Wreckage of ‘Carnauba’, a 1930s vintage Sikorsky S-38 aircraft, a beloved icon
of SC Johnson's early history, was found on July 5, 2000, in seawater off of an
Indonesian island of West Irian Jaya. The company decided to recover this aircraft from
seawater, conserve it, and display it in its museum, as part of their rich heritage. The
objective was to study the aluminum alloy used on the aircraft for its chemical and
mechanical properties, suggest the corrosion mechanism of aluminum alloy 2024 in
seawater, and recommend preservation methods for the same. Chemical analysis
performed on the samples collected from the site revealed that copper was the primary
alloying element. Copper is responsible for increasing the strength. However, copper is
also the reason for pitting corrosion of the aluminum alloy, causing material loss and
reducing the structural stability of the wreckage. Copper forms intermetallics with other
elements, such as magnesium and aluminum, and is distributed in the aluminum matrix
heterogeneously. In order to study the corrosion mechanism of aluminum alloy 2024, it
was subjected to potentiodynamic tests in sodium chloride solution. In the presence of an electrolyte like seawater, the difference between the potentials of these intermetallics
and the surrounding aluminum matrix creates a galvanic cell. The galvanic cells serve as
sites for localized corrosion. Chloride ions are responsible for pitting of alloy 2024. A
pitting potential of around -600mV was observed when sodium chloride was used as an
electrolyte. The average corrosion rate measured for wrought aluminum alloys was
around 0.05 mm/year. The thesis provides guidelines or recommendations for the
procedure to be followed in recovering aircraft from seawater, and retain it in its as
found condition. Recommendations about various measurements like pH, dissolved
oxygen, salinity, pressure, temperature, and velocity need to be taken and the visual
assessment needs to be done before the aircraft is hauled from the seawater were
specified. After the aircraft has been recovered, recommendations for handling, cleaning,
and prevention of corrosion using coatings such as carnauba wax and inhibitors such as
chromates, have been stated.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-3002 |
| Date | 15 May 2009 |
| Creators | Gujarathi, Kedar Kanayalal |
| Contributors | Griffin, Richard B. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | electronic, application/pdf, born digital |
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