Before Selecting Tools: Assessment Feasibility Mapping for Challenging-to-Inspect Pipelines

Unpiggable pipelines are often discussed as if the main problem is the absence of inline inspection. In practice, the more important issue is not simply whether a pig can pass through the line. The real integrity question is whether the operator understands which parts of the system can be assessed with confidence, which parts remain uncertain, and what combination of engineering, inspection, monitoring, and mitigation is required to manage that uncertainty.

For challenging-to-inspect pipeline systems, the first step should not be selecting a technology. It should be building an assessment feasibility map.

An assessment feasibility map is an engineering view of the pipeline that identifies where different integrity assessment methods can be applied with confidence, where inspection or access limitations exist, and where residual uncertainty must be managed through additional engineering assessment, monitoring, mitigation, or validation.

In practical terms, this includes inspectability, but the objective is broader than inspection access alone. The purpose is to define the feasibility, coverage, and confidence of each integrity assessment option.

Why "Unpiggable" Is Not a Sufficient Technical Description

A pipeline may be considered unpiggable for many reasons. It may have tight bends, short-radius elbows, reduced-bore valves, back-to-back fittings, insufficient launcher or receiver facilities, unknown internal restrictions, diameter changes, low flow, intermittent operation, or operational constraints that prevent tool passage.

In some cases, the physical geometry is the limiting factor. In others, the limiting factor is operating pressure, flow condition, product type, commercial interruption, or uncertainty in as-built records.

These differences matter because they lead to different integrity strategies. A line that cannot accept a conventional inline inspection tool may still be suitable for modified inspection tools, hydrotesting, direct assessment, LRUT screening from accessible locations, targeted excavation, external corrosion assessment, or engineering assessment based on validated field data.

Conversely, a line that appears accessible may still have poor integrity confidence if the credible threats are not matched to the selected assessment method.

The term "unpiggable" should therefore be treated as the beginning of the engineering discussion, not the conclusion.

What an Assessment Feasibility Map Should Capture

A practical assessment feasibility map should divide the system into meaningful integrity segments. These segments may be based on pipe diameter, material, age, coating type, cathodic protection system, operating environment, pressure class, product, terrain, crossings, sleeves, casings, aboveground transitions, facility tie-ins, historical repairs, or known damage mechanisms.

For each segment, the map should capture four categories of information.

First, the physical and operational constraints should be recorded. This includes features that prevent pigging, access limitations, excavation restrictions, road or rail crossings, river crossings, urban interfaces, facility congestion, isolation limitations, and outage constraints.

Second, credible threats should be identified. External corrosion, internal corrosion, stress corrosion cracking, seam weld defects, girth weld concerns, dents, mechanical damage, geohazards, fatigue, and third-party damage should not be assumed generically. They should be screened against actual operating history, environment, coating, CP performance, fluid characteristics, and past inspection evidence.

Third, the available assessment methods should be matched to the threats. ECDA may be relevant for external corrosion where the required indirect inspections and direct examinations can be performed. ICDA may be relevant where internal corrosion mechanisms are credible and operating conditions support the methodology. SCCDA may be considered where stress corrosion cracking is credible, but it requires careful attention to susceptibility, coating, soil, stress, and validation evidence.

LRUT may support screening of road crossings, sleeved sections, and other access-limited areas, but it does not replace detailed flaw sizing or fitness-for-service assessment. Hydrotesting may demonstrate pressure containment, but it may not provide the same information about remaining life, corrosion growth, or subcritical cracking.

Fourth, the residual uncertainty should be explicitly stated. This is often the part that is missing from conventional inspection planning. An assessment plan is not complete simply because a technique has been assigned. The operator should understand what the technique can detect, what it cannot detect, what coverage is achieved, what assumptions are being made, and what engineering controls are required to manage the remaining uncertainty.

Practical Engineering Observations

In many aging pipeline systems, the highest-risk areas are not always the longest segments. Short, complicated sections near facilities, road crossings, sleeves, casing ends, low points, dead legs, tie-ins, and historical repair locations can dominate uncertainty. These areas may not be convenient to inspect, but they often deserve more engineering attention than long, uniform pipe runs with stable operating and inspection history.

Another common issue is over-reliance on single-data streams. CP readings, coating condition, close interval survey results, soil data, leak history, wall thickness readings, or LRUT screening results each provide useful information, but none of them alone represents a complete integrity assessment. The strength of an assessment feasibility map is that it integrates these inputs into a defensible decision framework.

The map also helps prevent technology-driven integrity planning. Without a structured map, operators may select an inspection tool because it is available, familiar, or commercially attractive. With a structured map, the question changes: what threat are we trying to manage, what confidence is required, what method can provide that confidence, and what additional verification is needed?

Link to Integrity Management Requirements

Canadian pipeline integrity expectations require more than isolated inspection activities. A credible integrity management program should demonstrate that threats are identified, assessment methods are appropriate, records are maintained, condition monitoring is planned, and integrity decisions are traceable.

