Originally Posted by uncle Ray
It is possible to over protect a vessel with an ICCP system, if the voltage is too high for an excessive period of time it will cause Hydrogen embrittlement and as a result of this the likes of valve stems and spades made of lesser noble metals will suffer, reference cells are strategically placed around the vessel to monitor the voltage output but as most ICCP units are placed to the aft of the vessel the reference cells up Fwd will give a lesser reading to the aft reference cells therefore a happy medium must be reached. Once the ICCIP system has been switched on for the first time it will take many days for it to become fully effective and vice versa if it is switched off it will take just as long to UN protect the vessel, Ive heard of some vessels switching off the system from time to time to prevent any problems such as embrittlement.
I think it is highly unlikely that one will come across hydrogen embrittlement on a hull unless and unusually it is made of high tensile steel. Again, even that would, I think, be more likely due to manufacturing than free hydrogen absorbed from its interface with the paint.
I did hear it talked about WRT MV Arctic and extremely cold water operations but I think that, too, was eventually discounted.
I am no metallurgist nor am I a gambler but I will take a bet that one is more likely to diagnose one's ICCP putting out too much from a side full of missing paint than waiting for the odd crack from hydrogen embrittlement. Any metallic suffering from overprotection will not involve it having been sacrificial, by definition, although with the Russian system it might well have been burned off!