Readings from the deep
Anything that can help terminal operators cut the cost of regulatory compliance will generate a willing audience and during the ILTA show this past June, news of an audacious and innovative robotic in-tank inspection tool was very well received.
The ILTA trade show was short on new kit, the main advances being in the software field. However, a radically new unit was being exhibited by Solex Robotics, designed to carry out API 653 inspections in aboveground storage tanks (ASTs) without the need to take tanks out of service. Solex describes the Maverick inspection unit as a "submarine that goes in gasoline". It consists of a remote-controlled submersible robot, purged with nitrogen and pressurized and equipped with an array of ultrasonic sensors. The unit is lowered into an AST and is driven remotely around the tank floor, relaying sensor readings back to the control unit. The great attraction of the system is that the tank can remain in service while the inspection is carried out and does not need to be drained and cleaned. This can, the developer says, produce very significant cost savings.
Maverick has been developed over more than two years by Solex under a research contract with the US Department of Energy's (DOE) Office of Industrial Technologies (OIT), supported by commercial interests including Lockheed Martin, General Electric, BP Amoco, and Exxon/Mobil. The first prototype was tested in January 1997 and by November that year the first field generation unit was ready. This version was tested at Mobil's Paulsboro refinery and the trials resulted in an improved, second generation unit which incorporated a non-sparking casing. This unit was trialled in a floating roof, 120 ft diameter tank filled with diesel. After improvements to the positioning software, another version was tested in a 50 m diameter fuel tank fitted with an internal floating roof. Colonial Pipeline provided another jet fuel tank to test an upgraded unit with improved sensor software in September 1998 and the following month the near-complete system was tested at the National Aeronautical and Space Administration's (NASA) Neutral Buoyancy Laboratory. Emergency retrieval systems were added and the first commercial version was revealed this past June in Houston.
The unit's largest job so far involved the inspection of a 53 m diameter, floating roof AST at BP Amoco's Port Hudson, Louisiana facility. The tank contained more than 200,000 barrels of light crude at the time of the inspection and the oil company calculated that it saved more than $185,000 by using Maverick as opposed to traditional inspection methods. The tank had been in continuous use since its construction in 1979 as a gathering point from where crude oil is transmitted by pipeline to a barge loading facility. In order to carry out a conventional inspection, it would have been necessary to empty the tank, clean out the sludge, clean and degas the tank and hire barges for 35 days to provide alternate storage capacity.
The Port Hudson job was not simple. Sampling provided an estimate that the tank bottom was covered with a two-inch layer of sludge, well within the capabilities of the unit to cope with. However, once inside, the unit encountered sludge up to 25 inches deep, completely submerging the Maverick. Counter measures were successfully employed to dissipate the sludge and allow the unit to map the entire floor, taking more than 100,000 discrete ultrasonic readings. Another problem arose with the fibreglass bottom coating which at first was thought to be a major obstacle to taking accurate readings. However, Solex managed to match the sensor transducers with the substrate and "gate" the fibreglass thickness.
In addition to time and cost savings, using Maverick substantially reduced the environmental impact of the operation. Taking a tank out of service inevitably results in a loss of vapours to the atmosphere whereas with Solex's system such losses are restricted to the period when the unit is being installed via the access hatch. Solex estimates that, using a conventional inspection procedure at Port Hudson, the tank would have released more than 100 tonnes of carbon dioxide and volatile organic compounds (VOCs) to the atmosphere; using Maverick this was reduced to less than half a tonne.
Presenting the Maverick to an expectant audience during the ILTA conference, Solex president Don Hartsell pointed out that the petroleum industry as a whole is trying to drive down costs while at the same time requiring its service suppliers to provide high-quality equipment. The Maverick remote-controlled inspection tool fits into this trend by allowing terminal operators to prove their storage assets to a high level of accuracy with no downtime and at a cost which may be up to 80 percent lower than conventional techniques.