1、A Guide to Leak Detection for Aboveground Storage Tanks PUBLICATION 334 FIRST EDITION, MARCH 1996 -I- d- Strategies fir Today i Environmental Partnership American Petroleum Institute s documenting perfor- mance improvements; and communicating them to the public. The foundation of STEP is the API Env
2、ironmental Mission and Guiding Environmental Principles. API standards, by promoting the use of sound engineering and operational practices, are an important means of implementing APIs STEP program. API ENVIRONMENTAL MISSION AND GUIDING ENVI RON M ENTAL PRINCIP LES The members of the American Petrol
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10、nd offering assis- tance to others who produce, handle, use, transport or dispose of similar raw materi- als, petroleum products and wastes. A Guide to Leak Detection for Aboveground Storage Tanks Health and Environmental Affairs Department PUBLICATION 334 FIRST EDITION, MARCH 1996 American Petroleu
11、m Ins titute API PUBLX334 96 0732290 0554078 338 SPECIAL NOTES i. API PUBLICATIONS NECESSARILY ADDRESS PROBLEMS OF A GENERAL NATURE. WITH RESPECT TO PARTICULAR CIRCUMSTANCES, LOCAL, STATE, AND FEDERAL LAWS AND REGULATIONS SHOULD BE REVIEWED. 2. API IS NOT UNDERTAKING TO MEET THE DUTIES OF EMPLOYERS,
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17、I PUBLX334 96 W 0732290 0554079 274 W FOREWORD This document is intended to provide the reader with a background in leak detection technologies for aboveground storage tanks in petroleum service. This document was developed by Vista Research, Inc. under the guidance of the API Leak Detection Workgro
18、up and the API Storage Tank Task Force. The document incorporates information on leak detection technologies from APIs research and from the experience of workgroup members. While an attempt has been made to discuss the main types of leak detection methods, the reader should recognize that there may
19、 be other forms of leak detection not discussed in this publication. The reader should also be cautioned that claims made by leak detection vendors should be carefully evaluated and that API does not endorse any of the leak detection technologies discussed in this publication. API publications may b
20、e used by anyone desiring to do so. Every effort has been made by the Institute to assure the accuracy and reliability of the data contained in them; however, the Institute makes no representation, warranty, or guarantee in connection with this publication and hereby expressly disclaims any liabilit
21、y or responsibility for loss or damage resulting from its use or for the violation of any federal, state, or municipal regulation with which this publication may conflict. Suggested revisions are invited and should be submitted to the director of the Health and Environmental Affairs Department, Amer
22、ican Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005. API PUBLr334 96 0732290 0554080 T9b CONTENTS Page INTRODUCTION . 1 Who Should Read This Booklet? . 1 A Note of Caution 1 THE STATISTICAL NATURE OF THE TESTING PROCESS 2 The Concept of Performance . 2 Declaring a Leak 3 LEAK DETEC
23、TION TECHNOLOGIES SUITABLE FOR ABOVEGROUND STORAGE TANKS 4 Demonstrations . 4 A Quick Overview 4 VolumetriciMass Technology . 8 The Nature of the Signal . 8 Sources of Noise 10 Key Features . 11 Demonstrations . 13 Acoustic Technology . 14 The Nature of the Signal . 14 Sources of Noise 16 Key Featur
24、es . 17 Demonstrations . 18 Soil-Vapor Monitoring Technology 19 The Nature of the Signal . 19 Sources of Noise 19 Key Features . 20 Demonstrations . 21 Inventory Control Technology . 22 The Nature of the Signal . 22 Sources of Noise 22 Key Features . 23 Demonstrations . 23 DEVISING THE BEST TESTING
25、STRATEGY FOR A PARTICULAR SITE . 24 Familiarity with the Site . 24 Operational Considerations 24 Cost Considerations . 24 Assessment of Vendors Claims . 25 Combining Technologies Effectively 25 Using Multiple Tests 25 GLOSSARY . 26 BIBLIOGRAPHY 29 API PUBL*334 9b 0732290 05540BL 922 A Guide to Leak
26、Detection for Aboveground Storage Tanks Introduction boveground storage tanks (ASTs) are widely used in A the U.S. petroleum industq. These tanks are usually clustered in large terminal facilities, and store a variety of products, both crude and refined. The type of AST addressed in this booklet is
27、a vertically oriented cylinder (“shell”) constructed of welded or riveted steel plates. It may have a fixed roof or one that floats on the product surface and moves up and down as product is added or withdrawn. The bottom of the AST is in contact with the soil or with a backfill material such as san
28、d or gravel that provides a buffer between the tank and the soil underneath it. This booklet examines many of the known AST leak detection technologies in their generic forms. Its purpose is to demonstrate not only how to select a workable leak detection method but also how to select the technology
29、that is best suited to a particular application. It is also intended as a tool for understanding the uncertainties associated with advanced leak detection technologies. One other type of AST leak detection methodology is where specific tank bottom and foundation designs are used. As these undertank
30、leak detection designs are cov- ered in detail in API Standard 650, they are not discussed in this document. This method of leak detection dealing with tank bottom and foundation designs can only be installed at the time of tank construction or during a major renovation. However, the leak detection
31、methods described in this report can typically be installed on most tanks dur- ing normal operations. has the potential to supplement the regular internal and external inspections that are standard in the industry. Leak detection in ASTs is also regulated by some state and local authorities. All of
