When "No Burst" Burst

Russell Zeckner, P.E., C.F.E.I.

 Fluidmaster and other manufactures of plumbing supplies have for several years offered premium water supply line products for faucets, toilets, washing machines, water heaters, dishwashers and icemakers.  These products typically feature a stainless steel wire braided exterior over an inner plastic tube.  Fluidmaster’s “No-Burst” product line is probably the best well known of the brands.

These products’ use a stainless steel braided exterior to provide the homeowner with a strong sense of security related to the long term integrity of their water supply lines as compared with the less expensive plastic, copper, or rubber tubing and hoses commonly used in the past.  The flexibility of these products also eases installation and allows even unskilled homeowners to make competent repairs.

 Such products appear to be ideal and as a result they have been utilized extensively by homeowners and plumbers alike.  They dominate the shelves of retailers such as Lowes and Home Depot.  Unfortunately, hidden problems lurk.

Several years ago Donan Engineering began receiving braided stainless steel supply lines that showed catastrophic failure in the form of bursting.  Our analysis of the failure uncovered a fault that most would not suspect.  The stainless steel braid had failed because of corrosion.  Yes, the stainless steel rusted and failed.  Once the braid’s stainless steel wires had corroded they lost strength and could no longer contain the pressure produced by a normal household water supply and they burst and often caused significant water damage losses.

Most laypersons believe that stainless steel cannot corrode, but that is an inaccurate perception.  When stainless steel is exposed to oxygen it almost instantaneously forms a microscopic layer of corrosion over its entire surface.  This corrosion layer seals off the underlying stainless steel from further oxidation and, unlike plain steel or iron, the corrosion stops.  If stainless steel is scratched or scraped the protective corrosion layer is lost, but it quickly reforms and the protection continues.

The corrosion of steel is enhanced by the presence of chlorides (Cl^-).  The chemical nature of chlorides makes it a strong and effective disinfectant and as a result it is found in numerous household cleaning products found in any supermarket.  Chlorides are always found in those products that advertise that they contain chlorine bleach.

The braided stainless steel coverings of the supply lines slightly pulsates and move with changes in water pressure and as result of phenomena such as water hammer.  This movement causes the braid’s wires to rub against one another resulting in the protective corrosion layer being lost and then reformed over and over.  With each reformation of the corrosion layer minute amounts of the steel are lost.Unlike solid plastic, copper or rubber tubing, the surface of the braided stainless steel supply line will capture water.  The water and any chemicals it contains seeps through the braid and then is trapped and remains liquid between the steel and the supply line’s inner plastic tubing.  If the trapped liquid contains chlorides the corrosion that occurs along with the braids’ movement is enhanced.  This phenomenon is known as chloride stress corrosion and it is the ultimate cause of the braid’s and therefore the supply line’s failure and bursting.

Chloride stress corrosion is a well understood phenomenon within the scientific community.  Chloride containing products targeted for use in kitchens, bathrooms and the laundry have been available to homeowners for decades.  Based upon these facts Donan Engineering has successfully argued that the manufacturers of these braided stainless steel supply line should have understood the potential for their corrosion and failure in a normal household environment.  We have concluded that their failure is a manufacturer’s defect.