CWI Weld Discontinuities and Defects 2 — Questions and Answers
Question 1: Which discontinuity is characterized by a groove melted into the base metal adjacent to the weld toe that is left unfilled by weld metal?
- Overlap
- Undercut (Correct answer)
- Underfill
- Cold lap
Correct answer: Undercut
Undercut is a groove melted into the base metal at the weld toe or root that is not filled by weld metal, reducing the effective cross-section.
Question 2: Lamellar tearing in a weld joint is most likely to occur in which orientation relative to the base metal surface?
- Parallel to the surface (Correct answer)
- Perpendicular to the surface
- At 45 degrees to the surface
- Along the weld centerline
Correct answer: Parallel to the surface
Lamellar tearing occurs parallel to the plate surface due to through-thickness stresses acting on planes of low ductility inclusions.
Question 3: A weld that shows excessive convexity is most likely to cause which problem in service?
- Reduced tensile strength
- Stress concentration at the weld toes (Correct answer)
- Hydrogen cracking
- Incomplete fusion
Correct answer: Stress concentration at the weld toes
Excessive convexity creates stress concentrations at the weld toes due to the abrupt geometric transition, which can initiate fatigue cracking.
Question 4: Which type of crack propagates along the weld metal centerline, typically caused by solidification shrinkage and low-melting-point constituents?
- Transverse crack
- Longitudinal centerline crack (Correct answer)
- Toe crack
- Root crack
Correct answer: Longitudinal centerline crack
Longitudinal centerline cracks form along the weld axis as the weld solidifies, driven by shrinkage stresses and segregation of low-melting impurities.
Question 5: According to AWS standards, which condition describes 'overlap' in a weld?
- Weld metal extending beyond the joint groove
- Protrusion of weld metal beyond the weld toe onto base metal without fusion (Correct answer)
- Excessive reinforcement height
- Weld metal deposited over a previous pass without cleaning
Correct answer: Protrusion of weld metal beyond the weld toe onto base metal without fusion
Overlap is the protrusion of weld metal beyond the weld toe or root onto the base metal surface without fusion, creating a notch-like condition.
Question 6: A weld inspector finds scattered porosity throughout the weld. Which cause is LEAST likely responsible?
- Contaminated base metal
- Excessive travel speed (Correct answer)
- Moisture in the flux
- Inadequate shielding gas coverage
Correct answer: Excessive travel speed
Excessive travel speed more commonly causes incomplete fusion or underfill rather than scattered porosity, which is primarily caused by gas entrapment from contamination or shielding failures.
Question 7: Which discontinuity is unique to resistance spot welding and appears as a hollow cavity within the nugget?
- Piping porosity
- Expulsion void
- Shrinkage void (void in nugget) (Correct answer)
- Cold weld
Correct answer: Shrinkage void (void in nugget)
Shrinkage voids in resistance spot welding form at the nugget center as the molten metal solidifies and contracts, leaving a hollow cavity.
CWI Weld Discontinuities and Defects 2
Which discontinuity is characterized by a groove melted into the base metal adjacent to the weld toe that is left unfilled by weld metal?