TOFD: Flaw Sizing You Can Take to the Engineer

Millimetre-level through-wall sizing on code welds — typically scanned alongside PAUT in a single pass.

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Time of Flight Diffraction (TOFD) Inspection

TOFD is an advanced ultrasonic technique that sizes flaws by timing sound diffracted from their tips — delivering through-wall height measurements conventional methods can't match. CIC provides TOFD inspection across Alberta, usually paired with phased array in a single encoded pass: PAUT detects and locates, TOFD sizes with precision.

How TOFD Works — and Why Sizing Is Its Superpower

Two probes straddle the weld, one transmitting, one receiving. Instead of relying on reflection amplitude like conventional UT, TOFD times the faint signals diffracted from the top and bottom tips of a flaw — and because arrival time converts directly to depth, flaw height comes out with millimetre-level accuracy regardless of the flaw's orientation or how strongly it reflects. Amplitude-independence is the point: mis-oriented cracks that under-call on amplitude methods can't hide their tips from TOFD.

Where TOFD Earns Its Place

  • Fitness-for-service inputs — accurate flaw height drives remaining-life and acceptance calculations; oversizing forces repairs you didn't need, undersizing is worse

  • Code weld examinations — encoded TOFD alongside PAUT satisfies detection-plus-sizing requirements in one scan

  • Thick sections — full through-wall coverage in a single pass where radiography needs multiple exposures

  • Repair decisions — monitoring known indications between outages with repeatable, comparable data

TOFD and PAUT: Better Together

TOFD has known blind spots near the outside and inside surfaces (the lateral wave and backwall zones), and it sizes better than it characterizes. PAUT covers those near-surface zones and images the flaw; TOFD nails the height. That's why our standard advanced-UT scan plan for critical welds runs both techniques on one encoded pass — each technique auditing the other, one report at the end.

Frequently Asked Questions

What is TOFD inspection used for?

TOFD is used to detect and — above all — accurately size flaws through the wall of welds and components. Typical applications are code weld examinations, fitness-for-service assessments, thick-section inspection, and monitoring known flaws over time with repeatable encoded data.

Is TOFD better than PAUT?

They solve different halves of the problem: PAUT detects, locates and images; TOFD sizes through-wall height with the best accuracy of any field UT technique. On critical welds the answer is usually both, scanned together in one pass — which is how CIC runs them.