Tank Restoration at TransCanada
CommTank was hired to perform the tank inspections using a Magnetic Flux Leakage (MFL) scanner and Ultrasonic Test (UT) equipment. The MFL can scan large areas of steel quickly and provide an audio alarm when corrosion is encountered. The UT equipment measures the thickness of steel through coatings. When the MFL flagged a questionable area the UT equipment was used to measure each corroded area to determine how much steel was still present. The tanks were found to have pitting in the steel floor and on the tank walls. The UT thickness measurements showed a significant metal loss in the flagged areas with a remaining thickness of 0.225 inches. The nominal bottom plate thickness was .375 so the steel had lost .15 inches due to corrosion over the 25-year life span of the tank. The tank was also checked for level and deflection using a rotating laser and found to be within the maximum permitted by API 653.
The new coating for TransCanada's storage tanks, polyamide epoxy, was chosen for its chemical resistance to fuel oil. Polyamide epoxy is designed to protect steel and concrete in industrial exposures. CommTank was also contracted to repair and coat the tanks to meet the ASTM and SSPC standards for coating applications. New steel plates were welded to areas that had shown thinning and vacuum box testing was used to test the welds for leaks. The aboveground storage tanks and secondary containment enclosures were prepped by sandblasting to a near white metal and coated with an immersion grade epoxy primer. Each tank offered limited access in the form of manways so all staging and equipment had to fit through 36" round openings. Exterior coatings were applied in four applications with the final two being acrylic polyurethanes. After all coatings have cured CommTank will perform holiday testing using a high-voltage detector in accordance with NACE RP-01-88. A properly applied lining should provide a service life of 10-to-20 years so it is critical to confirm that there are no thin or uncoated areas.