_20201019_010851论文igu2009docswgcfinal00602

1、24thWorld Gas Conference, Buenos Aires, Argentina 2009NEW FOCUS ON SAFETY OF GAS DISTRIBUTION IN THENETHERLANDSAuthorHenk van Bruchem (Netbeheer Nederland/Kiwa Gas Technology, The Netherlands)TABLE OF CONTENTS1 Background2 Aims3 Methods4 Results5 Conclusions1.BackgroundMarket liberation and price re

2、gulation present the risk of decreasing quality and decreasing safety of gas distribution grids. For this reason the State Supervision of Mines was appointed in 2006 as regulator for the safety of gas grids.Earlier (in 2001) the Dutch Safety Board started to investigate accidents in gas distribution

3、 systems. The reports of these investigations often contained far reaching recommendations.At more or less the same time, improved uniform recording of (causes of) accidents and incidents was implemented. This provided better opportunities for analysis, which led to increasing insight into underlyin

4、g causes of gas distribution accidents and incidents and an increased awareness of safety.These three developments have caused the Dutch energy grid operators to start various activities to investigate if safety could be improved, and to implement measures to effectuate improved safety.Previous to t

5、hese developments, safety was considered to be business as usual. Accidents were sometimes found to be unavoidable. But now there is a new focus on safety and more accidents are found to be avoidable.2.AimsThe aim was and is to make gas distribution as safe as reasonably possible.3.MethodsSeveral me

6、thods were used:1. An expert group was formed for the safety of gas gridsIn 2005 an expert group Safety of grids was formed. This group consisted of 6 high level representatives from energy grid operators, one representative from Kiwa Gas Technology, two representatives from EnergieNed (the predeces

7、sor of Netbeheer Nederland, the branch organization of the energy grid operators) and one independent integrity management consultant.2. A safety indicator was developedThe safety indicator is a single quantitative parameter which is calculated from the risk of several precursors (unique combination

8、 of asset and circumstances which has led to an accident e.g. third party damage to a connection line).3. An investigation into additional barriers against accidents was carried outIn risk analysis (tripod or bow-tie), an unwanted effect (e.g. an explosion) of an occurrence (e.g. a gas leak) can be

9、avoided by placing a barrier (e.g. odorizing the gas, so that it can be detected before an explosion occurs). One of the recommendations of the expert group safety of grids was to investigate additional barriers against accidents. This was carried out by a working group.4. Actions were taken to incr

10、ease safety culture e.g. through the organization of workshopsOne workshop was organized by Netbeheer Nederland to give a follow up to the recommendations of the expert group with regard to safety cultureAnother workshop, organized by Kiwa Gas Technology, was aimed at methods of how to change safety

11、 culture at company level and at employee level.5. Seeking innovative methods to be able to carry out more work without gas releaseIn September 2004 there was an accident in which a mechanic suffered burns while repairing a gas leak. This was investigated by the Dutch Safety Board. One of the recomm

12、endations of this board was to carry out an investigation into innovative methods to carry out work without the release of gas. This work was carried out by Kiwa Gas Technology.6. An investigation was started into the diffusion of gas from leaks in the soilThis work was carried out by two university

13、 graduates, under the supervision of Kiwa Gas Technology. Atheoretical model was developed and validated with practical experiments. One of the reasons for this work was an explosion of a house in March 2004, due to a gas leak several meters away (service linedisconnected from mains because of third

14、 party damage)7. A structure for independent investigation of major accidents/incidents was set up (with focus on root causes)The first investigations of accidents by the Dutch Safety Board were carried out from the perspective of safety alone, so not from the perspective of gas grids. As a conseque

15、nce, the quality of some of the recommendations was not optimal. Therefore the grid operators decided to set up their own structure for investigation of gas accidents. This had to be independent, so that the results would be accepted by the Dutch Safety Board. It was decided to let Netbeheer Nederla

16、nd (the association of Dutch energy grid operators) take control of the investigations. Kiwa Gas Technology was selected as independent gas expertise centre to carry out these investigations.8. Existing informal measures to prevent third party damage to underground infrastructure were formalized in

17、legislationUntil 2008 there was no formal obligation to report digging activities and to obtain information about the location of pipelines and cables. The main incentives to do so were liability in case of damage and refusal of insurance companies to pay for damages. Nevertheless, there was a high

18、number of digging incidents.In 2004 there was a large gas explosion in Belgium, which caused concern for the safety in case of damage by digging. This all caused the development of a law in the Netherlands.9. A guideline was developed for careful diggingThe law mentioned above has an obligation for

