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L <br /> 4.2 Ultrasonic Integrity Inspection <br /> Although API 1631 does not require internal ultrasonic inspections, it suggests that <br /> visual inspections could be supplemented by them (or by hammer tests), in case visual <br /> inspection is not sufficient. In our observations in Oklahoma and Colorado, the tanks <br /> were found to be in excellent condition, visually, so further testing was not necessary. <br /> The State of California requires internal ultrasonic inspections along with visual <br /> inspections. They further stipulate that in order for a tank to be suitable for lining, the <br /> average wall thickness as determined by ultrasonic inspection on a 1-foot grid be no <br /> less than 75% of the original wall thickness; API 1631 does not have a corresponding <br /> requirement. <br /> With the assistance of Rockey's, Inc., we obtained an inspection report performed <br /> for Rockey's by an inspector in California. The inspector is a Registered Professional <br /> Engineer, who is also a Registered API 653 inspector. The tank was a 20,000-gallon <br /> tank, 10 ft in diameter and 34 ft long, used to store diesel fuel at the Los Angeles <br /> International Airport. It was inspected on March 30, 1995, pursuant to lining. <br /> The inspection report covered both the visual inspection and the ultrasonic survey. <br /> The visual inspection discovered six repairable holes of 1/2-in diameter or less in the <br /> tank over several square feet of area, and another tiny pinhole that could be lined over <br /> without repair. A few areas of corrosion and pitting were found, but only one small <br /> area (3-in diameter) had significant corrosion. The bottom third of the tank had some <br /> pitting due to sludge corrosion, but the pits were tiny; the largest was measured to be <br /> 0.06 in deep. <br /> Sketches of the tank side walls and heads were provided to illustrate how the <br /> survey was performed (how the survey points were numbered). A computer printout <br /> was provided with the results of the survey. A total of 1246 ultrasound readings were <br /> taken. The detailed findings were then summarized. The summary found that the <br /> minimum thickness of the walls, which were originally nominally 0.375 in thick, was <br /> 0.300 in, or 80% of the original thickness. <br /> In summary, it appears that this survey meets the requirements of California, and <br /> that the results of the survey indicate that the tank can be lined. <br /> MRI-ApplicM4069-FR 13 <br />