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Determination of the Safety Distances Between Natural GasTransmission Pipelines and Facilities in their Proximity

GHEORGHE ZECHERU, IONUT LAMBRESCU* Petroleum Gas University of Ploiesti, 39 Bucuresti Blvd., 100680, Ploiesti, Romania

The paper presents the particularities of accomplishing risk analyses with the purpose of establishing thesafety distances – SD, between the pipes belonging to the natural gas national transmission system – NTSand facilities (people, animals, buildings, crops, orchards, forests etc.) placed in the their vicinity. In order tocheck if the distances between the National Gas Transportation Pipeline- NGTP and neighboring facilitiesare SD, the authors developed a procedure and a software for the risk assessment, which make use of a setof formulas validated by experimental results presented in the paper and information from the data base(built by the authors and presented briefly in our work) regarding the supervision of the technical state andrecording of the accidents that took place in the last 19 years on the NGTP from NTS. Also, in the paper, onedescribes the way the technical solutions verified using the procedure and the software built by the authorscan be selected and ranked (in view of implementation) by applying the ALARP principle and the cost –benefit analysis.

Keywords: Natural gas transmission pipeline – NGTP , Risk assessment, Potential Impact Area – PIA, Individual risk transect profile – RTP, Risk matrix – RM, Safety distance – SD

A facility (people, animals, residential, industrial or socialbuildings, crops, orchards or forests etc.) is situated at a safetydistance – SD from a natural gas transmission pipeline – NGTPlocated in its vicinity, if its presence do not influences in anunacceptable manner the technical risk associated to the pipefunctioning, defined through the probability p of the likelihoodof occurrence of a technical accident on it and by the gravityof the consequences G of such an event [1,2]. Because thenatural gases are non-toxical substances, but withasphyxiating potential, belonging to the category ofsubstances with high flammability (F+), the scenario thathas to be considered in evaluating the risk associated to aNGTP corresponds (fully or partially) to the followinghazardous events [3-9]: a) NGTP yield, loses its tightness andleakage/release of a fraction of the transported gas occurs;the natural gas leakage are not detected and quickly stopped,and the gases concentration of the area’s atmosphere wherethe leakage took place surpasses the lower flammability limit– LFL; c) in the area where the leakage occurred, conditionsfor ignition or self-ignition of the air and natural gas mixtureescaped from the pipe are present, a deflagration,accompanied by fire takes place. The research conducted todate proved that a pertinent evaluation of the technical riskassociated to a NGTP functioning, can be obtained consideringonly the effects of the thermal radiation resulted if this scenariomaterialises, corresponding to the occurrence of technicalaccidents accompanied by fire [3-5].

In order to assess this way the risk associated to a NGTP,consisting of building the individual risk profile – RTP for thefacilities in its vicinity and in assessing the admissibility of therisk with the help of the risk matrix – RM, one uses the procedureelaborated by the authors, described in detail in [7, 9, 10],which is based upon the calculus schemes presented in figure1 and the following formulas, with the physical quantities andconstants specified in tables 1, 2 and 3:

- formulas for calculating the exposure intensity for thefacilities in the vicinity of NGTP (fig. 1.a):

* email. ilambrescu@upg-ploiesti.ro; Phone: 0723 924551

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- formulas necessary for building RTP (fig. 1.b):

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(3)

(4)

(5)

- formulas necessary for building RM (equations for thelines C1, C2, C3 of the risc matrix – fig. 5) and fordetermining the allowable level of risk priad.

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- criteria for distances between NGTP and facilities in itsvicinity be SD:

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Fig. 1. Calculus schemes forevaluating the technical risk

associated to a NGTPa. The scheme of the influencearea for a deflagration with fire

(simplified model: a singlepoint heat source emitter

located at ground level, b. Thecalculus scheme for

building RTP

Table 1TECHNICAL CHARACTERISTICS OF NGTP FOR WHICH THE RISK

ASSESSMENT IS DONE

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Experimental partTo confirm the validity of the calculus schemes and

formulas, proposed for the assessment of the riskassociated to NGTP, briefly presented above, one used thedata synthesized in tables 4 and 5 and figure 2, recordedwhen technical accidents (deflagration with fire) that tookplace on the NGTP belonging to the transmission systemsin Romania and worldwide, were surveyed [3-8]. Theanalysis of those data highlighted that: a. the point sourceradiation model (fig. 1.a), that was the basis for developingthe formulas in group (1), is satisfactory; b. whenestablishing rie between NGTP and the facilities in its vicinity,one recommends to use: for people and animals qpsape = qpsaan= 7.25...14.5 kW/m2, and for other facilities, qpsabf = 25...28kW/m2; c. Ipc is an estimation parameter for the severity of thedeflagration with fire technical accidents type, which has agood correlation with rie and (implicit) with SD (fig. 2):

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Table 2PHYSICAL QUNTITIES THAT INTERVENE IN THE ANALYSIS OF THE TECHNICAL RISK ASSOCIATED WITH NGTP

Fig. 2. Experimental dependencies between quantities Ipc, qpsa and rie

Recorded data when deflagration with fire accidentstypes were surveyed showed that the probability pcocorresponding to different levels of consequences of the

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accidents, correlates well with the magnitude of thethermal dose (Sto sau Stl), that cumulates the action of thefactors qps and τe; figure 3 presents (for facilities in the vicinityof the NGTP for which a technical accident occurred) theexperimental dependencies pco = gpa(Sto), with pcoreprezenting the probability of death or severe injury of peopleand/or animals and pco = gob(Stl), with pco reprezenting theprobability of arson (secondary) and severe deterioration ofthe facilities like buildings, crops, forests etc.