For challenging-to-inspect pipelines, this is especially important because the absence of conventional inline inspection increases the need for documented engineering rationale.

An assessment feasibility map supports this requirement by creating a clear technical basis for the integrity plan. It shows why certain methods were selected, why other methods were not practical, how threats were prioritized, and how future assessments should evolve as new data becomes available.

How TES Canada Can Help

TES Canada supports pipeline operators by developing engineering-led integrity strategies for unpiggable and challenging-to-inspect pipeline systems. Our approach is not based on promoting a single inspection method. We help operators define credible threats, segment pipeline systems, evaluate inspection and assessment options, integrate available data, and develop defensible integrity management plans aligned with Canadian regulatory expectations.

For operators managing aging pipeline systems, facility-connected pipelines, road crossings, sleeved sections, or assets with incomplete inspection history, TES can support assessment feasibility mapping, direct assessment planning, LRUT strategy review, corrosion and crack assessment, fitness-for-service evaluation, and long-term integrity roadmap development.

The goal is not more inspection for its own sake. The goal is better integrity confidence, clearer engineering decisions, and a practical plan that can withstand operational, technical, and regulatory scrutiny.

Technical Context

Challenging-to-inspect pipelines may be limited by geometry, access, operating conditions, missing records, facility congestion, lack of launcher/receiver facilities, or inspection tool limitations. These constraints are common in older pipeline systems, facility-connected lines, low-flow systems, sleeved sections, cased crossings, and short pipeline segments near plants or terminals.

Problem Statement

When a pipeline cannot be conventionally pigged, operators may be forced to rely on partial inspection data, indirect survey results, historical records, or localized examinations. Without a structured engineering framework, this can lead to fragmented integrity decisions and unclear residual risk.

Why It Matters

A pipeline may be compliant with some inspection or monitoring activities but still have unresolved integrity uncertainty. For unpiggable or difficult-to-inspect systems, the quality of the engineering plan is as important as the inspection technology selected.

Damage Mechanisms Involved

• External corrosion
• Internal corrosion
• Stress corrosion cracking
• Mechanical damage
• Dents and deformation
• Seam weld defects
• Girth weld defects
• Fatigue
• Geohazard-related strain
• Third-party damage
• Coating degradation
• CP shielding or interference-related corrosion

Inspection / Assessment Methods

• Direct Assessment
• ECDA
• ICDA
• SCCDA
• LRUT
• UT thickness survey
• Targeted excavation
• Hydrostatic testing
• Pressure test review
• Close interval survey
• DCVG / ACVG
• CIPS
• Soil corrosivity assessment
• Coating assessment
• Fitness-for-Service assessment
• Engineering Critical Assessment
• Corrosion growth assessment
• Repair and mitigation planning

Engineering Workflow

• 1. Define the pipeline system and segment boundaries.
• 2. Identify pigging, access, operational, and data limitations.
• 3. Screen credible threats for each segment.
• 4. Match threats to feasible inspection and assessment methods.
• 5. Identify where direct examination or field validation is required.
• 6. Assess remaining uncertainty after each method is applied.
• 7. Prioritize mitigation, monitoring, repair, or reassessment actions.
• 8. Document the engineering basis for integrity management decisions.

TES Canada Perspective

TES Canada approaches challenging-to-inspect pipelines as an integrity engineering problem, not simply an inspection selection problem. The objective is to integrate inspection feasibility, credible threats, available data, standards expectations, and engineering assessment into a practical and defensible integrity management plan.

Practical Takeaway

Before selecting an inspection method for an unpiggable pipeline, operators should first map where assessment confidence is strong, where it is limited, and where additional engineering judgment or field validation is required.

Case Scenario

A pipeline operator has several short pipeline segments connected to facilities, crossings, and older assets with limited as-built records. Conventional inline inspection is not feasible across the full system, and available data includes CP surveys, limited UT readings, historical repairs, operating records, and selected NDT results.

What Happened

Inspection and maintenance activities were performed, but the information was not fully integrated into a single integrity decision framework. Some segments had reasonable confidence, while others still contained unresolved inspection and threat uncertainty.

Root Cause

The system was treated as generally "unpiggable" rather than being divided into assessment feasibility segments with defined threats, feasible assessment methods, and residual uncertainty.

What Was Missed

The operator had data, but did not have a clear engineering map showing which threats were addressed, which segments remained uncertain, and what follow-up assessment or mitigation was required.

What Would Have Prevented It

A structured assessment feasibility map would have helped connect available data, inspection limitations, threat screening, and assessment methods into a defensible integrity plan.

Lessons Learned

Unpiggable pipelines require more than alternative inspection techniques. They require a documented engineering process that explains how integrity confidence is developed, where uncertainty remains, and how future inspection, assessment, and mitigation will be prioritized.

TES Canada Perspective — Case Application

TES Canada can support operators by developing assessment feasibility maps, threat-based assessment plans, direct assessment strategies, LRUT screening plans, targeted excavation logic, and FFS/ECA workflows for difficult-to-inspect pipeline systems.