Technical Guideline Instruction Bulletin. DVGW G 501 (M) May Airborne remote gas detection

Transcription

1 Technical Guideline Instruction Bulletin DVGW G 501 (M) May 2012 Airborne remote gas detection

2 The DVGW Deutscher Verein des Gas- und Wasserfaches e.v. Technisch-wissenschaftlicher Verein (German Technical and Scientific Association for Gas and water, a registered association Technical- Scientific Association) has been supporting the gas and water sectors since 1859 with a focus on safety, hygiene and the protection of the environment. Setting the technical rules, the DVGW encourages ongoing progress in this sector. The DVGW and its approximately 12,000 members work out the overall recognised technical rules applicable to gas and water engineering; they audit and certify products, persons and companies, initiate and support research projects and offer training courses covering the entire range of relevant gas and water topics. The DVGW Technical Rules constitute the basis of the technical self-management and self-responsibility of the German gas and water industry and guarantee the safe and secure supply of gas and water at the highest international level. The DVGW is an independent non-profit organisation free from economic lobbyism and political influence. ISSN Price group: 5 DVGW, Bonn, March 2012 DVGW German Technical and Scientific Association for Gas and water Technical-Scientific Association Josef-Wirmer-Straße 1-3 D Bonn Phone: Telefax: info@dvgw.de Internet: Reprint and photomechanical reproduction, also of excerpts, is only permitted with the approval of the DVGW e.v., Bonn. Distribution: Wirtschafts- und Verlagsgesellschaft Gas und Wasser mbh, Josef-Wirmer-Str. 3, Bonn Phone: Fax: info@wvgw.de Incaternet:

3 Airborne remote gas detection Contents Foreword Scope Normative references Terms, Symbols, Units and Abbreviations Requirements Measuring range Detection threshold and sensitivity Measuring errors Function checks Indications Data logging Limitations of use Cross sensitivities Aeronautical approval Eye safety Operating instructions Operator training Geo-information with respect to pipeline routes Test Object of the test and documents Verification of general requirements Verifying the measuring range Verifying the detection threshold and detection sensitivity Verifying the function checks Indications Data logging Cross sensitivities Aviation permission Eye safety Operating instructions DVGW G 501 Instruction Bulletin 03

4 6 Quality assurance Performance Annex (informative) A.1 Detection threshold A.2 Test set-up and execution to verify the in-flight detection sensitivity A.3 Determination of the maximum permissible deviation of the gas pipeline geo-information DVGW G 501 Instruction Bulletin

5 Foreword The systematic above ground inspection for leaks in gas distribution systems is a focal point in the inspection of gas distribution systems and is performed in accordance with the specifications of DVGW Code of Practice G Inspection of gas pipeline systems with operating pressures up to and including 4 bar. For above ground inspection, gas concentration measuring instruments complying with the requirements of DVGW Code of Practice G Gas leak detection and gas concentration measuring devices for leakage survey on gas supply systems shall be used. The extraction is performed with carpet or bell probes. Apart from the traditional measuring methods based on the semiconductor sensor and the flame ionisation detector, the continuously enhanced laser-based detection of methane has also been available during the last few years. The DVGW Remote gas detection project group has analysed different airborne remote gas detection methods in terms of their efficiency. In addition, the currently most sensitive airborne system was compared with traditional measuring systems. As a result of this work it can be stated that during the tests conducted under pseudo -field conditions, the remote gas detection system examined reliably detects even the lowest methane concentrations. The current technical status of airborne remote gas detection leads to the conclusion that these are basically suited for the above ground inspection of high pressure gas pipelines inside and outside of built-up areas. Following this, the Technical Committee on Gas transmission pipelines resolved to approve airborne pipeline monitoring systems that meet the requirements of this Instruction Bulletin for the above ground inspection of gas transmission pipelines, the maintenance of which is regulated by DVGW Code of Practice G Steel gas pipelines for operating pressures above 5 bar Maintenance. This Instruction Bulletin formulates requirements, test criteria and implementation instructions for the airborne remote gas detection. Amendments None Earlier editions None DVGW G 501 Instruction Bulletin 05

