by any suitable method including but not limited to an oxidation process in examples of the invention wherein the impeder is internally cooled with a cooling medium the sheet can be rolled with a bobbin or one or more removal spindles to form one or more coolant passages within the impeder element suitable but not limiting thickness of the sheet is in the range of the diameters stated above for the high temperature wires used in other examples of the invention fig5 illustrates one example of use of an impeder of the present invention in an electric induction welding process stock material 90 which may be a metal sheet is driven through weld box 92 in the direction indicated by the arrow to bring opposing edges of the stock material together ac current flowing through induction coil 94 which surrounds the stock material creates a magnetic field that couples with the stock material induced currents in the stock material weld the opposing edges of the stock material together as they pass through the weld box to form a product 96 such as a tube or pipe an impeder of the present invention for example impeder 10 shown in fig1 a and fig1 b is inserted into the stock material generally in the region shown in fig5 in all examples of the invention wherein a cooling medium is used a coolant with.