Defecte La Sudura
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Transcript of Defecte La Sudura
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Welding defects1
The purpose of this training material is to
tell about various welding defects and their
effects to the strength of metal construction,
and also how to avoid welding defects.
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Welding defects2
THE WELD : The weakest point of metal construction?
Reasons why the welded seam is weakest point of metal construction: Welding defects
Wrong sequence of welding
Welding stresses
Welding deformation
Base material overheating
Characteristic of material variation
Damage usually starts from area of welded seam
Weakness of welding seam is a result of Welding defects
A weld which is made the correct way is as strong and as hard as otherparts of the metal product
F F
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Welding defects3
How to eliminate welding seam faults?
Careful and faultless welding work
Correct filler material selection
Use the correct welding parameters and welding technique
Work according to the WPSs ( Welding Procedure Specification )
Follow the manufacturers instructions and recommendations
Follow the heat input recommendation
For impact ductility and strength F F
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Welding defects4
What is welding defect?
Discontinuity in the weld Difference in the form of the weld
Welding defects are for example:
Cracks in the weld
Failure in penetration
Undercutting
Porosity in the weld
Lack of fusion
Spatter
Welding defect means: Deviation from perfect weld
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Welding defects5
Welding defects are grouped to the following six main groups:
Cracks Lack of fusionCavity Wrong shape
Solid inclusion Dimensional error
Welding defects can be divided roughly to the three groups:
Wrong shapes
Surface defects
Internal weld defects
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Welding defects6
Two-dimensional defects are flat surface and known also as crack
type defects
Two-dimensional defects are sharp-pointed:
Very dangerous for joint durability
Two-dimensional defects are:
Various cracks
Lack of fusion
Short joint penetration
Surface and internal weld defects are grouped to two and
three-dimensional:
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Welding defects7
Three-dimensional defect also known as volumetric, ball-shapeddefect or cylindrical without sharp pointed shape
Three-dimensional defects are:
Pores and other cavities
Inclusions, if they have not sharp-pointed shape
Undercuts, if they have round bottom
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Welding defects8
Micro crack
Longitudinal crack
In weld metal
On fusion line
On heat affected zone In base material
Cross crack
In weld metal
On heat affected zone
In base material
Cracks on the welding area: ( Cooling down and strength causes these cracks)
Welding zone
Fusion zone
HAZ Heat affected zone
Heat affected area
Base material
Fusion line
Weld metal
Base material
HAZ
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Welding defects9
Radiation crack
In weld metal
On heat affected zone
In base material
Crater crack To longitudinal direction
Across
Radially
Cracks on the welding area: ( Cooling down and strength?? causes these cracks
Welding zone
Fusion zone
HAZ Heat affected zone
Heat affected area
Base material
Fusion line
Weld metal
Base material
HAZ
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Welding defects1
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Crack group
In weld metal
In heat affected zone
In base material
Branch crack In weld metal
In heat affected zone
In base material
Cracks on the welding area: ( Cooling down and strength causes these cracks )
Welding zone
Fusion zone
HAZ Heat affected zone
Heat affected area
Base material
Fusion line
Weld metal
Base material
HAZ
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Welding defects1
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Some crack types which appear during or after welding
Hot cracks
Cold cracks
Hydrogen cracks
Seasoning crack
Cracks are most dangerous welding defects
A crack could be a signal of larger problems in welding
Wrong selection of base material
Failure in welding instructions
One welding seam can include one or several cracks
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Welding defects1
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Hot cracks in the weld
Longitudinal solidified crack in weld metal
Often, on the center line of welded seam or on fusion line
Form in high temperature when weld pool starts to solidify
Can also appear on fusion line or as a cross crack in heat effected zone
