Flexible Water Hose Failures: A Case Study and General Design Considerations
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CASE HISTORY—PEER-REVIEWED
Flexible Water Hose Failures: A Case Study and General Design Considerations Richard Taylor . Thomas Eagar
Submitted: 23 February 2016 / Published online: 16 March 2016 Ó ASM International 2016
Abstract Flexible water hoses (or flexible hose connectors) have become commonplace in recent years and provide a low-cost and convenient alternative to rigid pipe. Unfortunately, inadequate designs, particularly with regard to the selection of materials and material parameters, have made some hoses prone to failure. Such failures are often initiated by incidental exposure to corrosive substances commonly found in homes (including chlorides in tap water) that attack and corrode the stainless steel metal braid. A failure of the braid then leads to a rupture of the water-carrying tube. We evaluate the design considerations pertinent to flexible water hose failures and consider a recent failure scenario that illustrates some key points. Keywords Austenitic stainless steel Corrosion Failure analysis Pipe burst Plastics SEM Stress corrosion cracking
Introduction Failures involving flexible water hoses have become more common as their use has proliferated in residential settings. Flexible water hoses connect household plumbing to fixtures such as sinks and appliances. Their popularity is due to ease of installation as a consequence of the hoses’ flexibility and quick connections that eliminate the need for soldering or threading. In many cases, failure of the hose can be traced to simple design considerations, specifically, to the grade of R. Taylor (&) T. Eagar MIT - Materials Science and Engineering, 77 Massachusetts Ave. 4-142, Cambridge, MA 02139, USA e-mail: [email protected]
stainless steel selected for the metal braiding as well as the thickness and material of the elastomeric tube. Manufacturers, distributors, and tradespeople should consider the foreseeable use and environment of flexible hoses in light of these facts and familiarize themselves with alternatives less prone to failure.
A Case History A recent case demonstrates many of the key design considerations. The incident in question involved a flexible water hose connected to a faucet (Fig. 1). The metal braiding on the hot water side was compromised and a rupture occurred in the elastomeric tube, which caused flooding and considerable property damage. Upon examination of the hose it was found that the tube braiding was heavily frayed with large portions missing, displaced or loose (Fig. 2). The rupture in the rubber hose was consistent with a failure from hoop stresses on the tube, having formed longitudinally along the length of the tube. The hoop stress on a thin-walled tube can be calculated with the Barlow formula as follows [1]: Hoop stress; psi ¼
PressureðpsiÞ outside diameterðin:Þ : 2 wall thicknessðin:Þ
For a household water pressure of 80 psi, an outside tube diameter of 0.50 in. and a wall thickness of 0.050 in., the hoop stress is calculated to be 400 psi (2.8 MPa). This stress is within the range of brea
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