Research of electro-magnetic spectrum method prospecting underground pipeline joint

Based on the secondary magnetic distribution characters in frequency domain, the formation and transmission characters of faradic current were analyzed and the abnormal regularity resulting from pipeline depth change was discussed. The results indicate that when electromagnetic method is used to detect underground metal pipelines in frequency domain, the non-metal joint of mental pipeline may cause the decay of observed signals because of the influence of the inner current of mental pipelines. This phenomenon is easy to be confused with the abnormal characters resulting from depth variation. This study demonstrates that the two kinds of abnormals can be differentiated effectively by the ratio parameter method.