6 1 Scope The Instruction Bulletin on hand defines the requirements and test criteria applying to remote gas detection integrated aboard aircraft (helicopters or airplanes) and designed to aerially monitor both buried natural gas transmission pipelines as well as above ground natural gas transmission pipelines that are suited for airborne remote gas detection, both inside and outside built-up areas. Portable hand-held measuring instruments or methods combined with motor vehicles shall not be dealt with in this paper, as due to their flat observation angle to the surface compared to detection from the air they are subject to modified requirement criteria. The same applies to continuously emitting laser systems. Accordingly, this Instruction Bulletin applies exclusively to active optical systems using pulsed lasers according to the DAS LIDAR method (differential absorption and scattering light detection and ranging) and/or the DIAL method (differential absorption LIDAR) in accordance with VDI Guideline The gases to be detected by means of remote gas detection are the methane-rich gases of the 2nd gas family according to DVGW Code of Practice G 260. The remote gas detection dealt with in this Instruction Bulletin is designed for the above ground inspection for leaks. In the event of a methane indication, the above ground inspection according to DVGW Code of Practice G shall be carried out. 2 Normative references The documents cited below are required for the application of this document. For dated references, only the edition referred to applies. However, parties to agreements based on this DVGW system of rules are encouraged to apply the most recent editions of the normative documents indicated below. For undated references the latest edition of the document referred to applies (including all amendments). Listed DIN standards may be part of the DVGW system of rules. DVGW G 260 (A), Gasbeschaffenheit DVGW G (A), Inspection of gas pipework systems with operating pressures up to 4 bar DVGW G (H), Gasspür- und Gaskonzentrationsmessgeräte für die Überprüfung von Gasanlagen DVGW G (A), Steel gas pipelines with an operating pressure greater than 5 bar Maintenance DVGW GW 120 (A), Netzdokumentation in Versorgungsunternehmen DIN EN (VDE 0837), Safety of laser products DIN , Plans for Public Utilities, Water Resources and Long-distance Lines; Plans for Longdistance Pipelines, Technical Regulation of the DVGW VDI Richtlinie , Fernmessverfahren Messungen in der Atmosphäre nach dem LIDAR-Prinzip Messen gasförmiger Luftverunreinigungen mit dem DAS-LIDAR 14 DVGW G 501 Instruction Bulletin

7 3 Terms, Symbols, Units and Abbreviations Target means the spot where the laser light hits the soil surface. Albedo means the soil's reflection ability. Measuring errors are understood to be invalid, individual measurements outside the operating and flight parameters to be specified in the operating instructions. The airspeed is defined as the speed of the aircraft above ground. DGG Deviation of the gas line geo-information (in the GIS) DAS Differential absorption and scattering DIAL Differential absorption LIDAR GIS Geographic information system LIDAR Light Detection and Ranging SCW Scan Corridor Width SAA System aiming accuracy 4 Requirements A remote gas detection system basically does not measure the gas concentration at the emersion point of a natural gas leak, but analyses the methane content of an above ground gas-air-mixture generated by the release. The measuring system in principle consists of a light source and a receiver, typically a telescope with detector, as well as a correspondent electronic evaluation system and software. The aircraft (airplane or helicopter) carries the system. The system shall be equipped with a navigation unit to determine the position of the survey point on the ground. As there is a natural atmospheric methane background, remote gas detection systems will continuously indicate methane values. These methane signals are incorporated in the calculation of an alarm threshold, and a methane indication will only be generated on exceedance of this value. Minimum requirements on remote gas detection systems and their application will be listed below and explained in more detail in the subsequent sections. Two-dimensional inspection of a pipeline route with a minimum width of 4 m Inspection of minimum 25 % of the pipeline route surface Continuous inspection of an sufficient area incl. automatic documentation Continuous logging of flight speed, altitude and position DVGW G 501 Instruction Bulletin 07

