Fundamentals of Visual inspection

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Fundamentals of VisualInspection


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General.Visual examination can be an invaluable tool when properly applied.In addition to locating surface flaws, visual examinations can be anexcellent process control technique to help identify welder’s problems.

Visual examination is a method for identifying surface flaws andimperfections. Quality control program consisting essentially of visual

inspection should include a continual sequence of examinationsperformed during all phases of welding. This will allow visualinspection of the exposed surfaces as they occur in the weldingsequence.

It has been shown that a conscientious program of visual inspectionoccurring before, during, and after welding can result in discovery ofthe ma ority of all defects.

The sooner the examination process is introduced into the system,the better the coverage.


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Prior to Welding.!rior to welding, some typical action items requiring attention by thevisual inspector include"

#. $eview drawings and specifications.

%. &hec' qualification of personnel to be utili(ed.

). $eview materials to be utili(ed *heat number or + T stamp-.

. &hec' fit/up and alignment of weld oints.

0. &hec' preheat, if required.

If the inspector pays particularly close attention to these preliminaryitems, many problems which might occur later can be prevented. It isvery important that the inspector 'nows exactly what requirementsare to be met.


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Joint Fit-Up.1or a weld, the most critical part of the base material is that areawhich has been prepared to accept weld metal in some form of ointshape. The importance of the oint fit prior to welding cannot bestressed enough. Therefore, the visual examination of oint fit/up is ofhighest priority. Items that may be considered prior to welding include"

#. +rove angle

%. $oot openings

). 2oint alignment

. 3ac'ing

0. &onsumable insert

4. 2oint cleanliness

5. Tac' welds

6. !reheat

7ll of these factors could have a direct bearing on the resultant weldquality.


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Joint Fit-Up.

If the fit/up is poor, then the weld will most li'ely be of substandardquality as well. 8xtra care ta'en during the oint assembly can greatlyimprove welding effectiveness. 9ometimes, examination of the ointprior to welding will reveal irregularities within code limitations, but

these become areas of concern and can be watched carefully duringlater steps. 1or example, if a T/ oint for fillet welds exhibits anexcessive root opening, the si(e of the required fillet weld should beincreased the the amount of root opening present. 9o, if the inspector'nows that this situation exists, the drawing or weld oint can bemar'ed accordingly, and final determination of weld si(e compliancecan be correctly interpreted.


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After Welding.Many people feel that visual inspection commences once the welding hasbeen completed. However, if all of the previously discussed steps have beentaken before and during welding, this final phase of visual inspection will beaccomplished easily. It will simple provide a check to be sure that the stepstaken have resulted in a satisfactory weld. Some of the various items whichrequire attention after welding has been completed are:

. !inal weld appearance

". !inal weld si#e

$. %eld length

&. 'imensional accuracy

(. )mount of distortion

*he basic purpose of final weld inspection is to assure the weld+s quality.*herefore, visual e amination of several things are required. Most codesand specifications describe the e tent of the discontinuities that areacceptable, and many of these can occur on the surface of the completed

weld.


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Discontinuities.Typical discontinuities found in welds are"

:hile code requirements may permit limited amounts of some ofthese discontinuities, crac's, and incomplete fusion defects are neverallowed.

#. !orosity

%. Incomplete fusion

). Incomplete oint penetration

. ;ndercut

0.


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Discontinuities.!or structures e posed to cyclic or fatigue loading, the criticality ofthese surface discontinuities is increased. In conditions such asthese, visual e amination of the surface may be the most importantinspection which can be performed. *he e istence of undercut,overlap, and improper contour results in stress raisers- fatigueloading can cause premature failures which propagate from these

naturally occurring transitions. *hat is why, many times, the propercontour of a weld can be much more important than the actual weldsi#e, since a slightly undersi#ed weld, free of abrupt surfaceirregularities, could perform more satisfactorily than a weld ofadequate si#e e hibiting a poor contour.

*o determine if compliance has been attained, the e aminer shouldcheck to see if all welds meet drawing requirements for si#e andlocation. !illet weld si#es can be determined by using one of severaltypes of weld gages to rovide a more efficient and accuratemeasurement of si#e. /roove welds should be measured for properreinforcement on both sides of the 0oint.


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Butt Weld Splice otes.#. The bottom of all top flanges will be aligned.%. 9equence of welds" web first, lower flange second, and upper

flange last. ;se twin arc technique on web and lower flange.

). 3ac'ing strips and extension bars shall be used on welded splices.3ac'ing strips shall be plate % x 0x *flange= #>>-. 8xtension bars

shall be 0> long and same thic'ness as the smaller flange onwhich they are to be used with the same edge beveled as theflange plate.

