1、API PUBL*322 94 0732290 05LL30 2T5 An Engineering Evaluation of Acoustic Methods of Leak Detection in Aboveground Storage Tanks HEALTH AND ENVIRONMENTAL AFFAIRS API PUBLICATION NUMBER 322 JANUARY 1994 *bG Strategies fw Today5 Environmental Fartnmbip American Petroleum Institute 1220 L Street, Northw
2、est 8 Washington, D.C. 20005 API PUBL*322 94 9 0732290 0539333 131 9 An Engineering Evaluation of Acoustic Methods of Leak Detection in Aboveground Storage Tanks Health and Environmental Affairs Department API PUBLICATION NUMBER 322 PREPARED UNDER CONTRACT BY: JAMES W. STARR, AND JOSEPH W. MARESCA,
3、JR. VISTA RESEARCH, INC. MOUNTAIN VIEW, CALIFORNIA AUGUST 1993 American Petmleum Institute API PUBLx322 94 m 0732290 0519132 O78 m FOREWORD API PUBLICATIONS NECESSARILY ADDRESS PROBLEMS OF A GENERAL NATURE. WITH RESPECT TO PARTICULAR CIRCUMSTANCES, LOCAL, STATE, AND FEDERAL LAWS AND REGULATIONS SHOU
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6、TAINED IN ITY FOR INFRINGEMENT OF LETTERS PATENT. API PUBLS322 94 m 0732290 0519133 TO4 m ABSTRACT The design of an aboveground storage tank (AST) leak detection system based upon passive- acoustic methods requires a detailed understanding of the acoustic leak signal and the ambient noise field agai
7、nst which the signal is measured. As part of Phase III of the American Petroleum Institutes (APIs) project to develop and evaluate the performance of different technologies for detecting leaks in the floor of ASTs, a set of controlled experiments was conducted in a 40-ft- diameter tank during June 1
8、992. Two sets of holes of various diameters, ranging from 0.5 to 3 mm, were drilled in the tank floor. These holes released product (water) into one of two backfill materials: native soil or sand. Two types of acoustic signals were generated and studied: (1) the continuous leak signal produced by tu
9、rbulent flow through a hole in the floor of the tank, and (2) the impulsive leak signal produced by bubbles collapsing in the backfill beneath the tank floor. The analytical and experimental results of this project suggest that a passive acoustic system can be used to detect small leaks in ASTs. The
10、 experiments have shown that the impulsive leak Sig- nals identified through laboratory and field simulations are persistent and measurable within an AST. The experiments yielded two very significant findings, which must be addressed in the data collection and signal processing schemes used to detec
11、t leaks with the passive-acoustic method: ( 1) the multipath signals (leak-to-wall-to-sensor or leak-to-surface-to-sensor), which are associated with the direct path signal (leak-to-sensor), are very strong and may be stronger than the direct path signal, and (2) the time delays of the multipath sig
12、nals relative to the direct path signal for each sensor in the wall array may be very different. Both phenomena are due to acoustic propagation in the highly reflective confines of a right circular cylinder AST. During the experiments, a data collection procedure and a signal processing algorithm we
13、re used to separate the impulsive events associated with the leak from the strong multipath reflected Sig- nals. All of the leaks that were generated in the floor of the 40-fi-diameter tank were success- fully detected and located. API PUBL*322 94 = 0732290 0539334 940 ACKNOWLEDGMENTS We wish to exp
14、ress our gratitude to the members of the API Storage Tank Task Force and the Work Group for AST Monitoring for their cooperation, their technical support, and their assistance in coordinating this project. We would like to acknowledge the support and encouragement of the chairperson of the Work Grou
15、p, Mr. James Seebold, and the API staff member monitoring the program, Ms. Dee Gavom We especially acknowledge the help of Mr. John Collins, of Mobil oil, who provided technical input to the research and was instrumentai in coordinating the field tests at the Mobil Refinery in Beaumont, Texas. For t
16、heir helpful suggestions in reviewing this document, we would like to acknowledge Det Norske Veritas. Inc., CTI, Inc., and Physical Acoustics Corporation. Finally, we acknowledge the help of Monique Seibel and Christine Lawson of Vista Research in edit- ing and typesetting this document. iii API PUB
17、LX322 94 0732290 05LL35 887 TABLE OF CONTENTS EXECUTIVE SUMMARY Section 1 : INTRODUCTION . . Section 2: BACKGROUND Section 3: SUMMARY OF RESULTS . Section 4: CONCLUSIONS AND RECOMMENDATIONS . Section 5: IMPORTANT FEATURES OF A PASSIVE-ACOUSTIC METHOD WITH HIGH PERFORMANCE . Section 6: REPORT ORGANIZ
18、ATION . REFERENCES . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . , , . . . , . . , , . . , , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Appendix A: The Acoustic Signal Produced by a Leak in the Floor of an Above- ground Storage Tank . Appendix 3: A Passive-Acoustic M
