The First Word in Protective & Marine Coatings

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October 22 - October 28, 2012

Under what conditions should small-diameter blisters (<1.5 inches) in a water tank lining be repaired/repainted? Should the blisters be broken and the substrate examined?

Selected Answers

From Tom Schwerdt of Texas Department of Transportation on October 26, 2012:
     If the blisters aren't growing any further and there isn't active corrosion, it's probably better to just leave well enough alone until the whole tank is recoated. If the blisters are growing or there is active corrosion, repairs should be undertaken.

From Giuseppe Santagata of NACE Certif. Coat. Insp. level III # 2737 on October 24, 2012:
     Blister formation indicates lining failure, so the lining shall be repaired properly. To know the probable causes, the blister shall be broken and internal liquid and substrate examined for soluble salt contamination or for presence of eventual inclusions (e.g. abrasive residual, dust, etc.) In order to issue after the exam the right procedure for cleaning and recoating, it is preferable to have the coating manufacturer's assistance during the investigation and issuance of the repair procedure.

From James Albertoni of CA Department of Water Resources on October 22, 2012:
     It really depends on what's behind the blisters and what the tank is holding. If testing of the liquid behind the blister shows it to be relatively non-corrosive, the steel shows no signs of active corrosion, and the liquid in the tank is not all that permeable to the coating (or is non-corrosive), then the blisters should be okay to leave; however, notice that you have to break a couple blisters to determine this. Either way, any blisters you do break should always be repaired prior to putting the tank back into service.

From Murjan Murjan of Sirte Oil Company on October 22, 2012:
     Spot repairs are required. Just remove the blisters using spot blast-cleaning and recoat the repair areas.

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