Coating thickness measurement methods – Non-Destructive Testing

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

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