Welding Defects - Types, Causes and Remedies

List of various welding defects are as follow :


list of welding defect

(1) Cracks :


The crack in a weld may be a discontinuity produced either by the tearing or fracture of the metal. A crack occurs in the weld by tearing when it is in a plastic state and is solidifying from the molten state and still above 550 degrees. This is caused due to more Sulphur contents in the weld metal and inadequate quantity of manganese to take care of Sulphur. Fracture of the weld occurs due to uneven cooling of the weld and improper welding techniques. A crack visible at the weld surface is called surface crack and that inside the weld and not visible from outside is called internal crack.

Following reason are responsible for the occurrence of the cracks :


  1. The hardness of the joint
  2. Ductility of the base metal
  3. Hardenability & presence of Sulphur & carbon in the base metal.
  4. Concave shaped weld bed
  5. More travel speed during arc welding
  6. Uneven contraction of the joint
  7. More hydrogen content in an electrode
  8. Improper welding method.


Reason for crack
Remedies
1.      High rigidity of joint

  •   Preheating
  •   Residual stress relieving
  •   Reduction of shrinkage stresses by using back step or block welding.

2.      More sulphur content in metal

  •   Add filler metal having less sulphur content.

3.      Too much dilution
  •   Change welding current and speed
  •   Connect electrode with negative terminal and   arrange for face end butter before starting   welding.

4.      Defective electrode
  •   Change electrode or carryout baking of   electrode for removing moisture.

                                            
(2) Distortion :


portion or base metal under an arc during welding gets heated. While the cooling starts where the weld is completed. This is causing a considerable difference in temperature different parts of the workpiece. Due to this difference Of temperature, some portion of the workpiece may expand &
may contract. This type of happening causes weld distortion, which is three dimensional.

This defect may be Of three types :

1. Longitudinal shrinkage parallel to the weld line.
2. Transverse shrinkage perpendicular to the weld line.
3. Angular changes caused around the weld line. 

 Reason for distortion are as under :

  1.  To take more than one pass using small diameter electrode. 
  2.  Arc speed is less. 
  3.  Type of groove. V groove allows more metal filling in comparison to U-groove, hence more distortion is caused in v-groove weld. 
  4.  More residual stresses present in the base metal. 
  5.  Improper welding method. 


To prevent these types of distortions following remedies such as:

  1.  Keep contraction Index as less as possible by filling the weld using only required amount of filler metal.  
  2.  Keep centroid of weld & part cross-section nearer. Keep weld nearer to neutral axis & achieve equal weld around the axis. 
  3.  proper tacking should be done. 
  4.  Keep required or slightly more arc speed. 
  5.  Use the double groove to reduce angular distortion. 
  6.  Complete welding in minimum numbers of weld pass. 
  7.  Use back step or skip-technique. 
  8.  prepare the joint such that shrinkage forces act in desired direction & prove helpful. Complete the joint so that the effective force becomes zero. 
  9.  Remove the unwanted forces left after welding. 


(3) Incomplete penetration :



Incomplete penetration refers to the ability of an arc to reach or penetrate a narrow corner and this defect can be overcome in extreme cases by using deep penetration electrode or high current.

Incomplete penetration defect is caused by the following reasons :


  1.  Failure of root face of a butt weld to reach fusion temperature for its entire depth.
  2.  Failure of weld metal to reach to the root of a fillet weld leaving a void.
  3.  Use of oversize electrode
  4.  High travel speed of the electrode
  5.  Less current and more arc length
  6.  Improper design of the Joint
  7.  The root surface is greater than required and groove is small.
  8.  Electrode angle with the work surface Is less than 70 to 80 degree.
  9.  The wrong polarity of electrode & method of holding electrode. 


Reason

Remedies

       1.      Thick root face & insufficient root
  • Design joint of proper geometrical shape.

       2.      Oversize electrode
  • Use electrode of small diameter and more root opening.

       3.      Insufficient heat
  • Follow the welding process correctly

       4.      Slag is floating nearer to arc
  • Arrange proper position of electrode or workpiece.



(4) Inclusion :


Slag and other foreign matter entrapped in the weld during welding arc called inclusions. Such matters do not found opportunity to float above the surface, they remain inside the weld. This may disturb the continuity of the weld and reduce the strength of the joint.

This defect is caused due to the scale, corrosion, dust and dirt present on the surface of workpiece and electrode. If this inclusion is allowed to float on the molten weld metal during cooling, then it will form a slag on the weld surface and it can be easily removed by chipping.

Reasons for inclusions are as under : 


  1.  Incorrect Joint preparation 
  2.  The incorrect size and type or electrode 
  3.  Higher current 
  4.  Lower arc length 
  5.  Inadequate cleaning of each run during multi-run welding 
  6.  Improper welding technique 
  7.  Incorrect tacking 
  8.  Joint angle kept is less. 


Reason
Remedies
       1.     Slag is not removed.
        1.  Clean the weld surface before starting each new pass.
       2.      Presence of refractory oxide.
         2.  Clean the weld bed by wire brush.
       3.      Tungsten present in the weld metal.
        3.  Use electrode having more diameter to prevent contact between electrode and workpiece.
       4.      Pieces of electrode coating are in the joint.
        4.  Prevent the use of damaged electrode.


(5) Porosity and Blow-holes :


During welding, the gases dissolved from the atmosphere into the weld metal are released out during solidification and cooling of weld. These gases cause blow holes and porosity in the weld. A crowded group of gas pores in the weld is called porosity.

