以(yi)管(guan)道作為陽(yang)(yang)(yang)極(ji)，從外部通入(ru)電(dian)(dian)(dian)(dian)流(liu)，一般(ban)將(jiang)加速(su)腐(fu)(fu)(fu)蝕，腐(fu)(fu)(fu)蝕電(dian)(dian)(dian)(dian)流(liu)隨陽(yang)(yang)(yang)極(ji)極(ji)化(hua)而增大(da)。但是對可(ke)以(yi)鈍(dun)(dun)化(hua)的(de)金屬(shu)則會出現另一情況，當電(dian)(dian)(dian)(dian)位(wei)(wei)隨電(dian)(dian)(dian)(dian)流(liu)上(shang)升(sheng)，達到致鈍(dun)(dun)電(dian)(dian)(dian)(dian)位(wei)(wei)后，腐(fu)(fu)(fu)蝕電(dian)(dian)(dian)(dian)流(liu)急(ji)速(su)下降(jiang)，甚至可(ke)下降(jiang)幾萬倍，以(yi)后隨電(dian)(dian)(dian)(dian)位(wei)(wei)上(shang)升(sheng)，電(dian)(dian)(dian)(dian)流(liu)不變，直到過鈍(dun)(dun)區(qu)為止。利(li)用(yong)這個原理(li)Edleanu 首先提出陽(yang)(yang)(yang)極(ji)保護的(de)概念，以(yi)需(xu)要(yao)保護的(de)設備(bei)為陽(yang)(yang)(yang)極(ji)，導入(ru)電(dian)(dian)(dian)(dian)流(liu)，使電(dian)(dian)(dian)(dian)位(wei)(wei)保持在(zai)鈍(dun)(dun)化(hua)區(qu)的(de)中段（以(yi)免波動時(shi)進入(ru)活(huo)化(hua)區(qu)），腐(fu)(fu)(fu)蝕速(su)率(lv)可(ke)保持很低(di)值，通入(ru)的(de)電(dian)(dian)(dian)(dian)流(liu)就表(biao)示設備(bei)的(de)腐(fu)(fu)(fu)蝕速(su)率(lv)。這種方法需(xu)要(yao)一臺恒(heng)電(dian)(dian)(dian)(dian)位(wei)(wei)儀，用(yong)以(yi)控制(zhi)設備(bei)的(de)電(dian)(dian)(dian)(dian)位(wei)(wei)。因(yin)為它只適用(yong)于(yu)接觸鈍(dun)(dun)化(hua)溶液的(de)可(ke)鈍(dun)(dun)化(hua)金屬(shu)，所以(yi)用(yong)途受限制(zhi)。工業上(shang)已(yi)用(yong)于(yu)處理(li)硫(liu)酸、磷酸、碳酸氫(qing)銨生產(chan)液、硝銨混(hun)肥(fei)等的(de)不銹鋼(gang)或碳鋼(gang)制(zhi)的(de)各種管(guan)道設備(bei)。