Pressure and temperature fluctuations in underground storage tank pipelines containing gasoline

A common method of detecting a small leak in a pressurized underground storage tank pipeline system containing petroleum is to monitor the pressure in the line. This paper presents theoretical models to predict the pressure changes associated with leaks and product temperature changes in pressurized pipelines. These models have been validated in experiments at retail petroleum facilities and the EPA's UST Test Apparatus. A heat conduction model is used to estimate the waiting period prior to the beginning of the test that is long enough to allow the product temperature changes to be negligibly small, and an exponential pressure-decay model is used to estimate the test duration that allows the pressure drop associated with small leaks to exceed the threshold. The results suggest that a test duration of 15 to 60 min is required to detect leaks as small as 0·1 gal/h and a waiting period of up to 6 to 12 h is required for the temperature changes in a 2-inch diameter pipeline to be negligible after the last dispensing of product through the line.