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Metal hose - for city buried technical evalua

发布日期: 2012-7-20          浏览次数: 968


Qualitative and quantitative and semi-quantitative risk assessment method, half quantitative method is most widely used. Semi-quantitative evaluation methods are mainly Muhlbauer nemeses score () method (hereinafter referred to as nemeses method) [2] and Fuzzy comprehensive evaluation (Fuzzy Assessment) method [3]. In this paper, paper analyses of gas pipeline risk assessment based on the present research, these two kinds of methods in city buried steel gas pipeline risk assessment of applicability is analyzed.


In nearly 30 years' development and research and application practice in pipeline risk assessment technique in many countries play an obvious economic benefits and social benefit [1]. Our country has the fifteen technology plan will be buried city gas pipeline risk evaluation as an important research content.

 

1 the city gas pipeline and pipelines of major differences


In the actual investigation and study, city gas pipeline buried in design, construction and management have inherent characteristics, it and long-distance pipeline has many different places, in choosing the risk assessment methods often want to consider is the characteristics of evaluation system and the data can be obtained. Mainly displays in:


(1) the pipeline in different natural conditions


Long-distance pipeline laying in the wild, surface layer is usually dirt, suffer civ conditions, such as the enroach on of larger lightning, cold, storm or floods, earthquakes, etc, these elements conditions upon the influence is long-distance pipeline should be considered in the factor [6]. City gas pipeline buried due to the surface layer is mostly cement or asphalt pavement, pipe suffer cold lightning floods and other natural force condition the influence is less.

 

(2) pipeline in the planning and construction process differ


The city gas pipeline network with the development of urban construction gradually formed, and develops unceasingly. Pipeline construction initial lack of perfect management system, design, construction and the completion acceptance standards often uneven, anticorrosive coating the quality defects such as relatively more. Pipelines are usually built for the same period, there are perfect for survey, design, construction, completion, check and accept a standard and procedures, such as anticorrosive coating quality relatively less. A balanced and defects


(3) pipeline corrosion protection in different forms


Our city buried pipeline most did not make cathodic protection, gas pipeline anticorrosion coating are relying on the role, anticorrosive coating tiny construction defect often can cause conduit of large area corrosion. Pipelines are all of the use of cathodic protection and anti-corrosion layer dual function inhibition outside corrosion, and cathodic protection way for more impressed current cathodic protection.

 

4 pipeline structure with different [19, 20]


Urban gas pipeline distribution for mesh, elbow, valve, tee, stone and coagulation water pipeline accessories such as densely, often 100-500 m have a branch pipes or valve and pipe diameter changes generally, different capable person is qualitative pipe together common. Pipelines are usually the same pipe single pipe, tubes, valve and pipe diameter changes very little.

 

5 pipe testing and maintenance in a different way


Urban gas pipeline management relative passivity, is often received leakage alarming until after leakage repair, belongs to the mouth after maintenance, And the city gas pipe diameter changes frequently, valves, water pipe, elbow etc coagulants densely, are difficult to use intelligent the pig testing. The foreign ministers long-distance pipelines has established the perfect management system, its maintenance detection focuses on intelligent the pig on-line inspection, can discover in time, the defects in the pipeline system for forecasting to maintenance. 6 pipeline corrosion in different forms


City buried gas pipeline need not consider atmospheric corrosion, and tube corrosion is not obvious, the main corrosion damage from soil corrode action. Long-distance pipeline corrosion and damage of soil erosion, not only should consider to consider in atmospheric corrosion and corrosion.


7 pipeline in different humane environment


Urban gas pipe laying in densely populated areas, circumjacent environment complex, once leakage occurs, fire, explosion, can cause serious casualties and property losses. Pipelines are usually equipped in the wild thinly populated regions, surrounding buildings, circumjacent environment information distribution less easy assurance, after has the accident casualties is not big.

 

8 conveyance medium pressure difference


Urban gas pipeline in urban areas more for medium-voltage conveying [21], and long-distance pipeline more adopts high voltage transmission.

