Cleaning up the Cracks in Plumbing

Plumbing has come a long way since the Romans invented aqueducts and lead pipes. The production of steel pipe helped indoor plumbing become practical at the turn of the 20th century. By 1940, threaded steel pipes were being supplanted by lighter and easier-to-install copper tubing. As the plastics industry matured, a variety of relatively inexpensive plastic pipes hit the market in the 1970s and 1980s, with varying degrees of success. After reliable potable water supplies opened up a market for a multitude of devices that use water in the home and workplace, practical considerations led to the practice of installing shutoff valves for each apparatus so that minor repairs or replacements could be done without closing the main entry valve to a building. This article will focus on issues and risks associated with “supply tubes,” the lines that connect a shut-off valve to the toilet, faucet or other apparatus downstream from the shut-off valve.

The Evolution of Supply Tubes

One hundred years ago, it was not unusual to see a series of threaded steel pipes running directly into a toilet tank or to the bottom of a faucet. The first generation supply tubes were chrome-plated, semi-rigid, 3/8-inch copper tubes that could be artfully bent to connect some shut-off valve with the toilet or faucet. The handyman soon found out that “artful” bending was a little bit more complicated than it looked. Kinked tubes did not work well and the combination of cutting and bending often resulted in a tube that was too short for its intended purpose. This opened up a market for a semi-rigid plastic supply tube made from cross-linked polyethylene (known as “PEX” for short).

PEX were installed with compression fittings basically the same way as the obsolete 3/8-inch plated copper tubes, but PEX was barely flexible enough to contort to the needs of the installation without any pre-bending. The trouble with supply tubes, especially for toilets, is that they are normally visible. Although they are easy to install, PEX supply tubes tended to be somewhat ugly. While shiny, chrome-plated copper tubes gleamed in bathrooms everywhere, PEX tubes were drab white or grey plastic proudly printed with references to the various ASTM or NSF standards to which they conformed.

Once again, creative manufacturers came to the rescue of both the plumber and the interior designer. They developed a modern, flexible supply tube covered with a shiny, braided stainless steel jacket. These modern tubes are fitted at each end with nuts and gaskets sized perfectly for the standard compression fittings used for the rigid and PEX tubes. In fact the shiny, braided steel wire jacket covers a rather homely flexible black rubbery hose that actually carries the water. The hose is a good water barrier but, by itself, it cannot resist the water pressures normally found in buildings. The braided steel jacket is literally the knight in shining armour for the inner hose, supporting the hose against internal water pressures that would otherwise cause it to burst open.

Risks and Supply Tubes

Stainless steel is generally more corrosion-resistant than so-called “mild” steels. Stainless steel owes its corrosion resistance to alloying elements such as chromium, which form thin films of intractable protective oxide on the surface of the stainless steel. However, chloride ion is the Achilles heel of stainless steel: chloride, which is found in salt or muriatic acid, breaks down the protective surface oxides and circumvents the “stainless” property, leading to its corrosion.

Normally, flexible supply tubes in cabinets under the sink are not exposed to salt or, hopefully, acid. Yet we have seen a surprising number of failures of braided tubes due to this type of attack. The culprit is usually some household-cleaning product stored in the same cabinet where the flexible hose is located. Cleaning products with “bleaching” or “disinfecting” properties, as well as most dishwasher detergents, contain hypochlorites. This class of chemical gives bleach its “bleaching” property and also acts as a disinfectant in swimming pools. The trouble with hypochlorite solutions is that they produce volatile hypochlorous acid, one of the chemicals responsible for the “chlorine” smell associated with bleach and swimming pools. Even solid (powder) formulations will produce hypochlorous acid vapour due to exposure to ambient humidity.

The braided, stainless steel jacket of the flexible supply tube is not only susceptible to attack by chloride ion (a byproduct of the hypochlorite), but it is also vulnerable to “stress cracking corrosion” due to the tensile forces induced in the wires by the water pressure inside the rubbery hose. Instead of causing a general corrosion and accompanying warning signs, chloride ions attack preferentially between the individual steel crystals, or “grains,” that make up the wire. As a result, the wire breaks squarely, as if it was cut by a small saw blade. As the wires break, the (formerly) shiny flexible hose starts to resemble a cactus, with little stainless steel spines (from the individual broken wires) sticking out. Once enough of the wires break, the elastomeric hose underneath is no longer supported against the internal water pressure, so it balloons out and finally explodes. This results in a flood. And, as insurance adjusters will point out, this type of failure inevitably happens five minutes after the occupants of some building have left for the day (or night).

Who’s At Fault?

In this type of loss, the insurer will often ask the technical expert if any party is at fault.

• Should the homeowner have stored a routine household-cleaning product in the cabinet underneath the kitchen or bathroom sink?
• Should the manufacturer of the cleaning product have put a warning on the product label, indicating that the cleaning product might result in the corrosion of this type of flexible supply tube?
• Should the manufacturer of the flexible supply tube with the braided stainless steel jacket have warned the installer (or ultimate owner) that the hose could fail when installed in proximity to certain types of cleaning products?

The technical explanation for this type of failure and loss is very simple. But the answer to all of the above questions may in fact be a resounding, “I’m not sure.” For example:

Given the multitude of materials and consumer products on the market, it is hard to argue the average consumer should have the technical knowledge required to recognize all sorts of product and material interactions.

Federal regulations already outline very precise labelling requirements for the sort of cleaning product that can lead to this type of failure. But labelling regulations cannot be expected to cover each and every eventuality — unless the consumer is expected to bring home and read a telephone book-sized information manual with every product he or she purchases.

The National Plumbing Code already requires that this type of (flexible) supply tube meet a plethora of performance criteria, including pressure resistance and a lack of toxic ingredients. Should the Plumbing Code really be expected to delve into material-specific properties? (For example, the same hypochlorite vapours that destroy the stainless steel jacket in question will not induce a similar failure in copper or PEX plumbing.)

It is difficult to assign blame in this type of failure, but perhaps property owners need to be held more accountable. The type of failure under discussion, like many other failures in buildings, normally occurs over a period of months or even years. Thorough annual inspections of all exposed components in a building would help to identify this type of failure before it becomes catastrophic.  In the meantime, everybody sho
uld move those “bleaching action” cleaners out of any cabinets
in which these braided supply lines are found.

1. The French translation of “supply tube” is tuyau d’alimentation. The common French term for “supply tube” is “speedway” (actually “le speedway”). The author is unable to explain the origin of this term.
2. Interestingly, one supplier of braided flexible supply tubes has started adding the instruction “install only in exposed
locations” to their label.