以(yi)管(guan)道作為(wei)(wei)陽(yang)(yang)極，從外部通(tong)入(ru)電(dian)(dian)(dian)(dian)流(liu)(liu)，一般將加速(su)(su)腐(fu)蝕，腐(fu)蝕電(dian)(dian)(dian)(dian)流(liu)(liu)隨(sui)陽(yang)(yang)極極化而(er)增大。但是對可(ke)(ke)以(yi)鈍(dun)化的金屬則會出現另一情況，當電(dian)(dian)(dian)(dian)位隨(sui)電(dian)(dian)(dian)(dian)流(liu)(liu)上升，達到(dao)致鈍(dun)電(dian)(dian)(dian)(dian)位后，腐(fu)蝕電(dian)(dian)(dian)(dian)流(liu)(liu)急速(su)(su)下降(jiang)，甚至可(ke)(ke)下降(jiang)幾(ji)萬倍，以(yi)后隨(sui)電(dian)(dian)(dian)(dian)位上升，電(dian)(dian)(dian)(dian)流(liu)(liu)不(bu)變(bian)，直到(dao)過鈍(dun)區(qu)為(wei)(wei)止。利用這個(ge)原(yuan)理(li)Edleanu 首(shou)先提出陽(yang)(yang)極保護(hu)的概念，以(yi)需要保護(hu)的設備(bei)為(wei)(wei)陽(yang)(yang)極，導入(ru)電(dian)(dian)(dian)(dian)流(liu)(liu)，使電(dian)(dian)(dian)(dian)位保持(chi)(chi)在鈍(dun)化區(qu)的中段（以(yi)免波動時進(jin)入(ru)活化區(qu)），腐(fu)蝕速(su)(su)率可(ke)(ke)保持(chi)(chi)很低值，通(tong)入(ru)的電(dian)(dian)(dian)(dian)流(liu)(liu)就表示(shi)設備(bei)的腐(fu)蝕速(su)(su)率。這種(zhong)方法需要一臺恒電(dian)(dian)(dian)(dian)位儀，用以(yi)控制設備(bei)的電(dian)(dian)(dian)(dian)位。因為(wei)(wei)它只適用于接觸鈍(dun)化溶液的可(ke)(ke)鈍(dun)化金屬，所以(yi)用途受(shou)限制。工業(ye)上已(yi)用于處理(li)硫(liu)酸(suan)、磷(lin)酸(suan)、碳(tan)酸(suan)氫(qing)銨生產液、硝銨混肥等(deng)的不(bu)銹鋼(gang)或碳(tan)鋼(gang)制的各種(zhong)管(guan)道設備(bei)。