1、API PUBL*3239407322900543765260ACKNOWLEDGMENTSWe wish to express our gratitude to the members of the API Storage Tank Task Force andthe Work Group for AST Monitoring for their cooperation,their technical support,andtheir assistance in coordinating this project.We would like to acknowledge the suppor
2、t andencouragement of the chairperson of the Work Group,Mr.James Seebold,and the APIstaff member monitoring the program,Ms.Dee Gavora.We especially acknowledge thehelp of Mr.John Collins,of Mobil Oil,who provided technical input to the research andwas instrumental in coordinating the field tests at
3、the Mobil Refinery in Beaumont,Texas.Finally,we acknowledge the help of Monique Seibel and Christine Lawson of VistaResearch in editing and typesetting this document.d without license from IHSNot for ResaleAPI PUBL*323940732290054376b1T7ABSTRACTThere are two approaches to detecting leaks in an above
4、ground storage tank(AST)by means ofthe volumetric method.The first is the conventional approach in which measurements of thelevel and temperature of the product are made with a precision level sensor and a vertical arrayof temperature sensors.The second is a mass measurement approach which employs a
5、 differen-tial pressure sensor to measure the level changes.In a tank with vertical walls,a differentialpressure sensor inherently compensates for the level changes produced by thermal expansion andcontraction of the product between the pressure port and the product surface.As part of Phase III of t
6、he American Petroleum Institutes(APIs)project to develop and evalu-ate the performance of different technologies for detecting leaks in the floor of ASTs,a con-trolled experiment was conducted in a 117-ft-diameter tank during late May and early June 1992.The purpose of this experiment was to evaluat
7、e the performance of both approaches tovolumetric testing.The tank contained a light fuel oil,and data were collected over a continuous28-day period.The analytical and experimental results of this project suggest that a volumetric system can beused to detect small leaks in ASTs.Analysis of the level
8、 temperature approach indicates that thelargest source of volume fluctuations was thermal expansion of the product.It was found thateffective compensation for this expansion could be achieved,and leak rates as small as 1.9 gal/hcould be reliably detected in a single 24-h test.Furthermore,extending t
9、he test period to 48 hwould significantly improve leak detection performance,resulting in a detectable rate of about1.0 gal/h.While in theory differential pressure systems should achieve a higher level of performance thanthe level temperature systems,this was not the case.The setup of the differenti
10、al pressure mea-surement system is extremely sensitive to air temperature changes,and to a lesser extent,thelocation of the bottom pressure reading.Regardless of the approach used,volumetric leak detection tests achieve their highest perform-ance when the level of the product in the tank is low(appr
11、oximately 3 ft),and the test duration isat least 24 h(48 h if possible),the test is begun and ended at night,and accurate temperaturecompensation is applied.When the test duration is significantly less than 24 h,it is not possibleto accurately compensate for the effects of diurnal temperature changes.CoprotAneceanPeteenrANot for Resale
