Unit Operations - Basic to Advance

A: A sounds tempting if you’ve seen inlet throttling on test separators, but nothing else on the drawing supports inlet control. C plays on brownfield tag reuse, yet the signal line type and bubble style match level control, not pressure. D fits the reality of half-built projects, but manual valves aren’t shown with actuator symbols and signal lines. The inconsistency is the valve drawn upstream of the nozzle while still functioning as a liquid dump; that’s a drafting error that shows up a lot in 1990s as-builts.

A: A mixes up hydraulics with pressure rise; incompressible liquid can drive large forces but not fast pressure excursions. B sounds like a conservative simplification, yet API doesn’t ignore two-phase flow casually. D is a common field myth and collapses as soon as you look at independent protection layers. The real driver is time response: vapor compressibility means pressure climbs quickly when outlets are blocked, reaching set pressure before liquid thermal expansion becomes limiting.

A: A proves valve actuation but tells you nothing about the transmitter accuracy. B checks signal integrity and scaling, which feels safe, yet it completely bypasses the sensing element. D gives calibration confidence but requires removal, breaks impulse lines, and burns time you don’t have. Using water to flood the boot ties the sensor to the physical level reference that actually matters during operation, without disturbing the installation.

A: A feels right because high level is linked to carryover, but a trip still reacts slower than severe slugs. C and D are real degradation mechanisms, yet they’re chronic, not acute trip-level hazards. The shutdown only isolates inlet flow; if the gas outlet blocks while pressure continues to build, level protection does nothing to stop a pressure excursion.