Certified Pipefitter Instrumentation and Process Measurement — Questions and Answers
Question 1: On a P&ID, a circle with the letter 'FIC' and a tag number represents which type of instrument?
- Fire Inspection Controller — a heat detection device near a burner
- Flow Indicating Controller — an instrument that measures, displays, and controls flow rate (Correct answer)
- Fluid Injection Conditioner — a chemical dosing valve
- Filter Inlet Check — a differential pressure indicator across a strainer
Correct 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.
Question 2: What is the difference between gauge pressure (psig) and absolute pressure (psia)?
- Gauge pressure accounts for the weight of the fluid column above the measurement point; absolute pressure does not
- Gauge pressure is referenced to atmospheric pressure (reads zero at atmosphere); absolute pressure is referenced to a perfect vacuum (Correct answer)
- Gauge pressure is used for liquids; absolute pressure is used for gases only
- They measure the same quantity but gauge pressure is expressed in metric units and absolute pressure in imperial units
Correct 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.
Question 3: A pipefitter is installing an orifice plate in a flow measurement run. Which orientation requirement is critical?
- The orifice plate must be installed vertically regardless of pipe orientation
- The beveled (sharp) edge of the orifice must face upstream (into the flow) (Correct answer)
- The orifice plate tab must point downward to allow condensate drainage
- The orifice bore must be centered using a laser level before bolting the flange
Correct 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.
Question 4: What is the purpose of a thermowell when installing a temperature sensor in a pressurized process pipe?
- To insulate the sensor from ambient temperature so it reads only the process fluid temperature
- To provide a closed-end protective tube that lets the sensor be installed or removed without depressurizing the pipe (Correct answer)
- To amplify the temperature signal sent to the control room indicator
- To align the temperature sensor perpendicular to the pipe centerline during installation
Correct 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.
Question 5: Which flow meter type operates with no moving parts and measures flow using Faraday's law of electromagnetic induction?
- Turbine flow meter
- Positive displacement flow meter
- Magnetic flow meter (magmeter) (Correct answer)
- Variable area (rotameter) flow meter
Correct 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.
Question 6: In control valve terminology, what does 'fail-safe position' mean, and why is it specified?
- The position a valve moves to when it receives its maximum control signal, ensuring full throughput
- 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 (Correct answer)
- The valve's rated position after 10 years of service life, used for maintenance scheduling
- The factory-set position used during shipping to prevent internal damage
Correct 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.
Certified Pipefitter Instrumentation and Process Measurement
On a P&ID, a circle with the letter 'FIC' and a tag number represents which type of instrument?