1、 API PUBLX325 94 m 0732290 0526558 134 m An Evaluation of a Methodology for the Detection of Leaks in Aboveground Storage Tanks HEALTH AND ENVIRONMENTAL AFFAIRS API PUBLICATION NUMBER 325 MAY 1994 - E nvinmmmtal Partnenbip American Petroleum Institute 1220 L Street. Northwest 11 Washington, D.C. 200
2、05 API PUBL*325 94 O732290 0526559 O70 An Evaluation of a Methodology for the Detection of Leaks in Aboveground Storage Tanks Health and Environmental Affairs Department API PUBLICATION NUMBER 325 PREPARED UNDER CONTRACT BY: MICHAEL R. FIERRO ERIC G. ECKERT JOSEPH W. MARESCA, JR. VISTA RESEARCH, INC
3、. MOUNTAIN VIEW, CALIFORNIA MAY 1994 American Petroburn Institute FOREWORD API PUBLICATIONS NECESSARILY ADDRESS PROBLEMS OF A GENERAL NA=. WITH RESPECT TO PARTICULAR CIRCUMSTANCES, LOCAL, STATE, AND FEDERAL LAWS AND REGULATIONS SHOULD BE REVIEWED. API IS NOT U“G TO MEET THE DUTIES OF EMPLOYER!j, MAN
4、UFAC- TURERS, OR SUPPLIERS To WARN AND PROPERLY TRAIN AND EQUIP THEIR EMPLOYEES, AND OTHERS EXPOSED, CONCERNING HEALTH AND SAFETY RISKS AND PRECAUTIONS, NOR UNDERTAKING THEIR OBLIGATIONS UNDER LOCAL, STATE, OR FEDERAL LAWS. NOTHING CONTAINED IN ANY API PUBLICATION IS TO BE CONSTRUED AS GRANTING ANY
5、RIGHT, BY IMPLICATION OR OTHERWISE, FOR THE MANU- FACTURE, SALE, OR USE OF ANY METHOD, APPARATUS, OR PRODUCT COV- THE PUBLICATION BE CONSTRUED AS INSURING ANYONE AGAINST LIABIL- ERED BY LETTERS PATENT. NEITHER SHOULD ANYTHING CONTAINED IN ITY FOR INFRINGEMENT OF LETIERS PATENT. API PUBL*325 94 D 073
6、2290 0526562 729 ACKNOWLEDGMENTS We wish to thank the members of the API Storage Tank Task Force, Work Group for AST Monitoring, for their cooperation, their technical support, and their assistance in coordinat- ing the project. We would like to acknowledge the support and encouragement of Mr. James
7、 Seebold, the chairperson of the Work Group, and of Ms. Dee Gavora and Andrew Jaques of the Health and Environmental Main Department, the MI staff members mon- itoring the program. We would also like to acknowledge the contributions of the following individuais, compa- nies/individuais: Steve Tosten
8、gard, Jerry Engeihardt and Vince Rosero of Santa Fe Pacific Pipeline Partners. Inc., for the use of their companys terminai, and their invaluable assis- tance in coordinating the field test effort; Robert Bromvich, Gordon Ray and Chuck Hill, also of SFPP, for their efforts in planning and scheduling
9、 the experimental work; Bill Mat- ney, Jim Eschberger and Glenn Kauffman for their operational support; Jim Leaird and Dennis Biddle of Physical Acoustics Corporation; and David Watennan and Raiph Nicas- tro of Rohrback Cosasco System, Inc. We would also like to acknowledge Gregg Olson and Richard W
10、ise of Vista Research for their assistance in conducting the field test activities, and Monique Seibel and Christine Lawson of Vista Research for their efforts in editing and typesetting this document. API PUBLW325 94 0732290 0526562 665 TABLE OF CONTENTS EXECUTIVE SUMMARY . e5-1 BACKGROUND. 1-1 TES
11、T METHODOLOGY/PROPOSED AST LEAK DETECTION PRACTICE . 2-1 SITE DESCRIPTION 3-1 RESULTS 4-1 CONTROLTESTS 4-3 LEAK DETECTION TESTS . 4-8 CONCLUSIONS AND RECOMMENDATIONS 5-1 TEST METHODOLOGY . 5-1 PASSIVE-ACOUSTIC TECHNOLOGY . 5-2 SOIL-VAPOR MONITORING TECHNOLOGY . 5-4 VOLUMETRIC TECHNOLOGY 5-5 IMPORTAN
12、T TEST FEATURES 6-1 PASSIVE-ACOUSTIC TECHNOLOGY . 6-1 SOIL-VAPOR MONITORING TECHNOLOGY . 6-2 VOLUMETRIC TECHNOLOGY 6-3 REFERENCES R- 1 APPENDIXA A-1 APPENDIX B B-1 API PUBL*325 94 0732290 0526563 5TL H LIST OF FIGURES Fi eure 4- 1. 4-2. 4-3. Level-and-temperature data (control Tank) . . . . . . . .
