08:58 Feb-24-2009 Ajit Engineering, Inspector V.J.T.I., India, Joined Feb 2009 8
Once, I was measuring paint DFT for CS storage tank ( 2 coat epoxy). As I was not having paint specification , it was difficult to do the inspection. What should b the acceptance citeria i.e. min. DFT for painting if no specification ?
A typical 'generic' paint spec is .004" 'anchor profile' [sand blast depth], 1 - 2 mils [.001" - .002"] of primer, 2 - 4 mils for each layer of topcoat. Thus a 2-coat epoxy system should be 3 mils, minimum.
If this wasn't written into the contract, specification, or on the drawing, it will be impossible to enforce.
Although Roger is right in saying that you can't enforce anything without a specification, the figures he gave you for anchor profile and coating thickness are incorrect.
Anchor profile of .004" (100 microns) seems very high unless high build solvent free epoxies or GF vinyl esters are applied. 50-75 microns Rz would be a more typical anchor profile for thin film epoxy systems.
For 2 coats of epoxy inside a storage tank, I wouldn't be happy with anything less than 10 mils (250 microns) of film thickness. Although it can vary quite a bit per depending on the coating product and the preference of the different coating manufacturers, 2 coat epoxy systems for immersion are usually specified at 150 - 300 microns per coat.
Your best bet is to ask the coating manufacturer for guidance.