Welding seam can be broken only from surface or through whole seam
Hot cracks in the heat effected zone Hot cracks in heat effected zone are short, only 1 - 2 mm long
Can also be called by name melting cracks
Hot crack on center line Hot crack inside welding seam Hot crack on fusion line Hot cracks in heat effected zone
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Welding defects1
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Metallurgic factors
The solidification area and its width
The chemical composition
The micro structure
Geometrical factors The shape of welding groove ( length / width relationship )
Strength factors
The plate thickness
The steel construction and its stiffness
Depth
Width
Wrong depth / width relationship
Width
Depth
Correct depth / width relationship
The causes of hot cracking
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Welding defects1
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Effect of weld profile to the cooling and appearance of hot cracks
Cooling direction
Crack
Wrong Pass form
Molten weld pool
Cooling direction
Correct Pass form
Molten weld pool
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Welding defects1
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Prevention of hot cracking
Always select welding parameters so that depth / width ratio is >1 Surface of the weld joint must be cleaned from impurities
Welding with smaller parameters / penetration decrease the risk
Use a smaller air gap
Weld so that the welding stress is minimized
Weld so that the fillet weld becomes a little bit convex
Decrease the welding speedGood pass form
Worse pass form
Depth / width ratio > 1
Narrow and deep
Too fast welding speed
Correct welding speed
Weld pool Welding seam
Good pass formWorse pass form
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Welding defects1
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Hydrogen creates cracks together with stresses to the areaof microstructure which is hardened
Hydrogen cracks appear under 150C temperature
Hydrogen cracks have various names like:
Cold cracking Hardening cracking
Delayed cracking
Hydrogen cracks appear in the hardenable steels
If martensitic structure increases in the weld metal
Hydrogen crack
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Welding defects1
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Hydrogen cracks appear in places, which are:
The heat effected zone of the base material In longitudinal direction, under the welding seam
In the root, as a root crack
In the fusion line, beside welding seam
Across or longitudinal, in the heat effected zone or welding seam
Starts and stops of welding
Edge crack
Underbead crack
Root and longitudinal
crack
Cross crackEdge crack Underbead crack Root and longitudinal
crack
Cross crack
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Welding defects1
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Reasons that can cause hydrogen cracking
High carbon or blend components content in base material Too low or high welding energy / heat input
Large plate thickness or construction stiffness
Too low preheating or too low temperature between two
passes
Too much hydrogen in the weld metal or in filler material A groove profile, which increases strength in root weld
Too rapid cooling speed of weld metal ( frost etc )
Impurities in the welding joint
Humidity or moisture in the weld seam
The wrong heat treatment
Edge crack
Underbead crack
Root and longitudinal
crackCross crack
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Welding defects1
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Prevention of hydrogen cracking
Select base materials which have a low content of carbon or alloyingcomponent
Use a welding process where the content of hydrogen is as low as possible
( MIG / MAG )
Take care of the filler material storing and re-drying
Clean the surfaces of welding joint before welding Use sufficiently big heat input which is suitable for welding
requirements
Use preheating with thick base materials
Use post-heat treatment if possible
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Welding defects2
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Content of hydrogen in various welding process
Filler material Very low Low Medium Plenty
5 10 15 20 25 30
Hydrogen contest in weld metal HD ( ml / 100 g )
MMA rutile electrodes
FCW
SAW
MIG / MAG solid w ire
MMA basic electrodes
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Welding defects 1
Crater cracks
Longitudinal crater crack Cross crater crack
Star form crater crack
Grain structure change creates of crater crack
Wrong ending technique of welding
Prevention of crater crack
Return movement in the end of welding and stop welding on the welding seam
