CWI Metallurgy and Weld Discontinuities 3 — Questions and Answers
Question 1: Which element is most commonly responsible for increasing hardenability in low-alloy steels?
- Silicon
- Sulfur
- Manganese (Correct answer)
- Phosphorus
Correct answer: Manganese
Manganese is the most effective common alloying element for increasing hardenability, allowing martensite to form at slower cooling rates.
Question 2: What type of discontinuity results from entrapped non-metallic material (such as flux) within a completed weld?
- Porosity
- Slag inclusion (Correct answer)
- Tungsten inclusion
- Cold shut
Correct answer: Slag inclusion
Slag inclusions are non-metallic solid materials entrapped in weld metal or between weld metal and base metal, often caused by improper inter-pass cleaning.
Question 3: Hydrogen-induced cracking (HIC) in welds is also commonly known as:
- Hot cracking
- Cold cracking (Correct answer)
- Solidification cracking
- Liquation cracking
Correct answer: Cold cracking
Hydrogen-induced cracking is called cold cracking because it occurs at or near room temperature after welding is complete, unlike hot cracks which form during solidification.
Question 4: The carbon equivalent (CE) formula is used by CWI inspectors primarily to assess:
- Weld bead geometry
- Risk of hydrogen-induced cracking (cold cracking) (Correct answer)
- Susceptibility to porosity
- Likelihood of hot cracking
Correct answer: Risk of hydrogen-induced cracking (cold cracking)
The carbon equivalent formula estimates a steel's susceptibility to hydrogen-induced cold cracking by accounting for the hardenability effect of alloying elements.
Question 5: Which weld discontinuity is described as a depression or groove in the weld face that goes below the surface of the adjacent base metal?
- Undercut
- Underfill (Correct answer)
- Concavity
- Melt-through
Correct answer: Underfill
Underfill is a condition where the weld face or root surface is below the adjacent base metal surface due to insufficient weld metal deposition.
Question 6: What is the primary purpose of applying preheat before welding?
- To increase weld penetration depth
- To slow the cooling rate and reduce risk of cold cracking (Correct answer)
- To eliminate the need for post-weld heat treatment
- To increase deposition rate
Correct answer: To slow the cooling rate and reduce risk of cold cracking
Preheat slows the cooling rate of the weld and HAZ, reducing thermal gradients, minimizing martensite formation, and allowing hydrogen to diffuse out.
Question 7: In weld inspection terminology, what is a 'lamellar tear'?
- A crack running along the weld centerline
- A subsurface planar crack in base metal caused by through-thickness shrinkage strains (Correct answer)
- A crack at the weld toe
- A crack caused by excessive current
Correct answer: A subsurface planar crack in base metal caused by through-thickness shrinkage strains
Lamellar tearing is a subsurface cracking phenomenon in rolled steel plate caused by through-thickness tensile stresses acting on low-ductility inclusions, typically sulfide inclusions.
CWI Metallurgy and Weld Discontinuities 3
Which element is most commonly responsible for increasing hardenability in low-alloy steels?