A large gas cavity exceeding 1.5 mm in diameter is called blowhole. Both these defects are caused because of the use of a wrong electrode, excessive current, longer arc, poor weldability of base metal and improper welding technique.


                                 
Reason for porosity and blowholes
Remedies
       1.      More proportion of hydrogen, nitrogen & oxygen in atmosphere of welding.

 1. Reduce hydrogen in welding process, filler metal having more oxidiser and increase the shielding gas flow rate.
       2.      Fast rate of solidification
 2. Preheat or heat the workpiece more.
       3.      Base metal and filler metal are dirty.
 3. Clean the joint portion properly. Use clean filler wire and place them at the clean places.
       4.      Base metal-containing excess amount of sulphur
 4. Use electrodes with the basic slagging process.
       5.      Improper arc length and current
 5. Use proper welding conditions and process.



(6) Poor fusion :


Coalscence between base metal & filler metal should occur when both metals are in a molten condition. But some times during welding this is not happening. It is called poor fusion. Due to poor fusion stronger joint Is not made. These defects are seen at the root, sides or in between two weld beds in case of multipass weld.

The reasons responsible for poor fusion are as under:

  1.  Less current
  2.  More arc speed
  3.  Impurities on the job surface
  4.  Improper edge preparation
  5.  Use of improper electrode.
  6.  Use of improper welding process.


The remedies to prevent this defect are as under :


     
Reason for porosity and blowholes
Remedies
       1.      More proportion of hydrogen, nitrogen & oxygen in atmosphere of welding.

 1. Reduce hydrogen in welding process, filler metal having more oxidiser and increase the shielding gas flow rate.
       2.      Fast rate of solidification
 2. Preheat or heat the workpiece more.
       3.      Base metal and filler metal are dirty.
 3. Clean the joint portion properly. Use clean filler wire and place them at the clean places.
       4.      Base metal-containing excess amount of sulphur
 4. Use electrodes with the basic slagging process.
       5.      Improper arc length and current
 5. Use proper welding conditions and process.


(7) Under-cutting :


The under-cut is a groove cut into the base metal along the toe of a weld and left unfilled by the weld metal. The undercut is caused due to excessive arc length, current and speed of travel. The use of damp electrode is also often a reason for undercut. Magnetic arc blow may sometimes cause this defect. Excessive weaving and wrong angle of electrode should be avoided. The damp electrodes should not be used.

To prevent the occurrence of this defect welder has to carry out welding in a flat position and using multi-passes instead of a single pass.

It provides the change in shielding gas and welding process.

(8) Overlap :


The overlap is an imperfection at a toe or root of the weld caused by metal flowing on the surface of the parent metal without fusing to the later. This defect is continuous or broken in some places. This defect is often seen in fillet weld, which increases the weld size.

The overlap is caused by incorrect electrode and slow rate of welding. Lack of skill of welder to wave the electrode outside the weld zone is responsible for this defect. High current and bigger size of the electrode also leaving this defect.

When fillet weld greater than 7.5 mm inside done in a single pass, this defect is caused due to pulling over of filler metal on the base metal, low current, low travel speed, long arc, incorrect shape of weld and improper electrodes are the reasons responsible to cause overlapping.

Overlapping can be avoided by holding the electrode at a correct angle. Too large an electrode and too low a welding speed Should be avoided. Fillet weld size should be taken less than 9.5 mm an arc should be used skillfully.


(9) Arc Strikes : 


These are small granular points developing near the joint due to the melting of the surface. These defects cannot be remedied even though the cleaning is done by acid. It forms local hard zone and become the crack forming points.

This defect is caused due to striking of the electrode at incorrect places or by providing the wrong earth connection.


(10) Underfill :


When insufficient weld metal is filled then it cannot reach up to the base metal surface and cause a defect called underfill.

This is happening due to a small weld throat.

It can be prevented by reducing the travel rate or increasing the weld pass.


Types of  Welding defects
Types of  Welding defects 

(11) Lamination or delamination :



Defects caused in the weld are not only due to defective welding but some defects are called due to base metal. It includes this defect. Lamination defect is caused when impurities like slag and oxides get rolled in metal during rolling of the ingot.

When this defect intersects the joint then it is opening up is called the delaminating defect. This types of defect cannot be removed easily.

It can be removed by welding thick plate on it or by replacing the plate.


(12) Lamellar tears :



This type of defect is the crack inside and parallel to the surface. It is not found in the heat-affected zone and has layered construction. Such defect caused due to layers of non-metals. which are decomposed under the action of too high stress.

Such defects can be seen when the edges of the plate are opened out.

This difficulty can be avoided by small welds made by multi-pass welding. Because each new pass will heat treat its previous weld pass. Another way is to alter the joint design as shown in fig.

Dimensions of a weld can be measured by using a gauge.



Conclusion :

Remedies for preparing defect-free weld :


1. Proper edge preparation and Job setup and fit-up.
2. Use the electrode of proper size and type.
3. Use AC or DC supply as per the material & dimension of the Job.
4. Carry out welding keeping suitable arc length.
5. prepare welding joint using the proper welding process.
6. Control the arc speed accurately.
7. Welding should be done by keeping the electrode inclined at a suitable angle.
8. Start welding after cleaning the workpiece surface.
9. Remove rust, dirt & dust from the workpiece surface.
10. Weld the Joint after removing residual stresses from the workpiece material.

Also Read: What is Pattern and Its Types
Welding Defects - Types, Causes and Remedies Welding Defects - Types, Causes and Remedies Reviewed by Harish on April 18, 2020 Rating: 5

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