Skin Depth Frequency Table

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