SAW Metallurgy & Weld Quality Inspection 3 — Questions and Answers
Question 1: What solidification mode produces the most favorable microstructure for corrosion resistance in stainless steel SAW welds?
- Fully austenitic
- Primary ferrite with austenite transformation (Correct answer)
- Primary austenite with ferrite transformation
- Fully martensitic
Correct answer: Primary ferrite with austenite transformation
Primary ferrite solidification (FA mode) results in a weld containing 3–8% delta ferrite, which resists hot cracking and improves corrosion resistance.
Question 2: Lamellar tearing in heavy plate SAW fabrication is most likely caused by:
- Excessive arc voltage
- Low-toughness inclusions oriented parallel to the plate surface (Correct answer)
- Insufficient preheat
- High wire feed speed
Correct answer: Low-toughness inclusions oriented parallel to the plate surface
Lamellar tearing occurs when through-thickness shrinkage stresses tear the base metal along elongated manganese sulfide or oxide inclusions lying parallel to the rolled surface.
Question 3: In radiographic testing of SAW welds, porosity appears on the film as:
- Dark rounded spots (Correct answer)
- Light jagged lines
- Dark linear indications
- Light circular rings
Correct answer: Dark rounded spots
Porosity appears as dark, rounded spots on radiographic film because gas voids allow more X-ray transmission than surrounding solid metal.
Question 4: The purpose of postweld heat treatment (PWHT) stress relief is primarily to:
- Increase weld hardness
- Reduce residual stresses and temper the HAZ (Correct answer)
- Eliminate all weld defects
- Improve flux coverage
Correct answer: Reduce residual stresses and temper the HAZ
PWHT at sub-critical temperatures reduces residual welding stresses and tempers hard microstructures in the HAZ, improving toughness and reducing cracking risk.
Question 5: Which SAW flux type is most prone to moisture pickup and requires the strictest storage and rebaking procedures?
- Fused flux
- Bonded (agglomerated) flux (Correct answer)
- Mixed flux
- Neutral flux
Correct answer: Bonded (agglomerated) flux
Bonded fluxes are manufactured with binders and have higher porosity, making them more susceptible to moisture absorption than fused fluxes.
Question 6: A weld acceptance criterion requires an undercut depth not to exceed 1/32 in. This limit is specified because:
- Undercut reduces deposition efficiency
- Undercut creates a notch that reduces fatigue life (Correct answer)
- Undercut increases weld width
- Undercut causes spatter
Correct answer: Undercut creates a notch that reduces fatigue life
Undercut along the weld toe creates a mechanical notch that concentrates stress and significantly reduces the fatigue life of the welded joint.
Question 7: During macro-etch examination of a SAW cross section, what does a lack of root fusion appear as?
- Bright white columnar grains
- A dark rounded void at the center
- An unfused linear gap at the joint interface (Correct answer)
- A series of evenly spaced pores
Correct answer: An unfused linear gap at the joint interface
Lack of root fusion shows as a linear, unfused gap or seam at the root where the weld metal did not bond with the base metal.
SAW Metallurgy & Weld Quality Inspection 3
What solidification mode produces the most favorable microstructure for corrosion resistance in stainless steel SAW welds?