Photo 1 shows the quay wall’s serious corrosion and other deterioration prior to being repaired and protected from future corrosion, as shown in photo 2.

Acotec, which has applied its proprietary Humidur® corrosion protection formula to submerged structures around the world since 1985, just completed a $408,000 project in Okinawa, Japan, for the U.S. Army Corps of Engineers’ Construction Engineering Research Laboratory.

Acotec was called upon to repair a seriously corroded, 100-meter long quay wall in the Small Vessels Harbor of Naha Port, the second largest military port on Okinawa. While corrosion and extensive holing were easily visible above water, there was no indication of the condition on the piles under water.

The U.S. Army Corps of Engineers sought to evaluate the effectiveness of repair techniques on those heavily corroded piles, and to monitor the durability of the Humidur® corrosion protection system applied in dry conditions – below the water surface – by using the mobile cofferdam DZI.

Acotec’s state-of-the-art “Pacific Flyer” Cofferdam n° 23, which is six meters high and six meters long, was shipped with other equipment in two standard 12-meter containers, then off-loaded at the work site in late October 2008.

A team of three specialists and a site manager worked on the project for six weeks, successfully completing the work on December 11.

The size of the DZI mobile cofferdam allowed to work on five piles at the time, from the underside of the concrete copping beam to 4 meters down. After cleaning the steel surface of shells and vegetation over the full length, the underlying thick layers of amorphous rust (up to 2 cm thick) were removed with pneumatic tools.

The remaining steel thickness was systematically measured and revealed an average loss of 50% on both webs and flanges. There was a distinct corrosion pattern in the vertical section: extensive layers of amorphous rust and holing in the zone above water, and severe pitting under layers of amorphous rust from the splash zone to the low water line. In the lower parts there were peculiar pitting patterns and striations 3 to 4 meters deep.

In every set-up, five to 10 holes mainly at the 3-meter level needed to be plugged and covered with a steel doubler plate. In total, 84 holes were plugged and plates were welded in the underwater zone. Above water, 50 outpans have been completely remodelled with steel plates more than 1 meter high, bent to fit the original shape as closely as possible, as shown in photo 4.

The cost of the structural repairs and welding work had become very important, in comparison to the corrosion protection work. It was decided to do a maximum fully repaired and protected stretch of quay wall within the preset budget.

The job was completed to full satisfaction of the customer and within the planned time schedule and budget. Acotec provides a 10-year insurance warranty on the Humidur® corrosion protection for this project, although 25-year-old maintenance-free projects prove now that the service life can be extended up to 50 years.

To learn more, visit www.acotec.be,

e-mail at frederik.van.haute@acotec.be 

or call us at 0032 53 83 86 60.