What PEX Tubing and the Microwave Oven have in Common

old-microwave

I have a friend that is in the pipe and pipe fitting business. He distributes copper and steel pipe and fittings for commercial and residential applications. He is convinced that PEX tubing is going to give everyone cancer and advises everyone not to use it. He also thinks that microwave ovens will give you cancer and won’t go near one, much less eat anything that was cooked in one.

If he knew how PEX was made, he’d be even more freaked out.

PEX is the acronym for cross-linked polyethylene. A polymer is made up of long molecular chains made up of repeating units. Basically, a bunch of molecules are altered in a way that makes them link up end to end and become one large molecule. You will sometimes hear polymers referred to as large molecule materials. With some heat applied, the bonds between the molecular chains weaken and the material becomes a liquid which can be injected into a mold. Cross-linking refers to the process of linking these molecular chains together.

Cross-linking may sound like a subtle change but this small change has big effects on the properties. Extensive cross linking between the molecular chains makes the material non-melt processable or as we call it in the industry, a thermoset. The molecular bonds are too strong and the material will not flow like a liquid when heated. Think of a thermoset like concrete. If you heat it enough, it will decompose into its various constituents but it will not melt into a liquid so it can be reformed.

Cross-linked polyethylene is low density polyethylene that undergoes a chemical change which causes it to become cross-linked, in other words, a thermosetting polyethylene.

There are several methods that are used to accomplish the cross-linking. The methods are designated by a letter suffix on the finished product. PEX-A and PEX-B use different chemical methods to achieve the cross-linking but PEX-C is made by exposing the tubing to radiation. Oh the humanity!

The public’s fear and loathing of nuclear technology and radiation is a bit confounding to me. Everyone is in a panic about nuclear power but yet the microwave oven was one of the fastest adopted new technologies of the 20th century.

I suspect that most people don’t know that at least some of the PEX tubing that is becoming widely accepted in the building trades is produced by exposing the tubing to radiation, especially considering that it is used for drinking water.

PEX tubing has been in use in Europe since the early 1970s and in the US since the early 1980s. I first became aware of it on the TV show This Old House in the 1990 season where PEX tubing was used for an extensive remodel of a 1930’s adobe in Santa Fe. Currently, PEX tubing has been approved for use in all 50 states, even in the notoriously cautious California.

PEX has a long track record and there have been no major safety concerns. Polyethylene has a long history of use in food contact and medical applications. We even use it for joint replacements. I don’t think that any plastic material has the track record of polyethylene when it comes to safety.

However, if I was building or remodeling a house right now, I would be reluctant to use PEX. This is not because of a fear of plastic or radiation. A house is a big investment and home owners are reluctant to try new technologies in their houses because the risk/reward just does not justify it. The reward is that it is cheaper to install than copper plumbing. The risk is that it could be found to be unsafe or there might be durability concerns at some point. A house with this type of plumbing could become difficult to sell and thus be significantly reduced in value. It could require replacement which would be very expensive and disruptive. All you have to do is read about people that had polybutylene piping installed in their houses to see how difficult this is. This is why new technologies and building methods are slow to gain acceptance in housing.

It’s funny how the public accepts some technologies easier than others. While some of the older generations resisted adopting microwave ovens when they first came out, the microwave oven has been widely accepted by the public. On the other hand, building a nuclear power plant is nearly impossible in the United Stated these days but has been widely accepted in Europe. I suspect that fear of nuclear power in the US has a lot to do with movies like The China Syndrome. Hopefully no one makes a movie about the horrors of PEX tubing anytime soon.

Well, I have to go. I have to get a fire going in the fireplace to cook dinner. Natural gas causes cancer you know.

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