Smith, Samuel W.

Formation of calcareous deposits on marine structures under cathodic protection reduces the current required to protect the surface, as time progresses. Computer aided design methods to date rely heavily on polarization data obtained from laborious and expensive in situ experiments. The present approach lays the foundation for a new design method in which the formation of calcareous deposits is modeled from first principles, based on precipitation and diffusion of ions of the constituent compounds in the boundary layer. Calcareous deposition in a one dimensional boundary layer was modeled and this model was used successfully to simulate the cathodic protection of a rotating cylinder in artificial sea water. Precipitation rate constant of Mg(OH)$\sb2$ was determined and the pH on the cylinder surface was estimated to be one tenth of a pH unit higher than that required for the precipitation of magnesium hydroxide from sea water.

The influence of hydrodynamic parameters and limiting
current density by cathodic protection on a steel cylinder in
flowing water is investigated. The limiting current density
variations along the circumference of a circular cylinder are
determined for different flow velocities. Several methods
are also used to relate the cathodic current density
distribution to variations in hydrodynamic and diffusional
boundary layer thickness along the circumference of the
cylinder for laminar and turbulent flow regimes. a
comparison of experimental current densities on a cylinder to
that predicated by theory is also examined.

The efficiency of cathodic protection of steel in seawater
is partially due to calcareous deposits. To better understand
deposits, expericents are conducted testing the effects of variables
such as tecperature, velocity, and applied current, on
film formation and protection capabilities. It is the intent
of this thesis to investigate differences in using recirculating
seawater rather than once-through seawater in these experiments.
It is believed that these differences were caused by an increase
in dissolved organics in the recirculating bath. Data is in
the form of current needed to maintain a potential of -1.0v SCE
since differences in current help describe differences in film
properties.

The influence of hydrodynamic parameters and cathodic
polarization on the formation of calcareous deposits on a
steel plate in flowing seawater is investigated. Current
density variations on the plate are determined for a
combination of applied potentials and seawater
velocities. Equations are developed to relate the
cathodic current density distribution to variations in
hydrodynamic and diffusional boundary layer thickness
along the plate for laminar and turbulent flow regimes. A
comparison of experimental current densities on a bare
plate to that predicted by theory is examined. Effects of
flow on the formation and properties of calcareous
deposits are discussed in light of recent developments in
marine cathodic protection.