Flow Induced Failures of Copper Drinking Water Tube

• Main Author: Coyne, Jeffrey Michael
• Other Authors: Environmental Engineering
• Format: Others
• Published: Virginia Tech 2014
• Subjects: Flow Induced Failure; Erosion Corrosion; Copper; Concentration Cell Corrosion; Particle Impingement; High Velocity Impingement
• Online Access: http://hdl.handle.net/10919/32765; http://scholar.lib.vt.edu/theses/available/etd-05142009-142412/

Excessive water flow velocities can contribute to rapid failures of copper premise plumbing systems. This is the first fundamental study to scientifically isolate mechanistic impacts from distinct flow induced failure mechanisms that include concentration cell corrosion, cavitation, particle/bubble impingement and high velocity impingement. Concentration cell effects resulting from exposing different copper surfaces to different flow regimes created a strong electrochemical cell that caused rapid corrosion that persisted for periods lasting from hours to days in certain waters. Free chlorine appeared to inhibit this effect in a range of waters. Under typical water chemistries the resulting non-uniform attack diminished, presumably due to formation of a protective scale or rust layer. Consequently, concentration cell corrosion would not be a major contributor to damage from high flow rates in the range of fresh waters investigated. In experiments using an ultrasonic processor, implosion of vaporous cavitation bubbles against a copper surface caused dramatic pitting, considerable copper weight loss, and, in some cases, the development of pinhole leaks. Changes in water chemistry and the existence of a pre-existing protective scale layer had nearly no mitigating effects on copper cavitation damage. An exponential relationship was found between the initial copper pipe wall thickness and the time necessary to cause a leak via vaporous cavitation. On the basis of this relationship, a Type M tube would be expected to last 23 and 3000 times less than a Type K and L tube, respectively, when facing continual cavitation attack. However, it was not possible to re-create cavitation damage in any practical circumstance that was tested in copper pipes, even though it is strongly believed that cavitation can play a practical role in service failures. On the basis of the above results, it was hypothesized that brief intervals of cavitation could remove protective scale from portions of the copper pipe surface exposed to high turbulence. In this case, even if minimal damage from cavitation occurred directly, it could allow concentration cell corrosion to become a significant contributor to non-uniform corrosion damage. On the basis of preliminary testing, it appears that this idea has considerable merit. A combination of brief cavitation and waters that create strong concentration cell effects is expected to cause serious damage to copper pipe. These potential synergies are deserving of additional research. In experiments testing the effect of high velocity jets (17.5 ft/sec) impinging against submerged copper plates perpendicularly and longitudinally, plates in heated sea water were aggressively gouged and penetrated. It is believed that the copper plate damage resulted from a combination of mechanisms including concentration cell corrosion, cavitation implosion, and high velocity impingement. Impingement of sand on the surface of copper tube created very little damage. This was surprising given prior reports in the literature. === Master of Science