Evaluation of degradation of coatings
BS EN ISO 4628-10:2003 pdf free.Paints and varnishes – Evaluation of degradation of coatings一Designation of quantity and size of defects, and of intensity of uniform changes in appearance一 Part 10: Assessment of degree of filiform corrosion.
This part of ISO 4628 describes a method for assessing the amount of fihiform corrosion developed from a scribed mark by measuring the length of the longest filament L and the most frequent length Al of the filaments.
Pictorial examples provided in Annex A of this part of ISO 4628 illustrate different ratings for the length of the longest filament L and the most frequent length Al of the filaments. A comparison of the test panels with the 12 pictures in Annex A does not supersede the obligatory numerical assessment (method I or 2).
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1 filiform corrosion type of corrosion proceeding under a coat of paint, varnish or related product, in the form of threads, generally starting from bare edges or from local damage of the coating.
NOTE 1 Usually the threads are irregular in length and direction of growth. but they may also be nearly parallel and of approximately equal length.
NOTE 2 Filiform corrosion can also occur under other protective coatings.
NOTE 3 Usually the threads follow the direction of extrusion of a metal substrate, do not cross over one another and need to be initiated by aggressive ions.[ISO 4623-1:2000 and ISO 4623-2:2003]
Carry out the assessment under good illumination.
3.2 Method 1
This applies where there is regular filiform corrosion [see Figure 1 a].
measuring the maximum distances L and Lp in millimetres, from the scribed line to the point to which the filiform corrosion has developed on the lft-hand side and on the right-hand side respectively [see Figure 1 a)], in order to calculate the length of the longest filament L, which is the mean value of L and Lp measuring the distances M and Mp, in millimetres, from the scribed line to which the majority of filaments have developed on the lft-hand side and on the right-hand side respectively [see Figure 1 al], in order to calculate the most frequent filament length M, which is the mean value of M and Mr.
3.3 Method 2
This applies where there is iregular fliform corrosion [see Figure 1 b)].
4 Expression of results
Express the numerical ratings for the length of the longest filament L and the most frequent filament length M as follows:filiform corrosion, L5/M3.
This means the length of the longest filament is 5 mm and the most frequent filament length is 3 mm.
5 Test report
The test report shall contain at least the following information:
a) all details necessary to identify the coating examined;
b) a reference to this part of ISo 4628 (ISO 4628-10:2003);
c) the type of surface examined, its size and, if appropriate, its location;
d) the result of the assessment in accordance with Clause 4;
e) an indication of the ilumination under which the assessment was carried out;
f) whether the coating was stripped or not;
9) any unusual features (anomalies) observed during the assessment;
h) the date of the examination.Evaluation of degradation of coatings