Many pipelines cannot accommodate conventional ILI tools due to geometry, lack of launchers/receivers, tight bends, variable diameters, valves, tees, deposits, product limitations, or access constraints. These pipelines are often described as unpiggable or difficult-to-inspect. This does not mean they are unmanageable — it means the integrity strategy must be engineered differently.
A large proportion of industrial pipeline systems — particularly in LNG, petrochemical, and terminal facilities — contain sections that cannot be inspected by conventional ILI. Without a structured PIMS approach, these sections may accumulate risk without defensible management.
Technical Context
What Makes a Pipeline Unpiggable?
- Lack of launcher/receiver facilities
- Tight bends or complex geometry
- Variable diameters or reduced bore components
- Valves, tees, dead legs, branch connections, or restrictions
- Low flow, intermittent service, or unsuitable product conditions
- Internal deposits, wax, sludge, or debris
- Lined or non-metallic sections
- Road crossings, sleeved/cased sections, buried transitions, or inaccessible areas
Why Unpiggable Pipelines Require a PIMS Approach
A Pipeline Integrity Management System (PIMS) integrates pipeline data and asset hierarchy, threat identification, risk assessment, inspection method selection, direct assessment and verification, defect assessment using FFS/ECA where applicable, mitigation and repair planning, data management and traceable decisions, reassessment intervals, and continuous improvement. PIMS is not a software product alone — it is a structured engineering and management process.
Direct Assessment Methods: ECDA, ICDA, and Related Approaches
When ILI is not feasible, structured direct assessment methods may be used for relevant threats. ECDA addresses external corrosion on buried metallic pipelines. ICDA addresses internal corrosion where fluid, water, flow, and operating data support the assessment. ADCA or similar approaches may be used for aboveground or atmospheric corrosion. Direct assessment requires reliable data, appropriate threat applicability, field verification, and engineering judgement.
Role of Advanced NDT and External Screening
Multiple methods may be combined: LRUT/Guided Wave UT for long-range screening from accessible locations; UT thickness measurement and corrosion mapping for local confirmation; PAUT/TOFD where welds or flaw characterization require advanced UT; digital radiography for profile assessment; PEC for screening average wall loss through insulation/coating/fireproofing; CIPS/DCVG/ACVG for buried pipeline coating/cathodic protection assessment; and excavation/direct examination where required.
From Inspection Findings to Engineering Decisions
Inspection results must be converted into decisions: continue operation, monitor, re-inspect, repair, sleeve/reinforce, replace, derate or modify operating envelope, improve cathodic protection/coating/drainage, clean or treat internal corrosion threats, or update reassessment interval. Where defects are found, FFS or ECA may be required.
TES Canada Practical Experience
TES Canada's leadership and team have practical experience managing and supporting large-scale pipeline inspection and risk assessment activities covering approximately 3,700 km of above-ground and buried pipelines, including direct assessment and long-range ultrasonic inspection strategies for difficult-to-access and unpiggable sections. This experience supports a pragmatic approach: use screening to prioritize, then verify and assess using appropriate local methods.
TES Canada approaches unpiggable pipeline integrity through an integrated PIMS framework: threat identification and risk ranking, ECDA/ICDA/ADCA support, LRUT screening strategy, advanced NDT method selection, FFS and ECA support, and PIMS development and data structuring.
Standards & References
- CSA Z662 — Oil and Gas Pipeline Systems
- ASME B31.8S — Managing System Integrity of Gas Pipelines
- NACE/AMPP SP0502 — Pipeline External Corrosion Direct Assessment Methodology
- API 1160 — Managing System Integrity for Hazardous Liquid Pipelines
- API RP 580 / API RP 581 — Risk-Based Inspection
- API 579-1 / ASME FFS-1 — Fitness-for-Service
- ASTM E2775 — Guided Wave Testing of Above Ground Steel Pipework
- ISO 18211 — Long-range inspection of pipelines using guided wave testing
Need support with this type of technical challenge?
TES Canada can help you assess the issue, select the right inspection or engineering approach, and develop a practical integrity management solution.
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