Use the crater filling function of the welding machine
Decrease welding parameters / Energy with Minilog function
Fill the end crater by short spots during end of weld metal cooling time Use ending plates which are cut away after welding
Crater crack
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Welding defects 2
Cavity and porosity types Single cavity
Ball-shaped gas cavity
Smooth porosity
Porosity group
Localized porosity
Formed group of various pores
Cavity and porosity inside the welded seam
Linear porosity
Longitudinal linear porosity in the weld
Elongated Porosity
Longitudinal big pore
Surface pore
Open to the surface of welded seam
Single crack
Smooth porosity
Localised porosity
Linear porosity
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Welding defects 3
Reasons that can cause cavity and porosity
Gas pores inside welding seam, can come from:
Filler material moisture Rust, oil and other impurities
Thick paint layer on the welding area
Poor gas shielding in the MIG / MAG welding
Wind in the welding environment
Too low shielding gas flow
Too big shielding gas flow
High shielding gas flow in start
Water or oxygen in the shielding gas
Too long welding arc or too high welding speed
Too large oscillation or too long stick out length
Too small welding power
Cavities insde of weld
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Welding defects 4
Prevention of the cavity and porosity
Eliminate impurities from the base material surface
Eliminate wind from the welding area
Keep filler material dry from moisture and humidity
Clean and dry surfaces of the welding joint
Check the gas flow
Check the gas flow hoses and flow meter
Increase welding current sufficiently
Use correct the welding parameters ( U, I, Wfs )
Use correct the arc length and travel speed
Dont use too wide oscillation ( max gas nozzle diameter )
Use multi pass welding technique Preheating eliminates risks with thick base materials
Weld seam without cavities
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Welding defects 6
Prevention of slag and oxide inclusions
Remove slag or oxide carefully from weld surface
Make the root opening with a grinding machine until the pure part of the weldis visible
Weld seam so that the weld profile is not too high
Point the welding arc correctly in to the welding groove, to the edges
Make sure that the slag and weld metal are not mixed into the welding arc
Use the correct welding parameters
Use the correct travel speed
Wrong seam form
Critical point for slag inclusion
Smooth seam form decrease risk of
slag inclusion in multi pass welding
Welding defects2
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Welding defects 7
Reasons that can influence Tungsten inclusions ( TIG )
Tungsten electrode touches the weld pool in the beginning or during TIG welding
Head of Tungsten electrode is melts ( too small Tungsten diameter ) Wrong type / alloy of Tungsten electrode
Melted part of electrode goes to the weld pool
Scratch ignition
Broken electrode head inside weld pool
Wrong shielding gas
Oxygenous shielding gas
Dirty base material
Rust, oil, paint, humidity
Air contamination of Tungsten electrode
Tungsten inclusion ( TIG )
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Welding defects 8
Grain of crater crack
Part of copper contact tip is melted to the weld pool
Over heated contact tip ( Cooling disturbance )
Too small MIG gun ( > 250 - 300 A use water cooled MIG gun )
Too short stick out length
Non original and Non genuine consumable parts Prevention of copper inclusion
Use original consumable parts
With spray arc welding use M 8 thread current tips
Check the operation of water cooling
Increase stick out length ( max 25 mm )
Clean spatter carefully from welding head to eliminate arc inside gas nozzle
Too long contact tip can cause copper
inclusion if it touch to the weld pool
Copper inclusion ( MIG )
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Welding defects 9
Incomplete joining between the weld metal and the basematerial or between intermediate welding passes
Joint surface
Between welding passes in multi pass welding
Infusible root face in root seam ( lack of fusion in root pass )
Sometimes also called, lack of side weld fusion or lack of side wall fusion
Lack of fusion
Lack of fusion in a joint surfaceLack of fusion in a root pass
Lack of fusion between welding passes
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Welding defects Reasons that can cause lack of fusion
Molten weld metal rolls in front of the welding arc on the cold base material
Too low welding speed
Too high wire feed speed to the selected welding voltage
Too high welding current in relation to the welding speed
Faulty MIG gun / electrode angle
Too narrow groove angle
