NDT (PT) Theory and Demonstration

A: A feels almost boring, which is why people second‑guess it. One 5 °C step below baseline, one minute added. B sounds like a safety move, but you're inventing margin that isn't in the written practice and that becomes a nonconformance in an audit. C is a classic adjacent‑domain leak from heat transfer; PT dwell is about capillary action and viscosity, not bulk conductivity. D treats dwell like a Kelvin‑based process variable, which it isn't, and quietly stretches the time by 50% with no basis in the procedure.

A: Start with geometry. 10 µm is 1e‑5 m. Multiply by 1 m² and you get 1e‑5 m³, which is 10 mL. A lines up with that back‑of‑envelope. B feels practical because anyone who's sprayed knows there's waste, but the question is about what’s needed to wet the surface, not what the can dispenses. C confuses coverage with flooding; PT doesn't work better when it’s swimming. D drops three orders of magnitude by thinking in terms of molecules instead of a continuous film.

A: A tracks the physics. High humidity interferes with solvent evaporation and the developer’s ability to pull penetrant back out, so indications spread and lose contrast; extending development within allowed limits is the controlled response. B mixes up temperature and humidity; viscosity isn't the lever that's moving. C sounds optimistic but ignores that water competes in the flaw and blunts contrast. D is a panic move that skips re‑cleaning, trapping moisture and contaminant in the discontinuity, making the next cycle worse.

A: Unit conversion decides this. 1 W/m² is 100 µW/cm². So 8 W/m² is 800 µW/cm². C follows that through and calls the fail. A trips over the same math but then waves it through anyway. B invents a correction factor that isn’t in play unless the measurement setup is wrong. D is tempting if you’ve been burned by the wrong meter before, but the question already states a UV-A reading.