以管(guan)道(dao)(dao)作為陽(yang)極，從外部通入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)，一(yi)(yi)般將加速(su)(su)腐蝕(shi)(shi)，腐蝕(shi)(shi)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)隨陽(yang)極極化(hua)(hua)而增大(da)。但是對可以鈍(dun)化(hua)(hua)的金屬則會出(chu)現另一(yi)(yi)情況(kuang)，當電(dian)(dian)(dian)(dian)(dian)位(wei)隨電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)上升，達到(dao)(dao)致鈍(dun)電(dian)(dian)(dian)(dian)(dian)位(wei)后(hou)，腐蝕(shi)(shi)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)急速(su)(su)下降(jiang)，甚至(zhi)可下降(jiang)幾萬倍(bei)，以后(hou)隨電(dian)(dian)(dian)(dian)(dian)位(wei)上升，電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)不(bu)(bu)變，直到(dao)(dao)過(guo)鈍(dun)區(qu)為止。利用(yong)(yong)(yong)這個原理Edleanu 首先提(ti)出(chu)陽(yang)極保(bao)(bao)(bao)護的概念，以需要保(bao)(bao)(bao)護的設(she)備為陽(yang)極，導入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)，使電(dian)(dian)(dian)(dian)(dian)位(wei)保(bao)(bao)(bao)持在鈍(dun)化(hua)(hua)區(qu)的中(zhong)段（以免波動時進(jin)入(ru)(ru)活化(hua)(hua)區(qu)），腐蝕(shi)(shi)速(su)(su)率可保(bao)(bao)(bao)持很低值，通入(ru)(ru)的電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)就表示設(she)備的腐蝕(shi)(shi)速(su)(su)率。這種方(fang)法需要一(yi)(yi)臺恒電(dian)(dian)(dian)(dian)(dian)位(wei)儀，用(yong)(yong)(yong)以控制(zhi)設(she)備的電(dian)(dian)(dian)(dian)(dian)位(wei)。因為它只(zhi)適用(yong)(yong)(yong)于接觸鈍(dun)化(hua)(hua)溶(rong)液(ye)(ye)的可鈍(dun)化(hua)(hua)金屬，所以用(yong)(yong)(yong)途受限制(zhi)。工業上已用(yong)(yong)(yong)于處(chu)理硫酸、磷酸、碳酸氫(qing)銨生產液(ye)(ye)、硝銨混肥等的不(bu)(bu)銹鋼或碳鋼制(zhi)的各種管(guan)道(dao)(dao)設(she)備。