Metallography

A: Governing principle: Screening metallography methods indicate susceptibility, not pass/fail acceptance. Here, Practice A (oxalic acid etch) only flags potential sensitization; calling it 'acceptable' overstates what the method can prove two weeks before MC. Option B traps engineers who remember ferrite limits from weld metallurgy and import them into an intergranular corrosion test where they don’t govern acceptance.

A: Governing principle: Fractography can indicate mechanism, not process control effectiveness. Intergranular cracking with secondary cracks supports hydrogen-assisted cracking, but it doesn’t prove PWHT was effective or even applied. Option C attracts engineers who equate brittle appearance with low stress without separating fracture mode from stress history.

A: Governing principle: Etchant choice must resolve the feature of interest without distortion. Blanket use of 2% Nital can wash out tempered martensite detail, hiding carbide distribution that matters for failure analysis. Option D catches engineers who jump to grain size rules even when the metallography objective isn’t grain size determination.

A: Governing principle: Section orientation controls which thermal gradients are visible. A transverse section captures the full thermal profile from weld metal through HAZ into base metal, which is what you need near MC. Option B tempts engineers used to weld metal chemistry checks, not microstructural gradient evaluation.