Spray arc welding out of position is forbidden
Too wide oscillation
Too small welding power
Too long arc length
Magnetic arc blow ( MMA ) Impurities in fusion face
Molten weld metal rolls to the front
of welding arc and cause lack of
fusion
Welding defects3
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Welding defects Prevention of lack of fusion
Use correct welding technique
Welding parameters
Welding speed
MIG gun angle and stick out
Use correct recommended types and sizes of welding grooves
Use correct welding power
Use correct arc length
Use correct groove angles and openings
Change position of earth cable to the better place in work piece ( MMA )
Clean surfaces of welding joint and passes
Wire brush / Grinding machine
Grinding disc / Grinding machine
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Welding defects
Separation between real and nominal penetration Appears, when fusion face or faces are not melted
If requisite penetration is not reached
Incomplete penetration
Incomplete penetration in fillet weld Requisite penetration
Incomplete penetration in V- groove root pass
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Welding defects Reasons that can cause incomplete penetration
Incorrect joint shape
Too high root face
Too small air gap
Too small groove angle
Wrong MIG gun / MMA electrode angle
Misalignment
Wrong MIG gun angle Too small welding current / welding energy
Too thick filler material
Wrong location of the seams in butt joint welding
Especially when welded from both sides
Perpendicularity Slag or oxide is rolling to the front of welding arc
Misalignment in the joint
Wrong location of the seams
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Welding defects
Incorrect shape of the weld seam Means incorrect surface profile of welded seam ( top and root side )
Incomplete geometry of welded seam
Correct parameters, travel speed and welding technique together
with the correct weld groove dimensions guarantee good weld
results
Wrong weld shape and dimensions
h = 0,1 x b + 1,5 ( mm )
h1= 0,1 x c + 1,5 ( mm )
h1
h
b
c
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Welding defects
Appears in the base material, beside the welding seam Longitudinal or discontinuous cavity, which the molten weld
metal has not filled
Different types of undercutting
Continuous undercut
Discontinuous undercut
Root side undercut
Undercut between welding passes
Local undercut
Continuous undercut
Continuous undercut Discontinuous undercut
Undercut between welding passes
Undercut
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Welding defects Prevention of undercut
Use correct welding current / energy
Use correct and constant stick out length Use correct MIG gun / MMA electrode angle
Use correct arc length
Use correct and constant travel speed
Correct tendency of welding arc
Point arc to the lower plate in fillet weld
Use only small oscillation if its needed
Use multi pass technique in fillet joint
In case of openings dont try to fill large gaps with single pass
In large openings, fill gaps with root pass before top pass
Better welders location to improve visual contact
Correct tendency of welding arc
1.0 mm from corner of the fillet weld
1 - 2 mm
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Welding defects
Unsymmetrical fil let weld
What is a unsymmetrical fillet weld A fillet weld that has been welded uneven or irregularly to 1 plate
The welding seam lays too much on the lower plate side
Unsymmetrical weld causes typically undercut and lack of fusion to vertical plate
Reasons that cause unsymmetrical fillet weld
Wrong welding gun angle
Too high welding parameters
Too low travel speed
Prevention of unsymmetrical fillet weld
Use correct welding gun angle
Decrease productivity or increase welding speed
Correct profile
Unsymmetrical profile
Correct / Unsymmetricalfillet weld profile
Welding defects4
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Welding defects
Appears in one side or on both side of root pass Reasons that can cause undercut in root pass
High root face of the welding groove
Too small / large air gap
Too small / big welding current / energy
Wrong welding technique
High pressure of backing gas ( TIG )
Prevention
Use the correct size air gap and root face
Use the correct welding energy and backing gas pressure
Use the correct oscillation and delay time in both groove edges
Undercut in root of welding seam
Undercut on both side of root pass
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Welding defects
Too much weld metal in a welding seam
Too high cap form in the welded seam
Reasons that can cause excess weld metal
Too slow welding speed compared to the productivity of filler material
Too low capacity of groove or joint without groove ( V,X and Y etc.)