19、ethod of Detecting Leaks in the Floor of an Aboveground Storage Tank: Field Test Results . ES- 1- 2- 1 3- 1 4- 1 5- 1 6- 1 R- 1 A- 1 B- 1 API PUBL*322 94 0732290 051913b 7L3 EXECUTIVE SUMMARY INTRODUCTION The design of a leak detection system based upon passive-acoustic methods requires a detailed u
20、nderstanding of the acoustic leak signal and the ambient noise field against which the signal is measured so that robust data collection and signal processing algorithms can be developed. As part of Phase III of the American Petroleum Institutes (APIs) project to enhance and evaluate the performance
21、, in actual operational environments, of different technologies for detecting leaks in the floor of aboveground storage tanks (ASTs), a set of controlled experiments was conducted in a 40-ft-diameter tank at the Mobil Oil refinery in Beaumont, Texas, during June 1992. The tank was filled with water
22、and two sets of holes of different diameters, ranging from 0.5 to 3 mm, were drilled in its floor. The holes in the center of the tank floor released product into a native-soil backfill, and the holes along the periphery of the tank floor released product into a sand backfill. Two types of acoustic
23、leak signals were generated and studied under realistic con- ditions: (1) the continuous leak signal produced by turbulent flow through a hole in the floor of the tank and (2) the impulsive leak signal produced by bubbles collapsing in the backfill beneath the tank floor. BACKGROUND The API has comp
24、leted three phases of a leak detection project for ASTs. The purpose of Phase I was to assess different leak detection technologies to determine which had the greatest potential for field application. Phase II addressed in detail two of the methods studied in Phase I: passive- acoustic and volumetri
25、c methods. Phase III built on the insight gained in Phase II with regard to the acoustic leak signal and ambient noise field. The objectives of Phase III, which addressed both volumetric and passive-acoustic leak detection technologies, were: to determine, in the case of acoustic methods, the nature
26、 of the acoustic leak signal resulting from realistic leaks in the floor of an operational AST; to determine, in the case of volumetric systems, if differential pressure (mass-measurement) systems have significant advantages over the con- ventional level and temperature measurement systems; 1 Experi
27、ments were also conducted as part of Phase III to evaluate the performance of volumetric methods of leak detection for ASTs. The results of the volumetric study are provided in a separate API document entitled An Engi- neering Evaluation of Volumetric Methods of Leak Detection Systems for Abovegroun
28、d Storage Tanks by James W. Starr and Joseph W. Maresca, Jr. ES-1 API PUBL*322 94 0732290 05LL37 b5T W to characterize the ambient noise encountered under a wide range of test conditions for both detection technologies; to evaluate data collection and signal processing techniques that would allow th
29、e detection of the leak signal against the ambient noise; to identify any operational issues for implementation of methods based on either technology; to demonstrate the capabilities and, if possible, make an estimate of the performance, of both technologies through field tests; and to identify, in
30、the case of both volumetric and passive-acoustic technolo- gies, those features of a leak detection test that are necessary for achiev- ing high performance. CONCLUSIONS The analytical and experimental results of this project suggest that a passive-acoustic system can be used to detect small leaks i
31、n ASTS. The experiments have shown that the impulsive leak Sig- nals identified through laboratory and field simulations during Phases II and III appear to be per- sistent and are measurable within an AST. The experiments yielded two very significant findings, which must be addressed in the data col
32、- lection and signal processing schemes used to detect leaks with passive-acoustic methods: (1) the multipath signals (leak-to-wall-to-sensor or leak-to-surface-to sensor), which are associated with the direct-path signal (leak-to-sensor), are very strong and may often be stronger than the direct-pa
33、th signal, and (2) the time delays of the multipath signals relative to the direct-path Sig- nal for each sensor in the wall array may be very different. Both phenomena are due to acoustic propagation in the highly reflective confines of a right cir- cular cylinder AST. The former phenomenon, which
34、is produced by wall focusing, is particu- larly important, because the inherent assumption in the design of the existing acoustic detection algorithms is that the largest leak signal is produced by the direct-path signal. The impulsive leak signal is detectable, because, as part of the signal proces