13、. . . . . . . . . . . . . . 4-4 Mass-measurement data (control Tank . . . . . . . . . . . . . . . . . . . . . . . . 4-4 Acoustic events: (a) surface events (control tank, simulator OFF); (b) floor events (control tank, simulator OFF). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6 Acous
14、tic events: (a) surface events (control tank, simulator ON); (b) floor events (control tank, simulator ON) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7 Level-and-temperature data (Tank 9) . . . . . . . . . . . . . . . . . . . . . . . . 4-10 Mass-measurement data (Tank 9) . . . . . .
15、 . . . . . . . . . . . , . . . . . . . . 4- 10 4-4. 4-5. 4-6. LIST OF TABLES Table 3-1. 4-1. 4-2. AST Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 Summary of Tank Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2 Summary of Leak Detection
16、 Tests . . . . . . . . . . . . . . . . . . . . . . . . . . 4-8 API PUBLS325 94 0732290 052b5b4 438 = EXECUTIVE SUMMARY INTRODUCTION The American Petroleum Institute has undertaken a significant technical effort to define and advance the state of the art of leak detection in aboveground storage tanks
17、 (ASTs). This report presents the results of Phase N of the API leak detection program. The three research efforts that preceded Phase IV were focused on the assessment of leak detection technology for ASTs and a detailed evaluation of passive acoustic and volumetric measurement methods. Field tests
18、 conducted on operational ASTs as part of the Phase III effort demonstrated that accurate leak detection could be accomplished through acoustic and volumetric techniques, and suggested specific changes in system design and test protocol to improve the performance of each technology. Based upon the P
19、hase III results, general recommendations were made regarding further experimental work. In addition, a methodology was developed which combines multiple AST testing technologies in order to assess the integrity of an AST. The proposed methodology may also include multiple tests with each technology
20、. This methodology is designed to verify the presence of a leak in the case of a detection, and thereby minimize the occurrence of erroneous decisions bzsed on test results which indicate the presence of a leak when none exist (false alarms). Effectively combining independent test methods should res
21、ult in a very robust leak detection practice. Three leak detection techniques were selected for evaluation in the Phase IV program: passive- acoustics, volumetric methods (including both level-and-temperature and mass measurement systems), and soil-vapor monitoring. Though soil-vapor monitoring was
22、not evaluated in the previous phases of APis research, it was identified as a technology of interest to the industry and was included in this phase. Individually, all three of these technologies are believed to have the potential for reliably detecting small leaks in the floor of an AST. When used t
23、ogether, the reliability of the test results increases. ES- 1 API PUBL*325 94 D 0732290 0526565 374 D Other AST leak detection technologies exist, and new technologies and new implementation techniques are being developed. Other technologies may perform equally well in a similar test methodology; ho
24、wever, API has limited the focus of this research to the three technologies mentioned above. The test methodology presented here is one example of a method to improve the reliability of a test decision through the used of multiple testing techniques. The proposed leak detection methodology was appli
25、ed to 14 ASTs during an eight-week period between 15 March and 3 May, 1993, at a facility provided by Santa Fe Pacific Pipeline Partners, Inc The objectives of the Phase IV study were: to assess the applicability of the general features of the three AST leak detection technologies (acoustic, volumet
26、ric, and soil-vapor monitoring technologies) over a wide range of tank types, petroleum fuels, and operational conditions 0 to assess the applicability of a general leak testing methodology for ASTs which involves multiple tests at multiple product levels in the tanks to determine the integrity of 1
27、4 ASTs using two or more test methods CONCLUSIONS Based on the results of all tests performed, none of the 14 ASTs tested is believed to be leaking. Since there were no indications of a leak, the performance of the proposed test methodology could not be directly evaluated for its effectiveness in re
28、ducing false alarms or missed detections. Based on a study of the noise environment for each of the test methods included in the methodology, however, the proposed methodology is believed to have met the requirements for incorporating independent test methods with reasonable probabilities of detecti
29、on. The results of passive-acoustic testing performed in this test series indicates that the data collection and analysis approach based on the recommendations from Phase III, and demonstrated in this program, can be employed on a wide range of tanks with a low probability of false alarm. Acoustic l
30、eak detection tests differentiate acoustic leak signals from impulsive ES-2 - API PUBLX325 94 W 0732290 0526566 200 W noise events primarily on the basis of the estimated spatial origin of the signal and on its duration. A detection is made when a number of acoustic events are located in an area on
31、the tank floor that is consistent with the location accuracy of the acoustic sensor array. The two sources of false hits, which can lead to false detections, are non-leak sources of impulsive acoustic signals generated at the floor of an AST, and the mislocation of impulsive acoustic signals that or
