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TIME OF FLIGHT DIFFRACTION (TOFD)

For accurate flaw sizing TOFD is one of the most accurate techniques especially for internal defects.
For screening and sizing since TOFD can detect all the flaws in the beam coverage irrespective of orientation it has a high probability of detection. The fact that inspection data is collected in B or D-scan form also improves the detection of cracks, in the presence of signals from geometric features such as mismatch, and weld defects such as excess penetration or undercut.

Change Monitoring
TOFD is one of the most accurate methods available for measuring the growth of flaws.
TOFD is fast becoming the most preferred inspection method in the search for preferential

Weld Root Erosion and Corrosion
The speed and accuracy is unmatched by any other technique.

 

TOFD for Weld root Erosion

Grey Scan Image

Features of this Technique

  • One sweep single axis scan resulting in inspection speeds of up to 150mm per second

  • Grey scale image for ease of interpretation

  • Accuracy to with in 0.1mm achievable

  • Repeatability

  • Permanent record

  • Overlays can determine corrosion rates

Benefits of TOFD

  • Detection is independent of defect orientation

  • Sizing is not dependent on amplitude of the signal

  • Superior inspection reliability

  • Accurate sizing

  • Reliable propagation monitoring

  • No necessity to shut down plant as inspection can be deployed "on-line"

  • Hard Copy Evidence

  • Repeatable

  • Easy Storage of data

Disadvantages of TOFD

  • No simple amplitude threshold for selecting reportable defects.

  • All the TOFD inspection data has to be visually analysed in order to select the reportable defects

  • Not so suitable for defects near to the inspection surface since they may be hidden by the lateral wave and the sizing accuracy deteriorates near to the inspection surface.