Direct Assessment Basics

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)

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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

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Factors Impeding Piggability

• Telescopic Connections
• Small Diameter Pipelines
• Short Pipelines
• Sharp Radius Bends

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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

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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

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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

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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

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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

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Keys to Successful DA (cont.)

• Data Management
• Collection, Integration, Analysis
• Data Quality
• Understand Limitations of DA
• Provide Detailed Procedures for All Process Steps

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Todays 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

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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)

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4 Step ECDA Process of NACE RP0502

• Pre-assessment
• Indirect Assessment
• Direct Physical Examination
• Post-assessment

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Pre-assessment

• Process Similar to Risk Assessment
• Assemble and Analyze Risk Factor Data

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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

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Pre-assessment

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

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Pre-assessment

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

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Pre-assessment

• Feasibility Influenced by
• Degree of Shielding (Coating type, Terrain)
• Accessibility (Pavement, Water Crossings, Casings)

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Pre-assessment

• Establish ECDA feasibility regions
• Determine which indirect methods are applicable
  to each region
• Tools may vary from region to region

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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

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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)

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Indirect Inspection

• Pearson
• Ultrasonic
• Waveform
• Soil Resistivity, Pipe Depth

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Indirect Inspection

• Direct Current
• Measure Structure Potential
• Identify Locations of High CP Demand to Small Area

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Indirect Inspection

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

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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)

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Indirect Inspection

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

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Indirect Inspection

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

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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

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Indirect Inspection via CIS

• Secondary Interpretation
• Change in potential profile
• Amount of IR drop (Low or High)
• ON and OFF Readings are Desirable

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Indirect Inspection via DCVG

• Measures Voltage Gradient in Soil
• CP Current Greatest Where Coating is Damaged

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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

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Direct Physical Examination

• Establish Priority Categories from Indirect
  Inspection
• Excavations for Direct Examination

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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

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Direct Physical Examination

• Categorize Indications
• Immediate Action Required
• Schedule for Action Required
• Suitable for Monitoring
• Excavate and Collect Data Where Corrosion is Most
  Likely

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Direct Physical Examination

• Characterize Coating and Corrosion Anomalies
• Establish Corrosion Severity for Remaining
  Strength Analysis
• Determine Root Cause

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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)

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Direct Physical Examination

• If No Indications
• At Least 1, and 2 for 1st ECDA
• Choose More Corrosive Region

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Direct Physical Examination

• Dig a Bell Hole
• Visual Inspection
• Coating Condition
• Ultrasonic Testing
• Radiography
• Soil Chemistry and Resistivity

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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

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Direct Physical Examination

• Remaining Strength Analysis
• ASME B31G
• RSTRENG

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Direct Physical Examination

• Determine Root Cause
• For Example
• Low CP
• Interference
• MIC
• Disbonded Coatings
• Construction Practices
• 3rd Party Damage

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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)

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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

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Post-Assessment

• Linear Polarization Resistance (LPR)
• Probe or Existing Buried Coupon
• Coupon Retrieval
• Assess ECDA Effectiveness

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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

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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

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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