of steel piping. In addition, some plastic piping, e.g., PVC, is offered with standard dimension ratio (SDR) ratings, which mean the piping system will maintain a more-or-less uniform pressure rating at a specified temperature regardless of pipe diameter.
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