As we saw in reactions (2.1) and (2.2), corrosion occurs by the movement of electrical charge from the anode (a positively charged area of steel where the steel is dissolving and forming rust) to the cathode (a negatively charged area of steel where a charge balancing reaction occurs turning oxygen and water into hydroxyl ions). This means that the process is both electrical and chemical, that is, electrochemical. We have also seen that, in the case of chloride attack, patch repairs are only a local solution to corrosion and repairing an anode may accelerate corrosion in adjoining areas due to the incipient anode effect (Section 6.2.1 and Figure 6.5).