Certain federal, state and local regulations apply to aboveground storage tanks that contain oil and hazardous liquids. These regulations can require facilities to develop and implement spill prevention and response plans designed to prevent the discharge of oil into navigable waters and adjoining shorelines. The regulations require facilities to have processes and countermeasures in place to prevent spills from aboveground storage tanks. Hence under tank containment such as liners (HDPE or Bentonite materials) are installed directly under the tank bottom of aboveground storage tanks. Cathodic Protection (CP) is the most commonly used method for protecting tank bottoms and since the past decade all the new tanks are mostly constructed with CP systems. However, in some cases, CP is no longer applicable. For tanks that were installed without a CP system, installation of CP after the tank is put in service may not be possible, particularly if the tank has a liner. Also, for tanks whose CP systems are inadequate or failed, the replacement of these systems requires access to the tank bottom, which is very costly and often impractical.

Vapor corrosion inhibitor (VCI) as an alternative for corrosion control of underside tank bottom with liner has been investigated. Ten electric resistance (ER) probes were installed in-between the underside tank bottom and the liner through the ring wall. These probes were grouped into 3 groups (group 1: probes 1, 2, 3, 4, 5, and 6; group 2: probes 7 and 8; group 3: probes 9 and 10). The groups of probes are 120 degrees from one another and are installed through 114 inch (3.18cm) openings. Probes in group 3 were placed 5 feet (1.52 m) away from the edge of the tank bottom, group 2 probes were placed 15 (4.57 m) feet away from the edge of the tank bottom and group 1 probes were placed at 5 feet (1.52 m), 15 feet (4.57 m) and 35 feet (10.668 m) away from the edge of the tank bottom plate. A specified volume of VCI was applied through a leak detector port 24-inch (60.96 cm) from the edge of the tank bottom plate, towards the center. The applied quantity saturated the spaces in the sand directly between the plate and the soil interface to create a thin film that protects the tank from corrosion activities. As expected, the initial corrosion rates at the different locations differ and tend to decrease with time. Corrosion probes used to monitor the rate of corrosion shows a pattern likened to a tank under cathodic protection. Finally, the investigation was further monitored and the data collected was used to predict the effectiveness of VCI in the control of corrosion at the underside/bottom of steel tanks.

Subject
Water, Cathodic protection, Sand, Corrosion rate, Sour environments, Volatile corrosion inhibitors, Thickness loss, Liquids, Aboveground storage tanks, Corrosion probes, Corrosion protection, Tank bottoms, Electrical resistance probes
Keywords:
Vapor corrosion inhibitor, electrical resistance probes (ER), above ground storage tanks (AST), HDPE Liner
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2017
Association for Materials Protection and Performance (AMPP)
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