SKIN DEPTH FREQUENCY TABLE
This table gives you the frequency (in kHz) at which a given alloy and material thickness will have a skin depth of 1.
It is recommend that this frequency and 2 times this frequency be mixed for a support plate cancellation when performing eddy current inspections of heat exchanger tubes with the given alloy and wall thickness.
Skin Depth/Frequency Table
\ Inch 0.010 0.018 0.020 0.022 0.025 0.028 0.032 0.035 0.042 0.049
\ mm 0.254 0.457 0.508 0.559 0.635 0.711 0.813 0.889 1.067 1.245
Alloy r \ BWG 31 26 25 24 23 22 21 20 19 18
ohm-meter ------------------- Frequency in kHz --------------------
Copper 1.724E-08 68 21 17 14 11 8.6 6.6 5.5 3.8 2.8
AL2024T4 5.766E-08 226 70 57 47 36 29 22 18 13 9.4
Adm Brass 7.184E-08 282 87 71 58 45 36 28 23 16 12
Al Brass 7.496E-08 294 91 74 61 47 38 29 24 17 12
90/10 1.771E-07 695 215 174 144 111 89 68 57 39 29
Chromium 1.959E-07 769 237 192 159 123 98 75 63 44 32
70/30 3.831E-07 1504 464 376 311 241 192 147 123 85 63
Zirc 5.070E-07 1991 614 498 411 318 254 194 162 113 83
Titanium 5.562E-07 2184 674 546 451 349 279 213 178 124 91
SS 304 6.897E-07 2708 836 677 559 433 345 264 221 154 113
SS 347 7.184E-07 2821 871 705 583 451 360 275 230 160 117
Inconel 1.014E-06 3981 1229 995 823 637 508 389 325 226 166
Tit6A1-4V 1.724E-06 6769 2089 1692 1399 1083 863 661 553 384 282
Graphite 7.837E-06 9497 7692 6357 4923 3925 3005 2512 1744 1282
\ Inch 0.058 0.065 0.072 0.083 0.095 0.109 0.120 0.134 0.148 0.165
\ mm 1.473 1.651 1.829 2.108 2.413 2.769 3.048 3.404 3.759 4.191
Alloy r \ BWG 17 16 15 14 13 12 11 10 9 8
ohm-meter ------------------- Frequency in kHz --------------------
Copper 1.724E-08 2.0 1.6 1.3 0.98 0.75 0.57 0.47 0.38 0.31 0.25
AL2024T4 5.766E-08 6.7 5.4 4.4 3.3 2.5 1.9 1.6 1.3 1.0 0.83
Adm Brass 7.184E-08 8.4 6.7 5.4 4.1 3.1 2.4 2.0 1.6 1.3 1.0
Al Brass 7.496E-08 8.7 7.0 5.7 4.3 3.3 2.5 2.0 1.6 1.3 1.1
90/10 1.771E-07 21 16 13 10 7.7 5.9 4.8 3.9 3.2 2.6
Chromium 1.959E-07 23 18 15 11 8.5 6.5 5.3 4.3 3.5 2.8
70/30 3.831E-07 45 36 29 22 17 13 10 8.4 6.9 5.5
Zirc 5.070E-07 59 47 38 29 22 17 14 11 9.1 7.3
Titanium 5.562E-07 65 52 42 32 24 18 15 12 10 8.0
SS 304 6.897E-07 80 64 52 39 30 23 19 15 12 10
SS 347 7.184E-07 84 67 54 41 31 24 20 16 13 10
Inconel 1.014E-06 118 94 77 58 44 34 28 22 18 15
Tit6A1-4V 1.724E-06 201 160 131 98 75 57 47 38 31 25
Graphite 7.837E-06 915 728 594 447 341 259 214 171 140 113
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