CEESI/VSL European Flow Measurement Workshop! Lisbon, March 25 th -27 th 2014!

Transcription

1 "#$"%&' On-line Conditioned Based Maintenance of" Gas Ultrasonic Flow Meters" " A practical application" " CEESI/VSL European Flow Measurement Workshop Lisbon, March 25 th -27 th 2014 Stephen Peterson Sr. Metering Engineer, Onegas UK Jan Peters TL Metering Maintenance & Calibration, UIO 1 Company Profile & Presenters ONEgas: Combined business unit of: - Shell UK Exploration & Production (Shell) - Nederlandse Aardolie Maatschappij B.V. (NAM) Area of operations is the Southern North Sea (Europe) Operational Asset Management by NAM NAM is a 50/50 joint venture from Shell/ExxonMobil Presenter: Stephen Peterson, ONEgas UK %'

2 "#$"%&' Personal Introduction Steve Peterson, employed by Shell UK Ltd. Aged 53, been in process measurement and control for 36+ years. Joined ICI aged 16 in 1977 as an apprentice Instrument Artificer. Left ICI in 1984 to work offshore as an Instrument Technician. First started specialising in metering in Apart from 2 brief spells, 1 in the Nuclear Industry and 1 in the Iron and Steel Industry in South Africa I have worked almost exclusively as as a metering specialist. Joined Shell in Current role is as Senior Metering Engineer for Shell UIO in the ONEgas West Asset responsible for maintenance and project delivery. I hold the role of metering technical authority for project delivery. I have 3 sons and since Christmas Day 2013, 1 granddaughter. I have 2 main interests outside my family, which are connected to CBM as well. Personal Introduction To ensure the Performance and the Availability for this type of equipment. Conditioned Based Maintenance is applied Manually. #'

3 "#$"%&' Background Gas Ultrasonic flow meters (GUSM s) have been in use for fiscal and allocation purposes in the UK for ~15 years. It has generally been accepted practice in the UK for the GUSM s to be removed from service on a periodic basis for a wet flow calibration at one of the approved gas flow calibration laboratories. The period between each recalibration is usually determined by two main criteria; The sales / allocation agreement pertinent to the metering system The GUSM repeatability from previous calibrations Most systems in the UK have generally adopted a rule set whereby a new GUSM must be re-calibrated as follows: After 6 months in service Again after an additional 6 months If the flow weighted mean shift between each calibration has been < 0.3 % on subsequent recalibration an extension to the calibration frequency to 12 months can be applied. Calendar Based Calibrations Why did/do we do it? To remain in compliance with Government legislation and demonstrate to our pipeline partners that we are operating within the agreed uncertainties Its the only method available to demonstrate the above IS THIS REALLY TRUE? DTI Guidelines Section Multi-path ultrasonic flow meters incorporate a variety of diagnostic tools that can either individually or collectively be employed for health care monitoring. The use of data acquisition features that permit this information to be logged (and perhaps accessed remotely in real time) is strongly recommended, as it may eventually be possible to use this information to justify an extension to the interval between meter recalibrations. Pipeline User Agreement The ultrasonic flow meters at each Exit Measurement Point shall be subject to independent calibration after an initial period of three (3) months operational service and after each subsequent period of three (3) months operational service (or such other period as may reasonably be required by the SEAL System Operator and approved by the SEAL Pipeline Owners). Looks Like Room For Negotiation '

4 "#$"%&' Background It is a known fact that transit time ultrasonic flow meters provide a wide range of data that can either individually or collectively be employed for health care monitoring. It is interpreting this data that is key to the principles of CBM. However, at this time due to lack of available data, none of the CBM diagnostics are able to provide a Quantitive value for a shift in meter performance. They do, however, provide Qualitive data that can form the basis of any decision made to remove a meter from service for recalibration. Background The system studied in this paper was supplied with 5 identical 20 meters and was commissioned in 2000 and will concentrate on the performance of 1 meter, installed in Dec It is a delivery point into the UK National Transmission system and is operated by Shell UIO, Onegas UK The meters are 4 path with the transducers in a Gaussian configuration. This system was the first UK delivery point to utilise ultrasonic technology. As this was a relatively unknown technology at the time the initial recalibration period was set at 90 days As a consequence a large data set of calibration history of 53 separate calibrations has been crearted and none of the meters exceeded the 0.3% FWME shift criteria. &'

