National forensic engineering firm, U.S. Forensic, recentlyundertook a large project to investigate a large number of braidedstainless steel water heater connector failures for one of thelargest property carriers in the country. Michael DeHarde, P.E.,and Brian Darr, P.E., worked on the months-long project todetermine the cause of the leaks associated with the braidedstainless steel brand water heater connectors commonly sold at themajor big box hardware centers.

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U.S. Forensic was one of several forensic engineering firmsapproached to work on the project, and was selected based in parton the proposal to actually test each unit and photograph theresults of the test, rather than just visually inspect, as proposedby others. As NASA Rocket Scientist Wernher von Braun famouslysaid, “One test result is worth 1,000 expert opinions.”

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The process began even before the subject connectors werereceived by acquiring several exemplar connectors to understand theas-supplied condition of the connector and to develop an inspectionprotocol. An exemplar connector was cross sectioned to understandthe interior make up of the hose and to assist in the design andmanufacture of a durometer that could measure the hardness of theplastic interior materials.

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The durometer was first tested in an exemplar connector. Then,each reportedly failed hose was visually inspected, measured andphotographed both externally and internally to document thecondition of the hose upon receipt. Once the received condition wasdocumented, each connector was tested to confirm a leak existed inthe connector. The location and cause of the leak was observed andthen photographed internally using a high-end articulatingborescope to document the failure region.

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After analyzing multiple connectors of differing sizes, mostbeing 12, 18 and 24 inches in length with ¾-inch female fittings oneither end, the findings were consistent. U.S. Forensic's testingverified that the leaks were present within the inner plastic tubesand were the result of their prematurely decomposing and flakingapart. This material defect led to a breach of the internal wall,which caused the water release and the resultant damages at thevarious properties across the country.

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In some cases, U.S. Forensic was supplied with the other waterheater connector, which had not failed. While the second connectorshowed some changes, this second connector did not have theextensive level of degradation found on the failed connector. Thisprovided valuable information. While in most cases we were notprovided the identity of whether the connector was either a hot orcold connector, U.S. Forensic believes that the failed connectorswere primarily the hot water, or outgoing, connectors. A rule ofthumb for dealing with plastic is for every 10 degrees Celsius oftemperature rise, the chemical reaction rate doubles.

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Fig. 1: The custom made durometer and cross sectionedexemplar connector.

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Fig. 2: Internal borescope images revealing thedecomposition of the interior plastic tubing.

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This manufacturing or design defect in many cases ultimatelycaused the braided stainless steel housing of the connectors tocave in, deform, and/or twist. It was determined that a chemicalreaction caused the plastic tubing in the connectors to decompose,and this decomposition caused the connector to structurallydeform.

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U.S. Forensic understands that codes and industry standardsdon't always address the needs of a good scientific investigationto determine root cause failure analysis. While the ASME A112.18.6Flexible Water Connectors 4.3 Hydrostatic Burst Test: Connectorrecommends the connectors should be pressurized at 250 psi at 180Fand held at that pressure and temperature for 0.5 hours, it doesnot address or test for long-term creep in plastic. U.S. Forensicis constantly developing new tools and procedures to push theenvelope of product liability failure analysis. U.S. Forensicengineers now hold 3 patents, were responsible for 2 nationalmanufacturer vehicle service campaigns, and helped author the newASHRAE standard for air conditioning flexible duct installationprocedure. Stay tuned for the results of U.S. Forensic testing onvarious plumbing connectors that more closely mimic real-worldconditions of connectors and a laboratory recreation of these waterconnector failures.

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By Michael DeHarde, P.E. and Brian Darr, P.E., U.S.Forensic

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