SAW Metallurgy & Weld Quality Inspection 2 — Questions and Answers
Question 1: What is the primary cause of hydrogen-induced cracking (HIC) in SAW welds?
- Excessive preheat temperature
- Diffusible hydrogen from moisture in flux (Correct answer)
- Too high travel speed
- Insufficient arc voltage
Correct answer: Diffusible hydrogen from moisture in flux
Moisture absorbed in SAW flux decomposes in the arc and introduces diffusible hydrogen into the weld metal, which can cause HIC in susceptible microstructures.
Question 2: Which non-destructive testing method is most effective for detecting subsurface lack-of-fusion defects in a SAW weld?
- Liquid penetrant testing
- Magnetic particle testing
- Ultrasonic testing (Correct answer)
- Visual inspection
Correct answer: Ultrasonic testing
Ultrasonic testing can detect internal volumetric and planar defects such as lack of fusion that are inaccessible to surface methods.
Question 3: In the heat-affected zone (HAZ), the region immediately adjacent to the fusion line is called:
- Subcritical HAZ
- Intercritical HAZ
- Coarse-grained HAZ (Correct answer)
- Fine-grained HAZ
Correct answer: Coarse-grained HAZ
The coarse-grained HAZ (CGHAZ) is closest to the fusion line, where peak temperatures cause significant austenite grain growth.
Question 4: A SAW weld bead shows excessive convexity. What is the most likely consequence?
- Improved fatigue life at the toe
- Stress concentration at the weld toes (Correct answer)
- Better fusion at the root
- Reduced distortion
Correct answer: Stress concentration at the weld toes
Excessive convexity creates a sharp angle at the weld toes, acting as a stress riser that reduces fatigue resistance.
Question 5: Carbon equivalent (CE) formulas are used to predict:
- Flux consumption rate
- Weld metal oxygen content
- Susceptibility of steel to hydrogen cracking (Correct answer)
- Travel speed requirements
Correct answer: Susceptibility of steel to hydrogen cracking
Carbon equivalent quantifies a steel's hardenability and its tendency to form brittle martensite, indicating risk of hydrogen-induced cracking.
Question 6: Which type of weld discontinuity is classified as a planar defect and is most detrimental to structural integrity?
- Porosity
- Slag inclusion
- Undercut
- Crack (Correct answer)
Correct answer: Crack
Cracks are planar defects with essentially zero radius of curvature at their tips, making them far more damaging than volumetric discontinuities under loading.
Question 7: What does a Charpy V-notch test primarily measure in weld metal evaluation?
- Tensile strength
- Hardness
- Notch toughness and transition temperature (Correct answer)
- Yield strength
Correct answer: Notch toughness and transition temperature
The Charpy V-notch test measures absorbed impact energy, used to determine notch toughness and ductile-to-brittle transition temperature of weld metal.
SAW Metallurgy & Weld Quality Inspection 2
What is the primary cause of hydrogen-induced cracking (HIC) in SAW welds?