FIELD INSIDE INDUCTION HEATED TUBE

[electricalquest]

I hope someone can help with this one. We have an inconel tube, diameter 6 ft, wall thickness 0.625 inch, pumped at 3000Hz with 900 KW external coil. The calculated reference depth is 0.348 inch, so the thickness to reference depth ratio is less than 2. How much of the field is inside the tube in percentage of total field? I searched Tudbury Vol 1 and 2, and could not find a way to calculate it. My gut feel is that "most" of the field is in the outer skin reference depth area doing its job heating the tube and very little is inside the tube, but I need a quantified answer. Thanks, to anyone who will help.