Why does the solenoid valve coil corrode?

The solenoid valve coil terminal has water ingress due to poor sealing, and all the corrosion of the terminal is on the positive electrode, while the negative electrode is intact.
It can be judged that poor sealing of solenoid valve coil and water ingress are the primary cause of corrosion of the terminal. However, due to the poor site conditions, the impact of coal on the coil is inevitable, so there is no guarantee that there is no water at the coil terminal.
Due to the presence of water at the terminal and the salt in the water, it acts as an electrolyte;
 So there was a galvanic reaction
For the negative electrode, when the coil is energized, all electrons flow to the negative electrode, and the corrosion current on the surface of the negative electrode terminal drops to zero or close to zero. This prevents the terminal from losing electrons and prevents the terminal from corrosion.
This is the so-called cathodic protection of impressed current.
For the positive electrode, the situation is the opposite. It becomes the sacrificial anode in the "Sacrificial Anode Cathodic Protection Law".
Therefore, even copper, which is chemically inactive, is quickly corroded, and the terminal is broken, causing failure and shutdown.