以(yi)(yi)管(guan)道(dao)作為(wei)(wei)陽(yang)極(ji)，從外(wai)部通入電(dian)(dian)(dian)流(liu)(liu)，一般將(jiang)加速腐(fu)蝕(shi)，腐(fu)蝕(shi)電(dian)(dian)(dian)流(liu)(liu)隨陽(yang)極(ji)極(ji)化(hua)而增大(da)。但是對可(ke)以(yi)(yi)鈍(dun)(dun)(dun)化(hua)的(de)(de)(de)金屬則會出現另一情況，當電(dian)(dian)(dian)位(wei)(wei)(wei)隨電(dian)(dian)(dian)流(liu)(liu)上(shang)升，達(da)到致鈍(dun)(dun)(dun)電(dian)(dian)(dian)位(wei)(wei)(wei)后，腐(fu)蝕(shi)電(dian)(dian)(dian)流(liu)(liu)急速下降，甚(shen)至可(ke)下降幾萬(wan)倍(bei)，以(yi)(yi)后隨電(dian)(dian)(dian)位(wei)(wei)(wei)上(shang)升，電(dian)(dian)(dian)流(liu)(liu)不(bu)變(bian)，直到過鈍(dun)(dun)(dun)區(qu)為(wei)(wei)止。利用(yong)這個原(yuan)理Edleanu 首先(xian)提出陽(yang)極(ji)保護(hu)的(de)(de)(de)概念，以(yi)(yi)需(xu)(xu)要(yao)保護(hu)的(de)(de)(de)設(she)備(bei)為(wei)(wei)陽(yang)極(ji)，導入電(dian)(dian)(dian)流(liu)(liu)，使電(dian)(dian)(dian)位(wei)(wei)(wei)保持在(zai)鈍(dun)(dun)(dun)化(hua)區(qu)的(de)(de)(de)中段（以(yi)(yi)免波(bo)動時進(jin)入活(huo)化(hua)區(qu)），腐(fu)蝕(shi)速率(lv)可(ke)保持很低值，通入的(de)(de)(de)電(dian)(dian)(dian)流(liu)(liu)就表示設(she)備(bei)的(de)(de)(de)腐(fu)蝕(shi)速率(lv)。這種(zhong)方法(fa)需(xu)(xu)要(yao)一臺恒(heng)電(dian)(dian)(dian)位(wei)(wei)(wei)儀(yi)，用(yong)以(yi)(yi)控(kong)制(zhi)(zhi)設(she)備(bei)的(de)(de)(de)電(dian)(dian)(dian)位(wei)(wei)(wei)。因為(wei)(wei)它只適(shi)用(yong)于接觸鈍(dun)(dun)(dun)化(hua)溶液(ye)的(de)(de)(de)可(ke)鈍(dun)(dun)(dun)化(hua)金屬，所以(yi)(yi)用(yong)途(tu)受限制(zhi)(zhi)。工業上(shang)已(yi)用(yong)于處理硫酸、磷酸、碳(tan)(tan)酸氫銨生產液(ye)、硝(xiao)銨混肥等的(de)(de)(de)不(bu)銹鋼或(huo)碳(tan)(tan)鋼制(zhi)(zhi)的(de)(de)(de)各(ge)種(zhong)管(guan)道(dao)設(she)備(bei)。