Coating thickness measurement methods

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 E^1,2 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 E^1,2 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