 

2 conclusions


1 nemeses model can't be directly used in urban gas pipeline risk assessment. Method of evaluation objects is nemeses pipelines, because of pipelines and city gas pipeline buried steel structure and environment in many aspects such as the difference is larger, the premise supposition nemeses method and corrosion models were difficult to suitable for urban pipeline. In the unique Chinese management system, nemeses involved in management method, and it is difficult to analyze score city pipe to the actual situation of also makes nemeses method makes the corresponding improvement before application.


(2) fuzzy comprehensive evaluation method in dealing with many factors combined effect of system, more suitable for urban gas pipeline risk assessment. It not only on the system of evaluation in subjective and objective relatively uniform, but also can can quantify said some unavoidable fuzzy concepts. Fuzzy comprehensive evaluation handle highly nonlinear ability, can be man's subjective influence to the minimum. Affect the city buried steel gas pipeline is very complex factors and fuzzy, but the person's subjective factors also more, adopts the fuzzy comprehensive evaluation method of factors affected city buried steel gas pipeline risk assessment, the more comprehensive objective, scientific and feasible.

 

3 city buried pipeline risk assessment methods of application


3.1 nemeses method applicability analysis


Not only the comprehensive consideration nemeses law affecting pipeline system security the various factors (including third-party damage, corrosion factor, design factors, the incorrect operation factors), and is considering a conveyance medium for leakage harmfulness, leakage state effects on people, in long-distance pipeline engineering application in a success. But because of pipelines and city buried gas pipeline has very big distinction, nemeses method cannot completely around city buried gas pipeline risk assessments, reason lies in the following aspects:


1 no nemeses method or ill-judged factors


A. soil stray current corrosion factors, influencing factors, all is nemeses method in ill-judged and did not consider the evaluation factors, but as a city buried gas pipeline risk assessment, especially corrosion damage assessment, but important evaluation indexes.


B. city buried pipelines due to laying in densely populated areas, often appear peccancy tie up the situation, this is buried city gas pipeline factors to consider. Long-distance pipeline laying in the wild, basically no illegal tie up phenomenon, so nemeses method in does not consider this aspect factor effect.


E. of accident consequences estimate is the important content in the risk assessment. Most laying pipelines in the wild open area, the influence of nemeses model consequences only considered the population density, for property loss and environmental pollution consideration owe weeks. City buried gas pipeline should be given not only casualties, must also be considered property damage, repair economic investment, etc and the physical damage to the environment, the enterprise and the influence of social reputation and other intangible loss.


(2) nemeses method need in certain parameters is difficult to provide domestic


A. in China's current city buried gas pipeline management and operation system, many design, operation, and operation, management and maintenance of standards and specifications with Chinese characteristic, the method mentioned in nemeses measures and regulate most does not apply to our country. As mentioned in the nemeses method called "to keep shout system" the service system. The us transportation department of conventional keep shout system defined as: by two or more utility companies, government departments or other underground facilities operators, establish a common communication system, provide a phone number to mining contractor and the public, request notifications and record them in excavation activity's content [6]. At present domestic urban pipeline management system under no conditions by using this measures.


B. because the city buried steel gas pipeline often bury in the driveway cement road surface, and with other municipal installations crisscross embedment, many test methods such as "tube ground potential test", "secret" difficult to implement time-interval measurements, read the accuracy of the data can also be difficult to guarantee. City gas pipeline buried steel pipeline accessories reticulation distribution, numerous, tube detector in pipe in difficult to carry out effective inspection work, therefore, tube detector project also difficult to implement. The practical situation make nemeses method used in the city buried steel gas pipeline risk assessments above 3 items (tube ground potential test, dense time-interval measurements and tube detector) evaluation content scoring will decide hard.


E. pipelines due to the characteristics of conveyance medium pipeline corrosion inside need to consider, and want to consider the ground pipe atmospheric corrosion, these models can only be used for long-distance pipeline. Because the city gas pipeline corrosion is not obvious, at home and abroad in most urban gas pipeline corrosion evaluation are ignoring within, and the ground pipe is not considered a smaller number of atmospheric corrosion.

