In-Service Oil Tank Cleaning and Inspection System: Results of Eight (8) Independent Validations

摘要

The structural integrity of bulk liquid storage tanks has been a major area of concern to the petrochemical industry for a number of years. Although API 653 remains the industry standard relative to tank inspection and maintenance, the frequency of testing and inspection can also be affected by various state and local regulations. The schedule of this inspection process may depend on a number of factors including the age of the tank, its proximity to groundwater, the leak record of the tank, the date of the tank's last integrity test, the construction material of the tank, the product stored, soil conditions, previous corrosion rate calculations, etc. One of the critical areas of integrity testing is that of the tank bottom. Traditional methods of bottom inspection have required the emptying of the tank's product and a thorough cleaning and degassing prior to the allowance of personnel entry for a floor inspection. There are significant advantages to the tank owner if proper bottom inspection can be completed while the tank is in-service. Robotic technology is now available as a method for acquiring quantitative information for determining the integrity of aboveground storage tank floors while the tank remains on-line and in-service. API 653 allows the use of robotics as an alternative method for assessing the condition of a tank floor as long as certain conditions are met. The purpose of this paper is to summarize the results of tests at several operating refineries and terminals comparing in-service ultrasonic bottom inspections of tanks to the results of traditional out-of-service inspections. Each tank was inspected using an oil tank inspection system operated by InTANK Services, Inc. The first test was conducted in 1994 and the last test completed in March 2000. All validations were conducted by independent tank inspection organizations or the tank owner's tank inspection staff. All validation inspectors were API-653 certified inspectors. The objective of the in-service inspections was to quantitatively establish the parameters that would set the next internal inspection. This was achieved by providing the capability of returning to precise locations within the tank over a span of several years in order to compute accurate corrosion rate calculations.