Direct Assessment for Canadian Pipelines: Where ECDA, ICDA, and SCCDA Add Value — and Where They Do Not

Direct Assessment is frequently proposed as the default alternative when inline inspection is not feasible. It is well established, recognized under AMPP/NACE methodology, and capable of producing defensible integrity results — but only when applied as a structured engineering process rather than a generic substitute for inspection. Treating Direct Assessment as a single survey, a single NDT pass, or an automatic stand-in for inline inspection tends to produce results that look complete without actually closing the integrity question. ECDA, ICDA, and SCCDA each address a different credible threat, require different supporting data, and carry different limitations. Selecting among them — and applying them correctly — depends on engineering judgment, not on the fact that a pipeline happens to be unpiggable.

Direct Assessment Is a Process, Not a Tool

Direct Assessment is not a survey technique or an NDT method. It is a structured, multi-stage process — pre-assessment, indirect inspection or data integration, direct examination, post-assessment, and a defined reassessment interval — defined under AMPP/NACE methodology for each threat type. Running an indirect survey in isolation, or performing one round of direct examination without the supporting stages, is not Direct Assessment in the sense the standards intend, even if the activity contributes useful data. The confidence an operator can place in the result is grounded in the same underlying logic as the qualification rigor expected of inline inspection systems under API 1163 — in both cases, confidence depends on the demonstrated reliability of the detection and examination methods used, not simply on completing the activity. Each stage exists to manage a specific source of uncertainty: data quality, threat credibility, examination prioritization, and confirmation that findings represent the condition of the segment as a whole.

ECDA: Where It Adds Value

ECDA is suited to segments where external corrosion is the credible threat and the supporting data — coating type and condition, cathodic protection performance, soil corrosivity, and indirect survey history (CIS, DCVG/ACVG) — is available and reasonably reliable. Pre-assessment defines indirect inspection regions based on coating and CP history; indirect inspection identifies and prioritizes locations where anomalies suggest corrosion activity; direct examination confirms actual condition at prioritized locations; and post-assessment integrates findings into a remaining-life and reassessment-interval decision. Where operating and CP history is well documented, ECDA can provide a defensible basis for managing external corrosion on segments where ILI is not feasible.

ECDA: Common Limitations

ECDA depends on the indirect survey methods actually detecting the relevant condition, which is not guaranteed. Cathodic protection shielding — from disbonded coating, rock shield, casings, or certain coating types — can mask corrosion activity from CIS and DCVG surveys, producing a false sense of adequate protection. Poor or incomplete CP and coating records limit the ability to define credible indirect inspection regions in the first place. Complex or mixed coating systems and AC interference can complicate survey interpretation, and inaccessible locations — paved areas, sensitive terrain, congested facility tie-ins — limit where surveys and examination can actually be performed. Where more than one threat is credible on a segment, ECDA addresses only the external corrosion component; over-reliance on CP data alone, without corroborating direct examination, is one of the more common practical missteps.

ICDA: Where It Adds Value

ICDA is suited to segments where internal corrosion is the credible threat, typically in low-flow, wet-gas, or intermittently operated systems where electrolyte can accumulate at low points rather than being continuously swept through the line. Pre-assessment establishes whether flow regime and operating history support the methodology; modeling identifies locations most likely to accumulate liquid based on elevation profile and flow conditions; direct examination at those locations confirms whether internal corrosion is present; and post-assessment characterizes the segment and defines monitoring or reassessment needs. Where operating history is well understood, ICDA can direct limited examination resources to the locations where internal corrosion is actually most likely, rather than examining a segment uniformly.

ICDA: Common Limitations

ICDA's value depends heavily on the accuracy of the operating history used to model flow and liquid accumulation. Where flow rates, product composition, or operating mode have changed over the asset's life — common on facility-connected or intermittently operated lines — the modeling assumptions may not reflect actual historical conditions. Limited or absent fluid sampling makes it difficult to confirm whether assumed electrolyte chemistry matches reality, and unknown internal deposits or solids can mask or contribute to corrosion in ways the standard modeling does not fully capture. Short, facility-connected lines with variable or poorly documented service history are particularly difficult to assess with confidence using ICDA alone — the underlying assumptions require validation, not acceptance at face value.

SCCDA: Where It Adds Value

SCCDA is a susceptibility-based screening methodology, applied only where stress corrosion cracking is a credible threat based on coating type, soil and environmental conditions, operating stress level, and operating pressure history. It identifies and prioritizes segments for direct examination based on factor combinations associated with SCC susceptibility, rather than detecting cracking directly through an indirect survey. Where prior SCC evidence exists on comparable segments, or susceptibility factors clearly align, SCCDA can direct limited and costly crack-detection NDT to where it is most likely to be productive — supporting more defensible prioritization than uniform or no coverage.

SCCDA: Common Limitations

SCCDA screens for susceptibility; it does not detect or size cracks itself, and should never be treated as equivalent to crack-like flaw detection. Confirming or ruling out SCC at a prioritized location requires NDT specifically capable of detecting and sizing crack-like indications — a materially different requirement than the metal-loss-oriented methods used in ECDA and ICDA. Material and toughness assumptions feeding any subsequent ECA carry significant weight and should be defensible, not default values. A hydrotest pass is sometimes proposed as a substitute confirmation step; it demonstrates that no crack-like flaw reached critical size at the test pressure on that day — it does not confirm the absence of subcritical cracking or its growth rate. Treating an SCC-susceptible segment as primarily a wall-loss problem is one of the more consequential mismatches in challenging-to-inspect pipeline programs.

Practical Example: Same Pipeline, Different Direct Assessment Logic

The same generic pipeline system can require different Direct Assessment logic across its length, depending on the threat actually credible at each segment.

A coated, buried segment with cathodic protection anomalies and no internal corrosion concerns points toward ECDA-style logic — indirect survey prioritization followed by direct examination at flagged locations.

A low-flow, wet-gas section of the same system points toward ICDA-style logic — flow and elevation-based modeling to identify likely accumulation points, followed by targeted examination there.

A segment with a susceptible coating type, corrosive soil conditions, and sustained high operating stress points toward SCCDA-style logic — susceptibility screening followed by NDT capable of crack detection and sizing, not wall-thickness measurement alone.

The pipeline being unpiggable is the same fact in all three cases. The credible threat, the supporting data, and the appropriate Direct Assessment logic are not.

What Makes Direct Assessment Defensible?

A program that holds up to engineering and regulatory scrutiny needs more than a completed survey. It should be able to show:

• Credible threat identification specific to the segment
• A data quality review confirming that records support the chosen DA methodology
• Segmentation based on real differences in threat, environment, construction, operation, or coating/CP condition
• Integration of indirect findings or data review into prioritization
• Direct examination planning that tests the actual prioritized threat
• Validation between indirect findings and direct examination results
• Documented assumptions and limitations
• Explicit residual uncertainty
• Reassessment interval logic based on uncertainty, corrosion/crack growth considerations, and operating conditions
• Linkage to the operator's broader integrity management program

How TES Canada Can Help

TES Canada supports operators in applying Direct Assessment as a structured engineering process, not a generic substitute for inline inspection. Our role includes threat screening to confirm which DA methodology applies to a given segment, assessment feasibility review, prioritization of indirect findings for direct examination, excavation prioritization, and integration of Direct Assessment results into FFS, ECA, and broader integrity roadmap decisions.