8 Minimum requirement of a detection threshold of 2 ppmm according to VDI Guideline 4210 (see Annex A.1) Detection of above ground methane concentrations arising under defined test field conditions given an underground gas release with volume flowrate of 150 l/h. Detection of this test scenario under flight conditions Detection of methane on account of an underground leakage of 150 l/h under flight conditions Measuring errors shall be identified and marked The number and distribution of valid measurements shall not be under its minimum Continuous verification of the operational reliability Automatic signalling and logging of any occurring errors Verification of system readiness by means of function checks for an accurate determination of the measuring position ( 2 m deviation) Methane indications shall be displayed Automatic data logging as well as subsequent archiving Verification of limitations of use and their documentation prior to initial commissioning Theoretical verification of cross sensitivities for the atmospheric gases CO 2 and H 2O Metrological verification of the cross sensitivity for further hydrocarbons Operating instructions incl. information retrieval and consideration of meteorological conditions Aeronautical permit for the typical area of application if a minimum flight height of 150 m is underrun, also in built-up areas Proof that the system is safe to the eyes Operator training and regular refresher courses for staff Geo-referenced accuracy of the pipelines to be inspected In the event of a methane indication, an above ground inspection in accordance with DVGW Code of Practice G shall be carried out 4.1 Measuring range A gas volume mixture located near ground level is subject to atmospheric transportation processes. So as to be able to detect the gas volume mixture even in case of spatial diffusion (drift and dispersion), the remote gas detection shall cover the area ± 2 m to the right and left of a natural gas pipeline ( pipeline route ). This shall be guaranteed taking into consideration the beam guidance error. At the same time, it shall be verified by means of simulations or other suitable proofs that more than 25 % of the previously 14 DVGW G 501 Instruction Bulletin

9 mentioned pipeline route surface are continuously analysed under permissible flight and operating p a- rameters. In addition, continuous monitoring and logging during operation shall ensure that the pipeline route is covered both in longitudinal and transverse direction with an adequate number of measurements (at least one measurement in four equally large sectors adjoining in lateral direction per 5 m length of pipeline). If this is not the case, the pipeline section shall be identified and marked as not validly inspected, logged and indicated to the operator. 4.2 Detection threshold and sensitivity So as to be able to determine already during the development stage of a remote gas detection system whether the method offers a minimum in detection sensitivity, it is imperative to determine a detection threshold pursuant to VDI Guideline 4210 prior to installation in an aircraft. This detection threshold shall not exceed 2 ppmm. An airborne remote gas detection system shall be able to reliably detect the above ground methane concentrations that are based on underground leakages of 150 l/h when used under flight conditions in a suitable test scenario (see and Annex A.2) 4.3 Measuring errors As a matter of principle, it is imperative to ensure the detection of measuring errors, as the non-detection of a natural gas leak may give rise to hazards for man and the environment. Requirements in connection with the prevention of measuring errors are described below. A distinction shall be made between measuring errors that are automatically detected by the system during operation and measuring errors which are prevented by means of function checks. In order to avoid measuring errors, the measuring system must constantly monitor its own operational reliability. Any occurring malfunctions shall be immediately reported to the system operator and automatically logged Function checks It is necessary to establish function checks that are carried out on a regular basis in order to monitor the measuring function both in view of the natural gas component to be detected and of determining the position of the laser beam's target point on the ground. At the same time, it shall be ensured that the target point centre of the laser beam in flight deviates a maximum of 2 m from the geographically referenced position. The result of the function check shall be immediately displayed to the operator and logged. In case of deviations from defined areas, an alarm shall be automatically signalled to the operator Indications If increased methane concentrations are detected in the atmosphere, this shall be automatically signalled to the operator. Time and position of the indication shall be logged. If this involves a direct hazard, the company responsible for pipeline operation shall be informed without delay. Otherwise, the company responsible for pipeline operation shall be immediately informed of the results of the surveying flight as soon as these are on hand. It is not permissible to evaluate a gas release solely on the basis of a methane indication's signal strength. Local characteristics in the soil and on the surface as well as the meteorological conditions at DVGW G 501 Instruction Bulletin 09

