A new 300 metre long deep water quay under construction at London's Tilbury Docks, for Tilbury Container Services, is to have its steel piles protected against advanced low water corrosion (ALWC) by a BAC Corrosion Control impressed current cathodic protection (ICCP) system.
BAC has been awarded the contract by AMEC Capital Projects to design, supervise specialist installation activities, test, commission and maintain the cathodic protection (CP) system for one year. The ICCP system uses constant current power supplies energizing ISOMMO mixed metal oxide anodes, which are mounted with cantilever supports on the front face of the piles.
BAC developed ISOMMO anodes as a more cost effective and easier to handle alternative to equivalent silicon iron and magnetite anodes. The tubular device comprises a titanium tube with a mixed metal oxide coating that activates the titanium electrically enabling it to function as an anode. It has a very low consumption rate (micrograms per ampere/year). With the cable connection in the middle of the tube, at a crimped section, even current distribution along the anode's length is assured.
ALWC is a recently discovered phenomenon of bacterially activated corrosion, which is normally concentrated at the low tide level. Historically, corrosion rates at these levels were thought to be very low but since UK coastal waters are now a lot cleaner, deposits that used to exist on the steel piles have disappeared and the amount of bacteria that is able to live in the water has increased. Corrosion rates from this form of attack can be many times more than the previously accepted norm.
It has been found that if a CP system is installed when the structure is built ALWC does not occur, however for existing structures where CP is not fitted and ALWC is evident BAC Corrosion Control have developed LATreat ® a 3 stage treatment to arrest the problem.