19、careful digging, but no specifications as to how this must be carried out. Therefore, the industry took the initiative to draft a guideline for careful digging. This guideline specifies when and how many test holes have to be dug, and when mechanical digging may take place.10. An investigation was s

20、tarted to increase knowledge about adsorption of odorant from leaking gas in the soil.In some accidents it was found that the inhabitants did not smell gas before the accident happened. Upon investigation no anomalies in the odorization were found. For this reason it was suggested that odorant can b

21、e adsorbed in the soil. A literature search was carried out to find more facts about adsorption of odorant in the soil.4.Results1. An expert group was formed for the safety of gas gridsThe expert group formulated 25 recommendations in the field of increasing the safety of grids, more effective self

22、regulation, change of the safety culture and communication. These recommendations were consequently developed into further investigation and/or implementation plansIn 2006, the group published its final report. This contained 25 recommendations to improve safety, self regulation, safety culture, com

23、munication and general aspects. A few examples:-formulate criteria when the network operator has to supervise third party digging activities investigate the effectiveness of odorisationseek additional measures to determine the quality of pipelines introduce a biennial safety plan and safety reportin

24、troduce a certified system to report accidents and incidents secure the expertise of personnel by regular training and testing stimulate safe working by improving the safety cultureconduct consultations with municipalities for safe and well protected pipeline routesadapt communication policies. Comm

25、unicate in more languages (to take immigrants into account), take account of people who do not recognize the smell of gas-organize a workshop to translate the generic recommendations to specific work plans for grid operators.initiate a programme to come to a more universally accepted prioritisation

26、method for replacement policy in the Netherlands-The result of the expert group was a set of recommendations. These still had to be implemented, so there was no immediate effect on the safety of the gas grids. The report did result in a better awareness of safety,which is a very valuable result in i

27、tself.2. A safety indicator was developedSince 2005 an annual analysis provides insight into the causes of accidents and incidents. This results in a list of precursors (unique combinations of asset an circumstances which lead to an accident or incident). The number of times these precursors occur,

28、is standardized and weighed (standardization per 1000 connections or per km, weighing factor 10 for negligible, 1,000,000 for catastrophic), resulting in safety subindicators.Addition of all subindicators gives the safety indicator (see Distribution Safety Indicator; Flonk et. al.; presentation 4.2E

29、F.02 WGC 2006, Amsterdam for more background).The safety indicator has led to a better recording of accidents and incidents and has provided more insight into factors leading to accidents/incidents.Although work is still being carried out to get a better validation of basic data, the safety indicato

30、r is a good comparison tool. Data from the safety indicator can be a good input for risk matrices, so they form a good steering instrument for risk control. The effect of proposed measures on the safety of the grid can be better estimated by evaluating the effect on the individual precursors of the

31、safety indicator. Since the safety indicator is a single numerical value, it can be used to set managerial targets.3. An investigation into additional barriers against accidents was carried outA working group came up with the following fourteen ideas for additional barriers:a)b)c)d)e)f)g)h)i)j)k)l)m

32、)n)periodic odorization surgeleak detection with the help of smart metering gas detectors in above ground spacesgas detectors in underground crawl spacesgas detectors for people with a bad sense of smellgas stoppers (devices that will shut off the gas supply when the flow is too large) better sealin

33、g of building facadesinformation campaignhigher frequency of leak detection surveysadditional mechanical protection of pipelines and stations new and/or better materialsdetection equipment for pipelines improvement of pipeline data (drawings) prevention of damage by diggingEach additional barrier wa

34、s weighed against the risk factors of the precursors of the safety indicator. Since the safety indicator pertains to grid operator infrastructure (mains and connection lines), a second weighing was carried out against circumstances in buildings. A correction factor was applied for feasibility. The g

35、eneral score of this weighing process is shown in figure 1.300250200150100500Figure 1Scores of fourteen additional barriers against accidentsOf these fourteen additional barriers, two were implemented (1. an information campaign focussing on the smell of gas and the national one call telephone numbe

36、r and 2. prevention of third party damage (see 8 and 9 below). Three additional barriers are still under investigation (1. periodical increase in odorization level, 2. gas detectors in crawl spaces, 3. excess flow valves in connection lines).The use of new/better materials (instead of old materials)

37、 was left to individual grid operators.4. Actions were taken to increase safety culture e.g. through the organization of workshopsThere has been no investigation into the effect of the workshops which were organised. There is no doubt, however, that there is an increased awareness which has led to a

38、n improved safety culture. Unsafe work methods are actively discouraged. Work methods have been changed to reduce the riskAt one company, the active use of safety culture principles has led to a reduction of identified risks and reduction of sick leave. The result of one of the workshops was that a

