08239 Corrosion of Civil War Era Sub Marine Explorer, Inter-Tidal Zone, Bay of Panama

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Product Number: 51300-08239-SG

ISBN: 08239 2008 CP

Author: Donald L. Johnson, Brent M. Wilson, James P. Delgado, Larry E. Murphy, and James D. Carr

Publication Date: 2008

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Degradation of the upper wrought-iron hull of Sub Marine Explorer in the tidal zone has occurred as a result of corrosion, mechanical abrasion, and impact. A larger portion of the lower cast-iron hull that remains submerged is better preserved. Upper hull corrosion rate was determined through direct hull-thickness measurement, examination of the physical and chemical properties of the concretion, and corrosion potential measurements (Ecorr). In general, corrosion rate decreases from top centerline to sand line and from bow to stern. Transects in the interior working chamber show the reverse from bow to stern, suggesting that external tidal flow pattern directly affected the corrosion rate. X-ray diffraction data reveal that iron is trapped in concretion as slightly magnetic gamma Fe2O3 (maghemite) and FeCO3 (siderite). Concretion Equivalent Corrosion Rate (CECR) and direct measurement of wrought iron hull thickness yield an estimated total corrosion rate of 0.066 mmpy (2.7 mpy), or 0.033 mmpy (1.3 mpy), per side, which agrees well with earlier corrosion research in the Panama Canal Zone. Ecorr data and visual observation suggest that the cast-iron hull portion below the low tide level has a slightly lower corrosion rate.