Time of Light Diffraction- NDT Technique - spectro.in NDT... · TOFD is a Non Destructive Testing which is reliable welding inspection technique with high detection rate. Time of

Time of Light Diffraction- NDT Technique

TOFDisaNonDestructiveTestingwhichisreliableweldinginspectiontechniquewithhighdetectionrate.

Time of Flight Diffraction is based on the Principle of

Diffractionincontrasttore�lectionofultrasoundasusedin

conventional UT. Diffraction takes place at its extremities

whenultrasoundisincidentatlineardiscontinuitysuchas

crack.Thedepthofcracktipscanbecalculatedautomatically

bytrigonometryapplicationbyusingthemeasuredtimeof

�lightofthepulse.TOFDisverysensitiveindetectingallthe

typesofdefect,irrespectiveofitsorientation.

ToFDisanadvancedinspectiontechniqueusesthe

diffractedsound initiating fromthe �lawtips.And

whichdoesnotrelyonthere�lectivityofthe�law.Itis

abletodetect�lawsirrespectiveoftheirorientation

ortype.

Acoupleofprobessitontheoppositesidesofaweld.

Oneoftheprobesemitsanultrasonicpulsewhichis

pickedupbytheprobeontheotherside.

Inanundamagedpipe,thesignalspickedupbythe

receiver probe are from two waves: one which

travelsalongthesurfaceandtheotherre�lectsoff

the far wall.When a crack is present, there is a

diffractionoftheultrasonicwavefromthetip(s)of

thecrack.Byusingthemeasuredtimeof�lightof

the pulse, the depth of a crack tip is calculated

trigonometrically.

AdvantagesofTOFD

This unique ultrasonic technique has greatadvantageindetectionof�laws,speedanditisthemostaccuratedefectsizingtechnique.

TOFD is proven to be a technique, whichcombineshighdetectionratewithaveryhighreliability in pre-service and in-serviceinspections.

Absenceofradiationisoneofitsmostimportantadvantagesforweldinspection

Nearly independent of fluctuation in surface conditions.

Defect position and size can be exactly determined.

ApplicationAreasofTOFD

Pre-serviceinspection

Ø Weldinspectionofvessels,pipelinesandplates

In-serviceinspection

Ø Weldinspectionofvessels,pipelinesandplates

Ø Detectingcorrosionunderneathreinforcement

ringsofnozzles

Ø Detectingcorrosionunderneath

Ø Reinforcementringsofnozzles

Ø Claddingthicknessmeasurement

Ø Determiningdepthofcracks

No evacuation of areas during operationbecausenoradiationisused.

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