Corrosion Assessment and Probability of Exceedance


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After explaining in-line inspections and their valuable use in determining metal loss and corrosion threats in pipelines, Mr. Patrick Vieth discusses how the data from in-line inspections can be analyzed in a probabilistic method known as the Probability of Exceedance (POE). He talks about the historical development of POE, how it is used today and applications for it.

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Corrosion Assessment and Probability of Exceedance

  1. 1. Corrosion Assessment and Probability of Exceedance Overview Pat Vieth November 06, 2008
  2. 2. Industry <ul><li>Pipeline Industry </li></ul><ul><ul><li>relies heavily on in-line inspection technologies </li></ul></ul><ul><ul><li>for assessing pipeline integrity. </li></ul></ul><ul><li>By using ILI, </li></ul><ul><ul><li>pipeline operators are able to manage many potential integrity threats . </li></ul></ul><ul><ul><li>Prioritize from the standpoint of risk </li></ul></ul><ul><li>One of the primary threats is corrosion management </li></ul><ul><li>Metal loss surveys </li></ul><ul><ul><li>performed on over 50,000 miles of pipelines each year in North America. </li></ul></ul><ul><ul><li>Technologies employed </li></ul></ul><ul><ul><ul><li>magnetic flux leakage (MFL) and ultrasonics (UT) </li></ul></ul></ul><ul><li>Transmission and Gathering pipelines –Hazardous liquid and natural gas </li></ul><ul><ul><li>Over 500,000 miles of pipelines in North America </li></ul></ul><ul><ul><li>have undergone at least one metal loss survey. </li></ul></ul><ul><ul><li>Many pipelines have been or are now being re-assessed. </li></ul></ul>
  3. 3. Industry (cont) <ul><li>The ILI surveys </li></ul><ul><ul><li>provide data on the severity of metal loss identified by the tool </li></ul></ul><ul><ul><li>Location </li></ul></ul><ul><ul><li>Depth and length </li></ul></ul><ul><li>Since these tools provide a significant amount of data </li></ul><ul><ul><li>used for many aspects of integrity management, </li></ul></ul><ul><ul><li>a probabilistic method for utilizing these results has been developed. </li></ul></ul><ul><li>The method is commonly referred to as </li></ul><ul><ul><li>Probablity of Exceedance or POE </li></ul></ul><ul><ul><li>Relies upon metal loss survey data for corrosion management </li></ul></ul><ul><ul><li>Is the focus of today’s presentation </li></ul></ul>
  4. 4. Three Topics <ul><li>Brief Overview of Corrosion Assessment </li></ul><ul><li>Probability of Exceedance (POE) </li></ul><ul><ul><li>Historical Development </li></ul></ul><ul><ul><li>How it is used today. </li></ul></ul><ul><li>Applications of POE </li></ul>
  5. 5. 1. Brief Overview of Corrosion Assessment <ul><li>Many models are available for assessing the severity of corrosion </li></ul><ul><li>Most commonly used models are B31G and RSTRENG </li></ul>
  6. 6. Corrosion Assessment – Failure Criterion
  7. 7. Predicted Failure Stress
  8. 8. 2. POE Historical Development <ul><li>Historical Development </li></ul><ul><ul><li>Methodology developed beginning in the early 1990’s </li></ul></ul><ul><ul><li>Pipeline operator </li></ul></ul><ul><ul><ul><li>was looking for analysis methods to quantify the risk </li></ul></ul></ul><ul><ul><ul><li>based upon multiple ILI surveys </li></ul></ul></ul><ul><ul><li>These early methods relied upon Baysian Statistical methods </li></ul></ul><ul><ul><ul><li>were very complex </li></ul></ul></ul><ul><ul><ul><li>Considered the dependent and independent variables </li></ul></ul></ul><ul><ul><ul><li>Required establishing prior probabilities </li></ul></ul></ul><ul><li>Value of the results became apparent </li></ul><ul><ul><li>Evolved into a simplified process </li></ul></ul><ul><ul><li>Recognized it’s value in a relative ranking </li></ul></ul>
  9. 9. <ul><li>Requires the development of a correlation between the ILI survey and the field findings </li></ul><ul><ul><li>Depth of metal loss – evaluates the potential for a leak to occur </li></ul></ul><ul><ul><li>Pressure carrying capacity – evaluate the potential for the predicted failure pressure to be less than the MOP. </li></ul></ul>
  10. 10. Probability of Exceedance (POE)
  11. 11. Regression - Leak
  12. 12. Regression - Failure <ul><li>Rupture (Depths and Lengths) </li></ul>SRF (Stress Reduction Factor)`
  13. 13. Cumulative POE <ul><li>Probability of Exceedance </li></ul><ul><ul><li>Can be establish for each reported metal loss anomaly </li></ul></ul><ul><ul><li>Once a POE is calculated, the cumulative POE can be calculated for a: </li></ul></ul><ul><ul><ul><li>Pipe Joint </li></ul></ul></ul><ul><ul><ul><li>Potential Excavation Location </li></ul></ul></ul><ul><ul><ul><li>Valve Segment for Prioritization </li></ul></ul></ul><ul><ul><ul><li>Entire line segment </li></ul></ul></ul>
  14. 14. Cumulative POE
  15. 15. 3. Applications of POE <ul><li>Quantify </li></ul><ul><ul><li>Defensible decision-making process </li></ul></ul><ul><li>ILI Tool Performance </li></ul><ul><ul><li>Correlations between ILI reported dimensions and field measurements </li></ul></ul><ul><li>Projected Corrosion Growth </li></ul><ul><ul><li>Incorporate best information available on corrosion growth </li></ul></ul><ul><ul><ul><li>Correlations between multiple ILI surveys </li></ul></ul></ul><ul><ul><ul><li>Corrosion models </li></ul></ul></ul><ul><li>Risk Management </li></ul><ul><ul><li>Identify locations of largest risk reduction </li></ul></ul><ul><ul><li>Prioritization </li></ul></ul><ul><ul><ul><li>High Consequence Areas </li></ul></ul></ul><ul><ul><ul><li>Re-Assessment Justification and Prioritization </li></ul></ul></ul>