This document provides an overview of direct assessment (DA) and external corrosion direct assessment (ECDA) as alternatives to in-line inspection (ILI) or hydrotesting for assessing pipeline integrity when those methods are not feasible. It describes the multi-step ECDA process involving pre-assessment, indirect assessment using tools like CIS and DCVG, direct examination including excavation and testing, and post-assessment. The document outlines benefits and limitations of ECDA and emphasizes the importance of collecting and integrating data to identify corrosion threats and determine reassessment intervals.

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

51. Post-Assessment
 Perform at Least 1 Extra Dig at Random
Location
 Pipe Condition Should be Better than at
Indications
 For 1st ECDA
 Additional Dig at Low Priority Indication
 Company-specific Performance Metrics

52. ECDA Summary
 There is No Panacea for Pipe Integrity
Verification
 All Tools Have Limitations
 External Corrosion Direct Assessment
is Based on the Use and Integration of
Existing and Emerging Technologies

53. ECDA Summary
 External Corrosion Direct Assessment
can be Effective if Properly Applied
 Requires Effective Data Collection and
Management as well as a Commitment
to Validation
 Operators Choose Best Tools to Achieve
Pipeline Reliability, Safety, and Asset
Preservation