Effects of Bubble Behavior on Erosion Corrosion of Copper Tubes in Hot-Water Supply System

The survey results of recent 120 leakage accidents showed that most of erosion corrosion failures of copper tubes in hot-water forced circulation system have been experienced at the downstream of joints of the return tubes. This tendency was the same as that of the research in 1996. The erosion corrosion of copper tube was observed when the concentration of dissolved oxygen in the hot-supply water was supersaturated and higher than that in supplied tap water. Therefore, it was presumed that erosion corrosion of copper tube was caused by the bubbles formed by pressure change in hot-water forced circulation system. The results of Computational fluid dynamics (CFD) simulations and the observation of the flow pattern in the model plumbing equipment showed that the locus of the micro-bubbles affect of the erosion corrosion of copper tube. According to the Young-Laplace equation, more small bubbles have high pressure in inside of the bubble, and maintain as the bubble without coalesce or collapse of bubbles. Consequently, it could be considered that erosion corrosion of copper tube occurred and propagated when the protective films formed on the tubes surfaces were continuously broken by micro-bubbles.