Table 3CHARACTERISTICS OF THE FACILITIES FROM THE NGTP VICINITY FOR WHICH THE RISK ANALYSIS IS DONE

a) COSTT is calculated applying the procedure presented in [9] and includes the following costs: insurances in case of death or serious injury of peopleinvolved in the accident; losses generated by death or injury of animals from the accident area; clients compensation for the unplanned outages of theNGTP functioning; lost gas due to the accident; reinstatement NGTP after the accident (pipes, components, materials and repair labor, recovery andrehabilitation works of the land etc.); damage inflicted to facilities (buildings, installations, vehicles etc.) burned; damage inflicted to plantations,forests, crops, affected by the accident etc.

In order to characterize the risk associated with NGTPbelonging to the national natural gas transmission system –SNT, by estimating the probability of accidents occurrenceand by appreciating the magnitude of their consequences,but also by defining technical solutions for mittigating the riskand evaluating the efficiency of their application, the authorsdesigned, structured and realized a data base that includes allthe information regarding the behaviour in time (last 19 years)of NGTP from SNT [7-9].

Fig. 3. The probability ofoccurence for

deflagration with fireaccidents, with differentlevels of thermal dose

reaching facilities in thevicinity of NGTP

Table 4TECHNICAL DEFLAGRATION WITH FIRE ACCIDENTS TYPE PRODUCED ON NGTP

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continuated table 4

Table 5THE MAIN CONSEQUENCEIES OF THE ACCIDENTS IN TABLE 4

a) The effective safety factor of NGTP Fbe = (p/Rt0,5min)(De/2s); b) LBP - length of pipeline rupture; c) size of crater formed in the pipe failure area; lC– crater width; hC - crater depth; d) tef – time from release to ignition; e) Sae – impact area; f) three holes on NGTP, with cross sections: Asg = 52 mm2;Asg = 6 mm2 and Asg = 0.8 mm2

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Using this data base (updated, for NGTP belonging toSNT, on an annual basis), one produced the histograms infigure 4 (that synthesize the main information regardingNGTP from SNT and utters the values fcc and pci obtained bya statistical analysis) and one established: a. The values of theconstants from the equations of the lines C1, C2 and C3 of MR(fig. 5): KR1 = 10000 lei·year, KR2 = 100 lei·year, KR3 = 1 lei·year;b. The values of the correction factors FrP, FrM, FrV: FrP = 1, forunderground and above ground NGTP, without protectionelements, FrP = 0.35, for NGTP mounted in protection tubesand FrP = 0.16, for undergraound NGTP protected withconcrete elements [9];

FrM = 1, if there are no markings on the NGTP route, FrM =0.5, if there are markings on the NGTP route and FrM = 0.35, ifthe NGTP route has markings that specify TelVerde (free phonecalls); FrV = 1, if on the NGTP route (in the vicinity of the areaexposed to risk) there are block valves, with manual operationand FrV = 0.5, if the block valves can be remote controlled; c.the formulas (in which values are introduced in the unitspresented in table 1) for the correction factors FrF, FrT, FrH andFrta, depending on the solutions (physical and procedural) forrisk mitigation applied when the NGTP was constructed,or with the occasion of maintenance works [3-11].

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Fig. 4. Technical characteristics of the NGTP from SNT andfrequency of accidents on this system

Results and discussionsThe built data base allowed the authors to transpose

the procedure they have devised for the evaluation of therisk into a Matlab stand alone application that builds RTPand RM for the facilities in the vicinity of any NGTP andallows to appreciate if the risk lies within the admissibilityarea, and the distances between NGTP and the facilities inits vicinity can be qualified as SD. In table 6 and in figure 5are presented, for a representative case study, the inputdata in the Matlab application (which is the property of theSNT operator), the results that the application provides andthe advantages of using it. As can be seen, a case studyimplies the following stages: a. stating the initial technicalcharacteristics of the NGTP (De, p, γg) and calculation ofthe danger index Ipc; b. design of NGTP in several versions,

