Instrumentation and Process Measurement Flashcards
6 cards from real PIPEFITTER practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Instrumentation and Process Measurement flashcards as text
On a P&ID, a circle with the letter 'FIC' and a tag number represents which type of instrument?
Answer: Flow Indicating Controller — an instrument that measures, displays, and controls flow rate
On a P&ID, instrument tag letters follow ISA 5.1 standard: the first letter identifies the measured variable (F = Flow), and subsequent letters indicate the function (I = Indicating, C = Controlling). FIC therefore means Flow Indicating Controller — it measures, displays, and controls flow.
What is the difference between gauge pressure (psig) and absolute pressure (psia)?
Answer: Gauge pressure is referenced to atmospheric pressure (reads zero at atmosphere); absolute pressure is referenced to a perfect vacuum
Gauge pressure (psig) reads zero at local atmospheric pressure — it measures pressure above or below atmosphere. Absolute pressure (psia) equals gauge pressure plus atmospheric pressure (~14.7 psia at sea level) and is measured from an absolute zero reference (perfect vacuum). Many process calculations require absolute pressure.
A pipefitter is installing an orifice plate in a flow measurement run. Which orientation requirement is critical?
Answer: The beveled (sharp) edge of the orifice must face upstream (into the flow)
An orifice plate creates a calibrated pressure drop across a sharp-edged restriction. The sharp (beveled) edge must face upstream so the flow contracts cleanly through the orifice. Reversing the plate distorts the flow coefficient and introduces significant measurement error.
What is the purpose of a thermowell when installing a temperature sensor in a pressurized process pipe?
Answer: To provide a closed-end protective tube that lets the sensor be installed or removed without depressurizing the pipe
A thermowell is a closed-end tube welded or threaded into the pipe. The temperature sensor slides inside it and senses process temperature through the well wall, but remains physically isolated from the process fluid. This allows sensor replacement under pressure without process interruption.
Which flow meter type operates with no moving parts and measures flow using Faraday's law of electromagnetic induction?
Answer: Magnetic flow meter (magmeter)
A magnetic flow meter (magmeter) applies a magnetic field across the pipe and measures the voltage induced in the conductive flowing fluid. Because voltage is proportional to velocity by Faraday's law, flow rate can be calculated. Magmeters have no moving parts, no restrictions, and work well with slurries and corrosive fluids.
In control valve terminology, what does 'fail-safe position' mean, and why is it specified?
Answer: The position (open or closed) a valve automatically moves to when it loses its actuating energy (air or power), chosen to minimize hazard on failure
A fail-safe position is deliberately chosen based on process safety: a cooling water valve typically fails open (to maintain cooling on loss of signal), while a fuel gas valve typically fails closed (to prevent fire on signal loss). Specifying fail-safe position is a critical process safety design requirement.