iiw -welding defects

7/21/2019 IIW -Welding Defects

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Definition :

The change in the geometry or composition of an

object, it may be intentional or unintentional.

Such changes inherently affect the physical propertiesof the object and may in turn have an effect on the

objects ability to fulfill its intended use or service life.

Every discontinuity is not a defect but every defect is adiscontinuity.



Discontinuity is categorized in four stages

Inherent discontinuities.

Primary processing discontinuities.

Secondary processing discontinuities.

Service induced discontinuities.



Porosity

Location : Surface or Subsurface

Cause : Vaporized constituents in the molten eld metal are entrapped

during solidification.



Cluster Porosity


Cause : Vaporized constituents in the molten eld metal are entrapped

during solidification.



Slag nclusion

Location : Subsurface

Cause : Improper cleaning of previous eld pass and mi!ing of o!ides

on the base metal surface into the eld pool



!ac" of Penetration


Cause : Inade"uate penetration of the eld #oint root by the

eld metal.



!ac" of #usion

Location : SubsurfaceCause : $ailure of filler metal to coalese ith the base metal



joint groove can be characterised as follo$

% i& The distance that fusion e'tends into the

base metal is called depth of side$all

fusion

% ii& Depth of $eld bead in previous $eld

bead is called penetration depth,



()*+ : ead to ead Penetration

(-*+ : Side (all #usion

d : Penetration depth



#actors affecting Side$all #usion

% (elding oltage

% (elding Current

% (elding Speed% Shielding gas

% Cast of Electrode



%ider $used &one

Sideall

'ndercutting

Slag (ntrapments

)urn )ac* of the +ip

,ptimal

Voltage

Loer -eat Input

Lesser -eat Into the Sideall

Incomplete $usion into the Sideall

Intensive Spatter Short Circuiting

(elding oltage



(elding Current

%Deposition rate, arc stability and bead geometry $ill effectby $elding current. (eld bead depth $ill increase $ithincreasing $elding current. Current is basically directfunction of the $ire feed rate. Deposition rate $ill increase$ith increasing the $ire feed rate. ncreasing current

results into deep penetration into the bottom of the jointmuch faster than into side$alls and there $ill beunfavorable bead configuration.

% To over come this problem the current is "ept proportional

to travel speed.



(elding Speed

% (elding speed is set accordance $ith other$elding parameters /namely $elding current,$elding voltage&.

%(eld bead $idth is inversely related to travelspeed. 0t lo$ travel speed, a large molten poolmay be created, $hich $ill flo$ under the arc. tmay cause incomplete fusion into the side$allsand bet$een layers of deposited metal.

% 0t high $elding speed, heat input $ill beminimum and it $ill leads to incomplete fusion tothe side$alls.



% Shielding gas : Penetration pattern

/0r,C1- and 2i'ture&

% C1- have higher thermal conductivity than argon. #or a

given $elding current and arc voltage, the heat input is

higher for more thermally conductive gas, $hich resultsinto deeper penetration and higher deposition rates. The

greater penetration of C1- usually allo$s the use of

higher $elding speed. Thus, higher $elding speed and

higher deposition rate provides higher productivity in$elding



% The addition of C1- gas /in argon& dissociates $ith increasingtemperature into carbon mono'ide and o'ygen. This liberated o'ygenreact $ith iron and forms #e1. This #e1 is easily melted at higher

temperature and remain fluid. This increases the fluidity of the $eldpool and the ease $ith $hich it $ets the side$alls and also improvedthe bead shapes, the height of over fill is greatly reduced and $eld$idth is increased. This change in bead shape may be because ofreduction in surface tension of molten metal in the $eld pool



% Suc" ac"


Cause : here the eld metal has contracted as it cools and has been

dran up into the root of the eld.



nternal 3ndercut

Location : Surface

Cause : ,ver sized eld pool /related to e!cessive amperage0 travel

speed and electrode size.1



E'ternal 3ndercut

Location : Surface

Cause : ,ver sized eld pool /related to e!cessive amperage0 travel

speed and electrode size.1



1ffset or mismatch

Location : Surface

Cause : here to pieces being elded together are not properly

aligned.



Cold 4 5ot Crac"

Location : Surface or Subsurface.

Cause : 2 combination of atomic hydrogen0 hardenable material

and high residual stress.



nade6uate $eld reinforcement!ocation : Surface



E'cessive $eld reinforcement



Tungsten nclusion


3olten pool or filler metal comes in contact ith +ip of +ungsten

(lectrode



urn Through


Cause : +oo much heat causes e!cessive eld metal to penetrate

the eld zone



Secondary processing Dis.

+rinding Crac"s!ocation : Surface

Cause : !ocali7ed overheating of the material due toimproper grinding procedures.

5eat Treating Crac"s!ocation : Surface

Cause : 3neven heating and cooling that producesstresses e'ceeding the tensile strength of the material.

8uench Crac"s

!ocation : Surface

Cause : Sudden cooling from elevated temperature



Service induced discont.

#atigue

Location : Surface

Cause : Cyclically applied stress belo the ultimate tensile strength.

Creep

Location : Surface

Cause : 3aterial sub#ected to elevated temperatures and stress belothe yield strength.

Stress Corrosion Crac"ing

Location : Surface

Cause : Combined effect of static tensile load and corrosiveenvironment.

5ydrogen Crac"ing

Location : Surface

Cause : Combined effect of applied tensile or residual stress andhydrogen enriched environment.

iiw -welding defects

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