以(yi)管(guan)道作為陽(yang)極(ji)，從外部通入(ru)電(dian)(dian)(dian)流，一(yi)般將加速腐(fu)蝕(shi)(shi)，腐(fu)蝕(shi)(shi)電(dian)(dian)(dian)流隨陽(yang)極(ji)極(ji)化(hua)(hua)而(er)增大(da)。但(dan)是對可(ke)以(yi)鈍(dun)(dun)(dun)化(hua)(hua)的(de)金(jin)(jin)屬則會(hui)出現另一(yi)情況，當(dang)電(dian)(dian)(dian)位(wei)(wei)隨電(dian)(dian)(dian)流上升，達到(dao)致鈍(dun)(dun)(dun)電(dian)(dian)(dian)位(wei)(wei)后(hou)，腐(fu)蝕(shi)(shi)電(dian)(dian)(dian)流急速下降(jiang)(jiang)，甚至可(ke)下降(jiang)(jiang)幾萬倍，以(yi)后(hou)隨電(dian)(dian)(dian)位(wei)(wei)上升，電(dian)(dian)(dian)流不變，直(zhi)到(dao)過鈍(dun)(dun)(dun)區為止(zhi)。利用這個原(yuan)理Edleanu 首(shou)先(xian)提(ti)出陽(yang)極(ji)保護(hu)的(de)概念(nian)，以(yi)需要(yao)保護(hu)的(de)設(she)備(bei)(bei)為陽(yang)極(ji)，導(dao)入(ru)電(dian)(dian)(dian)流，使電(dian)(dian)(dian)位(wei)(wei)保持(chi)在鈍(dun)(dun)(dun)化(hua)(hua)區的(de)中段（以(yi)免波動(dong)時進入(ru)活化(hua)(hua)區），腐(fu)蝕(shi)(shi)速率可(ke)保持(chi)很低值，通入(ru)的(de)電(dian)(dian)(dian)流就表示設(she)備(bei)(bei)的(de)腐(fu)蝕(shi)(shi)速率。這種方法需要(yao)一(yi)臺恒電(dian)(dian)(dian)位(wei)(wei)儀，用以(yi)控制(zhi)(zhi)設(she)備(bei)(bei)的(de)電(dian)(dian)(dian)位(wei)(wei)。因為它只適用于(yu)接觸鈍(dun)(dun)(dun)化(hua)(hua)溶(rong)液(ye)的(de)可(ke)鈍(dun)(dun)(dun)化(hua)(hua)金(jin)(jin)屬，所(suo)以(yi)用途受限制(zhi)(zhi)。工(gong)業上已用于(yu)處理硫酸(suan)、磷酸(suan)、碳(tan)酸(suan)氫銨生產(chan)液(ye)、硝銨混肥等的(de)不銹鋼(gang)或碳(tan)鋼(gang)制(zhi)(zhi)的(de)各種管(guan)道設(she)備(bei)(bei)。