Determination of the Best Hydrodynamic Parameter for Modelling Flow on Cathodically Polarized Surfaces.
Abstract
Short and long term velocity experiments were performed utilizing a rotating cylinder electrode. This was to determine the best way to model in the laboratory the flow conditions in service on a cathodically polarized surface or on anodically polarized zinc. This was studied by measuring the cathodic current required to protect HY-80 steel, nickel, aluminum, bronze, and commercially pure titanium in flowing seawater. Potentiodynamic scans on a one inch diameter cylindrical specimen were run at rotation speeds of 50, 100, 200, 800 and 2000 rpm. The limiting current portion of the resulting polarization curves indicated that all three materials illustrated rotation speed dependent behavior. This behavior was consistent with a mechanism whereby the reaction kinetics are governed by oxygen diffusion through a fluid boundary layer. The currents measured for HY-80 were approximately an order of magnitude lower than those consistent with boundary layer diffusion, due to the formation of a barrier layer of calcareous deposits or fouling. Increased rotation speeds, which result in increased shear stresses resulted in currents more consistent with the diffusion model, indicating that higher velocities result in stripping away surface deposits or change the morphology of the barrier film. The effect of velocity on the anodic current output for zinc sacrificial anodes was also evaluated to determine the best way to model flow over a scarificial anode. Some velocity effects were observed, but could not be related to a specific reaction control mechanism.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 1986
- Accession Number
- ADA178490
Entities
People
- David W Taylor
- HP Hack
- Robert Guanti