10 the time of the surveying flight can influence the gas-air-mixture to be detected by means of airborne remote gas detection Data logging All data shall be saved in digital form so that pipeline sections rated as "not validly inspected" due to omission, measuring errors or inadequate coverage as well as the positions of methane indications can be clearly pinpointed. The data to be logged shall allow for a subsequent location. Data shall be archived to provide proof positive of a duly performed pipeline inspection. The methane indication shall be transmitted to the company responsible for the operation of the pipeline inclusive of date, time, position, responsible persons, method applied and meteorological conditions Limitations of use The limitations of use such as flight height, speed and horizontal deviation shall be demonstrated by means of a suitable test scenario as described under 4.2. At the same time, the conditions with respect to nature and condition of the soil and meteorological conditions shall be logged. A graduation of the limitations of use due to wind, insulation-induced thermal lifts or deteriorated backscattering properties of the soil, for instance due to humidity, shall be performed and integrated in the operating instructions in a meaningful manner. The operating instructions shall bind operating personnel to obtain information with regard to current regional meteorological conditions before starting on a flight and also during flight breaks. In addition, information as to the soil conditions that are presumably to be expected at the time of the inspection shall be obtained from the operating company. No surveying flights shall be performed if the soil is sealed by precipitation or frost. Above ground inspection shall not take place if the prevalent wind speed at a height of 10 m exceeds the wind speed that prevailed when detection threshold and sensitivity (5.2.2) where verified at a leakage rate of 150 l/h. Changes of the detection sensitivity due to a decrease of the soil surface's backscattering properties on account of humidity shall be taken into consideration in the operating instructions such that flights are for instance carried out at lower heights or reduced speed. On account of its knowledge regarding the gas distribution system and the topography, it falls within the responsibility of the company responsible for pipeline operation to evaluate and account for the use of airborne remote gas detection systems. The remote gas detection described in this instruction bulletin send light pulses from an approximately vertical position to the ground and thus require an optical accessibility of the ground surface of the pipeline route. Section 4.1 defines the requirements of adequate pipeline route coverage. In addition, it lists exemplary scenarios encountered in the course of the pipeline, for which the use of airborne remote gas detection should be carefully evaluated. Tree canopy Pipeline sections with crowns on one or both sides, which cover the area of the pipeline route such that they partly or completely prevent the optical accessibility for the emitted light pulses Narrow urban canyons Pipeline sections in narrow roads with immediately adjoining built-up areas in particular with hampered optical accessibility due to large roof overhangs, planting and similar 14 DVGW G 501 Instruction Bulletin

11 Alleys Pipelines below roads without middle grass strip, the edges of which (emersion points of the natural gas to the surface) are concealed by treetops Sealed surfaces Pipeline sections in the vicinity of residential buildings with sealed surface up to the building wall (bituminised pavement), large bituminised surfaces such as parking areas, etc. Before carrying out an inspection for leaks by means of airborne remote gas detection, the company responsible for pipeline operation shall determine whether, given the local circumstances, a subterranean propagation of the gas up to the buildings in built-up areas is more probable than a gas release at the soil surface close above the pipeline. If the subterranean soil structure does not prevent a potential gas release, these surfaces shall be considered unsealed within the meaning of remote gas detection. The use of remote gas detection is only meaningful, if surfaces that are suitable for a release such as green strips, kerbs or pavement joints, etc. fall within the scanned swath covered by the measuring system Cross sensitivities Cross sensitivities specified as ppm indicated faulty concentrations per ppm extraneous gas of the measuring system vis-à-vis the gases CO 2 and H 2O shall be verified by theoretical methods and shall not exceed ± Cross sensitivities to ethane, propane and butane shall be verified by metrological methods and shall not exceed ± Aeronautical approval A helicopter or aircraft-supported remote gas detection system shall be in possession of an aeronautical operating license. 4.5 Eye safety The measuring system shall be rated in one of the laser classes 1, 1M, 2 or 2M pursuant to DIN EN Operating instructions Operating instructions shall be compiled which shall comprise a description of the operating principle as well as instructions regarding the prevention of the causes for measuring errors listed under 4.3. In addition, they shall include information on occupational health and safety during the operation and commissioning of the system, also with regard to eye safety. Likewise, guidelines regarding aircraft operation during the pipeline inspection such as for instance the maximum lateral offset with respect to the route or conduct in case of bends and branches shall be included. Procedure instructions forming part of the operating instructions shall describe the report procedure for a methane indication so as to ensure a reliable transmission to the pipeline operator. The length of maintenance cycles for the system and for individual main components shall be specified. System interfaces to the aircraft and to separate units shall be described. DVGW G 501 Instruction Bulletin 11

