1、i DISTRIBUTION PIPE: REPAIR AND REPLACEMENT DECISION MANUAL A Technical Report OPERATING SECTION AGA American Gas Association CATALOG NO. XL0702 Assembled By: Jacobs Consultancy Inc. 5995 Rogerdale Rd Houston, TX 77072 iiNOTICE AND COPYRIGHT The American Gas Associations (AGA) Operating Section prov
2、ides a forum for industry experts to bring collective knowledge together to improve the state of the art in the areas of operating, engineering and technological aspects of producing, gathering, transporting, storing, distributing, measuring and utilizing natural gas. Through its publications, of wh
3、ich this is one, the AGA provides for the exchange of information within the gas industry and scientific, trade and governmental organizations. Each publication is prepared or sponsored by an AGA Operating Section technical committee. While AGA may administer the process, neither the AGA nor the tec
4、hnical committee independently tests, evaluates, or verifies the accuracy of any information or the soundness of any judgments contained therein. The AGA disclaims liability for any personal injury, property or other damages of any nature whatsoever, whether special, indirect, consequential or compe
5、nsatory, directly or indirectly resulting from the publication, use of, or reliance on AGA publications. The information contained therein is provided on an “as is” basis and the AGA makes no representations or warranties including any express or implied warranty of merchantability or fitness for a
6、particular purpose, In issuing and making this document available, the AGA is not undertaking to render professional or other services for or on behalf of any person or entity. Nor is the AGA undertaking to perform any duty owed by any person or entity to someone else. Anyone using this document sho
7、uld rely on his or her own independent judgment or, as appropriate, seek the advice of a competent professional in determining the exercise of reasonable care in any given circumstances. The AGA has no power, nor does it undertake, to police or enforce compliance with the contents of this document.
8、Nor does the AGA list, certify, test, or inspect products, designs, or installations for compliance with this document. Any certification or other statement of compliance is solely the responsibility of the certifier or maker of the statement. The AGA does not take any position with respect to the v
9、alidity of any patent rights asserted in connection with any items which are mentioned in or are the subject of AGA publications, and the AGA disclaims liability for the infringement of any patent resulting from the use of or reliance on its publications. Users of these publications are expressly ad
10、vised that determination of the validity of any such patent rights, and the risk of infringement of such rights, is entirely their own responsibility. Users of this publication should consult applicable federal, state, and local laws and regulations. The AGA does not, through its publications intend
11、 to urge action that is not in compliance with applicable laws, and its publications may not be construed as doing so. Any changes in this document that are believed appropriate should be communicated to AGA by completing the last page of this report titled, “Form for Suggestions to Change Distribut
12、ion Pipe: Repair and Replacement Decision Manual“ and sending it to: Operations this is how we did it. THE GROUND WORK We began investigating the relationship before main replacement and leak frequency more than ten years ago by studying 195 randomly selected CI main segments to which nothing was do
13、ne except to repair the leaks that occurred. Some very interesting relationships came to light. We found that there was an exponential relationship between the cumulative number of cast iron main breaks and the age of the pipe as shown below in Figure 1. We also found that a linear relationship resu
14、lted, if the cumulative number of breaks was plotted on a logarithmic rather than a natural scale as shown in Figure 2. Cumulative joint leaks, on the other hand, increased linearly with pipe age without being plotted on a logarithmic scale, as shown in Figure 3. Section 1 Budget Implications 7Secti
15、on 1 Budget Implications 8We then studied each segment individually. Much to our disappointment, we found the relationships between breaks, joint leaks, and pipe age, evident for the total 195 segment sample, were not statistically valid predictive tools for individual segments because of inadequate
16、 sample size. Nevertheless, we felt the need to make such predictions and theorized that applying the relationships developed for the larger sample was the best available predictive tool for the individual segments. We used the relationships to plan and implement a systematic main replacement progra
17、m. The resulting program definitely improved system leak performance. For example, a log scale plot of cumulative main breaks on the entire PSE all based, to one degree or another, on the relationships developed via our 195 segment study. The problem with these approaches was that they dealt with in
