12 November 2015 Recalibration of gas meters Experiences of GTS The value of Recalibration Robert Kruithof First European Recalibration Workshop NMi Euroloop, Rotterdam Robert Kruithof
Agenda Introduction GTS Custody transfer in general Recalibration and energy determination Maximum uncertainties Recalibrations GTS, requirements, experiences Gain of recalibration Important points for execution of (re) calibrations Summery Questions/discussion
Introduction Gasunie Transport Services: Grid The Dutch (GTS) and German (GUD) network Volume ~125 bcm gas p/a Length transport grid ~15.500 km Compressor stations 22 Blending stations 19 Pressure regulating stations 93 Export stations 14 Gas delivery stations 1.300 LNG ( incl peakshaver) 2 Nitrogen facility 2 Underground storage 1
Custody transfer in general Determine the energy amounts for invoices ( meter-to-bill ) Stakeholders, trading and balancing Energy based on measured gas volumes and CV Allocations for market parties ISO 9001 certified quality system Physical gas balance (exits - entries ) Periodic audits to ascertain and guarantee that process is in accordance with the agreed procedures and where possible to make improvements.
Recalibration and Energy determination Recalibrations important part of the quality system of GTS The volume measurements represent a large volume and thus a lot of money Recalibrations to guarantee gas meters are within uncertainty limits Results of the recalibration are used for years in correction Pay sufficient attention to recalibrations: the calibration facility should convince/show the customer that the service is performed in an orderly manner.
Maximum uncertainties Maximum uncertainty on energy Interconnection points (border stations) 0,75% (by law and mutual agreement) National market (city gate stations) 1,00% (by law) Uncertainty is determined by the instruments which are periodically calibrated on the station: p, T and CV. Maximum uncertainty gas meter 0,30%. Like the p, T and CV the gas flow meters are periodically recalibrated. The only way to calibrate gas flow meters is externally on a calibration facility. Diagnostics and comparison can be useful to monitor abnormal behaviour between 2 calibrations
Requirements for (re)calibration of gasmeters Calibration facility shall be accredited by the national council of accreditation in accordance with EN ISO/IEC 17025 and holds the Harmonised European Gas Cubic Meter The conditions at flow calibration shall resemble the conditions during normal operation wall roughness (coating), natural gas, temperature, pressure, diameters steps, pipe length, protrusions, bends, flow conditioners etc.) Calibration at least at 6 flow set points conform the OIML requirements (R137) (Qmin, 10 %, 25 %, 40 %, 70 % and 100 % of Qmax). Bi-directionally used gas meters are to be calibrated bi-directionally (certificates for each direction) After adjustment: gas meter deviations shall be less than the maximum permissible deviation (MPD). Linearity and steepness of the curve: The errors in the range between 0,25 Qmax and Qmax shall be within a band of 0,30 %.
Experiences with recalibration Border stations with Turbine and Ultrasonic, diam. 20 98 different meters calibrated in the period 2006 2012 2 meters in series (USM/USM, TM/USM and TM/TM) Drift or shift of a gas meter Historical analysis Numerical example
Gas meter parameters Error and Shift A graphical summary
Historical analysis Gas meter performance Shift as function of calibration interval Incl. extended intervals
Numerical example 20 meter at a border station Volume of 1 billion m3(n) per year 0,20% meter error -> 2 million m3 Represents about 500.000 Euro. For better and for worse What s the problem!? -> In individual case over- or under accounted for gas -> At least one of the interested parties is disadvantaged!
Gain of recalibrations At a network connection one of the connected parties (TSO/ producer/storage operator) is responsible for the measurement. To prevent subjectivity in the maintenance of the measurement, an independent third party should confirm that the flow meters are working within the agreed boundaries. A calibration facility can fulfil this role. In this way we demand periodical confirmation of the performance by an independent third party. Our goal is to: Periodical confirmation of good performance Limit the risk of mis-measurement (in time/financially) Reduce systematic errors
Important points for executing (re)calibrations Large or unexpected deviations should be investigated by means of verification measurements In case of USM also diagnostics Therefore the results of the calibration shall be clearly and directly visible, also for witnessing Monitoring of unlikely discontinuities Monitor meter The previous curve of meter under test Adequate scaling Preference for using more than one Master meter Possibility for remote witnessing Knowledge about the operational behaviour of the meter Diagnostics and comparison main and back-up at the station
Summary importance of recalibration Certificates are not endless sustainable Confimation meter still within uncertainty Fine-tuning of the meter reading, reduce error Adjustment and curve correction An independent validation of the flow meter is necessary. Diagnostics/Comparison Main-Backup only indirect prove Relationship with meter uncentainty not known Both meters can drift in same direction Diagnostics and OLC useful in between 2 calibrations, in combination with recalibration after several years
Thank you for your attention! Questions?