The 25-year challenge: stopping corrosion in its tracks



Frederik Van Haute, Acotec, Belgium


1985: The first industrial applications of the Humidur® protective system against ALWC
The first purchase order for the protection of quay walls from severe corrosion was undertaken by Acotec’s mother company General Coatings NV, at quay walls north of the Belgian city of Ghent. The Port of Ghent is connected with the North Sea via the 19-mile long Ghent-Terneuzen canal and the mouth of the River Scheldt. The canal was enlarged at the end of the Sixties. A sea lock system at Terneuzen provides passage between the canal and the Scheldt estuary.

1968: The finished berths were delivered. The berth walls were built using Z-profile sheet piles, made from a copper-iron alloy and pre-coated with coal tar.

1970s: Severe corrosion must have started somewhere in the 1970s, less than 10 years after the construction and exposure of the bulkheads. Incidents of subsidences at the bank were noticed in 1978, indicating pile holes below the water line. The canal water was seriously polluted by industrial waste water in that period. The composition of the bulk water was at the edge of fresh and brackish water, let’s say slightly brackish, containing around 1000ppm (parts per million) of salt.

1978: Underwater corrosion began to be incidentally observed. Acotec’s mother company started to investigate and discovered for the first time a strange form of severe corrosion, which was unknown at that time by authorities. It was considered an anomaly, an unusual but local phenomenon of pustule formation inside the biofilm covering the piles below water, and supposed to be caused by water pollution.

Our investigations were based on observations by divers, steel coupons cut out of the piles and samples of the biological film and tubercles covering the underwater part of the pilings, as well as research by the Brussels Pourbaix laborator ies Cebelcor. In that period corrosion speeds were considered to be 10 microns per year in magnitude, and thus hardly significant for strength calculations in comparison to plate thicknesses of 10mm. Corrosion below water was not considered as a harmful phenomenon.

It became clear that the severe corrosion with linear speeds of about 1mm per year (10mm of steel had been perforated over 10 years at these bulkheads) revealed a new and extraordinary form of corrosion. Pourbaix’s institute Cebelcor discovered that the origin was bacterial and was Microbially Induced Corrosion (MIC).

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