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Cathodic polarization behavior of mild steel exposed to selected flow velocities and slope parameters in natural seawater
Title
Cathodic polarization behavior of mild steel exposed to selected flow velocities and slope parameters in natural seawater.
Creator
Hugus, G. Dickson, IV., Florida Atlantic University, Hartt, William H.
Abstract/Description
Twenty-four test cells arranged in a pipe flow setup were assembled to investigate the effect of seawater velocity on the polarization behavior of galvanically polarized mild steel. Each 1023 steel pipe specimen of 10.8 em ID was coupled via a current limiting resistor to a mercury activated aluminum anode and exposed to a velocity of either 0.03, 0.09 or 0.30 m/s. The resistors were sized such that polarization was controlled according to one of six slope parameters. Steady state potential...
Show moreTwenty-four test cells arranged in a pipe flow setup were assembled to investigate the effect of seawater velocity on the polarization behavior of galvanically polarized mild steel. Each 1023 steel pipe specimen of 10.8 em ID was coupled via a current limiting resistor to a mercury activated aluminum anode and exposed to a velocity of either 0.03, 0.09 or 0.30 m/s. The resistors were sized such that polarization was controlled according to one of six slope parameters. Steady state potential and maintenance current density values were determined, and a steady state potential vs. current density curve was established for specimens in each velocity. Some specimens experienced a rise in cathode potential and current density after an apparent steady state had been reached. This was probably related to the influence of velocity on the protectiveness of the calcareous deposit. Of the specimens that experienced a rise in steady state potential and current density, a few were later observed to decrease in potential and current density and reach steady state. Steady state current density vs. velocity plots of specimens at steady state potentials of -0.78, -0.88 and -0.98 V showed that current density was directly proportional to velocity as well as relatively insensitive to potential. Ficks' first law was utilized in conjunction with an empirically derived dimensionless correlation that characterizes the behavior between fluid velocity and mass transfer of molecular species from the bulk solution to the cathode surface in turbulent seawater pipe flow. Calcareous deposit porosity constants were calculated and it was surmised that as velocity increased by a factor of three, the porosity of the deposits near 0.78 and -0.89 V increased by multiples of about two on average. Porosity at the above potentials increased with decreasing potential by a factor of a little over two. SEM micrographs were made and EDX analyses were performed on the calcareous deposits of selected specimens.
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Date Issued
1997
PURL
http://purl.flvc.org/fcla/dt/15501
Subject Headings
Cathodic protection, Seawater corrosion, Marine steel
Format
Document (PDF)
Adhesion of calcareous deposits formed on steel surfaces under cathodic polarization
Title
Adhesion of calcareous deposits formed on steel surfaces under cathodic polarization.
Creator
Luo, Jiunn-Shyong, Florida Atlantic University, Hartt, William H., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
A procedure has been devised to characterize the adhesion of calcareous deposits formed upon steel in association with cathodic polarization in seawater. This involved bending the substrate in-situ and characterization of deposit debonding in terms of visual appearance, changes in the cathodic current density and the net charge transferred in association with film disruption. Specific attention has been focused upon the influence of exposure time, applied potential, flow rate, temperature,...
Show moreA procedure has been devised to characterize the adhesion of calcareous deposits formed upon steel in association with cathodic polarization in seawater. This involved bending the substrate in-situ and characterization of deposit debonding in terms of visual appearance, changes in the cathodic current density and the net charge transferred in association with film disruption. Specific attention has been focused upon the influence of exposure time, applied potential, flow rate, temperature, substrate surface finish and electrolyte type upon deposit adhesion. Presence of a Mg-rich, inner film as well as the impingement of CaCO3 particles enhanced the adhesion of calcareous deposits. Electrostatic forces, Van der Waals attraction, and chemical alteration of precipitates could be important factors contributing to deposit adhesion.
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Date Issued
1991
PURL
http://purl.flvc.org/fcla/dt/12271
Subject Headings
Sea-water corrosion, Marine steel, Cathodic protection, Adhesives
Format
Document (PDF)
Effect of cathodic protection and cyclic frequency on corrosion fatigue of selected high strength steels in seawater
Title
Effect of cathodic protection and cyclic frequency on corrosion fatigue of selected high strength steels in seawater.
Creator
Badve, Ashwin P., Florida Atlantic University, Hartt, William H.
Abstract/Description
Study of selected candidate steels for offshore application was undertaken to observe the effects of cathodic protection and cyclic frequency on corrosion fatigue life. Keyhole Compact Tension Fatigue experiments under constant amplitude sinusoidal loading and stress ratio of 0.5 were performed on 25.4 mm thick specimens in natural sea water and also in air upon three different steels (Y.S. 500-563 MPa). These steels represented different strengthening techniques, namely precipitation...
Show moreStudy of selected candidate steels for offshore application was undertaken to observe the effects of cathodic protection and cyclic frequency on corrosion fatigue life. Keyhole Compact Tension Fatigue experiments under constant amplitude sinusoidal loading and stress ratio of 0.5 were performed on 25.4 mm thick specimens in natural sea water and also in air upon three different steels (Y.S. 500-563 MPa). These steels represented different strengthening techniques, namely precipitation hardening, direct quenching--a thermomechanical control process (TMCP), and controlled rolling. Cathodic polarization was in the range between freely corroding and -1.10 Volts (SCE). The tests were performed at a frequency of 0.3 and 1.0 Hz. The results are presented in the S-N and potential versus cycles to initiation format. No effect of frequency (1.0-0.3 Hz) was observed at cathodic protection of -1.10 V (SCE). The steels showed an increase in fatigue life to an optimum potential, and excessive potentials were detrimental. The fatigue life in dry air was greater than in laboratory air (~50% RH).
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Date Issued
1989
PURL
http://purl.flvc.org/fcla/dt/14494
Subject Headings
Marine steel--Fatigue, Offshore structures, Sea-water corrosion, Corrosion and anti-corrosives
Format
Document (PDF)