API PUBL 323-1994

$24.05

An Engineering Evaluation of Volumetric Methods of Leak Detection in Aboveground Storage Tanks

Published By	Publication Date	Number of Pages
API	1994	76

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Category: API

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Description

There are two approaches to detecting leaks from an aboveground storage tank (AST) by means of the volumetric method. The first is the conventional approach in which measurements of the level and temperature of the product are made with a precision level sensor and a vertical array of closely spaced, precision temperature sensors. The second is a mass-measurement approach, which employs a differential-pressure sensor to measure the level changes. In a tank with vertical walls, a differential-pressure sensor inherently compensates for the level changes produced by the thermal expansion and contraction of the product betweeen the pressure port, which is located near the bottom of the tank, and the product surface.

Because of the possibility of large horizontal gradients in the rate of change of temperature of the product in an AST (gradients which cannot be accurately measured with a single vertical array) the mass-measurement approach should, in theory, have a performance advantage over the conventional approach.

As part of Phase III of the American Petroleum Institute’s (API’s) project to develop and evaluate the performance, in actual operational environments, of different technologies for detecting leaks in the floor of ASTS’, a controlled experiment was conducted in a 117-ft-diameter tank at Mobil’s refinery in Beaumont, Texas, during late May and early June 1992. The purpose of this experiment was to evaluate the performance of both approaches to volumetric testing. The tank contained a light fuel oil, and data were collected over a continuous 28-day period. Two vertical arrays of thermistors were placed at two locations inside the tank to determine the magnitude of the horizontal gradients in the rate of change of product temperature. Temperature measurements of the tank’s exterior shell were also made.

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