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Direct Assessment Basics

Learn the fundamentals of direct assessment as a pipeline safety alternative, focusing on ECDA. Understand its limitations, applicability, and steps like pre-assessment and indirect tools selection.

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Direct Assessment Basics

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  1. Direct Assessment Basics Richard Lopez Office of Pipeline Safety Southwest Region

  2. Why Direct Assessment? • Alternative to ILI or Hydro Test When Not Feasible or Practical • Many Gas Transmission Pipelines are “Not Piggable” • The Cost to Make Them Piggable can be Prohibitive (from $1M to $8M per mile)

  3. Why Direct Assessment? • ILI or Hydro-testing Could Cause Customer Supply Interruptions • LDC Laterals Often Sole Source Supply • Pipeline Safety Improvement Act 2002 – Section 23 • TPSSC Equivalency Recommendation

  4. Factors Impeding Piggability • Telescopic Connections • Small Diameter Pipelines • Short Pipelines • Sharp Radius Bends

  5. Factors Impeding Piggability • Less than Full Opening Valves • No Alternate Supply if Pig is “Hung Up” • Low Pressure & Low Flow Conditions • Scheduling and Coordination is an Anti-trust Issue

  6. Features in Common with ILI • Indirect Examinations • Validation/Excavation/Direct Exam • Integrate & Analyze Data • Identify & Address Data Gaps • Identify Remediation Needs • Determine Re-assessment Intervals

  7. Factors Impeding Hydro-Test • Service Interruptions • Sole Source Supplies • Concerns of Causing Pipeline Damage • Dewatering Concerns/Difficult to Dry

  8. Factors Impeding Hydro-Test • Dewatering Concerns/Difficult to Dry • Growth of Sub-critical Defects • Water Availability & Disposal • No Characterization of Future Risk

  9. DA Basics - Overview • Distinct Assessment Process for each Applicable Threat (i.e., EC, IC, & SCC) • Scope of DA as an IM Assessment is more Limited than either ILI or Hydro

  10. DA Basics - Overview • May be the Assessment Method of Choice (esp. for Non-piggable Lines and Low-Stress Gas Lines that cannot be Hydro Tested) • Involves Integration of Risk Factor Data to Identify Potential Threats

  11. Keys to Successful DA • Expertise, Skill, Experience • Follow NACE Standards • Document Justifications for Not Implementing “Should” and “May” Recommendations in the Standards • Documents Reasons for Program Decisions and Options Selected

  12. Keys to Successful DA (cont.) • Data Management • Collection, Integration, Analysis • Data Quality • Understand Limitations of DA • Provide Detailed Procedures for All Process Steps

  13. Today’s Discussion will Focus on ECDA • NACE RP0502 has been Issued • ECDA Process is More Mature than ICDA or SCCDA • Overview of NACE RP0502 Process for ECDA

  14. Limitations of ECDA • ECDA Can Not Deal With: • Lines Susceptible to Seam Failure • Near-neutral pH SCC • Fatigue Failures in Liquid Lines • Internal Corrosion • Plastic Pipe • Pipe in Shielded Areas

  15. Limitations of ECDA • ECDA has Limited Applicability to: • Mechanical Damage (Only to the Degree that Coating is also Damaged)

  16. 4 Step ECDA Process of NACE RP0502 • Pre-assessment • Indirect Assessment • Direct Physical Examination • Post-assessment

  17. Pre-assessment • Process Similar to Risk Assessment • Assemble and Analyze Risk Factor Data

  18. Pre-assessment • Purpose: • Determine Whether ECDA Process is Appropriate and Define “ECDA Regions” • Select Appropriate Indirect Inspection Tools (e.g., CIS, DCVG, PCM, C-SCAN) • Complementary Primary and Secondary Tools are Required • Identify Inspection Expectations

  19. Pre-assessment • Data Collection (Table 1 of NACE Standard) • Pipe Related • Construction Related • Soils/Environmental • Corrosion Protection • Pipeline Operations

  20. Pre-assessment • ECDA Indirect Insp. Tool Feasibility • Complementary Tools – Evaluate pipe with different technologies (see table 2 of NACE RP0502)

  21. Pre-assessment • Feasibility Influenced by: • Degree of Shielding (Coating type, Terrain) • Accessibility (Pavement, Water Crossings, Casings)

  22. Pre-assessment • Establish ECDA feasibility regions • Determine which indirect methods are applicable to each region • Tools may vary from region to region

  23. Pre-assessment • What is a Region? • Segment is a Continuous Length of Pipe • Regions are Subsets of One Segment • Characterized by Common Attributes • Pipe with Similar Construction and Environmental Characteristics • Use of Same Indirect Inspection Tools Throughout the Region is Appropriate

  24. Indirect Inspection • Close Interval Survey (CIS) • Direct Current Voltage Gradient (DCVG) • C-Scan • Pipeline Current Mapper (PCM) • Alternating Current Voltage Gradient (ACVG) (PCM with A-Frame)

