What is Polypropylene Pipe?

M.J. Casey

Polypropylene pipe is used in many industrial settings due to its chemical and thermal resistance, affordability, and cost. It is frequently used in waste streams of all types, including residential and commercial environments. A byproduct of the distillation of petroleum products, polypropylene was discovered in the early 1950s and due to its relatively easy manufacture was in production within seven years. New uses have often been developed for this recyclable, resilient material.

Polypropylene pipes are less dense and cheaper to transport than metal fittings like copper pipes.
Polypropylene pipes are less dense and cheaper to transport than metal fittings like copper pipes.

This material is a straight-chain thermoplastic consisting of methyl groups on every other carbon with an empirical formula of C3H6. Polypropylene used for pipe is primarily isotatic, wherein the methyl groups are all in the same position on the carbon backbone, resulting in a medium molecular weight and a degree of crystallinity between that of low-density polyethylene (LDPE) and high-density polyethylene (HDPE). These properties produce a pipe that is resistant to acids, bases, and solvents and which is excellent in transporting industrial streams between processes. The material is tinted black or gray to decrease ultraviolet (UV) light degradation of the pipe and its contents.

Polypropylene pipe can be used in harsh environments.
Polypropylene pipe can be used in harsh environments.

Strongly caustic streams, including potassium hydroxide or sodium hydroxide solutions, may be carried in polypropylene pipes. By the use of fusion-weld joints, caustic attack on solvent-based adhesives is avoided. A glass additive is required to make polypropylene capable of handling biodiesel (methyl oleate) fuels. This type of pipe is not used with concentrated, strong oxidizing agents such as nitric acid.

In addition to harsh environments, polypropylene pipe is employed in the transport of distilled water in all but the most stringent requirements. The pipe’s lack of reactivity and the ability to fusion-weld joints without adhesives maintains the water’s purity. The pipe may be used in pressurized applications to 150°F (65°C) and to 180°F ( 82°C) in non-pressurized uses. Without modification, the pipe’s use is limited to 20 psi (138 kPa). Other liquid applications include service in the heating and cooling of buildings, providing an economical alternative to the use of air as the heat transport medium.

Polypropylene is manufactured from low molecular weight natural gas components or petroleum distillation byproducts using chromium catalysts at low pressures, a lower-cost process than HDPE. As polypropylene pipe is less dense than other thermoplastics and certainly much less dense than steel, iron, or copper pipes, transportation costs are lower. Piping made from polypropylene is recyclable and has a lifetime of about 50 years.

The pipe does not conduct electricity, another advantage over metal pipes in industrial settings. Homeowners sometimes feel polypropylene piping in residential waste systems is quiet because of its natural insulation properties. Polypropylene pipe itself is very tough and not subject to splitting. Go-kart racetracks and similar venues often employ polypropylene pipe as low-cost barrier or guard rails due to its ability to withstand stress and temperature extremes.

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