18、dividual segments rather than addressing the system as a whole; perhaps more importantly, they did not provide management with any tools to determine effectively what level of replacement activity would be best. THE TECHNOLOGY OF SYSTEM MANAGEMENT Not unlike other repair/replace decision makers, the
19、 basic premise of the new System Management approach is that main segments that have leaked in the past will be the segments most likely to continue to develop new leaks in the future. Every distribution system has an inventory of such pipe. For lack of a better word, lets call it “worn pipe.” Other
20、 things being equal, larger inventories of worn pipe result in more leaks. Therefore, controlling the number of leaks involves, controlling the magnitude of the worn pipe inventory. Section 1 Budget Implications 12Every year, additional pipe becomes worn and is added to the inventory of worn pipe. T
21、he way such an inventory is reduced is by replacing or otherwise retiring the worn pipe. If the replacement rate is less than the rate at which pipe is added to the worn inventory, leak rates increase, and, if it is greater, leak rates decrease. This of course, is an oversimplification of a very com
22、plex process. As we all know, the rate of main replacement is not the only factor involved. However, for PSE the replacement cost effectiveness of the individual segments within that inventory is anything but equal. Take note though, that the selection of individual segments is where most other syst
23、ems begin. For the System Management approach, it is merely a continuation of the process. The first rule of thumb to use in selecting individual segments is that the segment should have a history of leakage, either breaks or joint leaks, or both. It would be nice if both breaks and joint leaks occu
24、rred on the same segments. In PSE in other words, where one additional dollar of capital expenditure will reduce O for example, for bare steel services, the $3.5 million which results from other programs is more than adequate to cover the optimum program pace previously discussed, so no additional f
25、unding for bare steel service renewal is required. Without consideration of the relationships between many different activities there may be the tendency to invest in several discrete activities with the consequence of double funding. The synergy model has helped CPCo to understand the relationships
26、 between programs and, in effect, solve multiple problems with the same dollar. THE CULTURE CHANGE One of the more important challenges in implementing the decision analysis process was to encourage the nine individual customer service centers to look at the work being evaluated on an SBU basis. In
27、past organizations, each operating area would be given an allotment of the budget. Each area could then choose to complete the work they deemed necessary throughout the year. Decision analysis establishes specific replacement criteria and moves away from the “gut feel” method of decision making. Usi
28、ng decision analysis has eliminated the “competition” aspect of the budget allocation process. Projects are evaluated quantitatively based on field information. Funding is allocated based on expected capital maintenance results. Local management is then accountable, by objective, to achieve those re
29、sults. Compensation is linked to these expected results thereby closing the loop between planning and execution. In order for decision analysis to work as effectively as possible, all non-emergency projects should be evaluated by a model before the job is constructed. Decision analysis is most effec
30、tive when the budget for the company is not artificially controlled by past spending patterns or intuition. This was a major culture change for CPCo since past budget allocations were based in part on presentations from managers or on “how much they had last year.” CPCo employees are now developing
31、an understanding of the synergies between programs. Previously, budget requests were made based on the total funding needed to complete all projects. Understanding synergies has allowed managers to complete two projects with the same dollar. NEXT STEPS Decision analysis is only the first step in the
32、 risk management process. In the risk management process shown in Figure 4, decision analysis is being used as a risk assessment tool (identifying hazards and using company specific data to quantify probabilities and consequences). CPCo has identified least NPV cost replacement programs at current r
33、isk levels. Section 1 Budget Implications 24FIGURE 4 The risk-management process. Risk management requires the use of innovative ways to reduce current risk levels through new, innovative prevention and mitigation measures. When probabilities and consequences (ie, risk) can be reduced, new optimum p
