This invention falls into the field of devices designed to guarantee the cathodic protection, using a non consumable electrode, of tanks containing liquid, in particular boilers. A tubular element (4), which also has other functional roles within a boiler to be protected against corrosion, is made, at least partially, of titanium or a material with the equivalent anti-corrosion characteristics. The said tubular element fulfils the function of a non-consumable electrode. The surface of the said tubular element may have one or more active and passive sections.