一般地下管線之陰極防蝕保護標準，都採用管對地電位更負於-850mV(Cu／CuSO4)，這種判定方法會受到天候及土壤種類的影響，而造成不同IR降之差異，若以極化電位測量則可以得到較正確的管線電位值。由於目前管線埋設太過擁擠，管線間遮蔽現象相當嚴重，以至防蝕電流無法均匀分佈，若以電位量測法是無法了解的。因此本研究即針對管線間之遮蔽象，設計各種不同遮蔽條件，並配合預先設計之測試管及參考電極，以電流量測法來探討遮蔽現象對陰極防蝕效果的影響。

Generally, a pipe-to-soil potential of -850mV vs. copper-copper sulfate reference electrode(CU$CuSO4)or more negative is the most widely used as a criterion for determining the acceptable degree of cathodic protection applied on the underground pipeline. However, geomophology, weather, and geology may interfere with the above criterion and result in the difference in IR drop. Although the difference in IR drop can be overcome by measurement techniques and deduce a optimized potential (i.e. polarized potential), this potential is actuallya mixed potential of all buried pipes in a local area. It seems very difficult to be aware of the potential distribution along the buried pipeline, because of the shield effect resulted from the arrangement and numbers of pipes situated in the same area. The purpose of this study is tried to clarify the effectiveness of cathodic protection under shielded condition. In order to simulate the shielded effect, the tested samples and reference electrodes were designed to locate in a different distance. It is also emphasized to understand the disadvantage of existing buried pipes and to study the improvement method. Due to the lack of consideration of shield effect in the past, it is hope that the experimental results can create a better and more correct design concept of cathodic protection and extend the service life of buried pipes.