"Ship Coating Technology" (edited by Ship Technology Research Institute of CHINA State Shipbuilding Corporation) 9.2.8 Pinhole inspection of coating film: "During the drying process, due to improper temperature, high humidity and other reasons, there will be holes that are difficult to find by naked eyes. Small holes that penetrate the coating——pinholes. The existence of pinholes will undoubtedly make it easy for corrosive media (water, oxygen, etc.) to pass through them to reach the protected metal surface and cause corrosion, making the coating less than expected protective effect".
Generally, non-thick film coatings often need to go through several coats to achieve the specified film thickness. For example, in the ship painting, the outer panel of the hull generally needs to be painted with about 5 layers of paint, and the film thickness can reach about 200 μm. In this way, even if each layer of paint film has individual pinholes, after several layers of paint are superimposed, the pinholes will penetrate The probability of penetrating the entire coating film is very small, so there is no need for pinhole inspection. On the contrary, thick film coatings are relatively difficult to dry due to the thickness of the film (each coating can be more than 100 μm), and the possibility of pinholes is greater than that of general non-thick film coatings, and Often, one or two coats can meet the specified film thickness requirements, so the probability of pinholes penetrating the entire coating film is relatively high, and pinhole inspection is necessary.
In ship painting, such as cargo oil tanks (often also ballast tanks) of petroleum product carriers, most of them are painted with 2~3 pure epoxy paints (total thickness is about 250 μm), ballast Water Tanks of cargo ships are often Use 1~2 coats of thick film tar epoxy paint (total thickness 200~250 μm). These thick film coating films called special coating areas are more likely to produce pinholes, and the protection of these tanks The requirements are very high, so in ship painting, pinhole inspection is mainly carried out in these areas. Inspection instrument: pinhole inspection instrument.
