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Hurricane Surge Corrosion Failure Analysis

Saltwater corrosion of hollow aluminum tubing and cast iron bathtub construction materials was a concern after a hurricane and storm surge covered a construction site.  The effect of the wind driven storm debris and sand on coated aluminum windows and patio doors was also evaluated.  Sections of aluminum alloy tubing from balcony railings, which had been partially submerged by the storm surge, visually indicated the presence of saltwater residue.  A scanning electron microscopic (SEM) photograph of dendritic salt crystal residue on an uncoated aluminum alloy surface is shown in Photograph A.

Saltwater Corrosion on Aluminum
Photograph A   (SEM) of a dendritic salt crystal residue on the uncoated aluminum surface.

A close-up view of the outside surface of an uncoated cast iron bathtub, exhibiting pitting corrosion , is shown in Photograph B.

Salt Water corrosion on cast iron bathtub.
Photograph B   Pitting corrosion on the outside surface of a cast iron bathtub.

Energy Dispersive Spectroscopy (EDS), a method of chemical fingerprinting, was performed on the dendritic residues.  The presence of sodium chloride (salt) was confirmed.  Residual chlorine is especially insidious in that removal by cleaning and neutralization is extremely difficult.  Chlorine is a very mobile atom, which will migrate to the base of a corrosion pit and any sharp corner or weld toe where cleaning and neutralization are difficult.  Once present on an unprotected metal surface, if not neutralized from the effect of saltwater exposure, chlorine, will promote rapid pitting corrosion. The resistance of cast iron to chloride attack, especially hydrochloric acid is very poor.  Complete chloride removal by neutralization was believed to be more expensive than replacement.

The client was advised to replace all bare, uncoated metal items subjected to the hurricane storm surge.

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J.E.I. Metallurgical, Inc.

5514 Harbor Town
Dallas, Texas 75287

Phone: (972) 934-0493
Fax: (469) 737-3938

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