Sheet piles, used as retaining walls, wharfs, and piers, are typically made of unprotected carbon steel (CS). This type is affordable and the general corrosion rate (wastage) is predictable. Despite the long and successful use of CS sheet pilings, there are reports of localised corrosion of CS pilings that have been identified as microbiologically influenced corrosion (MIC) ie. corrosion that is a result of the presence and activities of microorganisms. Microorganisms can produce localised attack including pitting, enhanced erosion corrosion, enhanced galvanic corrosion, stress corrosion cracking, and hydrogen embrittlement of CS. Microorganisms do not produce a unique corrosion morphology in CS that could not be produced abiotically.i
Corrosion of pilings in marine and estuarine environments
Accelerated low water corrosion (ALWC) is a particularly aggressive form of localised corrosion that has become a high profile problem, associated with unusually high corrosion rates of unprotected or inadequately protected CS pilings in marine and estuarine waters. The UK Institution of Civil Engineers described ALWC as “a matter of national importance”.ii
ALWC is a global phenomenon having been reported in all climatic conditions on unprotected steel pilings in contact with saline water (ie. seawater and brackish water) that is subject to tidal influences.iii A survey of port and harbour authorities in five Western European countries concluded that at least 13 percent of the ports were affected by ALWC.iv
The term ALWC does not define a corrosion mechanism. Instead the term denotes the precise location of the corrosion on the exposed pilings
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