September 5 - September 11, 2011
Is it necessary to holiday test the interior lining in the vapor phase (roof) of water storage tanks after coating?
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Lee Edelman of CW Technical Service on
September 5, 2011:
Usually, a holiday test is done below the overflow level, unless the specification calls for the roof section to be holiday tested. I recommend testing the roof section after a cure test is completed. Holiday testing will help to extend the life of the coating system. Care should be taken when testing the roof section. Usually, there are faying surfaces, spot welds, or seams not sealed. Depending on the type of tank, these surfaces will cause the holiday detector to go off. A visual inspection before holiday testing will let the inspector know where these areas are.
Gunnar Ackx of SCICON worldwide bvba on
September 6, 2011:
Because of the (economic) consequences of having to take a storage tank out of service for inspection and/or maintenance, I believe it is warranted for ANY immersion-service tank lining to be holiday-tested 100%, including the vapor phase, which is often MORE aggressive than the immersion service itself.
Only if the vapor phase is confirmed to be non-corrosive (or nitrogen blanketed), then maybe no testing is required, but in all other cases, I would definitely holiday-test the vapor phase as well.
Actually, the vapor phase and the bottom of the tank are the areas where most corrosion occurs, so also make sure that you look at the "design" of the storage tank to make sure that it allows for proper coating application (steel dressing, accessibility, crevices, etc.).
Of course, the above is only the tip of the proverbial iceberg, as I consider (qualitative) tank lining to be a specialty art within the coating profession.
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