The Advantages of Polymers Over Metal
Corrosion resistance: Metals are sensitive to oxidizers such as sodium hypochloride which is widely used for sanitation of tap water. In the case of stainless steel, the tap water can provoke the formation of rust over time. Brass, being an alloy of copper and zinc, is sensitive to galvanic corrosion leading to dezincification and the formation of microporous holes in the installation. Using brass fitting with multilayer pipes containing aluminum can lead to an electric potential between the aluminum and brass, and subsequent galvanic corrosion of the aluminum.
No scale deposit: Tap water – depending on its hardness level – may contain a high amount of calcium and magnesium carbonate which can easily precipitate. This precipitate, well known as scale, sticks strongly to metal surfaces. Scale deposit is much lower on polymer surfaces due to their high smoothness and low surface tension.
No biofilm adhesion: Due to the high surface smoothness achievable with polymers, biofilm adhesion is greatly reduced. This leads to less bacteria, even in dead zones, and therefore to cleaner water.
No contamination by heavy metals: Unlike for metal plumbing systems, there is no contamination of tap water with heavy metals when using polymeric installations.
Easy assembly: Assembly of metal installations usually comprises hot gas welding at high temperatures. For systems based on multilayer pipes and polymeric fittings, a wide variety of fixation systems are available for professionals as well as for do-it-yourself installers. No welding is needed.
Low noise: Polymeric piping systems transmit less noise from the motion of water which is important for waste water pipes. For pressure piping systems however, this is only a factor in areas where there are connections to older installations with different diameters.
Good thermal insulation: The thermal conductivity is a factor 100 to 1000 times lower for polymers than for metals used in plumbing. The "intrinsic" insulation properties of polymers make them the material of choice especially for hot water distribution and heating systems.
Lower cost: The cost of fittings made with corrosion resistant metals – in particular brass – is about 50% higher than for polymer fittings. This cost difference is partly due to volatile metal prices, while prices of polymeric raw material remained approximately at the same level. The second important factor is manufacturing costs. Metal fittings need several manufacturing steps while polymeric fittings can often be produced in one injection molding step.