Holiday Detection
Premature corrosion of a coated substrate is often caused by coating failures or damage. Coatings are applied to substrates to prevent corrosion, reduce abrasion, and minimise product contamination. The level of coating continuity required depends on the specific service conditions. In order to achieve long-term durability, it is crucial to apply and test a continuous coating.
Small discontinuities in coatings are often difficult to detect with the naked eye, which is why a holiday detection test is conducted. This test helps identify flaws in the coating. Some of the main types of coating flaws and discontinuities include:- Runs and sags
When the wet coating moves downwards due to gravity, resulting in uneven thickness with a thicker lower edge. - Cissing
This occurs when the coating breaks away from the surface due to contaminants like oil and grease. - Pinholes
These are created when air or solvent is trapped during the painting process, leaving small holes in the coating film. - Over thickness
Excessive coating thickness can lead to cracking due to internal stress. - Under thickness and misses
When the coating is not applied adequately, leaving areas of the substrate exposed or with low film thickness.
Cissing, pinholes, and misses exposing the substrate can be identified through a holiday detection survey. It is essential to correct coating defects in structures such as tanks, vessels, and pipeline internals that are meant for immersion services.
Coatings Radar App provides reviews of holiday detection methods and will discuss the relevant international standards utilised in the coatings industry and provide guidance on evaluating and reporting the test results.