Too thick diameter of filler material ( TIG welding )
Prevention Correct welding parameters
Correct groove type and size
Correct filler material diameter
Correct welding technique
Less full weld groove before top pass
Too high cap form in fillet weld
Too high cap form in butt weld
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Welding defects
Too much weld metal in a welding seam
Too high cap form in the welded seam
Reasons that can cause excess weld metal
Too slow welding speed compared to the welding productivity
Too high filling or too small grinding of the filling pass
Too thick diameter of the filler material ( MMA / TIG welding )
Too short delay times in the weld edges Prevention
Correct welding parameters
Correct groove type / size and grinding
Correct filler material diameter ( MMA / TIG )
Correct welding technique ( oscillation / delay time )
For top pass in MIG must
leave space 1,0 - 2,0 mm
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g
Excessive root profile Protrusion of root is too large from the base material
surface
Also known with the name excessive penetration
Various types of excessive root profile
Local high root reinforcement
Constant high root reinforcement
Through excessive penetration
Excessive root profi le
High root reinforcement
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g Reasons that can cause excessive root profile
Too large air gap
Too small root face Wrong welding parameters
Too short arc length
Too low welding speed
Too big MIG wire / MMA electrode diameter
Prevention
Correct the air gap and root face
Correct the welding speed and energy
Correct the oscillation movement
Correct the stick out length More delay time in the weld edges
0 - 4 mm
min 60
2 - 6 mm
> 10 mm
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gRoot concavity What is a root concavity?
Groove in a root cap which is created contraction and the root edges are melted Reasons that can cause root concavity
Too large root face in a welding groove
Too small air gap or variations of air gap
Too high welding speed
Too small welding energy
If backing gas pressure is too high ( TIG )
Prevention of root concavity
Use the correct size of root face and air gap
Use the correct welding energy Decrease the pressure of the backing gas ( TIG )
Root concavity in root cap
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g
Steep joining of the welded seam means Joint between the welding seam and the base material is too steep
Steep joining
Steep joining in the edge of welding seam
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gSteep joining on a weld edge
Appears on the edge of a welded seam
Weld metal has flowed to the surface of base material with out fusion
On the top of welding seam or on root side
Is normally caused by too high wire feed speed
Wrong use of backing bars cause steep joining on root side
Wrong MIG gun angle
Too low arc Voltage ( MIG )
Excessive penetration on root side
Excessive penetration on the top of welding seam
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g
What is welding spatter
Molten drops which fly out from the welding arc or molten weld pool and stick
to the surface of base material
Reasons that can cause spatter
Wrong welding parameters
Voltage, wire feed speed and arc length are not in balance
Too low or too high welding power
Variations of stick out length
Wrong MIG gun angle
Changes in openings between base materials
Impurities on base material surface
paint, rust, oil and humidity Often steel spatter starts corrosion on the base material ( thin paint layer )
Welding spatter
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Welding spatter
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Welding spatter
Prevention of welding spatter
Use the correct welding parameters for each welding case
Joint type ( butt joint, V-groove, X- groove etc. )
Out of position welding ( horizontal, vertical up / down , over head )
Use the correct welding power for each welding case
Keep stick out length constant
Weld with the correct MIG gun angle Remove impurities from the base material surface
Use anti spatter spray ( MIG )
Keep the MIG gun welding head and liner clean
Use the correct size MIG gun
Argon based mix gases produce less spatter than CO2
Use correct current in MMA welding
Welding defects5
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Spatter removal
Sand or glass ball blasting
Manual or machine wire brushing
Grinding with discs or with special grinding wheels
Mechanical cleaning with a file / chisel
Minimizing spatter
Thin primary paint decreases sticking of spatter to base material ( FCW ) Anti spatter spray layer over base material decreases the spatter sticking
Spray arc welding with Ar + CO2 decreases spatter
Use of FCW wire decrease spatter
Use of Synergic Pulse-MIG decrease spatter
Mechanized welding decrease spatter
Cleaning of spatter