5 "#$"%&' Background The SEAL Terminal is situated adjacent to the Shell Bacton Terminal and is operated by Shell UIE on behalf of the Pipeline owners. The Shearwater Platform, operated by Shell and the Elgin-Franklin Platform, operated by Total input sales quality gas into the Pipeline, which is reduced in pressure and heated prior to exporting via the Transco or IUK metering facilities. All of the main Sales Gas metering systems use Ultrasonic flow meter technology. The pipeline system has been in continuous production since late What is CBM? A system which allows defined diagnostics parameters to be monitored and recorded on a 24/7/365 basis and logs the data in an auditable format. Each individual diagnostic check has operator entered control limits, which alerts the operator when a control limit has been breached. The system has been configured to produce clear, concise reports that can be used to provide: " The basis for a change in recalibration philosophy from one based on time in service to one based on meter performance. " Hence indicative of a possible shift in meter calibration. ('

6 "#$"%&' Why adopt CBM? 53 calibrations have been performed on the 5 meters spanning 10 years with no inservice shift exceeding 0.3%, the current trigger level for processing a mismeasurement investigation. Financial cost of the calibration, including logistics and attendance at the test centre Safety concerns around the removal and handling of large pieces of equipment Planning and scheduling to ensure minimal down time without any gas deferral ETS legislation governing the venting and release of Hydrocarbon gases Availability of test slots, particularly for GUSMs above 10 The calibration facilities claiming uncertainties of approximately ± 0.23%, not the order of magnitude smaller uncertainty (± 0.03%) that fundamental metrological principles require for a true calibration. Potential for damage to the GUSM during removal, transportation or reinstallation. A real example CBM Application The CBM application was first installed in 2008 Upgrades to the meter transducers and electronics was required After the initial commissioning the flowing gas velocity through the GUSM was approximately 18 m/sec with one meter run in operation or 9 m/sec with two meters in parallel service. The flow has decreased over time. During 2013 due to operational issues the flowing velocity was between 2.5 and 8 m/sec, well below the initial footprint values. 2 upgrades have been made to the CBM system since initial installation The most recent upgrade in 2012 implemented automatic report generation. Prior to that the reports can be manually generated using data from the daily log files. $'

7 y = x x x Velocity (m/s) Gains (Aug - Dec 08) Footprint Gain (Dec 07) 5% -5% Poly. (Gains (Aug - Dec 08)) y = x x x Velocity (m/s) Gains (Aug - Dec 08) Footprint Gain (Dec 07) 5% -5% Poly. (Gains (Aug - Dec 08)) "#$"%&' Rule Set, what are we looking for? Rule 1 - Study gains over first months service and demonstrate that gains are not increasing on any transducer over time whilst the system was flowing. Rule 2 - Study Performance levels online and offline over first months service and demonstrate that Performance Levels are not decreasing on any transducer over time. Rule 3 Study Profile factor, Symmetry & Cross-flow over first months service and demonstrate consistency over time. Recommended limits of absolute change being as follows: Profile factor = ±0.5% of the mean during first month of service. Symmetry = ±0.5% of the mean during first month of service. Cross Flow = ±0.5% of the mean during first month of service. Rule 4 Demonstrate that the chromatograph AGA-10 SOS and that measured by the GUSM remains within ±0.21%. Rule 1 Gain study Gain to Velocity Ratio Chord A1 Gain to Velocity Ratio Chord A2 &$#$$ "(#$$ ""#$$ 2013 '&#$$ '%#$$ 2013 "$#$$ '"#$$ Gain (db) Gain (db) '#$$ %"#$$ '(#$$ %$#$$ &#$$ %#$$ "#$$ $ " '$ '" ($ (" Velocity (m/s) "#$$ $ " ($ (" )$ )" Velocity (m/s) )**+,-./+012./ * / *++,-./0,123/0 4/15/6/, 5+15/6/, 78,93:123/0 Gain (db)b) Gain to Velocity Ratio Chord A1 Gain (db)b) Gain to Velocity Ratio Chord A2 Although only Chord A is displayed here, the other 3 chords exhibited the same beahviour. Overall result against the rule set is a PASS )'

