Analysis on the shielding effect by metallic pipe line against electromagnetic induced voltage

The induced voltages are measured to verify whether there is a shielding effect by a metal pipeline like a gas or water provision against electromagnetic induction emitted from power line onto communication line. We installed the first pipeline, 300 m, with a telecommunication cable and measured induced voltages. And then we installed again the second pipeline and measured the voltages. There was a around 20% shielding effect by the first pipeline and 30% shielding effect by the second pipeline together against the usual induced voltage, 3 V in this experiment case, on the communication cable. We see that there would be a shielding effect by pipeline against electromagnetic induction from this result and could apply into the effectiveness of protection measures.