1、API PUBL8306 91 0732290 0510993 510 An Engineering Assessment of Volumetric Methods of Leak Detection in Aboveground Storage Tanks HEALTH AND ENVIRONMENTAL AFFAIRS API PUBLICATION NUMBER 306 OCTOBER 1991 American Petroleum Institute 1220 L Street, Northwest Washington, D.C. 20005 API PUBL+30b 92 H 0
2、732290 0510994 Y57 m An Engineering Assessment of Volumetric Methods of Leak Detection in Aboveground Storage Tanks Health and Environmental Affairs Department API PUBLICATION NUMBER 306 OCTOBER 1991 PREPARED UNDER CONTRACT BY: JAMES W. STARR AND JOSEPH W. MARESCA, JR. VISTA RESEARCH, INC. MOUNTAIN
3、VIEW, CA American Petroleum Institute API PUBL*3Ob 91 0732290 0530995 393 FOREWORD API PUBLICATIONS NECESSARILY ADDRESS PROBLEMS OF A GENERAL. NATURE. WITH RESPECT To PARTICULAR CIRCUMSTANCES, LOCAL, STATE, AND FEDERAL LAWS AND REGULATIONS SHOULD REVIEWED. API IS NOT UNDERTAKlNG TO MEET THE DUTIES O
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5、ANTING A“ RIGHT, BY IMPLICATION OR OTHERWISE, FOR THE MANUFACTRE, SALE, OR USE OF ANY METHOD, APPARATUS, OR PRODUCT COVERED BY LE“E.RS PATENT. NEITHER SHOULD ANYTHING CONTAINED IN THE PUBLICATION BE CONSTRUED AS INSURING ANYONE AGAINSTLIABILITY FOR INFRIGEMENT OFLEITERS PATENT. copyright 1991 Amcric
6、m Petroleum Institute ii API PUBLm30b 91 = 0732290 051099b 22T Ac kn owledginen ts This work was funded through a contract with the American Petroleum Institute (MI). We the authors wish to thank the members of the API Storage Tank Task Force, Work Group for AST Monitoring, for their cooperation, th
7、eir technical support, and their assistance in coordinating this project. We would like to acknowledge the support and encouragement of the chairperson of the Work Group, Mr. James Seebold, and of the API staff member monitoring the program, Ms. Dee Gavora. We especially acknowledge the help of Mr.
8、John Collins, of Mobil O to determine, in the case of volumetric methods, the sources and magnitude of ambient noise associated with measurements in an AST; to perform field experiments on a large, full-scale AST; and to recommend ways to improve existing AST leak detection methods. Conclusion diffe
9、rential-pressure-measurement methods (i.e., mass measurement methods), which are a type of volumetric method, can be used to detect small leaks in ASTs. Such methods can achieve a high level of performance because they are not affected by thermally induced volume changes in a tank with vertical wall
10、s. However, other sources of ambient noise, such as thermal expansion of the tank wall and evaporation and condensation of the product in the tank, do affect performance and must be compensated for separately. The analytical and experimental results of this project suggest that ES-1 1 The results of
11、 the acoustic study are provided in a separate API document entitled An Engineering Assessment of Acoustic Methods of Leak Detection in Aboveground Storage Tanks. by Eric G. Eckert and Joseph W. Maresca, Jr. API PUBLx30b 91 M 0732290 0530999 T39 M Summary of Results volumetric test in detecting smal
12、l leaks is limited by the magnitude of the uncompensated volume error and by the duration of the test. Because of the diurnal character of the volume fluctuations, tests that are less than 24 hours long may yield erroneous results. The data suggest that a test may have to be 48 to 72 hours long to r
13、educe the effects of uncompensated volume fluctuations. The field test data, collected at two different product levels over two three-day periods, indicate that volume changes of several hundred gallons per hour occur in response to ambient temperature changes. During both test periods, volume chang
14、es of as much as 1000 gallons were observed over a 24-hour period. Because of these large changes, it is necessary to compensate for the effects of temperature fluctuations occurring in both the product and the tank shell, and for the effects of evaporative product losses, if volume measurements are
15、 to be useful in detecting leaks. Analysis of the test data indicates that a small number of temperature sensors mounted on the external circumference of the tank can readily compensate for thermally induced changes in the volume of the tank shell. The largest sources of uncompensated volume changes
16、 were horizontal product temperature gradients and evaporative losses. The data suggest that the size of these volume changes was approximately 10 gallons per hour, with as much as 80% of this value being due to non-uniformity of the product temperature field. The effect of these changes (the “therm
17、al error“) can be minimized by using a differential-pressure-measurement system to monitor changes in the level of product in the tank. With this approach, a volumetric test should be able to detect leak rates as low as 1 gallon per hour, if evaporative losses can be minimized and if tests longer th