12 4.7 Operator training Staff deployed for the operation of a remote gas detection system i.e. the pilot and the operator shall successfully complete both theoretical and practical training courses imparting the mode of operation of the measuring method, the operation of the device as well as the procedure with regard to data transfer and the procedure with regard to methane indications. The training courses, their contents and the participants shall be documented. In order to point out modified operating procedures and to refresh the training course contents, training courses shall be repeated at least every two years, albeit with adapted scope. Documents that are suitable for training and refresher training will be supplied by the device manufacturer together with the operating instructions. 4.8 Geo-information with respect to pipeline routes The pipelines to be inspected by means of remote gas detection should be made available to the mea s- uring system with geo-referenced accuracy. Further details are provided in DVGW Code of Practice GW 120 as well as in DIN To prevent an airborne remote gas detection system from missing the area above the pipeline due to inaccuracies of the pipeline position in the geographical information system (GIS), requirements on the accuracy of the gas pipeline geo-information are specified. The maximum deviation of the gas pipeline geo-information (DGG) shall not exceed DGG 0,67 [1,5 m + 0,5 SCW SAA]. The minimum scan corridor width (SCW) and the system aiming accuracy (SAA) in [m] are taken into account when determining the maximum permissible deviation of the gas pipeline geo-information. Correlations as well as the calculation method are explained in Annex A.3. 5 Test Evidence for the suitability of the requirements on remote gas detection systems listed above shall be supplied prior to initial commissioning. This test shall be accompanied by an institution appointed by the DVGW, which lists and confirms the results of the test in writing. 5.1 Object of the test and documents All components required for the inspection of gas pipelines i.e. the aircraft, the measuring system (including power supply) as well as the system description and operating instructions shall be subjected to testing. 5.2 Verification of general requirements For the purpose of evaluation, the requirements mentioned in chapter 4 shall be verified by a suitable test laboratory that is approved by the DVGW. For this purpose, both theoretical considerations (for instance to prove an adequate coverage of the route within the limits of flight height and flight speed), measurements on the ground (for instance to demonstrate cross sensitivities and the detection threshold according to VDI Guideline 4210) as well as practical flight simulations on artificial and accurately defined leaks shall be performed. 14 DVGW G 501 Instruction Bulletin

