Various methods of NDT are used for the measurement of coating thickness – paint thickness, plating thickness, anodising etc. These methods may be X-ray, electron backscatter, magnetic, etc and the Table gives a broad guide to the most appropriate methods for various coatings and substrates.
Appropriate NDT techniques for coating thickness measurement
| Substrates / Coatings | Copper | Nickel | Chromium | Autocatalytic Nickel | Zinc | Cadmium | Gold | Palladium |
| Magnetic Steel | MX | X M1 | M X5 | M1 X6 | B MX | B MX | B MX | B MX |
| Non-magnetic stainless steel | X E4 | X M1 | X5 | B M1 X6 | BX | BX | BX | BX |
| Copper and alloys | – | X M1 | X | M1 X6 | X | BX | BX | BX |
| Zinc and alloys | X | X M1 | BX | X6 | – | BX | BX | BX |
| Aluminium and alloys | BX | BX M1 | BX | B E1,2 X6 | BX | BX | BX | BX |
| Magnesium and alloys | BX | BX M1 | BX | B X6 | BX | BX | BX | BX |
| Nickel | X | – | BX | – | X | BX | BX | BX |
| Silver | BX | BX M1 | BX | B X6 | BX | – | BX | X6 |
| Ni-Co-Fe alloys | M | M1 | MX | M1 | BM X | BM X | B MX | BM X |
| Non-metals | BX E4 | BX M1 | BX | B X6 | BX | BX | BX | BX |
| Titanium | BX | BX M1 | X | B E1,2 X6 | BX | BX | BX | BX |
| Substrates / Coatings | Rhodium | Silver | Tin | Lead | Tin-lead alloys | Anodic oxides | Non-metals | Vitreous and porcelain enamels | Aluminium and alloys |
| Magnetic Steel | B MX | B MX | B MX | B MX | MX B3 | – | BM X6 | BM X6 | BM X |
| Non-magnetic stainless steel | BX | BX E4 | BX | BX | X B3 | – | BE X6 | E X6 | BX |
| Copper and alloys | BX | BX | BX | BX | X B3 | E X6 | BE X6 | E X6 | X |
| Zinc and alloys | BX | BX | BX | BX | X B3 | – | BE X6 | X6 | X |
| Aluminium and alloys | BX | BX | BX | BX | X B3 | E X6 | E | E | – |
| Magnesium and alloys | BX | BX | BX | BX | X B3 | E X6 | E | – | – |
| Nickel | BX | BX | BX | BX | X B3 | – | BE X6 | X6 | X |
| Silver | X | – | X | BX | X B3 | – | BE X6 | E X6 | X |
| Ni-Co-Fe alloys | BM X | BM X | BM X | BM X | MX B3 | – | BM X6 | X6 | X6 |
| Non-metals | BX | BX | BX | BX | X B3 | – | – | – | BE |
| Titanium | BX | BX | BX | BX | X B3 | – | BE | – | – |
METHODS – KEY
B – beta back scatter
E – eddy current
M – magnetic/electromagnetic
X – X-ray fluorescence