. 7fter completion of the splice, remove the extension bars andbac'ing strip, grind smooth top, bottom, and edges of top and

bottom flanges and both sides of web. +rinding shall be doneparallel to length of beam.

0. &leaning and painting of weld area, after welding, shall be done inaccordance with +eorgia #??5 9upplemental 9pecifications9ection 0)0 and +eorgia #??0 @etric 9tandard 9pecifications9ection 0)0 and #??) 9tandard 9pecifications.


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Butt Weld Splice otes.4. :or' shall be protected from moisture, from any source, duringwelding and afterwards, until parts welded have cooled to

atmospheric temperature. Aeave web cope holes open.

5. 1or other minimum preheat and interpass temperature andinformation concerning welded splices, see +eorgia #??59tandard 9upplemental 9pecifications 9ection 0>#.>0, 9teel9tructures. BB *excluding 85># and 85>% - lowhydrogen electrodes shall be used for manual shield metal arcwelding.

6. :hen welding 79T@ 75>?@ +rade %0> and 79T@ 75>?@ +rade) 0 steel, welding shall be done using specifications of highergrade steel.

?. The minimum radius of the coping hole is %0 @@. The fabricatorwill determine the radius of the coping holes in such a manner asto provide a smooth transition between coping holes.


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Discontinuities - !rac"sHot 1racks 2 develop at3near Solidification


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Discontinuities - !rac"sHot 1racks 2 develop at3near Solidification


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!rac"s.1racks form in the weld and base metal when locali#ed stresses e ceed theultimate strength of the material. 1racking may occur at elevatedtemperatures during weld metal solidification, or after solidification, when theweldment has equali#ed in temperature. 1racking is generally associated withstress amplification near discontinuities in welds and base metal, or nearnotches associated with the weld 0oint design. High residual stresses aregenerally present, and hydrogen embrittlement is often also a contributor tocrack formation. %elding related cracks are generally brittle in nature,e hibiting little plastic deformation at the crack boundaries. 4arious types andlocations of weld #one cracks, some of which will not be visible during visuale amination of the weld surface.

1racks can be classified as either hot cracks or cold cracks. Hot cracksdevelop at elevated temperatures. *hey form on solidification of the metal attemperatures near the melting point. 1old cracks develop after solidification iscomplete. 1racking associated with hydrogen embrittlement, commonlyreferred to as 5delayed cracking.6 Is a form of cold cracking. Hot crackspropagate along grain boundaries. 1old cracks propagate both along grainboundaries and through grains.


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#$roat !rac"s.Throat crac's are longitudinal crac's in the weld face in the direction of the weldaxis. They are generally, but not always, hot crac's.


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%oot !rac"s.$oot crac's are longitudinal crac's in the weld root. They are generally hotcrac's.


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!rater !rac"s.&rater crac's occur in the weld crater and are formed by improper termination ofthe welding arc. 7 nonstandard term for crater crac's is star crac' though theymay have other shapes. &rater crac's are shallow hot crac's usually forming amulti/pointed star/li'e cluster.


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#oe !rac"s.Toe crac's are generally cold crac's. They initiate and propagate from the weldtoe where restraint stresses are highest. 7brupt profile changes at the toecaused by excessive convexity or weld reinforcement can amplify stresses,ma'ing the weld toe a more li'ely area for crac'ing to occur.

Toe crac's initiate approximately normal to the base metal surface. These

crac's are generally the result of thermal shrin'age stresses acting on a weldheat affected (one. 9ome toe crac's occur because the transverse tensile

properties of the heat affected (one cannot accommodate the shrin'agestresses that are imposed by welding.


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Under&ead and

'eat Affected (one !rac"s.;nderbead and heat affected (one crac's are generally cold crac's that form inthe heat affected (one of the base metal. ;nderbead and heat affected (onecrac's can be either longitudinal or transverse. They are found at regularintervals under the weld and also outline boundaries of the weld where residual

stresses are highest. ;nderbead crac's can become a serious problem.


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Discontinuities - Fusion

@olten weld metal running over unmelted base metal

1aulty electrode manipulation


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Incomplete Fusion.Incomplete fusion is termed as fusion which does not occur over the entire basemetal surfaces intended for welding and between ad oining weld beads.

Incomplete fusion can result from insufficient heat input or the impropermanipulation of the welding electrode. :hile it is a discontinuity more commonly

associated with weld technique, it could also be caused by the presence ofcontaminants on the surface being welded.