13 5.2.1 Verifying the measuring range The manufacturer shall verify by means of simulation or other suitable proof that at least 25 % of the area of a 4 m wide pipeline route are analysed under permissible flight and operating parameters. In addition, it shall be ensured that during operation too, the entire width of the pipeline route is evenly covered (i. e. at least one measurement in four equally large sectors adjoining in a lateral direction) at any position of the pipeline route, given a subdivision into 5 m long sections. The manufacturer shall prove to the inspection authority that relevant pipeline sections are identified in case of inadequate pipeline route coverage. In addition, it shall be possible to identify sections not to be covered (for instance because of tree canopy or other obstacles) in the data logging Verifying the detection threshold and detection sensitivity The detection threshold can be confirmed in analogy to VDI Guideline 4210 (Remote sensing). The parameters on which this method is based are explained in Annex A.1. For the purpose of testing the in-flight detection sensitivity, defined leaks are simulated on a test gas pipeline, to which natural gas volume flows are applied. A safe detection of the set leakage rates shall be demonstrated. Details regarding test implementation and test set-up are described in Annex A.2. It shall be verified whether the graduations of the limitations of use due to wind or insolation-induced thermal lifts have been incorporated in the operating instructions in form of a table or in another suitable form. Graduations shall be feasible Verifying the function checks So as to be able to test the system's ability to detect methane, a function check shall be implemented. This shall be done by placing a measuring body filled with a known volumetric content of methane in the optical path with subsequent verification of the displayed methane value, or in another demonstrably equivalent manner. The methane column introduced shall be that large that a methane indication is triggered. The automatic triggering of the signal shall be verified. The result of this function check shall be verified. The accuracy of the laser beam positioning shall be confirmed by means of a reference target. The position of the reference target shall be determined on the ground using a Differential Global Positioning System (DGPS) receiver. Subsequently, it shall be demonstrated in flight that the distance between the position of the reference target determined by means of laser system and the reference position is less than 2 m. The immediate display and the documentation of the function check results are substantiated by means of a demonstration Indications The operator alert if increased natural gas concentrations are detected in the atmosphere shall be demonstrated by means of the detection of artificial leaks of different sizes. The magnitude of the detected gas mixture volume shall be indicated. Subsequently, it is verified whether the methane indication including the geographically referenced position and time have been logged in the saved measurement data. This verification shall be performed in conjunction with the data logging test (see 5.2.5). DVGW G 501 Instruction Bulletin 13

14 5.2.5 Data logging The data of the surveying flight along a pipeline section of minimum 25 km length shall be screened, at the same time checking the documentation in view of adequate coverage, marked pipeline sections (that cannot be covered by aircraft or were invalidly covered) and the position of any methane indications. The plausibility of invalid measurements detected shall be verified on the basis of flight scenarios outside the permitted flight parameters. The instructions, which comprise regulations with respect to data archiving, shall be submitted Cross sensitivities Theoretical proof shall be provided in order to assess an adequately low cross sensitivity of the measu r- ing system to the gases CO 2 and H 2O occurring in the atmosphere. The cross sensitivities to ethane, propane and butane shall be demonstrated by means of metrological methods Aviation permission The aeronautical operating permission for the combination aircraft and remote gas detection system (which shall be expressly mentioned) shall be submitted Eye safety Proof of the measuring system's rating in view of the laser classification pursuant to DIN EN shall be submitted Operating instructions The operating instructions shall be submitted and checked for completeness. 6 Quality assurance Within the scope of quality assurance by the manufacturer (self-monitoring), the recurring performance of function controls (4.3.1 and 5.2.3) shall be stipulated. In addition, training courses for the operating personnel and annual refresher courses shall be provided. Training course contents shall cover the items contained in this Instruction Bulletin and in the operating instructions. The aviation permission shall be maintained and renewed, if this becomes necessary due to relevant changes to one of the system components. Every two years, tests by suitable test laboratories that are accepted by the DVGW shall be arranged for. These shall comprise the performance of function checks (4.3.1 and 5.2.3) and ensure that no changes to the system have impaired its detection characteristics. The entire test shall be repeated in case of significant changes to the remote gas detection system consisting of aircraft and measurement system. 14 DVGW G 501 Instruction Bulletin

15 7 Performance The above-ground inspection shall be performed in accordance with process or work instructions including operating manual and operating instructions (compare 4.3.2, 4.6 and 5.2.9). These are also object of the inspection of a remote gas detection system. During practical application of a remote gas detection system, Albedo steps and other constraints shall be taken into consideration by reducing the flight speed. The operating instructions shall, among other things, contain information about flight speeds, so that at least 30% of the route surface can be covered by laser spots, always taking into account the gas pipeline topology. DVGW G 501 Instruction Bulletin 15