  25. Indirect Inspection • Pearson • Ultrasonic • Waveform • Soil Resistivity, Pipe Depth

  26. Indirect Inspection • Direct Current • Measure Structure Potential • Identify Locations of High CP Demand to Small Area

  27. Indirect Inspection • Alternating Current • Apply AC signal • Determine Amount of Current Drain (i.e., Grounding) and Location • Identify Locations of High AC Current

  28. Indirect Inspection • Types of Direct Current Tools • Close Interval Survey (CIS or CIPS) • Direct Current Voltage Gradient (DCVG) • Types of Alternating Current Tools • Alternating Current Voltage Gradient (ACVG) • Pearson Survey • AC Attenuation (PCM, EM, C-Scan)

  29. Indirect Inspection • Purpose: • Locate Areas Where Coating Damage May Exist • Evaluate Whether Corrosion Activity is Present • Apply Primary and Secondary Tools

  30. Indirect Inspection • Timing Such That Conditions are Same • Overlay and Evaluate Data for Clarity, Quality, and Consistency • Distance Correlation Should be Good

  31. Indirect Inspection via CIS • May Detect Large Coating Holidays • Measure Pipe to Soil Potential at Regular Intervals (2.5 – 5 ft. Desirable) • Protection criteria • -850mV polarized potential • 100mV polarization

  32. Indirect Inspection via CIS • Secondary Interpretation • Change in potential profile • Amount of IR drop (Low or High) • ON and OFF Readings are Desirable

  33. Indirect Inspection via DCVG • Measures Voltage Gradient in Soil • CP Current Greatest Where Coating is Damaged

  34. Indirect Inspection via DCVG • Interrupt Rectifier to Determine ∆V • One Electrode • Two Electrodes • Parallel or perpendicular to ROW • Coating Holiday Size Indicated by % ∆V • Triangulation Used to Locate Holiday

  35. Indirect Inspection via ACVG • Impose AC current • Measure Gradient Between 2 Electrodes Spaced ~1m Apart • Gradient Corresponds to Current Flow

  36. Direct Physical Examination • Establish “Priority Categories” from Indirect Inspection • Excavations for Direct Examination

  37. Direct Physical Examination • Purpose: • Confirm Presence of Corrosion Activity • Determine Need for Repair or Mitigation • Evaluate Likely Corrosion Growth Rate • Support Adjustments to Excavation Scope • Evaluate Need for Other Technology

  38. Direct Physical Examination • Categorize Indications • Immediate Action Required • Schedule for Action Required • Suitable for Monitoring • Excavate and Collect Data Where Corrosion is Most Likely

  39. Direct Physical Examination • Characterize Coating and Corrosion Anomalies • Establish Corrosion Severity for Remaining Strength Analysis • Determine Root Cause

  40. Direct Physical Examination • In-process Evaluation, Re-categorization, Guidelines on Number of Direct Examinations • All “Immediate” Must be Excavated • Prioritize “Scheduled” & “Monitored” • If >20% Wall Loss Found, Examine at Least 1 More (2 More for 1st ECDA)

  41. Direct Physical Examination • If No Indications • At Least 1, and 2 for 1st ECDA • Choose More Corrosive Region

  42. Direct Physical Examination • Dig a Bell Hole • Visual Inspection • Coating Condition • Ultrasonic Testing • Radiography • Soil Chemistry and Resistivity

  43. Direct Physical Examination • Collect Data at Dig Site • Pipe to Soil Potentials • Soil Resistivity • Soil and Water Sampling • Under-film pH • Bacteria & SCC Related Data • Photographic Documentation

  44. Direct Physical Examination • Characterize Coating and Corrosion Anomalies • Coating Condition • Adhesion, Under Film Liquid, % Bare • Corrosion Analysis • Corrosion Morphology Classification • Damage Mapping • MPI Analysis for SCC

  45. Direct Physical Examination • Remaining Strength Analysis • ASME B31G • RSTRENG

  46. Direct Physical Examination • Determine Root Cause • For Example • Low CP • Interference • MIC • Disbonded Coatings • Construction Practices • 3rd Party Damage

  47. Post-Assessment • Evaluates Composite Set of Data and Assessment Results • Sets Re-inspection Intervals • Validates ECDA Process

  48. Post-Assessment • Remaining Life - Maximum Flaw • Maximum Remaining Flaw Size Taken Same as Most Severe that was Found • Second Maximum if Unique • If No Corrosion Defects, Same as New • Other (e.g., Statistical)

  49. Post-Assessment • Remaining Life Growth Rate • Measured Corrosion Rate • Maximum Depth / Burial Time • 16mpy (80% C.I. for Corrosion Tests) • 0.3mm/y if at Least 40mV CP Demonstrated

  50. Post-Assessment • Linear Polarization Resistance (LPR) • Probe or Existing Buried Coupon • Coupon Retrieval • Assess ECDA Effectiveness

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