Wear of Small Orifices by Streaming Current Driven Corrosion

Abstract

Wear on the upstream side of small metal orifices subject to large pressure drops (3000 psi) in phosphate ester base hydraulic fluids has been found to be the result of an electrochemical corrosion driven by a streaming current. A calculation for the current produced by the flowing fluid is described. Results of the calculation and of experimental work are given as evidence in support of the proposed wear mechanism. A large variation of wall shear stress along the metal surface is found to be necessary for the wear.

Pitting and Deposits with an Organic Fluid by Electrolysis and by Fluid Flow

“…A corresponding potential drop would also occur in the fluid in the direction of flow. This is the same magnitude as the open-circuit potential measured with a stationary ring-disk electrode in the flow system (1). Conduction from the fluid may therefore explain the large deviations from theory in Fig.…”

“…To understand the relationship of the electrochemistry of the phosphate esters to the flow induced wear mechanism, a brief description of that mechanism is given here. A detailed description has been published elsewhere (1).…”

Fouling Of Nuclear Steam Generators: Fundamental Studies, Operating Experience and Remedial Measures Using Chemical Additives

“…Investigations by Guillodo et al [114,115] and Barale et al [116,117] conducted in fast-flowing water (fluid velocity ≈ 10 m/s) under secondary chemistry conditions have reproduced the previous results of Woolsey et al [111]. Guillodo et al considered three mechanisms that could potentially contribute to deposit formation [115]: 1) electrokinetic effects [110,111,112], 2) flashing [67,68,108], and 3) particle trapping [67,68].…”

“…In this case, charge balance is restored by an additional current arising from oxidation/reduction reactions taking place at the surface. This phenomenon was proposed by Beck et al [110] to account for pitting of aircraft slide and sleeve hydraulic servo valves in a phosphate ester base hydraulic fluid, where the acceleration of the fluid through a gap at the interface of the slide and sleeve formed an anodic region on the surface of the sleeve and caused pitting of the sleeve. In the case of the fouling of flow orifices by magnetite, it is proposed that the acceleration of the fluid as it enters the orifice results in the formation of an anodic region at the entrance to the orifice and precipitation of magnetite via oxidation of ferrous ions [111,112].…”

“…Figure 14: Illustration of potential contributing factors to fouling of orifices under flow-boiling conditions [68]. An alternative mechanism for TSP fouling has been proposed based on work by Beck et al [110] and the investigations of the blockage of flow orifices used for boilers of Advanced Gas Reactors [111,112]. The mechanism is based on the effect of the streaming potential that develops when a fluid flows past a charged surface.…”