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Undercut.;ndercut creates a transition which should be evaluated for a reduction in crosssection, and for stress concentrations or notch effect which fatigue is aconsideration. ;ndercut, controlled within the limits of the specification, is notusually considered a weld defect. ;ndercut is generally associated withimproper welding techniques or weld parameters, excessive welding currents orvoltages, or both.


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)*erlap.


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Discontinuities - Penetration

!rocedure C preparation conflict

Inept welding shop supervision

1ailure to penetrate to oint root caused by improper procedure"


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Incomplete Joint Penetration.Incomplete oint penetration is defined as penetration by weld metal that doesnot extend for the full thic'ness of the base metal in a oint with a groove weld.The condition shown for the single V/groove weld will only be evident usingvisual examination if there is access to the weld root side. The condition shownon the double bevel T/ oint will not be evident on the completed weld, except atthe starts and stops.

Incomplete oint penetration may result from insufficient welding heat, improperlateral control of the welding arc. @any designs call for bac' gouging the weldroot with subsequent welding on that same side to ensure that there are noareas of incomplete oint penetration or incomplete fusion.


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Discontinuities - Welding

;nsuitable welding parameters

Inappropriate arc manipulation

;sually no ma or significance but detracts from appearance

Spatter:

Aive part of welding circuit ma'es accidental ob contact

&orrective action required

)rc Strike:

Improper starting technique

oor *ie2In:


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Spatter.9patter consists of metal particles expelled during fusion welding that do notform a part of the weld. Those particles that are actually attached to the basemetal ad acent to the weld are the most disconcerting form of spatter. !articleswhich are thrown away from the weld and base metal are, by definition, spatter.In total, spatter is particles of metal which comprise the difference between theamount of filler metal melted and the amount of filler metal actually deposited in

the weld oint.

Dormally, spatter is not considered to be a serious flaw unless its presenceinterferes with subsequent operations, especially non/destructive testing.


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Arc Stri"es. 7n arc stri'e is a discontinuity consisting of any locali(ed remelted metal,heat/affected metal, or change in the surface profile of any part of a weld orbase metal resulting from an arc. 7rc stri'es result when the arc is initiated onthe base metal surface away from the weld oint, either intentionally oraccidentally. :hen this occurs, there is a locali(ed area of the base metalsurface which is melted and then rapidly cooled due to the massive heat sin'

created by the surrounding base metal. 7rc stri'es are not desirable and oftennot acceptable, as they could lead to crac'ing during the cooling process orunder fatigue conditions.


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Discontinuities - Penetration Don/metallic

9lag


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Slag Inclusion.9lag inclusions are nonmetallic solid material entrapped in weld metal orbetween weld metal and base metal. 9lag inclusions are regions within the weldcross section or at the weld surface where the once/molten flux used to protectthe molten metal is mechanically trapped within the solidified metal. Thissolidified slag represents a portion of the weld’s cross/section where the metal isnot fused to itself. This can result in a wea'ened condition which could impair

the serviceability of the component. Inclusions may also appear at the weldsurface. Ai'e incomplete fusion, slag inclusions can occur between the weldand base metal or between individual weld passes. In fact, slag inclusions areoften associated with incomplete fusion.


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+easurements of Welding -Fillet Welds @ost used

:eld strength / E8ffective Throat’

:eld cost / function of weld si(e

!illet welds:


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+easurements of Welding -Fillet Welds @ost used

:eld strength / E8ffective Throat’

:eld cost / function of weld si(e

!illet welds:


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Fillet Weld Gage.The fillet weld gage offers a quic' means of measuring most fillet welds, of #C6in. *).% mm- through # in. *%0 mm- in si(e. It measures both convex andconcave fillet welds. To measure a convex fillet weld, the blade representing thespecified fillet weld si(e with the concave curve should be selected. The loweredge of the blade is placed on the base plate with the tip of the blade moved tothe upright member.

To measure a concave fillet weld, the blade representing the specified fillet weldsi(e with the double concave curve should be selected. 7fter placing the loweredge of the blade on the base plate with the tip touching the upright member, thepro ection formed by the double curve should ust touch the center of the weldface. This will measure throat si(e for the specified weld si(e. Fowever, if the

center portion of the gage does not touch the weld, the weld has insufficientthroat si(e.


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+easurements of Welding -Fillet Gages&onvex +age measures weld si(e from Eleg’ length *% measurements-


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+easurements of Welding -Fillet Gages&oncave +age measures throat // weld si(e read directly from gage butderived from" 9GTC>.5>5

Fundamentals of Visual inspection

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