C-Scan (Planar-Scan) — Definition & NDT Use
A two-dimensional top-down view of scanned area showing flaw location and size in a plan view (X-Y coordinates), with signal amplitude represented by color intensity. C-scans create a map of reflectors within the material from a single depth level, making it excellent for visualizing the plan-view extent of defects. This presentation is particularly useful for detecting delaminations in composites and mapping corrosion patterns in flat plate structures.
From the inspector's bench, C-Scan is run as a defined sequence: equipment verification on a known reference, scan setup against the procedure, scanning the part, and writing the indications into the report. In a composite, the layered structure means impedance changes at every ply boundary; a true delamination registers as a strong reflector at a depth that the C-scan can map across the part to size the affected area for an engineering disposition. Wall-loss measurements are compared against the recorded baseline, and a corrosion rate (mils/year) is back-calculated; that rate sets the next inspection interval and the trigger for any fitness-for-service or repair decision. Procedure writing, inspector qualification, and the reference block establish the chain that lets a remote engineer trust an indication called a kilometre away from the office.
C-Scan is selected when the failure mode the engineer cares about — surface crack, internal void, wall loss, lack of fusion — lines up with what the technique is physically capable of detecting. On aerospace components, NAS 410 personnel qualifications and tighter acceptance criteria mean the same indication may be flagged that would be passed on a structural weld.
- Etymology / Origin
- C-scan completed the A/B/C progression in early postwar UT instrumentation; the C display gives the plan-view (top-down) map.
- Formula
- I(x,y) = max_t |A(x,y,t)| within an evaluation gate; or amplitude at a fixed depth slice.
- Units
- Both axes in mm of scan distance; pixel value in % FSH or dB.
- Typical Range
- Composite delamination C-scans: probe 5–15 MHz, raster 0.5–1 mm; coverage rate ~50–500 cm^2/min.
- Measured / Produced By
- X-Y scanning bridge with immersion or squirter UT, or a 2-axis encoded contact scanner using a PAUT or single-element probe.
- Code References
- ASTM E2580 (composite C-scan); AMS 2154 (composite UT acceptance)
- Worked Example
- A 200 × 300 mm composite panel scanned at 1 mm pitch yields 60,000 A-scan readings; the C-scan colour-codes peak amplitude in the 1–3 mm depth gate to map a 12 × 25 mm delamination.
ASME Section V Article 4
Ultrasonic examination methods for welds and components.
ASTM E114 / E164 / E2375
ASTM straight-beam, contact, and wrought-product UT practices.
ISO 16810 / ISO 16811
General principles and sensitivity setting for industrial UT.
NAS 410
Aerospace personnel qualification and certification standard for NDT.
The most expensive mistake with C-Scan is treating it as a yes/no test rather than a characterisation — an indication called without a sizing strategy forces a repair where a fitness-for-service review might have left the part in service.
What does "C-Scan" mean in NDT?
A two-dimensional top-down view of scanned area showing flaw location and size in a plan view (X-Y coordinates), with signal amplitude represented by color intensity. C-scans create a map of reflectors within the material from a single depth level, making it excellent for visualizing the plan-view extent of defects
Which standards govern the use of C-Scan?
C-Scan is most often referenced under ASME Section V together with the relevant ASTM practice or the matching ISO standard for the method; the contract or purchase order will name the controlling document and edition for any specific job.
What other NDT concepts should I read alongside C-Scan?
The most directly related entries in this glossary are "a scan", "b scan", "phased array ut"; reading those together gives you the surrounding vocabulary used in inspection reports and procedures.