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Introduction
NDT personnel should be familiar
with the test method, know thepotential types of flaws in a particular
material and be familiar with their
effect on the structural integrity of theitem.
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Introduction
Failure of critical components
Catastrophic results
Loss of life
Loss of production
Loss of revenue Environmental damage
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Non Destructive TestingThe presence of flaws in critical
components increases the
compromise of system integrity.
NDT often provides the only method of
identifying damage and irregularities inmaterials which would lead to failure.
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FlawsDetection
InterpretationEvaluation
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FlawsMisinterpretation and/or improper
evaluation of flaws or improperperformance of NDT can have
catastrophic results
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FlawsTypes
Corrosion
Inherent flaws
Primary processing flaws
Secondary processing flaws In-service flaws
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CorrosionElectrochemical deterioration of a
metal resulting from chemical
reaction with the surrounding
environment.
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Inherent Flaws
Present in metal as the result of its
initial solidification from the molten
state.
Cont.
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Inherent Flaws
Cont.
pipe shrinkage cavity that forms at the top
of an ingot during metal solidification Shows up as irregular voids in finished
product
Cont.
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Inherent Flaws
Cont.
porosity occur when gas bubbles aretrapped as the molten metal in an ingotmold solidifies
shows up as laminations or seams in thefinished product
Cont.
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Inherent flaws Cont.
inclusions impurities
slag sulfides
cont
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Inherent flaws
Cont.
Shrinkage cracks
can occur in castings due to stressescaused by the metal contracting as it coolsand solidifies
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Primary Processing FlawsFlaws which occur while working the
metal down by hot or cold
deformation into useful shapes suchas bars, rods, wires, and forgedshapes
cont
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Primary Processing Flaws Cont
seams surface flaws, generally long,
straight, and parallel to the longitudinalaxis of the material
Can originate from ingot blowholes and
cracks and are formed by the drawing orrolling processesCont.
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Primary Processing Flaws Cont.
laminations are formed in rolled plate,
or sheet occur from internal fissures, i.e. porosity
Cont.
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Primary Processing Flaws Cont
cooling cracks stress cracks caused by
uneven cooling
generally longitudinal
long but not necessarily straight
Cont
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Primary Processing Flaws Cont.
forging laps results from metal being
folded over and forced into the surfacenot forming a solid piece
caused by faulty dies, oversized blanks,etc.
can occur on any area of the forgingCont.
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Primary Processing Flaws Cont.
cold shut failure of metal to fuse
occurs in castings when part of the metal
being poured into the mold cools and
does not fuse with rest of the mental into a
solid piece
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Primary Processing Flaws Cont.
incomplete weld penetration
failure of the weld metal to penetrate
completely through a joint before
solidifying
Cont.
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Primary Processing Flaws Cont.
lack of fusion
occurs in welds where the temperature hasnot been high enough to melt the parentmetal adjacent to the weld
sidewall lack of fusion
inter-run lack of fusionCont.
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Primary Processing Flaws cont.
weld undercutting surface flaw running
in the toe of the weld caused by welding at too high a
temperature
decreases the thickness of the parent materialat the toe of the weldCont.
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Primary Processing Flaws Cont.
weld crater cracks (star or spider cracks)
occur at the end of a weld run
Cont.
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Primary Processing Flaws Cont.
weld heat-affected zone cracks
occur because of stress induced in the
material adjacent to the weld by its
expansion and contraction from thermal
changesCont.
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Primary Processing Flaws Cont.
slag inclusion of nonmetallic solid
material within the weld forms on the surface of the weld during
the welding process
becomes imbedded when not removedprior to the next welding run
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Secondary Processing or
Finishing Flaws This category includes those flaws
associated with various finishing
operations heat treating
grinding
Cont.
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Secondary Processing or
Finishing Flaws Heat treating cracks are caused by
stresses setup by unequal heating or
cooling material thickness changes
stress risers
Cont.
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Secondary Processing or
Finishing Flaws Grinding cracks
thermal type cracks similar to heat treatingcracks and can occur when hardenedsurfaces are ground
usually shallow and very sharp, acts as astress riser as a potential source of fatiguefailure
Cont.
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In-Service Flaws
In-service flaws are formed after allfabrication has been completed and thepart has gone into service stress corrosion cracking
stress cracking
fatigue cracking
Cont.
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In-Service Flaws
Stress corrosion cracks can developwhen parts are placed under tensionstresses and are exposed to a corrosiveenvironment
Cont.
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In-Service Flaws
Stress cracking can occur when a partis stressed beyond the level for which itwas designed
Cont.
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In-Service Flaws
Fatigue cracks can occur in parts thathave been subjected to repeated orchanging loads while in service and aresurface connected will start at highly-stressed areas such as
stress risers
weld toe and HAZ undercut
lack of fusion arc-strike
chipping hammer damage
grinding cracks
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Factors and Considerations
Factors and considerations affecting theinspection critical nature of component
type of defect sought possible locations and orientations of flaws
maximum acceptable limits in size andallowable number of defects
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Codes and Specifications
Acceptance / Rejection criteria
Codes
example:
ASMESection V, Article IV
ASME B31.1
ASME B31.3
AWS D1.1
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Codes and Specifications
Know the code!