35、sing, the direct-path signal can be distinguished in time delay from the multipath signals associated with it. While the multipath complicates the signal processing for impulsive leak signals, it makes it impractical to exploit the persistent leak signal. During the experiments, a data collection pr
36、ocedure and a signal processing algorithm were used to separate the impulsive events associated with the leak from the strong multipath reflected Sig- nals. All of the leaks that were generated in the floor of the 40-ft-diameter tank were success- fully detected and located. ES-2 API PUBL*322 94 073
37、2290 0539338 596 This document presents the results of these acoustic experiments in two separate technical papers, which are attached as appendices. The first discusses the Characteristics of the acoustic leak signal and ambient noise field in an AST, and the second presents an engineering assess-
38、ment of a methodology for detecting small leaks in the tank floor. ES -3 API PUBL*322 94 m 0732290 0519139 422 m 1 INTRODUCTION This report summarizes Phase III of a research program conducted by the American Petroleum Institute (APT) to evaluate the performance of different technologies that can be
39、 used to detect leaks in the floors of aboveground storage tanks (ASTs). During Phase I, an analytical assess- ment of the performance of four leak detection technologies was investigated (Vista Research, Inc., 1989; Maresca and Starr, 1990). The four technologies included: (1) passive-acoustic sens
40、ing systems, (2) volumetric systems, especially differential pressure (or “mass ) measure- ment systems, (3) enhanced inventory reconciliation methods, and (4) tracer methods. During Phase II, field tests were conducted on a 114-ft-diameter AST containing a heavy naphtha. The purpose of these tests
41、was to make an engineering assessment of the performance of two of the above technologies, passive-acoustic sensing systems and volumetric detection systems. These tests were conducted at the Mobil Oil Corporation refinery in Beaumont, Texas, during May 1992. The results of the Phase II research pro
42、gram are described in two API final reports and three professional papers (Vista Research, Inc., 199 1 , 1992; Eckert and Maresca, 199 1 , 1992). During Phase III, additional field tests were conducted on a pair of ASTs in order to test the acoustic and volumetric leak detection strategies that emer
43、ged from the Phase II study and to fur- ther evaluate the current state of leak detection technology. These tests were also conducted at the Mobil refinery at about the same time of year as the Phase II tests. The acoustic tests were conducted in a 40-ft-diameter AST containing water, and the volume
44、tric tests in a 117-ft- diameter tank containing a light fuel oil. In the case of the acoustic tests, holes were drilled in the floor of the tank to allow realistic simulation of leaks into two different types of backfills beneath the floor. This report describes the results of the Phase III acousti
45、c tests; the results of the volumetric tests are described in a separate report, which consists of a brief overview of the work and two technical papers (Vista Research, Inc., 1993). The specific objectives of the Phase III acoustic experiments were: to characterize the two general types of acoustic
46、 leak signals (Le., con- tinuous and impulsive) produced by leaks in the fioor of an operational AST; to characterize the ambient noise that would interfere with each type of acoustic leak signal and that would be found in a typical AST under a wide range of refinery and environmental conditions; to
47、 demonstrate in a series of field tests data collection and signal pro- cessing techniques that would allow the detection of leaks in the floor of an AST; and 1-1 API PUBLS322 94 m 0732290 05LqL40 144 m to identify those features of a leak detection test that are crucial to achieving high performanc
48、e. The body of this report consists of a short technical summary of the work. Section 2 summarizes the relevant Phase II results that were further investigated in Phase III. Sections 3 and 4 summa- rize the important results, conclusions, and recommendations of this experimental project. Sec- tion 5
49、 presents the general features of a passive-acoustic method that will achieve a high level of performance. A detailed description of the field tests and analyses are presented in two professional papers, which are attached as appendices to the report. 1-2 API PUBL*322 9L1 M 0732290 05L9LYL 080 2BACKGROUND The choice of a particular strategy for the acquisition and processing of acoustic signals is strongly tied to the nature of the signal and the background noise field in which the signal is immersed. Studies of simulated leak signals have shown that the acoustic signal produc
