Stray existing rust. Roaming existing is the current that wears away and harms metal pipes beyond the security system style for underground flow. Roaming existing rust includes DC roaming present deterioration and a/c stray existing corrosion. The DC roaming present mainly originates from the dc electrified train, the DC electrolytic devices basing electrode, the anode ground bed in the cathodic protection system and more. The stray current flow process forms 2 deterioration batteries established by the exterior prospective distinction. One is that the existing flows out of the rail and also right into the steel pipe. The rail is the anode of the corrosion battery, and also rust happens. The various other is the current flowing out of the pipe back to the rail, the pipe is the anode that wears away the battery, rusts, the rail is the cathode, does not rust.