What are defects or faults of welding ?

The defects in the weld can be defined as irregularities in the weld metal produced due to incorrect welding parameters or wrong welding procedures or wrong combination of filler metal and parent metal.

It can simply be defined as:

“Defects introduced during welding beyond the acceptance limit that can cause a weld to fail”.

A defect does not allow the finished joint to withstand the required strength (load).

Visual defect /Surface weld defect/External defect

• –Over laps
• –Under cuts 
• –Excessive penetration
• –Surface porosity

Hidden defect/sub surface weld defect/Internal defect

• –Lack of fusion
• –Lack of penetration 
• –Shrinkage cavity
• –Slag inclusion

You may also know Details of welding defects

UNDER CUT –

 “A defect that appears as a groove formed in the BM adjacent to the toe of a weld along the edge of the weld & left unfilled by the weld metal”.

• Generally located parallel to the junction of weld metal & base metal at the toe or root of the weld
• Reduces the cross-sectional thickness of the base metal
• Acts as stress raiser in fatigue loading

Cause and prevention of undercut:

Cause – 

• High welding current & arc voltage
• Too large electrode dia
• Incorrect electrode angle
• Longer arc length

 Prevention:

• Use prescribed welding current for electrode size.
• Adjust electrode angle to fill undercut area.
• Correct travel speed, arc length, etc.
  

  Lack of penetration –

“Improper penetration of weld metal through the thickness of joint or weld metal not extending to the required depth into the joint root”

• Acts as stress riser from which a crack may propagate

Cause –

• Root gap too small
• high welding speed
• Low heat input
• Too large electrode dia

Prevention:  

• Proper joint preparation
• Proper heat input & welding speed
• Use suitable size of electrode
  

  LACK OF FUSION

“Lack of complete melting/ fusion of some portion of the weld metal in a joint”

• May be at the root, sides or between two runs.

• Reduces the strength of welds & makes welded structures unreliable.

Cause:

• Low welding current
• Excess welding speed
• Unfavourable heat input

Prevention:

• Maintain proper current & welding speed
• Proper cleaning of each bead.
  

  Slag inclusion-

Metallic or nonmetallic solid material entrapped within the WM, between weld passes or between WM & BM”.

• May be in the form of slag or any other foreign material, which does not get a chance to float on the surface of the solidifying WM

• H₂: the most undesirable inclusion (causing: cold crack)
• Lowers the strength of joint & make it weaker
• Non- metallic inclusion:-

–Most dangerous

–May be sulphide, oxide, silicate or aluminate type

–Acts as stress raiser

• Slag inclusions are elongated or globular pockets of metallic oxides and other solid compounds.

Causes for slag inclusion:

–Inadequate cleaning of weld metal between passes

–Rapid rate of welding

–Too large electrode

–improper current

–Long arcs

Prevention :

–Maintain proper current & heat input

–Proper cleaning of weld.

According to the American Society of Mechanical Engineers (ASME) welding defect causes are following :-

• Poor process conditions
• Operator error
• Wrong technique
• Incorrect consumables
• Bad weld grooves.

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