ITMC Welding Fundamentals 4 — Questions and Answers
Question 1: Which type of crack forms in the heat-affected zone (HAZ) and is associated with hydrogen embrittlement?
- Hot crack
- Cold crack (hydrogen-induced crack) (Correct answer)
- Crater crack
- Solidification crack
Correct answer: Cold crack (hydrogen-induced crack)
Cold cracks, also called hydrogen-induced or delayed cracks, form in the HAZ after the weld has cooled, driven by hydrogen, residual stress, and a susceptible microstructure.
Question 2: What is the recommended tungsten electrode type for welding aluminum with AC GTAW?
- 2% thoriated (red band)
- Pure tungsten or zirconiated tungsten (Correct answer)
- 2% ceriated (gray band)
- Lanthanated tungsten (gold band)
Correct answer: Pure tungsten or zirconiated tungsten
Pure tungsten or zirconiated tungsten electrodes form a balled end under AC current, which is ideal for AC GTAW welding of aluminum.
Question 3: A welder is cutting with an oxyfuel torch and the flame is oxidizing. What adjustment should be made to produce a neutral flame?
- Increase acetylene flow until the feather disappears (Correct answer)
- Increase oxygen flow until acetylene feather disappears
- Reduce both oxygen and acetylene equally
- Switch to DCEP polarity
Correct answer: Increase acetylene flow until the feather disappears
An oxidizing flame has excess oxygen; increasing acetylene flow adds fuel until the inner cone becomes sharp and the excess-acetylene feather disappears, achieving a neutral flame.
Question 4: What does a 'fisheye' discontinuity in a weld cross-section indicate?
- Excessive manganese in the filler metal
- Hydrogen entrapment causing an internal void with a bright center (Correct answer)
- Insufficient preheat causing fusion issues
- Overlapping weld passes
Correct answer: Hydrogen entrapment causing an internal void with a bright center
A fisheye is a hydrogen-induced discontinuity visible in a fractured weld surface, appearing as a bright circular area surrounding a void or inclusion.
Question 5: When welding stainless steel, why is it important to control heat input and use backing purge gas?
- To prevent warping only
- To avoid carbide precipitation and oxidation of the root pass (Correct answer)
- To increase travel speed
- To allow use of a smaller electrode
Correct answer: To avoid carbide precipitation and oxidation of the root pass
Excessive heat causes carbide precipitation (sensitization) at grain boundaries in austenitic stainless steel, and oxygen exposure of the root pass causes sugaring, both of which reduce corrosion resistance.
Question 6: In SMAW, what is the effect of using DCEP (electrode positive) versus DCEN (electrode negative)?
- DCEP provides deeper penetration and more heat at the workpiece
- DCEP provides more heat at the electrode and is used for thin materials
- DCEN provides deeper penetration because electrons flow to the workpiece (Correct answer)
- Both polarities provide identical heat distribution
Correct answer: DCEN provides deeper penetration because electrons flow to the workpiece
With DCEN, electrons flow from the electrode to the workpiece, concentrating heat at the base metal and producing deeper penetration, while the electrode runs cooler.
Question 7: Which nondestructive testing (NDT) method is most effective for detecting surface and near-surface cracks in ferromagnetic welds?
- Ultrasonic Testing (UT)
- Radiographic Testing (RT)
- Magnetic Particle Testing (MT) (Correct answer)
- Liquid Penetrant Testing (PT)
Correct answer: Magnetic Particle Testing (MT)
Magnetic Particle Testing uses magnetic fields and iron particles to detect surface and slightly subsurface discontinuities in ferromagnetic materials.
ITMC Welding Fundamentals 4
Which type of crack forms in the heat-affected zone (HAZ) and is associated with hydrogen embrittlement?