以管(guan)道(dao)作為陽(yang)極(ji)，從外(wai)部通(tong)入電(dian)(dian)流(liu)，一般將加(jia)速腐蝕(shi)(shi)，腐蝕(shi)(shi)電(dian)(dian)流(liu)隨(sui)陽(yang)極(ji)極(ji)化(hua)(hua)而增大。但(dan)是對(dui)可以鈍化(hua)(hua)的(de)(de)金(jin)屬(shu)則會出現另一情況，當電(dian)(dian)位(wei)(wei)(wei)(wei)(wei)隨(sui)電(dian)(dian)流(liu)上升，達(da)到致鈍電(dian)(dian)位(wei)(wei)(wei)(wei)(wei)后，腐蝕(shi)(shi)電(dian)(dian)流(liu)急(ji)速下(xia)降(jiang)，甚至可下(xia)降(jiang)幾萬倍，以后隨(sui)電(dian)(dian)位(wei)(wei)(wei)(wei)(wei)上升，電(dian)(dian)流(liu)不變，直到過(guo)鈍區為止(zhi)。利用(yong)(yong)這個原理(li)Edleanu 首先提出陽(yang)極(ji)保(bao)護(hu)的(de)(de)概念，以需要(yao)(yao)保(bao)護(hu)的(de)(de)設(she)備為陽(yang)極(ji)，導(dao)入電(dian)(dian)流(liu)，使電(dian)(dian)位(wei)(wei)(wei)(wei)(wei)保(bao)持在鈍化(hua)(hua)區的(de)(de)中段(duan)（以免波動時進入活化(hua)(hua)區），腐蝕(shi)(shi)速率可保(bao)持很低值，通(tong)入的(de)(de)電(dian)(dian)流(liu)就表示(shi)設(she)備的(de)(de)腐蝕(shi)(shi)速率。這種(zhong)方法需要(yao)(yao)一臺恒(heng)電(dian)(dian)位(wei)(wei)(wei)(wei)(wei)儀，用(yong)(yong)以控制(zhi)設(she)備的(de)(de)電(dian)(dian)位(wei)(wei)(wei)(wei)(wei)。因為它只適用(yong)(yong)于接觸鈍化(hua)(hua)溶液(ye)(ye)的(de)(de)可鈍化(hua)(hua)金(jin)屬(shu)，所以用(yong)(yong)途受限(xian)制(zhi)。工業上已(yi)用(yong)(yong)于處(chu)理(li)硫酸、磷酸、碳酸氫銨(an)生產液(ye)(ye)、硝(xiao)銨(an)混肥等的(de)(de)不銹鋼(gang)或碳鋼(gang)制(zhi)的(de)(de)各種(zhong)管(guan)道(dao)設(she)備。