a flexible ferromagnetic strip is used to induction - weld seams in polymer pipes . the strip is a blend of strontium ferrite , a surfactant , and an ldpe binder . a process to produce the profile is to mix the ingredients together followed by granulation and extrusion or calendering . the strip is used in conjunction with an induction coil sized to fit over a polymer pipe coupling containing the strip and separate segments of polymer pipe . the strip is heated by induction current induced by an electromagnetic field generated by the coil . the heated strip causes the polymer pipe segments to be thermoplastically welded together .