PEX (cross-linked polyethylene) brass fitting failures

Stage demonstration with PEX-A and PEX-B samples. West Coast material scientists alleging brass fittings are defective via dezincification; "hundreds of millions" in Las Vegas settlements, "billions" pending. Tom frames the litigation as bogus — predicted five-year lifetimes on 20-year-old installations. Connects to the externalities discussion (homeowners underwater on mortgages suing builders).

We ended up using galvanized pipe until about World War II, and then after World War II we started using copper pipe much more frequently. Today we actually use something else. Does anybody know what it is? PEX. [Tom holds up a PEX tube with a plastic fitting.] That's a PEX tube with a plastic fitting. This is a brass fitting. This is PEX, and that's PEX-B. PEX stands for cross-linked polyethylene — PE for polyethylene and X for cross-linked. There are two ways to cross-link it. You can hit it with electrons — that's PEX-A, the more expensive one. This is just like Charles Goodyear and sulfur and rubber. You're trying to make a cross-link of your polymer chains to make a three-dimensional structure. I'm getting some nods — some of you are material scientists and understand those things. PEX-B is chemically cross-linked, which is sort of what Charles Goodyear did with sulfur. You put sulfur in, and the double-bond sulfur ends up creating the cross-link between two polymer chains, and you end up with rubber.

Las Vegas / West Coast class actions on brass fittings (dealloying corrosion, not the tubing itself). Tom defers the dealloying mechanism to a later session.

No, PEX is cross-linked polyethylene. I'll talk about that in a second. That was what I was looking for, a piece of PEX. PEX tubing is fine. Some people are blaming the fittings. There's a billion dollars worth of lawsuits out in Las Vegas and the West Coast on PEX brass fittings, but that's another story. It's a corrosion problem called de-alloying. Maybe we'll talk about it when we get to dealloying-type attack. But anyway, they put in polybutylene, and the fittings are susceptible to stress corrosion cracking. So I talked about metals being energetically unfavorable — they want to go back to nature. If I went back thirty, forty years ago, people said, oh, plastics don't corrode. Ceramics don't corrode. Well, that's not true. They corrode by different mechanisms. Metals corrode by going back to their oxide or their sulfide. Plastics can degrade, and this is not necessarily by a chemical process.

Used to introduce the electron-beam cross-linking method shared with sandpaper manufacturing. Primary-bond-energy (1–3 eV) argument for why UV alone can crosslink and why most adhesives can't set at production line speeds.

Then, trying to save money, they went to PEX tubing — this stuff. [Tom holds up a sample of PEX.] They basically had to cross-link it. PEX-A is electron-beam cross-linked.