PVC & HDPE Plastic Pipes Permeation

Problem

A major pipe manufacturer wanted to sell plastic drinking water pipe but the potential customer had questions. The municipality were concered that trace amounts of chemical contaminants and solvents could permeate through the pipes wall and taint the drinking water, thus putting the public in danger.

Although some general guidelines existed, they were not comprehensive or specific enough to reassure the client. The specific chemicals detected in the soil were not covered in existing studies and there were no specific safe limits defined. This left the end client uneasy.

Action

One pitfall with discussing potential problems is that the more you talk about it, the more concerned the reader becomes. In such situations, it is wise to provide the bigger picture, so that the level of “threat” can be put into perspective. In this case, the report started with details about the reliability of plastic pipes in general, that they have very low environmental impact and that they are cost-effective. Metal pipes are more expensive, have far higher environmental impact and cost more. Although they are resistant to chemicals, they are attacked by high and low pH, leading to corrosion and penetration.

For these reasons, it would be better to install plastic pipes provided that they are suitable for the site in question. In one week, I was able to locate and read over 30 studies and two books on the subject including one study that was important but unavailable online. The science around plastic HDPE and PVC pipe permeation was reviewed and so was the science around the gasket rubber / elastomer materials.

Solution

By considering all factors such as the level of soil contamination, the polarities of the contaminants, their molecular weights, the depth of the pipes relative to the frost line, the incidents of pipe permeation in the region and so on, it was possible to write a comprehensive report.

Permeation of plastic pipes is extremely rare, and when it does occur, ~90% of the time gasoline and diesel fuel are the solvents in question. Because of their low polarity (Solubility Parameter), these are able to permeate through HDPE pipe which also has a low polarity (like dissolves like). In contrast, PVC pipe is extremely resistant to gasoline and diesel because it is a more polar material. The use of polar gasket materials such as nitrile rubber is indicated for areas with contaminated soil. The final report showed in detail why PVC was the best choice according to peer-reviewed science.

Immediately upon receiving the final report, my customer wrote…

“Chris … I cant tell you how impressed I am with your work. Thank you my friend. Merry Christmas and I look forward to collaborating with you again soon.”