C-Scan data can provide position-referenced ultrasonic evidence for a corrosion condition reported by an ILI system. The correlation task is to establish that the scanned area corresponds to the reported feature, reconcile the coordinate references, compare ILI-reported geometry with the field-mapped condition, and document any differences. C-Scan can refine or verify the local field dimensions used in assessment, but it does not by itself validate the overall ILI tool performance or determine the final engineering disposition.
Align the ILI call with the scan area
Start with the pipeline segment, ILI run, direction, feature identifier, reference welds, stationing, clock position and the field exposure. The scan record should identify the component, surface, scan origin, axial and circumferential axes, tile or pass and units. If the scan is stitched from multiple passes, retain the source association and review seams or gaps before relying on a boundary.
The ILI call and C-Scan may use different origins or feature definitions. An ILI system may report an interaction box, while the field scan shows a broader corrosion patch with several local minima. Record the relationship rather than forcing one outline to match the other.
- Reconcile ILI references with field welds, stationing and clock position.
- Establish that the scan covers the correlated ILI location and passes its quality review.
- Compare indication boundaries, minimum wall, profiles and source dimensions.
- Record whether the C-Scan correlates with, refines, resolves into multiple field features, or does not identify a corresponding condition within the examined area.
Confirm the mapped indication
Review the scan for coverage, coupling, noise, data dropouts and the expected corrosion response. Confirm the indication location against field references and photos. Use the mapped data to identify whether the feature is isolated, elongated, circumferentially broad or interacting with nearby metal loss. The review should state whether the C-Scan correlates with, refines, resolves into multiple field features, or does not identify a corresponding condition within the examined area.
Where the data supports it, document the indication's axial length, circumferential width, maximum measured metal-loss depth or percent wall loss, where calculated from a known reference wall thickness, minimum wall thickness, clock position and profile line. State the sizing rule, scan spacing, filtering or smoothing and any area that could not be examined. A mapped result with a gap is not the same as full coverage.
Use minimum wall and profile outputs as inputs
Minimum wall thickness is the lowest valid measured thickness within the reviewed scan area after applicable data-quality checks. The value should have a coordinate, units, source file or tile, and relationship to the ILI feature. A corrosion profile can show how the wall changes through the indication and whether a single minimum represents the feature adequately.
These outputs may be used with pipe diameter, nominal wall, material and pressure in a remaining-strength assessment. The selected method could be B31G, Modified B31G or an RSTRENG/effective-area assessment when the profile data and procedure support it. Calculated results are assessment inputs. A field C-Scan at one excavation verifies the condition within that examined area; it does not by itself establish the accuracy of the ILI tool across the full inspection run. Qualified engineers decide whether the coverage, uncertainty, interaction and operating context support the final disposition.
Preserve the comparison in the report
The final record should show the original ILI values, C-Scan values, accepted correlated location, measurement differences, assumptions, photos, map or profile and the assessment result. The C-Scan / Corrosion Mapping workflow supports scan stitching, indication review, minimum-wall data and report-ready evidence. The Pipeline Integrity workflow can connect that evidence to the anomaly, UT grid, calculation and repair record.
Questions inspectors ask
Does field C-Scan replace the original ILI record?
No. The two datasets serve different purposes and should remain linked and traceable.
What if the C-Scan shows several indications inside one ILI call?
Record the relationship and assess the features under the applicable interaction and sizing rules rather than hiding the individual minima.
Can the minimum wall alone establish remaining strength?
Not necessarily. The engineer must consider geometry, profile quality, interaction, material, pressure, uncertainty and the selected assessment method.