8 "#$"%&' Rule 2 Performance Study Performance % Jul-08 Sep-08 Oct-08 Dec-08 Performance % Dec-12 Jan-13 Mar-13 May-13 Jun-13 Aug-13 The performance of the meter has remained consistently above the threshold of 90%. Overall result against the rule set is a PASS. It should be noted however that the manufacturers guidelines state that performance above 25% is considered acceptable during operation and during calibration. Profile Factor, Symmetry and Cross Flow Study Velocity vs Profile Velocity m/sec Velocity Vs Profile y = x x Vel (m/s) The initial Rule Set allowed for a maximum shift in profile factor of <0.5% during the initial months of service. As can be seen the cumulative shift over 5 years has been ~1.1%. However recent independent testing has been carried out which has shown that a shift in profile factor as large as 5.0% has no effect on meter calibration. Year on year the shift has been significantly less than 0.5%. *'

9 "#$"%&' Profile Factor, Symmetry and Cross Flow Study Velocity vs Symmetry Velocity m/sec Symmetry Velocity Vs Symmetry y = x x Vel (m/s) The symmetry appears to have shifted significantly, predominantly during the past 2 years it has shown a flattening off against the agreed rule set this is a FAIL and requires further investigation. Profile Factor, Symmetry and Cross Flow Study Velocity Vs Symmetry Vel (m/s) Predicted Symmetry Hi Limit Lo Limit 2010 Symmetry Factor Velocity vs Symmetry %"&$ %"& %"%$ %"% %"$ % "##$ "## $ % %$ & &$ Velocity (m/s) '()*+,-)*./011)-( ,-678./011)-(0 Symmetry Factor %"' %"&$ %"& %"%$ %"% %"$ Velocity vs Symmetry The 3 graphs shown are from (top left) (top right) (left) % "##$ "## $ % %$ & &$ Velocity (m/s) ()*+,-.*+/0122*.)1 3,/4,2,. 45/4,2, /0122*.)1 It shows how the profile has flattened over time. This has not occurred on the other meter run. +'

10 "#$"%&' Measurement Integrity Checks,.#(,.#,.%(,.%,.,(, -,.,( -,.% -,.%( -,.# -,.#( Speed of Sound Percentage Difference (Measured vs AGA10) Speed of Sound Diff % Jul Aug Sep Sep Oct Nov Nov Dec Jan-09 The results below give the average deviations since As can be seen the deviations are well within the limit defined in the rule set and are therefore a PASS 2008 Ave Deviation = Ave Deviation = Ave Deviation = Ave Deviation = Ave Deviation = Ave Deviation = Overall conclusions Functional Checks Gains All transducer pairs on the meter continue to demonstrate excellent gain levels, comparable to initial installation. No degradation evident. Meter Performance No issues with average performance >98%. Process Condition Checks Profile factor - The meter is providing good agreement with the predictions generated versus the flow rate. Symmetry This meter run appears to be flattening across the flow range. The other meter run has not exhibited this behaviour. Cross Flow The meter has repeatedly given good agreement with the predictions generated versus flow rate. Measurement Integrity Checks This meter has continually demonstrated excellent agreement with the SOS value calculated from AGA10 %,'

11 "#$"%&' Acknowledgements I would like to personally thank the following people, who have worked with me throughout the years on this subject and without whose invaluable help this presentation would not have been possible. James Trail Petrofac Ltd. Colin Lightbody Petrofac Ltd. References 26 th International NSFMW St. Andrews: On Line Condition Based Monitoring of Gas USM s. S. Peterson et al. BS7965:2013 Guide to the selection, installation, operation and calibration of diagonal path transit time ultrasonic flow meters for industrial gas applications. UK DECC Measurement Guidelines Revision 8. NPD Report REP-40/2011: Criteria for condition based monitoring of ultrasonic gas flow meters. %%'

12 "#$"%&' Questions %#'