 

3 the corrosion model nemeses law shall not apply


A. nemeses method of corrosion model, the internal corrosion and atmospheric corrosion distribution

corresponding weights and score, which together account for over 40% of corrosion evaluation model. But the city gas pipeline buried in atmospheric corrosion, also need to evaluate the basic need not evaluate corrosion inside.


B. pipelines due to implement impressed current Catholic protection, when anticorrosive coating nonvulnerable soil corrosive, so little influence on soil erosion model nemeses corrosive which is only 4.2% empowerment heavy, and only consider soil resistivity a factor. For anticorrosive coating defect relatively more and no effective implementation cathodic protection city buried gas pipeline corrosion of the corrosion model, the soil has a significant effect, and soil erosion process is complicated, soil corrosive not only use soil resistivity judgment, consider bacteria corrosion, soil ph value, the influence of factors of soil water content.


C. because of long-distance pipeline stray current corrosion interference is lesser, nemeses model of stray current have empowerment heavy are also small, only accounted for corrosion evaluation by 4.2 percent. Whereas domestic urban gas pipeline generally by stray current interference, stray current corrosion caused by the effect is very obvious, it is to measure is one of important index of the pipeline corrosion.


Therefore, nemeses corrosion model need to undertake corresponding improving adjustment and calibration ability after applied in city buried gas pipeline corrosion evaluation.


4 evaluation objects and factors weights processing methods do not apply


A. nemeses method research objects of oil and gas pipelines, model and methods also around oil and gas pipelines. City buried gas pipeline have own structure and environment characteristics, therefore, nemeses method cannot directly applied in city buried gas pipeline risk assessment.


B. city gas pipeline risk formation is a contains numerous factors and the complex nature of the relation between the system. These factors interact and restraining each other, existing same-total-sum-game internal relations.

The inner relationship between objective existence, making the city buried gas pipeline risk in different environmental conditions and different risk panorama present, so this kind of internal relations cannot ignore. A fist hypothesis nemeses method that is that each factors between independent, obviously, this is currently in the city gas nemeses method piping applications exist deficiency [4].


C. nemeses method proposed will cause conduit accident factors differentiate for third party damage, corrosion and damage, design factors and the incorrect operation four types, these four factors of pipeline risk factors score is 0 ~ 100 points, namely, the weight of each factors are accounted for by 25%. This treatment is not rational, because each factor to affect different pipeline failure, each factors in pipeline risk assessment of the proportion of the different.


U.S. Department of Transportation Department of Transportation (DOT) statistics, abbreviation, in 1931 a 1986 America many pipeline accident, third-party damage occupied 40%, corrosion and damage for 30%. In our country, some areas of pipe accidents factors is endless and same. Relevant statistics show that in south China city gas pipeline accident, third party caused damage accidents accounts for 30%, corrosion and damage caused by accidents accounted for 56%. This suggests that different countries, different environment, different condition and different management system pipeline the cause of the accident is endless and same. If for any pipe are adopted the invariable factor rating score system, will be affected the result of evaluation accuracy and practical.
Therefore, use directly nemeses evaluation method city buried steel gas pipeline risks will result in serious deviations, it is necessary to improve the corresponding models and nemeses method is verified through practice only after they applications.

 

3.2 fuzzy comprehensive evaluation method suitability analysis


Since 1965 Zadeh fuzzy mathematics to create since [22], because of its quantitatively processing impact analysis and design process of various fuzzy factors, the fuzzy mathematical have been widely used in industry all areas of the industry. Fuzzy comprehensive evaluation is the application of fuzzy set theory of system and a method of comprehensive evaluation, which based on fuzzy mathematics, the application of the fuzzy synthesis principle, structural relationship level fuzzy subsets of the reflected the fuzzy evaluation index quantized things (i.e. determine membership), then reuse fuzzy transform principle of each index synthetic [22].


