30 Questions
What is a potential consequence of having a bad profile in one pass of a multi-pass weld?
Both A and B
Which of the following is a cause of overlaps or rolls?
The wrong tilt of electrode in making fillet weld in horizontal position
What is the effect of undercuts on the work?
They reduce the cross-section of the work
What is the likely cause of unfilled craters?
Sudden interruption of the arc
Which of the following is a cause of burn-through?
Excessive welding current coupled with low welding speeds
What is the effect of burn-through on the work?
It creates holes in the parent metal
What is the primary cause of surface porosity in welding?
Using electrodes with expired shelf-life
Which of the following metals is most prone to surface oxidation during welding?
Aluminum
What is the primary cause of excessive spatter in welding?
Unstable arc
What does a bad weld surface appearance typically indicate?
Bad workmanship
What is the primary cause of lack of fusion in welding?
Poor welding technique
What type of defect is often an indication of underlying subsurface porosity?
Surface porosity
What type of weld defects are surface cracks categorized under?
Visual or surface weld defects
What is a primary cause of surface cracks in welds?
Poor fit-up and incorrect welding procedures
What is the result of uneven heating of the workpieces during welding?
Development of distortion or warpage
What is the effect of a bad bead profile on a weld?
It has a considerable effect on the performance of the weld under load
What is a common characteristic of visual or surface weld defects?
They are visible to the naked eye
What is the category of weld defects that includes lack of fusion and lack of penetration?
Hidden or subsurface weld defects
What is the primary factor that determines the performance of welded structures or components in service?
Quality of fabrication
What is the primary reason for the generation of defects in weldments?
Poor welding skills
How does the presence of defects in weld joints affect the structure or component?
Impairs the strength of the structure or component
According to IIW, how many groups are weld defects classified into?
Six
What type of defect includes blowholes, porosity, and shrinkage?
Cavities
What type of defect includes undercut, underfill, and overlap?
Imperfect shape or unacceptable contour
What is the main cause of lack of fusion in welding?
Insufficient welding current
Where can subsurface cracks occur in a weld?
In the weld, HAZ, or base metal
Why are weld cracks considered dangerous?
They create a serious reduction in strength
What is the most common location for lack of penetration defects to occur?
In the root of the weld
What is the effect of increasing arc voltage on lack of penetration?
It increases the risk of lack of penetration
Why are subsurface cracks more serious in certain service conditions?
Because they can propagate and cause sudden failure under impact loading and low temperature service conditions
Study Notes
Weld Defects
- Weld defects can be categorized into two types: surface/visual defects and hidden/subsurface defects.
Surface/Visual Defects
- Surface cracks: the most dangerous defect, caused by high concentration stresses, poor fit-up, and incorrect welding procedures.
- Distortion/Warpage: uneven heating during welding, leading to welding stresses and distortion of the structure.
- Incorrect weld profile: bad bead profiles affect the performance of the weld under load.
- Overlaps or rolls: protrusions of weld metal beyond the bond at the toe, face, or root of the weld, caused by excessive welding current and wrong tilt of the electrode.
- Undercuts: grooves melted into the parent metal, reducing the cross-section of the work and leading to cracking.
- Unfilled craters: sudden interruption of the arc, reducing the cross-section of the weld and acting as a source of crack formation.
- Burn-through: holes burned through the parent metal, caused by excessive root gap, insufficient root face, and excessive welding current.
- Surface porosity: caused by using un-dried covered electrodes or electrodes with expired shelf-life, indicating potential subsurface porosity.
- Excessive spatter: unstable arc, wrong electrode selection, bare electrodes, heavy welding current, and poor technique of the welder.
- Bad surface appearance: bad workmanship, indicative of surface defects that may not be structurally important.
Hidden/Subsurface Defects
- Lack of fusion: incomplete fusion between parent metal and weld metal, or between layers of multi-pass welding, caused by insufficient welding current, electrode offset, high welding speed, and improper procedure.
- Subsurface cracks/hidden cracks: categorized by location (in the weld, HAZ, interface, or base metal), creating a serious reduction in strength and potentially leading to sudden failure.
- Lack of penetration: defect occurring in the root of the weld, caused by decreased welding current, increased arc voltage, and poorly directed arc.
Note: Some slides (IIT TIRUPATI 17-22) did not contain specific information, so they were not included in the summary.
Test your knowledge on the common defects that can occur in weld joints and their impact on the strength and performance of welded structures. Learn about the main reasons behind these defects and how they can lead to failure. Improve your understanding of welding techniques and best practices.
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