18、an 24 hours can be tolerated. The anayticd and experimental results of this project suggest that the performance of a I 1 ES-2 API PUBLX306 91 m 0732290 05LLOOO 359 = 1 Introduction This report summarizes Phase II of a research program conducted by the American Petroleum Institute (MI) to evaluate t
19、he performance of technologies that can be used to detect leaks in the floors of aboveground storage tanks. During Phase I, an analytical assessment of the performance four leak detection technologies was investigated i, 21. The four technologies included:. ( 1) passive-acoustic sensing systems, (2)
20、 volumetnc systems, especially differential-pressure (or “mass“) measurement systems, (3) advanced inventory reconciliation methods, and (4) tracer methods. During Phase II, field tests were conducted on an aboveground storage tank to make an engineering assessment of the performance of two of these
21、 technologies, volumetric detection systems and passive-acoustic sensing systems. This report describes the engineering assessment of the volumetric systems that were examined; the engineering assessment of acoustic systems is described in a separate report 3. The specific objectives of the Phase II
22、 research in the area of volumetric measurements were to: assess the current state of AST leak detection technology characterize the sources of ambient noise associated with volumetric measurements in an AST perform field experiments on a full-scale AST recommend ways to improve existing AST detecti
23、on systems The field tests were conducted at the Mobil Oil Refinery in Beaumont, Texas, on a 50,000-bbl, 114-ft-diameter AST containing a heavy naphtha petroleum product. The experiments focused on the ambient noise field and how it affects accurate detection of the volume changes due to a leak. API
24、 PUBLX306 91 O732290 05LLOOL 295 - 2 Background Volumetric systems are the most commonly used method of detecting leaks in underground storage tanks (USTs) 4-61. These systems typically measure the change in the level of product in the tank, they compensate for the thermal expansion or contraction o
25、f the product by measuring changes in the temperature of that product. Their method of compensating for other sources of background noise is to wait for the volume changes to become negligibly small. Volumetric leak detection systems that compensate directly for the thermally induced volume changes
26、in the product would seem to be directly applicable to the detection of leaks in ASTS. Differential-pressure-measurement systems (mass-measurement systems) are an example of this type of volumetric system. Because the cross-sectional area of the product surface is a constant regardless of the level
27、of product, mass measurement systems compensate directly for themally induced changes in the volume of product; they are, however, subject to other sources of uncompensated noise. As with USTs, the nature of the leak signal in an AST is well known. Unlike USTs, however, the signai in an AST is not a
28、ffected by the level of the groundwater, and, because the leak is in the floor of the tank, the pressure head above that leak is known. The primary focus of the field tests was to quantify the magnitude of the volume changes associated with important sources of system and ambient noise. 2 API PUBLr3
29、Ob 91 m 0732290 05LL002 121 m 3 Summary of Results In order to assess the environment under which a volumetric leak detection test on an AST might be conducted, a series of experiments were done on a single 50,000-bbl tank containing heavy naphtha. Instrumentation deployed in the tank provided infor
30、mation concerning level changes in the product as well as temperature changes in both the product and tank wall. The test data, collected at two different product levels over two separate three-day periods, indicate that volume changes of severai hundred gallons per hour occur in response to ambient
31、 temperature changes. During both test periods, volume changes of as much as 1000 gal were not uncommon over a 24-h period. Because of these large changes, compensation schemes are required if one is to be able to account for the effects of temperature fluctuations occurring in both the product and
32、the tank shell, and for the effects of evaporative product losses. When a single array of product temperature sensors was used, compensation of the measured volume changes for these thermal effects resulted in a net loss of product from the tank during both test periods. A large fraction of this los
33、s can be explained by the existence of horizontal temperature gradients in the product and by evaporative loss. Differences in the estimate of the product thermal volume obtained from two vertical thermistor arrays were found to range from less than 100 gai to as much as 400 gal for different test p
34、eriods. In addition to these product volume changes, the thermal expansion of the tank shell was found to approach several hundred gallons over a 24-h period, and could be accurately estimated by as few as six temperature sensors placed around the tank circumference. The product surface was found to