Fuzzy comprehensive evaluation method used in the gas pipeline risk assessment of the biggest advantage is that it not only facilitate will risk fuzzy quantitative, and uncertainty stroken practical and scientific and reliable, strong maneuverability. The fuzzy comprehensive evaluation method is more suitable for urban nemeses method of gas pipeline risk assessment, the main reason summarized as follows:


(1) the fuzzy comprehensive evaluation method in theory can completely suitable for urban buried gas pipeline risk assessment, because fuzzy comprehensive evaluation in handling the fuzziness and uncertainty factors have certain advantages, but will affect the city buried gas pipeline risk factors and its influence on reasonable quantitative, then use traditional mathematics method is analyzed, and get more than other methods can objectively reflect city buried gas pipeline risk situation assessment.


2 is the city gas pipeline risk assessment development request


In developing the gas pipeline risk assessment in the initial stage of the traditional research approach is hoping to find cause gas pipeline failure of all the factors, and on the basis of the variation in determine its probability density distribution function, to establish the city gas pipeline failure probability distribution model. However, the actual investigation process but found that affect gas pipeline failure numerous factors with uncertainty, some still unable to quantify. This case even established formulistic calculation assessment model, the result also and objective law somewhat deviation, the direct impact of gas pipeline risk assessment technical development. Therefore, we need to a can handle various risk factors of uncertainty, mainly is the uncertainty of parameters, and the mutual influence of comprehensive evaluation method. Therefore, a fuzzy mathematical concepts of gas pipeline half quantitative risk assessment, and fully understand the quantification and mutual failure factors of the relationship between the fuzziness, gas pipeline risk assessment is the effective method [25].


(3) with a mature theoretical basis


A. the fuzzy comprehensive evaluation method of nonlinear systems with handle highly ability. The fuzzy mathematics method is especially suitable for high nonlinear system or system mathematical model of inaccurate and even harder to get situation established primers. Fuzzy comprehensive evaluation is based on the evaluation process of nonlinear characteristics, it put forward by using the fuzzy of fuzzy algorithms, the evaluation theory for nonlinear mapping quantitative synthetic, thus obtains the quantitative evaluation of comparable results. Therefore, fuzzy comprehensive evaluation can reduce artificial subjective influence, get more objective quantitative results. B. fuzzy comprehensive evaluation to deal with the fuzzy, inaccurate or lack of necessary information uncertainty things modeling provides a good tool. For more complex systems, because there are many induced system accident, impact accident consequences of fuzzy factors, using fuzzy sets method to describe and deal with these fuzzy factors, can make the evaluation result closer to engineering practice [23]. City buried in the construction of gas pipeline initial not establish corresponding database, make a lot of evaluation data is missing, adopts the fuzzy comprehensive evaluation method just fill this deficiency.


C. comprehensive evaluation refers to various factors which influence the things or phenomena are generally evaluation, if this evaluation process involves fuzzy factors, is fuzzy comprehensive evaluation [24]. Due to the same object has a variety of attributes, or by many factors, therefore in the evaluation process will judge of a number of separate elements and partial elements integrated into a form. Comprehensive evaluation is from overall comprehensive reflect the differences between evaluated object to be evaluated object classification or sorting purpose.

 

D. fuzzy comprehensive evaluation is based on the theory of fuzzy mathematics. Fuzzy mathematics is with mathematics method research and treatment with "fuzzy" things of math. The fuzziness mainly refers to the objective things differences among transition unclear sex, it is a kind of objective attributes of things, and not man's subjective cognition reach objective reality, cause. Fuzzy mathematics is not accurate mathematical become ambiguous, but with the accurate mathematical method to deal with the fuzzy things. Using fuzzy set to express fuzzy concept, using subordinate function will fuzziness quantization, thus the fuzziness with traditional mathematics method analysis and processing.


More accord with city gas pipeline buried the actual situation


A. the fuzzy comprehensive evaluation method can according to city buried steel gas pipeline characteristics and environmental features flexible formulated for city buried steel gas pipeline risk assessment assessment structure and evaluation factors system, according to existing available evaluation data, establish suitable for China's urban gas pipeline actual evaluation model, get practical evaluation results.


