A standardized test method for this is the salt spray test:

https://en.wikipedia.org/wiki/Salt_spray_test

It looks like the samples have already been in the salt spray test. To check the integrity of the coating after the corrosive exposure, electrochemical methods such as electrochemical impedance spectroscopy are suitable.

Dear Atik Islam

I want to say that the characterization of ED paint quality, durability and protectivity should stand on international standardization which is not easy tasked since there is no one test covered all the characterization items such that mentioned in the question title (quality, durability and corrosion protectivity). Now if you look at the bundle of the ISO general test methods for paints and varnishes on the following google link, you can see the ED paint is common under paints and varnishes title and excluded alone for special cases in terms of many determination items:

https://www.iso.org/committee/47996/x/catalogue/

This issue is familiar with the industrial scale but less with laboratory research since , in general, the evaluation in industrial scale based on absolute figures for every single technical property of paint while most laboratory research based on the relative figures for verifying and ranking the paint integrity according to their few research variables and parameters. For that they practicing open circuit potential test and other electrochemical tests.

Hope my above contribution is helpful.

Best regards

Dear Dr. Atik Islam ,

as said before in another your question, it is not easy to answer this question (a bit generic) as there are many specific types of ASTM Standards to test / characterize the conformity of the different characteristics of an ED Costing on a pipe, which I suggest you take a look at, for example :

-Test Methods for Coating Adhesion by DeFelsko

Available at: https://www.defelsko.com/resources/test-methods-for-coating-adhesion

-International Standard by Elcometer

Available at: https://www.elcometer.com/en/international-standards.html

-QUALIFICATION TESTS FOR PAINT SYSTEMS by Petrobras

Available at: https://canalfornecedor.petrobras.com.br/media/filer_public/3c/4f/3c4f59d1-c85a-46ea-9706-3e9de5b67bdf/i-et-301000-1200-956-p4x-001_0_prelim.pdf

-ASTM Designation: B487−85 (Reapproved 2013)

Standard Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of Cross Section

Available at: https://www.galvanizeit.com/uploads/ASTM-B-487-yr-87-R-13.pdf

and so on...

As ASTM standard, you can try to have a look at the following web. site by Paint Square:

-Paint and Coatings Industry Standards

D870 Standard Practice for Testing Water Resistance of Coatings Using Water Immersion

Available at: https://www.paintsquare.com/standards/?fuseaction=view&id=1758

My best regards, Pierluigi Traverso.