More Reinforced Plastic Plumbing, Please

from “Rovings,” Professional BoatBuilder No. 155
Compiled by Dan Spurr

155 pvc 400Steve D’Antonio (all)

While PVC pipe is well suited for potable-water and sanitation systems, it lacks the resilience needed for raw-water applications.

I’m crawling through a bilge, flashlight clenched firmly in my teeth, during a vessel inspection when I come across a corroded and leaking assemblage of metallic plumbing fittings. Some of the components are green, which, while unsightly, isn’t worrisome. Others are pink, a sure sign of dezinc-ification; and the oozing emerald-colored seawater threatens the more troubling prospect of flooding and sinking.

Regrettably, this is an all-too-common occurrence. On countless occasions I have made the following entries in vessel inspection reports: “Stainless steel raw water fittings corroding, leaking”; “PVC fittings used for raw water, and poorly supported, risk of failure and flooding”; “Polyethyl-ene plumbing, designed for potable water use, used to supply raw water to wash down pump”; and “Brass pipe nipple used at seacock.” And these are just a few.

155 pink dezinc 400

The pink color of this broken plumbing elbow is a sure sign of dezincification.

Other than low- or no-zinc-content bronze, and proprietary glass-reinforced seacocks, most other metals, even the venerable stainless steel and many plastics, are susceptible to corrosion and/or stress failure (for more on stainless steel and its corrosion mechanisms, see “The Power and Peril of Stainless,” PBB No. 146). They are either less than ideal or simply never suitable for raw-water applications. Yet they are used aboard nearly every boat, in one application or another, because boatbuilders have few more attractive plumbing choices.

Common examples include cumbersome and leverage-inducing air-conditioning raw-water manifolds made from schedule 40 PVC pipe, welded stainless steel T- and Y-fittings that supply water to multiple consumers, and brass (which is not easy to distinguish from bronze) pipe nipples, plugs, and pipe-to-hose adapters.

I realize PVC is common in raw-water applications; however, I have seen it and other unreinforced plastics fail many times. If you pose this question to PVC-pipe-fitting manufacturers: “Can I use this for seawater plumbing in a boat? Oh, and if it fails, the boat will likely sink,” they are likely to make it clear that you do so at your own risk; it’s not what the product was intended for. To complicate matters, some brass—containing no more than 15% zinc, or embossed DZR (dezincification resistant) alloy—is considered acceptable. Alas, most generic copper-alloy plumbing components don’t indicate their elemental makeup. Even when the correct metal is used, it’s susceptible to failure via stray-current corrosion and lightning strikes.

When I make these observations, the inevitable response is “What should be used?” Often the answer isn’t simple. Glass-reinforced plastic such as Forespar’s Marelon, and New Zealand’s Trudesign composite plastic products come to mind. However, their fittings are limited primarily to seacocks, through-hulls, valves, and mating tailpieces, which have a straight rather than common tapered NPT thread. Some catalog industrial suppliers such as McMaster-Carr offer a small selection of glass-reinforced polypropylene and nylon pipe-to-hose adapters, but nothing in the way of couplings, T-fittings, or pipe nipples.

Thus, with each one of these observations I lament the dearth of reinforced plastic fittings—couplings, nipples, Ts, and pipe-to-hose adapters—suitable for raw water. I’ve discussed the need with reinforced-plastics manufacturers, and the invariable explanation for why there’s so little of it is the cost of tooling. We all know the marine market is miniscule compared to residential and commercial building; but wouldn’t these products have applicability across a wide swath of industries, which extend well beyond small boats? I believe a market exists; all that’s needed is a product line to fill the void.

I’ve thrown down the gauntlet. Now, someone, please rise to the challenge!

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