B. the fuzzy comprehensive evaluation method for complex system of gas pipeline risk assessment, can use multi-grade fuzzy comprehensive evaluation, will interrelated factors unified classification layered, first according to the minimum level of each factor to evaluate, then step up until finally reached the overall evaluation, evaluation results.


C. buried in the city of gas pipeline risk assessment, on one hand, because all kinds of failure factors are not can quantification and modeling, must use fuzzy mathematics method to solve. On the other hand, in the analysis process often will involve human experience and judgment, for example, "good construction quality" is a fuzzy events, "soil strong corrosion" is also a fuzzy events. The fuzzy set theory of basic function is to use language to represent the variable parameter accuracy [22], thus in the treatment of this problem than the traditional probability model to better reflect the objective reality. Admit fuzziness, use the thoughts and methods of fuzzy mathematics, will make as far as possible to achieve better results objectively the actual effect.


D. city buried gas pipeline in design, construction, operation, operation and maintenance of the process, from people, equipment, environment and other subjective and objective aspects, the influence of various factors on pipeline's influence is not independent, but each other associated with time, place, and the condition such as different and different. The connection between the various failure factors are objective uncertainty and contains subjective uncertainty, with a great ambiguity. The fuzzy comprehensive evaluation method does not cut off all the factors of the question of contact, but has fully considered the fuzziness relationship objective existence, we can make use of fuzzy comprehensive evaluation method to solve the conventional method cannot solve city buried gas pipeline risk assessment problem.


E. city buried gas pipeline risk assessment, each factors of integral pipeline risks of the proportion is not same, namely each factor is how important is not the same. Fuzzy comprehensive evaluation is not only a comprehensive consideration of the nature of the various factors, but also considers the importance of each factor. Using Delphi method, the AHP method to determine the weighing method will factors such as the influence degree of evaluation objects with [0, 1] within the numerical quantification [22], numerical size reflects factors on the size of the influence degree evaluation objects, numerical bigger influence degree is bigger, its representation in evaluation index system important degree is taller, to make the assessment result more close to reality, also more rationally.

 

4 gas pipeline risk assessment research status


(1) the domestic research situation of gas pipeline risk assessment


In the mid 1990s, China has carried out relevant safety assessment of oil &gas pipeline series of research and application of experiment work. In our country the earliest PanGuHua professor in 1995 by a comprehensive introduction of the United States "pipeline risk management handbook [13]. The ninth five-year plan period, China petroleum and natural gas corporation, and the national quality technology supervision and administration jointly organized the oil &gas pipeline detection and safety assessment technology research "national key torch-plan projects. Fifteen technology plan, further will risk assessment of urban gas pipeline as a key research contents.
Domestic oil and gas transmission pipeline risk assessment of technical development fastest. Researchers in foreign countries as a reference on the basis of research achievements, the integrated use of expert evaluation method and fault tree method and fuzzy mathematics and so on many kinds of analysis method, puts forward a series of feasible evaluation method [14-17].


Engineering application, 2000 southwest oil academy and China petroleum southwest branch jointly developed the "gas transmission pipeline risk assessment software" da lie in chongqing gas pipelines path the range of successful risk analysis and assessment, marking the international general pointrating method has been active in our country long oil tracheal path to the actual application level [18]. Foreign gas pipeline risk assessment research status


Along with the people of oil and gas transmission pipeline, foreign risk know increasing gradually development had emerging pipeline integrated management system [7], to all the factors of affecting pipeline integrity comprehensive, integrated management, from the draft working plan, processes and files to for pipeline risk analysis, understand the possibility of accident happening and consequences, establish prevent accident and emergency measures, regular pipeline integrity test and evaluation, and the content includes pipeline design, construction, operation and monitoring, repair, replacement, quality control and communication efc.so, and through pipe whole operation period. At present, the management system in the management of oil and gas pipelines are more and more attention.


(2) buried pipeline risk management earliest dates from the 1970s. American PRCI (true Intemationa1) to the ordinary Pipeline American and European Pipeline accident data statistics and classification, summed up 22 kinds of Pipeline failure caused by basic factors [4].