32、iginate from locations other than the floor of the tank (e.g., the product surface, tank shell, tank roof, etc.). The data collection and analysis approach used in this test series yielded no false events in any of the 14 ASTs tested. This is an extremely important result, because until now implemen
33、tations of acoustic technology have required that a test decision be made even though there may be many hundreds of false events indicated in the data. The primary noise sources identified in this test series originated at the product surface, and were due to condensate dripping on the product surfa
34、ce and noise associated with the motion of the ASTs floating roofs. No impulsive noise sources were found to have originated from the tank floor, even though all of the tanks tested had some internal floor-mounted structure. This is also an important result, because noise sources at the floor of an
35、AST could be difficult to distinguish from a leak signal. In the 14 ASTs tested, it was found that all noise sources recorded could be spatially discriminated from any possible leak signal through analysis of digital time series of the acoustic waveform. The soil-vapor monitoring test applied in Pha
36、se IV used pentane, which was present in the petroleum fuel, as the target vapor. Two types of hydrocarbon sampling systems tuned for the detection of pentane were used: a fiber optic sensor system capable of measuring concentrations of pentane on the order of 5 ppm, and a gas chromatograph capable
37、of measurements to 1 ppm. The results of the pentane injection test performed as part of the series of soil-vapor monitoring tests indicated that pentane propagation through the oiled-sand backfill under the tanks at the test site was too low for a leak to be reliably detected. In order to gain a be
38、tter understanding of the propagation characteristics of pentane, additional injection tests were performed at another site where the backfill material was sand that had not been oiled and was therefore much more permeable. This second series of injection tests resulted in a much more reliable detec
39、tion of the injected pentane. While soil-vapor monitoring techniques can potentially be used to detect leaks ES-3 API PUBL*325 99 0732290 0526567 147 in ASTs, it is apparent that the soil conditions at the test site limited the effectiveness of this technique. The effect of soil conditions on test v
40、ariability could be mitigated through the use of longer test periods and a more stable substance as the target vapor. In order for this technology to be effective operationally, and to achieve a reasonable probability of detection, the spacing of sensor wells and the duration of the monitoring perio
41、d must be carefully chosen. For best results, these decisions should be based on the propagation characteristics of the target vapor as measured at the test site prior to the conduct of a leak detection test. The other important source of error is the presence of water at the bottom of the AST durin
42、g a test. Unless water is removed, it will prevent the release of pentane and render the test ineffective. Water was drained from all ASTs prior to the start of the Phase IV test series. While the results of the soil- vapor monitoring tests are believed to be valid, there is insufficient information
43、 to assess the effects of any residual amount of water left at the bottom of these ASTs. The performance of volumetric tests, both those that use level-and-temperature measurements and those that use mass-measurement techniques, was consistent with that achieved during the Phase III experiments. Whi
44、le specific noise mechanisms differ in the two types of volumetric tests, the noise in both cases is driven by ambient temperature changes; in the Phase N test series, the two types of volumetric test had approximately equivalent levels of performance. As in Phase III, it was found that in order to
45、achieve good performance in both types of tests, accurate temperature compensation and test durations greater than 24 h were required. ES4 API PUBLX325 94 0732290 052b5b8 083 = Section 1 BACKGROUND The American Petroleum Institute has undertaken a significant technical effort to define and advance t
46、he state of the art of leak detection in aboveground storage tanks (ASTs). This report presents the results of Phase IV of the API leak detection program. The three research efforts that preceded Phase IV were focused on the assessment of leak detection technology for ASTs and a detailed evaluation
47、of two leak detection methods: passive acoustics and volumetric measurement (Vista Research, Inc., 1991; Vista Research, Inc., 1992; Vista Research, Inc., 1993a; Vista Research, Inc., 1993b). Field tests conducted on operational ASTs as part of the Phase III effort demonstrated that accurate leak de
48、tection could be accomplished through acoustic and volumetric techniques, and suggested specific changes in system design and test protocol to improve the performance of each technology. Based upon the Phase III results, three general recommendations were made regarding further experimental work. Fi
49、rst, perform tests on a wide range of operational ASTs using leak detection systems that incorporate the modifications in data collection and analysis suggested by the Phase III results. Second, develop and test a standard procedure for evaluating the performance of volumetric and acoustic leak detection methods in terms of the probability of detection (PD) and probability of false alarm (PFA). Finally, areas in which volumetric and acoustic methods could benefit from further technological development were identified. The Phase IV effort is intended to address the first of these
