APPLICATIONS OF VT
VT for joining processKhurram S Ahmad1CAUTIONNOT to be too
stringent to try to find or identify the micro defects by VT for
in-servicePut more efforts into finding out those easily visible
imperfects. Each method has its limitation of application Usually
VT can not find the micro defects PT or MT of other methods can be
adopted.
2JOINING PROCESSESMetal joints are formed through the
processesSolderingBrazingOxy-fuel gas weldingResistance welding
andarc weldingSome other processes, including diffusion bonding and
electron beam welding are also widely used in the industry
3JOINING PROCESSESVT at all stages of welding Before welding
During welding After welding Soldering45Material examination prior
to fabrication can eliminate conditions that tend to cause weld
defects.
PRIOR TO WELDINGVisual Testing56Scabs, seams, and scale Proper
edge preparation, dimensions and finishClearance dimensions of
backing strips, backing rings, and consumable insertsAlignment and
fit-up of work piecesVerification of correct materials by check of
recordsVerification of cleanliness requirements and condition of
tack weldsVerification of welding procedure and performance
qualificationPRIOR TO WELDINGVisual Testing67Welding process and
conditionsWelding variables Filler metalFlux and protective
gasesPreheat and interpass temperaturesDistortion controlInterpass
chipping, grinding or gougingInspection intervals (either time or
sequence)DURING WELDINGVisual Testing78Dimensional
accuracyCompletion of weldingSize of legs and throat of filler
weldsContour, reinforcement, and surface finish of weldsDegree of
underfill, undercut, and overlapWeld spatter, crater cracks,
impression marking, scratches, gouges, and strikes Handling
damageCompletion of post weld heat treatmentNondestructive
inspective and resultsAFTER WELDINGVisual Testing89Pay Attention
To:Visual inspection of welds in all steels may begin immediately
after the completed welds have cooled to ambient temperature.
Acceptance criteria for certain steels shall be based on visual
inspection performed not less than 48 hours after completion of the
weld.
Visual Testing910Pay Attention To:Research has shown that
delayed cracking can continue for several days after a weld has
cooled to room temperatureVisual Testing10