In 1985, American Battelle Columbus institute has published risk guidelines, first in investigation pipeline risk analysis using pointrating method [4]. W.K.M uhlbauer based on this summarizes the nearly 20 years develop oil and gas pipeline risk assessment and technological research achievements, in 1992 compiled the famous "pipeline risk management manual", detailed introduces the pipeline risk assessment model of expert grading, had become a world universal acceptance and as conducting buried pipeline risk assessment of the important reference [5], In 1996, the second edition of the book introduces different length adds a great occasion of pipeline risk assessment of correction model, increased environmentally sensitive areas, workplace stress and potential human errors in the assessment, and introduces in detail how to use the risks and costs of relationships based resource allocation model [6], In 2004, the book's third edition enriched the original risk management aspect content, in a clearer and more specific examples of establishing risk assessment of basic model program, increased the oil and gas pipelines across section risk assessment model of the method.


With the emergence of a new discipline and the development of new technology, new methods and new technology is also applied to buried pipeline risk analysis research. Such as literature [12] put forward by using the fuzzy neural network of buried oil pipeline defects simulation and simulated, and the buried pipeline classified various defects. GIS technology at present is also quickly become used to facilities management, life cycle detection, risk analysis, coordinated management, improve operation efficiency effective means. Pipeline GIS technology has been widely used in America, Norway, and other countries. In engineering application, abroad in early in the late 1960s began to notice pipeline engineering in considering in service pipeline detection and residual strength assessment, such as: American petroleum institute promulgated "risk-based inspection rules" (API 581) [8], the gas pipeline system integrity, supplementary documents "(ASME B31.8 S) [9], the corrosion residual strength determined already pipeline pressure pipeline standard complement, manual (ASME documents" B31G) [10]. Until the early 1990s, many American oil &gas pipeline has applied the risk management techniques to guiding pipeline maintenance work. Then Canada, Europe successively developed countries have joined the pipeline risk management technology development and application of the ranks. British Advantica company by statistic analysis of pipe material and disasters in simulation experiment of natural gas pipeline hazard factors of probability analysis and accident consequences quantification is established, on the basis of quantitative risk assessment technical pipeline, the expert analysis software PIPESAFE has been used in Britain and around the world countries of high-pressure gas pipeline [10]. Canada C - FFR company also successfully developed pipeline maintenance and inspection of risk analysis software package (PIRAMID), used for pipeline failure probability analysis, failure consequence and the total risk calculation [11].

 

Long-distance pipeline, Chinese scholars in long-distance pipeline reliability analysis, residual strength, life prediction, risk evaluation, etc have done a lot of research work, such as: the literature [14] using finite element analysis, establishing pipeline corrosion defects nonlinear analysis model for oil &gas pipeline containing defects in various outside loads on stress a strain of the numerical simulation, [15] realized the long-distance pipeline risk assessment of pipeline failure probability and consequences of quantitative evaluation to a certain research, proposes based on risk of oil &gas pipeline integrity maintenance decision method.


Because of city gas pipeline risk many influence factors, from design, construction, operation to the third party damage, corrosion and damage, and the consequences are research aspects as many as hundreds of relevant factors, together with our city gas pipeline construction early and did not establish corresponding history data and original design database, pipe into use after the operation situation of artificial depend entirely on record, a large number of data is missing, the objective situation increased establishing city buried gas pipeline risk assessment methods and models of difficulty, weaken the city gas pipeline reliability and authenticity of the original data. At present in the city buried gas pipeline risk assessment has not been formed system, complete risk assessment technique. The city gas pipeline system, literature [16] adopts the method of fault tree analysis to the pipeline liquefied petroleum gas (LPG) of fire and explosion causes and consequences are analyzed, established the gas leakage and arising from the fire and explosion accident risk assessment model, and then puts forward the risk assessment of the uncertainty of the problems and solving methods. [17] by using fuzzy risk assessment method to establish the gas pipeline network failure factors system and failure consequences of network system, and discusses the risk acceptable degrees, a more comprehensive considering the gas pipeline network failure probability and the influence factors of severcty failure consequences, overcome only rely on failure probability evaluation brings unilateralism and limitations.

 

 

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