1 / 12

Orifice Plate Meter Error

Orifice Plate Meter Error. Stuart Gibbons, Extraordinary Offtake Arrangements Workstream Meeting: 16 October 2009. Contents. What is the Issue? How was the error identified? What is the error? Route cause of the error. Impact. Timeline of events. Remediation. Summary.

bradley-crosby
Download Presentation

Orifice Plate Meter Error

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Orifice Plate Meter Error Stuart Gibbons, Extraordinary Offtake Arrangements Workstream Meeting: 16 October 2009

  2. Contents. • What is the Issue? • How was the error identified? • What is the error? • Route cause of the error. • Impact. • Timeline of events. • Remediation. • Summary.

  3. What is the issue? • A meter error has been identified potentially affecting 34 of National Grid’s Offtake meters across all 4 National Grid distribution networks. • Meter validations in accordance with ME/2 procedures. • Orifice plates are exchanged every 12 months in accordance with UNC.

  4. How was it identified? • An audit of an Offtake meter during July 2009 identified an anomaly on the physical measurement of the orifice plate. • A number of audits are undertaken on an annual basis at agreed offtakes following consultation with Ofgem. • Audits are conducted in accordance with GMR00022. • Auditor noticed orifice plate dimension of outside of normal tolerance after looking across a number of certificates. • This is not part of the routine audit process.

  5. Orifice bore dimension (d / mm) What is in error? • An error in the measurement of the orifice bore dimension of the orifice plate. • The dimensions of the plate are required in order to calculate the flow of natural gas through the meter.

  6. Route cause of the error. • Error traced back to calibration of the KEMCO 700 coordinate measuring machine (CMM)used to determine the orifice bore.

  7. Calibration. • Calibration of the Kemco 700 3 dimensional (CMM) machine undertaken on an annual basis by a UKAS accredited calibration facility. • Bias introduced following a calibration undertaken on the 13-10-2006. • Bias removed following a calibration undertaken on the 05-10-2007.

  8. Impact. • All orifice plates measured during this period will have been in error. • Results in a nominal dimensional error of ~ - 0.3116 mm in 311mm. • Approximately the same % error regardless of d. • Therefore as dimension to be measured increases then so does the error. • Equates to ~ 0.25% under read of volume gas throughput. • Equates to energy of ~ 600 GWh being underreported from the 34 meters. • Varies between 2-56 GWh per meter.

  9. Timeline – general.

  10. Timeline – site example.

  11. Remediation. • National Grid will ensure that O/P’s that have dimensional changes outside of the uncertainty of measurement are investigated. • National Grid will ensure that the CMM is checked on a routine basis to ascertain suitable repeatability.

  12. Summary. • A potential meter error at 34 orifice plate meter errors across our 4 Networks. • Additional checks now in place. • A potential under registration of ~ 600 GWh of energy at LDZ entry. • The measurement error notifications reported via the Joint Office in accordance with UNC conditions.

More Related