AWWA D106-16 pdf download.Sacrificial Anode Cathodic Protection Systems for the Interior Submerged Surfaces of Steel Water Storage Tanks
4.1.1 Criteria for protection. Te cathodic protection system shall main- tain the polarized tank-to-water potential at least as negative as –0.850 V to a copper/copper sulfate reference electrode (CSE) in contact with the stored water and the submerged tank surface, or at least 100 mV of cathodic polarization. The formation or decay of polarization can be measured to satisfy this criterion.
Cautionary Notes:
1. The 100-mV polarization criterion is only applicable to steel water storage tanks not having corrosion cells caused by connection to more noble metals such as copper, brass, or passive stainless steel (nonisolated dissimilar metals).
2. Dissimilar metals (e.g., stainless steel, copper, brass, etc.) installed inside the tank below the TCL shall be electrically isolated from the carbon steel tank components to which they are attached. Where electrical isolation is not possible, the application of a barrier coating on the more noble metallic components may be used in lieu of separate electrical isolation of components, provided that the selected coating system manufacturer validates the coating as having sufcient dielectric strength to provide a suitable barrier and that the coating can be properly applied and maintained.
4.1.2.2 Design life. Te design life of the cathodic protection system shall be calculated from the current discharge and consumption rate of the anodes. Te magnitude of current shall be that necessary to protect the tank in accordance with the criteria listed under Sec. 4.1.1, considering future coating deterioration. Te design of the sacrifcial anode cathodic protection system shall be capable of providing sufcient current to protect the tank for the full design life of the cathodic protection system.
4.1.2.3 Anode selection. Sacrifcial anodes shall be manufactured from either magnesium or zinc alloys. Te alloy shall be chosen to be compatible with water chemistry and design life.
4.1.2.4 Anode confguration. Te anode array shall provide and main- tain a uniform distribution of protective current without exceeding the potential limits described in Sec. 4.1.1. Te anode array shall incorporate satisfactory anode supports for the life of the system, including high fow rates that may be encoun- tered when the tank is flled or emptied. Te system design shall consist of sacri- fcial anodes with lead wires that connect to a collector cable, both ends of which terminate in a test box with a tank connection cable, a tank test lead, a calibrated shunt, and a reference electrode lead.AWWA D106-16 pdf download.