16 Annex (informative) A.1 Detection threshold The detection threshold is determined in analogy to VDI Guideline 4210 (Remote sensing) by measuring the zero concentration. The concentration determined in this manner fluctuates with a standard deviation σ stat. Taking into consideration the student factor t 0,95;N, the following is obtained for the detection threshold: C NG = t 0,95;N σ stat The detection threshold is determined during dry weather and at a meteorological visibility > 5 km, from N = successive measurements, at a target distance of 150 m and using a target with the following characteristics: Homogeneous reflection in the measuring wavelength range of 6 10 % Surface with Lambertian reflection characteristic (isotropic reflection, no specular reflection) Moisture-resistant, dirt-repellent material for long-term retention of the above mentioned characteristics A.2 Test set-up and execution to verify the in-flight detection sensitivity To verify the in-flight detection sensitivity, test leakages shall be effected that simulate the subterranean release of natural gas by sealed and unsealed surfaces. For this purpose, leakages shall be provided on buried pipelines with typical diameters for high-pressure pipelines and a cover of 800 mm so as to provide the gas as in real-life scenarios with the opportunity of preferentially propagating along the pipe body. In addition, these two scenarios of open and sealed surface represent the extremes of real -life gas pipeline routes. The test scenario sealed surface should reflect the situation of a road with sidewalk. The test pipeline is located underneath a completely sealed area, representing the road's bitumen layer. Laterally offset to this, provision shall be made for a surface that is partly sealed by paving tiles. The layout is sketched in the illustration below and shall not exceed the dimensions m². The sealing in the area of the road can for instance be realised by introducing sheeting between crushed rock and sand. The pipe trench should be filled with crushed rock in accordance with a typical road structure. The paving tiles (0,5 0,5 m², material: concrete) are laid in sand. The joint width shall not exceed 5 mm. The sealed surface shall be surrounded by a natural plant cover in the form of a green meadow. The flight direction should be parallel to the pipeline axis, i.e. along the parting line sidewalk and road area. 14 DVGW G 501 Instruction Bulletin

17 Figure A.1 Outline of an experimental set-up to verify the in-flight detection sensitivity with arrows depicting gas propagation and release and lines of identical gas concentration The test scenario unsealed surface should be designed in analogy to this. Here, the near-surface area shall be restored in line with the surrounding area. The plant cover of the test area shall correspond to that of the surrounding area and shall consist of a green meadow. While carrying out the test flights, the amount of leakage escaping from the test pipeline shall be measured. Suitable instruments shall be used for this purpose. As leakage medium, the methane-rich gases of the 2 nd gas family according to DVGW Code of Practice G 260 shall be used. The leakage rate of 150 l/h shall be reliably detected during both test scenarios. A reliable detection is proven, if at least four successful methane indications per leakage rate can be performed during five survey flights for both test scenarios. This proof shall be rendered for respectively three different flight heights and three different flight speeds within the typical range of application at minimum wind speeds of 2 m/s. During the test flights, all three components of the wind speed shall be detected non-stationary at a height of 10 m, so as to also record the thermal lifts and further flow effects at ground level. DVGW G 501 Instruction Bulletin 17

18 A.3 Determination of the maximum permissible deviation of the gas pipeline geo-information Figure A.2 Outline of minimum requirements on the measuring system aiming accuracy Even in the most unfavourable case of a summation of deviations of inaccurate geo-information regarding the real pipeline position and aiming accuracy deviations of the measuring system in the same dire c- tion, metering points are to fall within the possible emersion range of the subterranean gas release. This is the case if the criterion described below is met. DGG 0,67 [1,5 m + 0,5 SCW SAA] 0,67 Safety coefficient to ensure that the measuring spot falls completely within the gas release range 1,5 m Minimum propagation of a release at 150 l/h Table A.1 Maximum permissible deviation of the gas pipeline geo-information for given system aiming accuracies and scanning strip widths (each in m) SAA SCW ,00 1,67 2,33 3,00 4,67 6,33 9,67 16,33 1,5 1,33 2,00 2,67 3,33 5,00 6,67 10,00 16,67 1 1,67 2,33 3,00 3,67 5,33 7,00 10,33 17,00 0,5 2,00 2,67 3,33 4,00 5,67 7,33 10,67 17,33 14 DVGW G 501 Instruction Bulletin