by Ken Wright, FLC Midwest Region Support Office The U.S. Environmental Protection Agency (EPA) regulates underground storage tanks (USTs) in order to prevent soil and groundwater pollution caused by leaks or spills. In the late-1990s, the EPA announced new regulations for USTs. In addition to setting new standards for UST operation and performance, these regulations required that all existing USTs be upgraded to meet the new standards, upgraded to include cathodic protection, upgraded with an internal lining, or closed. The regulations also required that USTs more than ten years old be internally inspected to confirm the integrity of the tank prior to being upgraded. Furthermore, if cathodic protection was not installed, the UST must be internally inspected every five years.
The conventional method of internal tank inspection requires that the tank be emptied of its contents, purged and/or inerted to remove hazardous vapors, and unearthed. An access panel is then cut into the tank wall and a person enters the tank to desludge, clean (typically by grit blasting and vacuuming), and perform the inspection. This entry requires a confined space permit. Inspection is typically performed by visual observation, ultrasonic testing, and manual probing/hammering. Once the inspection is complete, the access panel must be sealed and the site restored. This entire process can take between two and five days. A team consisting of two technicians, one corrosion engineer, and one site safety officer are required during the course of events. The cost for each inspection typically ranges between $3,000 and $5,000, depending on the size, condition, and location of the tank. In 1999, the EPA estimated that there were more than 760,000 UST systems covered by the regulations. The U.S. Army owned and operated approximately 20,000 of these USTs. Because tank excavation and replacement costs typically start at $30,000, removing and replacing all of the USTs would be cost-prohibitive. Vincent Hock of the U.S. Army Engineer Research and Development Center, Construction Engineering Research Laboratory (ERDC-CERL) was developing a robotic method for the ultrasonic measurement of UST wall thickness. He recalls that the "new regulations caused a furor in the regulated community. All of the hubbub and furious activity in the industry" led him to coin the name "Fury" for the tank inspection technology. The Fury unit consists of four assemblies: the robot assembly (or steering head), the inspection assembly, the tether management assembly, and the operator console. The robot and inspection assemblies together are approximately 23" long and 4" in diameter. This size allows these assemblies to access most USTs through an existing fill pipe or riser, eliminating the need for human entry into the tank and all of the associated activities. The robot assembly supports and moves the inspection assembly using permanent magnet wheels and a 90° transition arm. This permits inspection of tank end-caps and overhead portions of the tank wall. The inspection assembly contains tank wall cleaning components and an ultrasonic transducer. The ultrasonic transducer is held perpendicular to and against the tank wall by a guide shoe. The guide shoe also directs couplant flow to the spot where the transducer contacts the tank wall. Liquids in the tank are used as couplant. The tether is approximately 150' long and provides an electrical ground for the robot and inspection assembly. The tether management assembly drives the tether in and out of the tank, as well as storing unused tether. The operator console allows a technician to control the movements of the robot assembly. The console also contains the ultrasonic data acquisition system and the power distribution unit for the entire system.
Fury can be inserted into a UST and operated by a single technician. The robot can then conduct ultrasonic measurements of tank wall thickness at a rate of approximately 90,000 measurements per hour. Due to the robot's capability for movement, over 95% of cylindrical wall and end-cap locations on a typical tank can be examined. In practice, Fury is submersible in water, fuel, and certain other chemicals; however, the system has not yet received the safety certification required for use in fuel or chemical storage tanks. Once this certification is received, Fury could be used to conduct inspections of fuel USTs without first draining them. The initial development of Fury was conducted by ERDC-CERL in conjunction with RedZone Robotics of Homestead, Pennsylvania, under a Small Business Innovative Research (SBIR) Phase II project. Fury's capabilities were validated as a part of an Environmental Security Technology Certification Program (ESTCP) project. Under the ESTCP project, Fury performed inspections of USTs at Fort Lee, Virginia, and Hunter Army Air Field (a sub-unit of Fort Stewart, Georgia). Based on these demonstrations, the Fury team estimated that a typical UST inspection would require less than one day and cost between $600 and $1,200. Thus, Fury is expected to provide significant savings in both time and money when compared to the standard inspection procedure. Fury was also used to perform corrosion inspection and to conduct measurements of steel sheet pile bulkheads along the Cuyahoga River at Cleveland, Ohio. Although maintenance and upgrade of sheet pile along the river is the responsibility of landowners, the U.S. Army was required to estimate the cost of repairing and/or replacing all sheet pile along the Cuyahoga. During Phase 1 of the project, visual condition assessments were conducted along the designated portions of the Cuyahoga and Old rivers. Fury was used in Phase 2 as a follow-on condition assessment of 12 selected locations. The conventional method of obtaining thickness measurements of sheet pile involves the use of a handheld acoustic sensor. The sensor can be attached to a pole and lowered into the water; however, it can be difficult to keep the sensor close enough to the sheet pile at depth. The handheld sensor can also be used by a four person dive crew to conduct the assessment. Fury successfully provided measurements of sheet pile thickness, allowing estimation of the corrosion rate of the sheet pile bulkheads. The total estimated cost of the Fury inspection was approximately equivalent to the cost of inspection by a dive crew. However, with the lessons learned during the course of the project it is expected that the cost of Fury inspection could be dramatically reduced. Fury is covered by a U.S. patent and is available for further development and/or licensing. According to Dr. Charles Marsh of CERL, the next step in Fury development could be obtaining the safety certification. He said, "We have spoken to Factory Mutual Research [a certified test laboratory] and have developed a plan to demonstrate the safety of the system for submersion in fuel, but it has not yet been implemented." The current version of Fury is capable of conducting ultrasonic inspections in nonexplosive liquids and atmospheres such as those encountered around ship hulls, selected areas of oil platforms, sheet piling, dams, and nuclear plants. Additional inspection capabilities (e.g., video, far field eddy current, or electromagnetic acoustic transducer) could be integrated into the Fury with relative ease. For more information, contact Dr. Charles Marsh or Vincent Hock at 1-800-USA-CERL.
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