Time Of Flight Diffraction (TOFD) is an ultrasonic Non-Destructive Testing (NDT) method which is an improved version of conventional manual ultrasonic testing using a pitch-catch scanning technique to offer accurate detection of cracks, slag and lack of fusion. There is no other NDT method currently available with similar grade of coverage, precision and speed.

As TOFD is a fully computerised system able to scan, store, and evaluate indicators in terms of height, length, and position, a permanent digital record can be retained for future use or audit.

With industry’s growing need for more reliable, simpler, accurate and cost effective techniques, Time of Flight Diffraction is establishing itself as a widely-used tool for the detection of flaws in welds.

TOFD offers the ability to accurately size and monitor pre-existing or growing in service discontinuities, it is becoming more and more important in chemical and refining plants especially when a Risk Based Inspection (RBI) approach is used.

Applications of TOFD:

  • Construction weld inspections.
  • High temperature weld inspections of up to nearly 500°C.
  • In service inspection at ambient or high temperatures.
  • Examination of steam drums used in power generation.
  • Root corrosion detection in vessels.
  • Intergranular stress corrosion cracking in welds.
  • Pre-service inspection of piping welds and duplex pipelines.
  • Welds on spherical storage tanks.
  • Comprehensive nozzle inspections.

Advantages of TOFD:

  • It is based on diffraction, so relatively indifferent to weld bevel angles and flaw orientation.
  • Precise sizing capability makes it an ideal flaw monitoring method.
  • Quick to set up and perform an inspection, as a single beam offers a large area of coverage.
  • Rapid scanning with imaging and full data recording.
  • Can also be used for corrosion inspections.
  • Required equipment is more economical than Phased Array.
  • Highly sensitive to all weld flaw types.
  • High probability of flaw detection and low ‘false call’ rate.
  • Flaw sizing is not dependent on signal amplitude.
  • Wide range of material thickness can be examined (6mm – 300mm).
  • Portable equipment.
  • Data is digitally stored for future reference or second opinion.
  • Compliant with most international and local codes/standards.

IACS NDT use PCN level 2 qualified personnel to perform inspections with MPA. All inspections are only carried out with client-approved procedures which follow the most recent international British Standards and/or client specifications. Procedures and risk assessments are submitted for client approval before commencement of the project.

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