METAL LOSS IN-LINE INSPECTION SURVEYS

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METAL LOSS IN-LINEINSPECTION SURVEYS

• LIMITS AND INACCURACIES

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BACKGROUND

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

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• INACCURACIES IN PRESSURE
• LIMIT CALCULATIONS

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RUPTURES
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LEAKS
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High Resolution Inspection Tool Stated Limits
and Inaccuracies

• API 1160
• Inspection Companys Specs

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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

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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

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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

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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
• gt 50 t 1
• 40 to 49 t 6
• 30 to 39 t 31
• 20 to 29 t 197
• 15 to 19 t 460

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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

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Ungraded Corrosion Areas

• 20 to 68 deep
• 0.25 to 25 inches long
• 0.25 to 10 inches wide
• Two exceeded RSTRENG

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Computer Display
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Computer Display
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Computer Display
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Computer Display
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Computer Display
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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

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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

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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

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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?