39、working group will be started to try to standardize grid risk control measures. Lack of proper grid risk control measures may result in accidents, which may result in requirements from regulators to replace large grid sections or a large number of connection lines.5. Seeking innovative methods to be

40、 able to carry out more work without gas releaseA risk evaluation was carried out to determine which activities are carried out where there is a free release of gas and which of these situations present the biggest risk. A number of conceptual solutions was conceived. These solutions were evaluated

41、for feasibility. Ten solutions were judged to have enough potential to be further developed. Figures 2 5 show a few examples. For eight of these solutions manufacturers were found who are in principle willing to make prototypes. At this moment the solutions are not yet ready for use in practice. Fie

42、ld testing is required to prove the effectiveness of the products.score (points)Figure 2 Schematic view of Incubator (type 3) to remove/replace main valve from connection line.Figure 3 Schematic view of a balloon on a stick to stop leaks. (limited application possibilities)Figure 4 Stamp grip to sto

43、p leaksFigure 5 Cover + suction to prevent the build up of explosive gas mixture above a gas leak6. An investigation was started into the diffusion of gas from leaks in the soilFirst a theoretical model was developed for the diffusion of gas through the soil. This model was transferredGastightMain v

44、alve connectionArmTransparant sleeveNew valveinto a computer programme. With this programme simulations were carried out. These were verified with controlled laboratory experiments. The results of the simulations correlated well with the experiments. In practice, however, there is no controlled envi

45、ronment. The number of variables is too large to use the simulations on practical cases. It was found that the diffusion of gas in soil is a complicated process. In wet soils small canals (of 1 2 mm diameter) are formed through which the gas is transported. Because of this phenomenon there is less c

46、ontact between the gas and soil particles, resulting in less adsorption of odorant (see 10 below). In inhomogeneous soils layering takes place. Gas is preferentially transported through layers with a larger permeability. This can result in spreading of the gas. This means that the leaking gas might

47、not be detected right above the leak, but a certain distance away.The knowledge from this study will be integrated in the course material for the training of leak survey technicians.7. A structure for independent investigation of major accidents/incidents was set up (with focus on root causes)The in

48、dependent investigations made it possible to carry out analysis of individual cases as well as trend analyses of all cases. Since 2005, 12 accidents were investigated, 2 incidents, and 4 cases where the accident was not caused by natural gas.In 2007 there were 12 accidents and 112 incidents. A subst

49、antial part of these cases was caused by third party damage. Another part was caused by construction or maintenance work on the gas grid. These conclusions provided further support for the activities to prevent third party damage (see 8 and 9) and for the innovation of methods to work without gas re

50、lease (see 5). In 2008 there were 24 accidents, figure 6 shows the causes of these accidents.Figure 6 Causes of gas distribution accidents in 2008Although the number of accidents is twice as high as that of 2007, so far no extra measures were taken. Damage by digging activities is still the biggest

51、cause, so it remains vital to try to prevent this damage. The category miscellaneous includes a lightning strike, an electrical short circuit and a case where somebody cut through the gas pipe instead of the sewage pipe.The benefit of the new investigation structure is that the lessons to be learned

52、 from accidents and incidents become available for all energy grid operators. The recommendations are often more nuanced, which ultimately results in lower costs for risk reduction measures.8. Existing informal measures to prevent third party damage to underground infrastructure were formalized in l

53、egislationThe new law has the following obligations:- diggers have to report planned mechanical digging activities and to request information about the location of pipelines and cables (at least three days in advance)- grid operators have to supply information about the location of their infrastruct

54、ure- diggers have to dig carefully- diggers have to give feedback in case a pipelines or cable is more than 1 m away from its location on the drawing-Orphan grids (grids of which the owner is unknown) will come under the care of municipalities- For grid operators with dangerous contents, the operato

55、rs have to take special safety measuresFor a transition period the information exchange will take place the old fashioned way, i.e. partly on paper, partly via e-mail. From November 2009 an automated completely digital system will be available (with uniform formats). From July 2010 everybody will ha

56、ve to use this digital system. The Telecom Agency has been appointed as regulator. The information centre in charge of the information exchange used to be operated by the grid operators, but is now operated by the land registry office. It is believed that the extra cost for this digital system will

57、be counterbalanced by the reduction in damages. So far the number of digging reports has increased but the number of damage incidents has not shown any reduction. Figure 7 shows the number of damages to natural gas distribution pipelines over the last four years, for instance. The total number of da

58、mages may even go up first, because some grid operators do not yet record all damages.Figure 7 Number of damages to gas distribution pipelines (including connection lines) due to digging activities. Note: the low number of damages in 2005 is due to incomplete registration in that year.It is widely recognized that the new law on its own will not be enough to result