1. METAL LOSS IN-LINEINSPECTION SURVEYS LIMITS AND INACCURACIES

2. BACKGROUND • Began use in 1960’s. • Initial inspection tools were low resolution, low power tools. • Suitable for finding where to look for corroded pipe. • Better resolution and power offered in 1980’s. • High resolution tools began use in late 1980’s. • Despite limitations and inaccuracies, pipelines began to calculate pressure limits based on in-line inspection grading in late 1990’s/early 2000’s.

3. INACCURACIES IN PRESSURE LIMIT CALCULATIONS

5. RUPTURES

6. LEAKS

7. High Resolution Inspection Tool Stated Limits and Inaccuracies • API 1160 • Inspection Company’s Specs

8. API 1160 Limits onHigh Resolution Tools • Cannot detect or reliably detect: • Narrow axial external corrosion • Cracks and crack like defects • Laminations and inclusions • Pipe mill anomalies • Can detect, but cannot identify or size: • Dents, wrinkle bends and buckles • Gouges

9. High Resolution PigSpec. Limitations • Cannot detect or unknown accuracy • Surface areas smaller than t x t • Axially oriented areas, width less than 2t • Areas interacting with weld, smaller than 3t x 3t • Minimum reported depth • For t x t to 2t x 2t, 0.4t • For larger than 2t x 2t, 0.2t • For larger than 3t x 3t, 0.1t • For areas interacting with weld, larger than 3t x 3t, 0.2t

10. High Resolution PigSpec. Accuracy • Width and length • Isolated pits, +t • Complex shapes, +2t • Depth • For less than t x t, unknown • For t x t to 2t x 2t, +0.2t • For larger than 3t x 3t, + 0.1t • For areas interacting weld, 3t x 3t and larger +0.2t

11. Case Study High Resolution Metal Loss Survey • 36 miles of pipeline • 695 metal loss anomalies deeper than 15% were reported • Breakdown on graded wall loss > 50% t 1 40 to 49% t 6 30 to 39% t 31 20 to 29% t 197 15 to 19% t 460

12. Field Inspection Results • 200 anomalies were excavated • Detailed records produced on 11 pipe joints covering 62 anomalies • 90% of anomalies were deeper than graded • 58% of anomalies were longer than graded • 43 ungraded corrosion areas were found

13. Ungraded Corrosion Areas • 20 to 68% deep • 0.25 to 25 inches long • 0.25 to 10 inches wide • Two exceeded RSTRENG

14. Computer Display

15. Computer Display

16. Computer Display

17. Computer Display

18. Computer Display

19. Needed Post Field Inspection Activities • Organize graded vs. found data • Regrade in-line inspection survey • New field inspection plan • Re-inspect and repair pipeline • Statistical analysis of areas not inspected • Apply future growth to anomalies

20. Statistical Analysis of Non-Inspected Areas • Bayes Theorem • First applied on TAPS • Also called probability of exceedance (POE) analysis • Probability that an anomaly will exceed a given integrity criteria

21. Non-Inspected Pipe POE Summary* POE %Number of Pipe Joints 20-29 5 30-39 3 40-49 4 50-59 7 60-69 2 70-79 5 80-89 3 90-99 1 * Exceeding RSTRENG without 10% surge allowance

22. OPS Position Needed on POE Non-Compliance Limits • Probability to Exceed Part 192 or Part 195 • Per anomaly? • Per pipe joint? • Per pipeline section? • Per pipeline inspection survey? • Per pipeline system? • 1%, 2%, 5%, 10%, More?