34、rioritization lists and synergies will result which will reduce costs while increasing safety. Prevention measures are steps taken before an event occurs to prevent it from happening. Cathodic protection or a damage prevention program would be examples of prevention. Mitigation measures are put in p
35、lace to reduce the consequences of an event after it has occurred. Mitigation examples would include leak survey and emergency response. Once implemented, prevention and mitigation measures will lead to an overall reduction in risk. Risk reduction then continues through monitoring and refinement of
36、the process. The overall result of better controlling and reducing risk will be the ability to lower the curve on the optimum program life diagram previously discussed; that is, complete the desired project at the same optimum pace but at a reduced NPV cost. CONCLUSIONS The future success of CPCo ga
37、s system safety efforts will be due, in part, to the implementation of the risk management process. The continued expansion of decision analysis models and improved company specific data will set the stage for new mitigation and prevention strategies. As such strategies are successfully implemented,
38、 lower risk levels will be obtained, increasing overall public safety while reducing net costs to the company. Section 1 Budget Implications 2590-DT-27 Risk Analysis in Distribution Design 1990 JAMES W. PETERS The Brooklyn Union Gas Company INTRODUCTION Cost control and service reliability are popul
39、ar topics when strategic issues facing LDCA Distribution Companies (LDCs) are under discussion. The ability to provide secure and uninterrupted gas service is crucial for growth and company image, both with the public and regulatory agencies. At the same time, the industry is facing unprecedented co
40、mpetition from alternate fuels, and cost control is essential to maintain a competitive edge in the market. On the surface, it would appear that these issues are contradictory. Improvement in service reliability should cost something-or does it? Risk analysis can provide the answer, especially from
41、a distribution design perspective. From a distribution engineers perspective, projects such as loops, backfeeds, and even valve placement are designed to reduce, minimize, and/or eliminate potential customer outages. They improve service reliability by acting as backups should a failure occur on a c
42、omponent of the distribution network. These “contingency projects are easy to cost out, but what about their benefits or true value? Their purpose is to maintain supply to an area of the distribution network in the event of a failure somewhere else. Two phrases stand out: “potential customer outages
43、“ and “in the event“ of a failure. They identify uncertainty. The Risk Analysis approach outlined here, when applied to the evaluation of proposed contingency projects, will: Quantify the uncertainty Define value of proposed projects (benefit/cost) Direct the allocation of financial resources Overal
44、l, this approach will facilitate risk management by improving system reliability while optimizing the allocation of financial resources. Essentially, it provides the means of balancing the major issues facing LDCs cost control and service reliability. Brooklyn Union Gas serves 1.1 million customers
45、in the New York City boroughs of Brooklyn, Staten Island, and Queens; it has a distribution network comprised of 3900 miles of main and 513,000 services. Over 94 percent of our customers are served off our low-pressure network. System pressures are regulated through 24 gate stations and 255 district
46、 regulators. Maintaining and improving service reliability has been and continues to be a key objective of Brooklyn Union. Significant effort has been expended in identifying and correcting weak links in the distribution network. Risk analysis targets projects where construction funds provide true v
47、alue to the company and our customers. WHAT IS RISK ANALYSIS? Risk analysis is defined as the review of events involving uncertainty. Almost everything in life involves some degree of uncertainty. Todays weather, sports events, and business issues involve uncertainty, and usually we make decisions b
48、ased on subjective review. Risk analysis provides a way of quantifying this uncertainty so as to arrive at objective decisions. The following are definitions: Section 1 Budget Implications 26 Risk-An event involving uncertainty; e.g., the potential of a main break on a high-pressure cast-iron main s
49、pur feeding a governor. Risk Assessment-Identification of consequences and value. Determination of the likelihood of the event and subsequent impacts (customer outage). Risk exposure with the cost of eliminating the risk to determine value is compared. Risk Management-Allocation and targeting of resources. Based on assessments and value of individual projects, the amount and allocation of funds are defined to manage the risk. The only mathematical concept required to perform a risk analysis is that of expected value. Expected value is defined as the weighing of all
