COP:durability; microcracking

4.13 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.


4.13A Microcracking : a

0 T internal diameter = 1.0 T external radius



4.13B Microcracking : b

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

4.13C Microcracking : c

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

4.13D Microcracking : d

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

4.13E Microcracking : e

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