32、the leak detection methods discussed in this booklet can provide results on a periodic basis, and some can accommodate continuous monitoring. AST owners have three important tasks when imple- menting a leak detection program: (1) to select a type of leak detection technology or technologies, (2) to
33、select specific systems based on those technologies, and (3) to develop a strategy for using those systems. Managers, operators and engineers are urged to explore a range of options before making these decisions. Leak detection as envisioned in this booklet is a tool that WHO SHOULD READ THIS BOOKLE
34、T? This booklet addresses a varied audience: terminal managers, tank owners and operators, and engineers involved in implementing recommendations on leak detection practices. booklet? What can each of these readers expect to gain from this A basic understanding of each of the different technologies
35、that will ensure some level of effective- ness when systems based on these technologies are applied at a given site. Each technology is described in terms of “key features” that effectively constitute a checklist against which comparisons of different systems can be based; “demonstration” techniques
36、 for verifying systems on site are also offered. An awareness of site-specific characteristics that may affect the performance of a given technology. Information on how to select a technology or combi- nation of technologies that best suits the needs of a particular site. An improved ability to esti
37、mate the impact of testing on facility operations in terms of cost and time. Greater confidence in interpreting the results of vendor-supplied evaluations. A NOTE OF CAUTION It must be understood that none of the techniques discussed in this booklet will detect a leak without fail 100 percent of the
38、 time and that each will occasionally produce false alarms. Furthermore, not all the technologies examined in this booklet have been tested. Claims made by vendors of leak detection services and equipment must be carefully evaluated, and whatever technology is selected must be appropriate for the si
39、te where it will be used. The scope of this report is limited to the description of several leak detection methods. Tank design, liners, cathodic protection, inspection, and operations are described in API Standards 650,651,652,653, and 2610. 1 API PUBL*334 96 m 0732290 0554082 869 m 2 API PUBLICATI
40、ON 334 The Statistical Nature of the Testing Process esting a tank for leaks is an example of the classical T statistical problem of finding a signal in a background of noise. A signal is a discrete and measurable event produced by a leak, whereas noise is any process or phenomenon unrelated to a le
41、ak that can mask or be mistaken for the leak. In this report, the concepts of signal and noise are described qualitatively for each technology. It is recog- nized that not all AST leak detection methods will have equivalent performance. The out-come of an AST leak detection test depends upon a combi
42、nation of parameters, including tank design, connections to piping and other tanks, weather, soil or backfill conditions, stored product, and environmental noise. Quantifying the performance of each method with respect to these parameters is beyond the scope of this report. All of the technologies d
43、escribed in this booklet, however, are considerably more sensi- tive than the conventional method of handgauging the tank (that is, taking a A reliable system must be able to differentiate b however, reliable detection usually requires a detailed understanding In order to evaluate the effectiveness
44、of a leak detection of the sources of noise so that ancillaq measurements can be used to effectively remove some of the noise from the data collected during a test. The noise left in the data after this removal can be significantly less than the original ambient noise, depending on the effectiveness
45、 of the noise removal techniques. In most cases, characterizing the effectiveness of a leak detection system comes down to characterizing the effectiveness of the noise removal techniques. THE CONCEPT OF PERFORMANCE The concept of performance as a way to measure the effectiveness or reliability of a
46、 leak detection system evolved from research on underground storage tanks (USTs). Although performance measures for AST leak detection are yet to be implemented, many of the same general concepts are expected to be applicable. Perfor- mance is defined in terms of the probability of detection, or P,
47、which is the likelihood that a test will detect a real leak, and the probability of false alarm, or Pf, which is the likelihood that a test will declare the presence of a leak when none exists. A related issue is the probabilio of missed detection, or Pmd, which is the likelihood that a test will no
48、t find a leak that does exist. Actual Conditions I LEAK NO LEAK Correct declaration Incorrect declaration The matrix above shows the possible outcomes of a leak detection test. When the measurements match actual condi- tions, the result is a correct test decision-either the detection of an actual le
49、ak or the confirmation that none exists. If the measurements do not match actual conditions, the test decision is incorrect-either a missed detection or a false alarm. A reliable leak detection system generates tests that have a high probability of detection (or non- detection when there is no leak) and low probabilities of false alarm and missed detection. API PUBL+33Y 96 0732290 0554083 7T5 A GUIDE TO LEAK DETECTION FOR ABOVEGROUND STORAGE TANKS 3 DECLARING A LEAK The basis for declaring a leak is the threshold. Test results that fall within the threshold are consid
