以(yi)管(guan)道作為陽(yang)極(ji)，從外(wai)部通入電(dian)(dian)(dian)(dian)流(liu)(liu)(liu)，一般將加速腐(fu)(fu)蝕，腐(fu)(fu)蝕電(dian)(dian)(dian)(dian)流(liu)(liu)(liu)隨陽(yang)極(ji)極(ji)化而增大。但是(shi)對可(ke)(ke)以(yi)鈍(dun)化的(de)金屬則會(hui)出現(xian)另一情況，當電(dian)(dian)(dian)(dian)位隨電(dian)(dian)(dian)(dian)流(liu)(liu)(liu)上(shang)升(sheng)(sheng)，達到致鈍(dun)電(dian)(dian)(dian)(dian)位后(hou)，腐(fu)(fu)蝕電(dian)(dian)(dian)(dian)流(liu)(liu)(liu)急(ji)速下(xia)降，甚至可(ke)(ke)下(xia)降幾萬倍(bei)，以(yi)后(hou)隨電(dian)(dian)(dian)(dian)位上(shang)升(sheng)(sheng)，電(dian)(dian)(dian)(dian)流(liu)(liu)(liu)不變，直到過鈍(dun)區(qu)為止。利(li)用(yong)這(zhe)個原理Edleanu 首(shou)先提出陽(yang)極(ji)保(bao)護的(de)概念，以(yi)需(xu)(xu)要保(bao)護的(de)設(she)備為陽(yang)極(ji)，導入電(dian)(dian)(dian)(dian)流(liu)(liu)(liu)，使電(dian)(dian)(dian)(dian)位保(bao)持(chi)在鈍(dun)化區(qu)的(de)中段（以(yi)免波動(dong)時進(jin)入活化區(qu)），腐(fu)(fu)蝕速率可(ke)(ke)保(bao)持(chi)很(hen)低值，通入的(de)電(dian)(dian)(dian)(dian)流(liu)(liu)(liu)就(jiu)表示設(she)備的(de)腐(fu)(fu)蝕速率。這(zhe)種方(fang)法需(xu)(xu)要一臺(tai)恒電(dian)(dian)(dian)(dian)位儀，用(yong)以(yi)控制(zhi)設(she)備的(de)電(dian)(dian)(dian)(dian)位。因為它只適用(yong)于接觸鈍(dun)化溶液(ye)(ye)的(de)可(ke)(ke)鈍(dun)化金屬，所以(yi)用(yong)途受限制(zhi)。工業上(shang)已用(yong)于處理硫酸、磷酸、碳酸氫銨生產液(ye)(ye)、硝(xiao)銨混肥等(deng)的(de)不銹鋼(gang)或碳鋼(gang)制(zhi)的(de)各種管(guan)道設(she)備。