Microcracking

Microcracking is microscopic cracking on the surface.

• Microcracking of the metallic and/or organic coating creates a crevice where the normal protection mechanisms of the coating are compromised. It can lead to premature corrosion failure.

The test requirement for paint adhesion in AS/NZS 2728 and by the NZMRM is a bend test over a nominated number of material thicknesses (T) and it is measured as the internal diameter.

The radius required to avoid microcracking on metallic coated and pre-painted steel is measured externally. To obtain an external radius, add two material thicknesses to the internal diameter, and divide the result by two.

Microcracking : a

microcrack(a).svg

0 T internal diameter = 1.0 T external radius

Microcracking : b

microcracking(b).svg

(b) 1 T internal diameter = 1.5 T external radius

Microcracking : c

microcracking(c).svg

(c) 2 T internal diameter = 2.0 T external radius

Microcracking : d

microcracking(d).svg

(d) 3 T internal diameter = 2.5 T external radius

Microcracking : e

microcracking(e).svg

(e) 6 T internal diameter = 4.0 T external radius