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establish for each version /design solution the factorsFrF...FrV and calculate the value for the global factor Frg; forexample, for the presented case study, one considered abase design solution V0, obtained applying thespecifications [1], without taking into consideration therequirements regarding the security of the facilities fromthe NGTP vicinity and more design solutions (V1...V3), forwhich several measures, physical and procedural, weretaken into account, that ensure risk mitigation associatedwith the presence of NGTP close to these facilities; c.definition of the characteristics and criteria of the scenarioconsidered to the risk analysis: for example, for thepresented case study, one considered the scenario of anaccident of type deflagration with fire, one measured theminimal distances dpe, dan si dob, between NGTP and thefacilities in its vicinity, one evaluated the level/severity ofthe accident consequences, by adopting a value for COSTT,one chose from the data base (see fig. 4) the values for kA,fcc and pci and one establised the admisible levels forintensity and duration of exposing the facilities in the NGTPvicinity in the case of an accident occurence (qpsape, teape,qpsaan, teaan, qpsaob, teaob); d. construction of RM, establish ofthe admissible risk level priad and validate the designsolutions for which all conditions (7) are met and, as aconsequence , distances dpe, dan and dob can be qualified asbeing SD (fig. 5).

One has to mention that for each design solution of thepresented case study, one has to apply the ALARP (As LowAs Reasonably Practicable) principle, and perform a cost –benefit analysis in order to establish the ratio (correlation,consistency) between the amount of expenses involvedby the occurrence of the event and the amount of expensesincurred by the measures implemented for the riskmitigation. For example, for the presented case study, itseems that by applying the ALARP principle, design solution3 (V3) (which assures an acceptable level of risk, becausetsi = 30 days, and the NGTP route is marked such as a valueof FrM = 0.35 is accepted), is preferred to design solution 2(V2) (for which the acceptable level of risk is assured byrealizing NGTP from steel pipes with a bigger wall thicknessand through burying the NGTP to a deeper depth).

Fig. 5. RTP and RM built for validation of design solutions of thepresented case study

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Table 6SYNTHESIS OFINFORMATION

REGARDING THECASE STUDY

PERFORMED WITHTHE MATLABAPPLICATION

ConclusionsWhen analyzing the risk and evaluating the safety of

any NGTP, the main danger that has to be considered, interms of probability and consequences of its occurrence,is the NGTP failure through deflagration accompanied/followed by fire, and the outcome that has to be evaluated,is the thermal effect (heat dissipation) on the facilities(people, animals, buildings, crops, orchards, forests etc.)in the vicinity of NGTP.

For each area on the route of a NGTP, the distancesbetween the NGTP and the facilities in its vicinity can beconsidered (qualified) as being safe distances (SD), if thetechnical risk associated to the exploitation of a NGTP prilies underneath an acceptable maximal level priad. In orderto check if the distances between a NGTP and facilities in itsvicinity are SD one has to perform a risk analysis, applying theprocedure and the software devised by the authors, that makesuse of formulas validated by the experimental results outlinedin the present paper and information from the data base (builtby the authors and presented synthetically) regarding thetechnical condition and recording of accidents occurred onNGTP from SNT in the last 19 years.

For any region on a NGTP route one ca assure that thedistances between NGTP and the neighboring facilities areSD, if, when designing NGTP and/or during preventive and/or corrective maintenance works on it, one choses andapplies the adequate technical solutions, of physical andprocedural nature (named and described in detail in[7,9,10]), validated using the ALARP principle and cost –benefit analysis, for mitigation/attenuation/treatment of riskassociated with the occurrences of technical accidentsduring the NGTP exploitation.

References1.*** Norme tehnice pentru proiectarea si execuþia conductelor detransport al gazelor naturale, Anexa la ordinul presedintelui ANRE nr.118/20132. *** ISO 31000:2009 – Risk management – Guidelines on principlesand implementation of risk management3.KINSMAN, P., LEWIS, .J., Contract research report 294, HSE Book,Chester, 20004.KINSMAN, P., LEWIS, .J., Research report 036, HSE Book, Liverpool,20025.ASHE, B.S.W., REW, P.J., Research report 084, HSE Book, Surrey,20026.KONERMANN, R., KUHL, C., LUDWIG, J., Research report 289, Berlin,20097.ZECHERU, G., s.a., Raport final, Contract de cercetare nr. 9/2009,Universitatea Petrol Gaze din Ploiesti, 20108.ZECHERU, G., DRAGHICI. G., DINITA. A., Raport de expertiza,Contract de cercetare nr. 32/2010, Universitatea Petrol – Gaze dinPloiesti, 20109.ZECHERU, G., LAMBRESCU, I., DINITA. A., Raport final, Contract decercetare nr. 2459/2014, Universitatea Petrol Gaze din Ploiesti, 201410.ZECHERU, G., LATA E.I., DRAGHICI. G., ALBULESCU, C., RiskAnalysis and Safety Evaluation forthe Natural Gas TransmissionPipelines, Buletinul UPG, Seria tehnica, vol LXIV, nr 4/2012, 15-2411.NILSSON, K., Preliminary hazard analysis of AGL’s proposed Daltonpower station, URS\13-B211, Planager Risk management Cosulting,2011

Manuscript received;: 24.03.2016