Flow Electrification and Non-Uniform Corrosion in Low Conductivity Potable Waters

Abstract

"Flow electrification" occurs whenever a fluid passes along a charged surface, creating an electrokinetic "streaming current" or "streaming potential' and is known to cause non-uniform corrosion (and other) problems in non-aqueous fluids. After observing unusual corrosion failures of copper in relatively low conductivity (≈150 μS/cm) potable water, a series of laboratory studies was conducted that verified flow electrification could also develop in aqueous systems and contribute to non-uniform corrosion. Relatively high direct streaming currents along pipelines were quantified in model systems with plastic dielectrics, which accelerated corrosion on the affected pipe section by up to 0.5 μA/cm 2 (assuming uniform corrosion). Very rapid non-uniform pipe failures (i.e., full wall penetration in 7 months) occurred in a system without dielectrics simulating a potable water recirculation system. The effects of flow electrification were virtually eliminated by addition of low levels of zinc phosphate, an inhibitor used in approximate 25% of potable water distribution systems. Flow electrification was also observed in plastic pipe systems with brass connectors. "Flow electrification" is a macroscopic manifestation of electrokinetic "streaming current" or "streaming potential," which develops whenever a fluid passes across a charged liquid-surface interface. Flow electrification of pipelines has been studied extensively over the last century in the petroleum industry, where explosion hazards and pipeline corrosion damage may result when very high voltages are generated via fluid flow in metallic pipes.1-4 Prior reports of flow electrification problems are limited to cases where the involved fluids have low electrical conductivity (e.g., non-aqueous fluids). Thus, for relatively higher conductivity fluids, such as potable water, consequences of flow electrification have largely been assumed irrelevant -although, the phenomenon has been considered theoretically 5 and practically 6-10 as summarized in Table I. Over the course of a decade of research into non-uniform corrosion of copper and dealloying-related failures of brass plumbing components in potable water systems, some practical observations of field failures could not be explained by conventional interpretations. In these cases, non-uniform pitting corrosion and failures were concentrated on the first pieces or sections of metal in the flow sequence, while identical materials downstream suffered no degradation even though they were exposed to identical flows (e.g., same pipe diameter, flow velocity and flow rate). Velocities in the pipes were well-below thresholds at which copper erosion corrosion is a concern (i.e., < 1.2-1.8 m/s), and many of the systems were parts of potable water recirculating systems with a break in electrical continuity at the hot water heater. Similar observations of non-uniform corrosion concentrated on the front portion of copper pipes in a flow sequence were also made during laboratory experiments designed to replicate the failures observ...

Vibration-to-Electric Energy Conversion via Electric Double Layer Redistribution of Graphene-Nickel Foam Electrode

“…It was found a significant potential is generated when an ionic solution flowed through the surface or channel of carbon nanomaterials, usually termed as streaming potential. [7][8][9][10][11] Besides the continuous flowing of ionic solution, the potential generation had also been observed when a droplet of ionic solution moved on the surface of the carbon nanomaterials. [12][13][14][15] The reason of potential generation is attributed to the redistribution of electric double layer (EDL) on the liquid-solid interface when ionic solution moves on the surface of carbon nanomaterials so as to induce potential difference in the carbon electrodes.…”