GB/T 31554-2015 Active

This standard specifies the method of using phase-sensitive eddy current thickness gauges to non-destructively measure the thickness of non-magnetic metal coatings on metal and non-metal substrates, such as: a) zinc, cadmium, copper, tin, or chromium coatings on steel substrates; b) copper or silver coatings on composite material substrates. Compared with the amplitude-sensitive eddy current method in GB/T 4957, the phase-sensitive eddy current method has no thickness measurement errors for coatings on smaller surfaces and surfaces with large curvature. At the same time, it is less affected by the magnetic properties of the substrate, but the phase-sensitive eddy current method is more affected by the electrical properties of the coating material. When measuring metal coatings on metal substrates, the electrical conductivity and permeability (σ, μ) of one material (such as the substrate material) should be at least 1.5 times that of the other material (such as the coating material). The relative permeability of non-ferromagnetic materials is 1.