35、 experience periodic fluctuations having magnitudes approaching 100 gai. These volume changes, coupled with the thermally induced volume changes, are large compared to the range of volume rates of interest. This active product surface thus permits the use of less precise sensors for the primary volu
36、me measurement. The accurate estimate of the rate of change of volume can then be obtained by sufficiently averaging through a volume time series to reduce the uncertainty in the rate to acceptable levels. As a result, a range of mass measurements, i.e., those made by pressure sensors, should be sui
37、table for use in a leak test. The abiiity of a volumetric test to detect small leaks is limited by the test duration and the magnitude of the uncompensated volume error. The current data indicate that a test duration between 48 and 72 h is required in order for the effects of uncompensated diurnal v
38、olume fluctuations to be reduced. Shorter test durations (less than 24 h) would yield erroneous results because of the diurnal character of the volume fluctuations. 3 API PUBL*306 91 0732290 0511003 Ob8 The largest sources of uncompensated volume were found to be evaporative losses and the non-unifo
39、rm thermal expansion of the product. The data suggest that the magnitude of these effects was roughly 10 gal/h, with as much as 80% of this value being due to inadequate spatial coverage of the product temperature field. Since a mass measurement system is not affected by horizontal temperature gradi
40、ents, and intrinsically compensates for thermally induced product volume changes, a volumetric test should be able to detect leak rates as small as 1 gd/h if the effects of evaporation can be minimized and if tests longer than 24 h can be tolerated. A API PUBL*3Ob 71 = 0732290 05LL004 TT4 W The work
41、 performed as part of the Phase II program is summarized in a technical paper prepared for publication in the engineering and scientific literature 7. This paper, a copy of which is presented in Appendix A of this report, describes the results of the experiments conducted with a volumetric leak dete
42、ction system during April and May 1991. Two three-day field tests were conducted on a 114-ft-diameter AST, and two levels of product (10 and 17 ft) were used during these tests. The paper describes the volume changes associated with each source of noise at each level of product. I 4 Report Organizat
43、ion 5 API PUBLx30b 91 m 0732290 05L1005 930 m References 1. J. W. Starr and J. W. Maresca, Jr. “Leak Detection Technologies for Aboveground Storage Tanks When In Service.“ Final Report for the American Petroleum Institute, Vista Research Project 2032, VistResearch, Inc., Mountain View, California (A
44、ugust 1989). 2. 3. J. W. Maresca, Jr., and J. W. Starr. “Aboveground Tank Leak Detection Technologies.“ Proceedings of the 10th Annual ILTA Operating Conference, Houston, Texas (June 1990). E. G. Eckert and J. W. Maresca, Jr. “An Engineering Assessment of Acoustic Methods of Leak Detection in Aboveg
45、round Storage Tanks. Final Report for the American Petroleum Institute, Vista Research Project 2032, Vista Research, Inc., Mountain View, California (25 October 1991). R. D. Roach, J. W. Starr, and J. W. Maresca, Jr. “Evaluation of Volumetric Leak Detection Methods for Underground Fuel Storage Tanks
46、,“ Vol. I (EFA/600/2-88/068a) and Vol. II (EPA/600/2-88/068b). Risk Reduction Engineering Laboratory, U. S. Environmental Protection Agency, Edison, New Jersey (December 1988). J. W. Maresca, Jr., James W. Starr, Robert D. Roach, and John S. Farlow. “Evaluation of the Accuracy of Volumetric Leak Det
47、ection Methods for Underground Storage Tanks Containing Gasoline.“ Proceedings of the I989 Oil Spill Coiference, Oil Pollution Controi, A Cooperative Effort of the USCG, AFI and EPA, San Antonio, Texas (1989). J. W. Maresca, Jr., J. W. Starr, R. D. Roach, D. Naar, R. Smedfjeld, J. S. Farlow, and R.
48、W. Hillger. “Evaluation of Volumetric Leak Detection Methods Used in Underground Storage Tanks.“ J. Of Hazardous Materials, Vol 26 (1991). J. W. Stan and J. W. Maresca, Jr. “Experimental Investigation of Volumetric Changes in Aboveground Storage Tanks.“ Final Report, American Petroleum Institute, Vi
49、staResearch Project 2032, Vista Research, Inc., Mountain View, California (to be submitted for publication). 4. 5. 6. 7. 6 A,PI PUBLJ30b 91 m 0732290 05LL00b 877 Appendix A Experimental Investigation of Volumetric Changes in Aboveground Storage Tanks J. W. Starr and J. W. Muesca, Jr. Vista Research, Inc. Mountain View, California A- 1 API PUBL*306 91 0732290 05LL007 703 = Experimental Investigation of Volumetric Changes in Aboveground Storage Tanks James W. Starr and Joseph W. Maresca, Jr. Vista Research, Inc. Mountain View, California 10 September 1991 Abstract In order to
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