Advanced Diagnostics & Troubleshooting Flashcards
7 cards from real CPT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Advanced Diagnostics & Troubleshooting flashcards as text
A gas chromatograph analyzer shows drifting baseline readings over a shift. Which factor should be investigated FIRST?
Answer: Carrier gas pressure and flow stability
Unstable carrier gas pressure or flow is the most common cause of baseline drift in a process gas chromatograph.
A compressor surge is detected. Which immediate operator action is CORRECT?
Answer: Open the recycle or anti-surge valve to increase flow through the compressor
Opening the anti-surge (recycle) valve increases the volumetric flow through the compressor, moving the operating point away from the surge line.
A pH analyzer consistently reads 0.5 pH units higher than a laboratory sample taken simultaneously. The BEST corrective action is to:
Answer: Calibrate the analyzer using fresh buffer solutions at process temperature
A consistent offset suggests calibration drift; recalibrating with fresh buffers at the actual process temperature will correct the systematic error.
An operator notices that a flow control loop is stable when flow is high but oscillates when flow is low. This behavior most likely indicates:
Answer: Valve hysteresis (stiction) that is significant relative to low-flow signal changes
Stiction (static friction) in the valve causes stick-slip motion that produces oscillation most apparent at low flow where small signal changes cannot overcome valve friction.
When a vortex flow meter is installed in a pipeline with high vibration, what is the expected effect on its output?
Answer: External vibration will be indistinguishable from vortex signals, causing false high readings
Vortex meters detect pressure fluctuations; external pipeline vibration creates false vortex signals that cause the meter to report erroneously high flow.
A process technician finds that two redundant temperature transmitters disagree by 8°F. The CORRECT troubleshooting approach is to:
Answer: Take a third independent measurement to determine which transmitter is in error
A third independent measurement (hand-held calibrator, thermocouple, or lab sample) identifies which of the two transmitters is out of calibration.
During a plant turnaround, a heat exchanger is hydrotested and passes. Shortly after return to service with hot process fluid, a leak develops. The MOST likely explanation is:
Answer: Differential thermal expansion between tubes and shell caused a tube-to-tubesheet joint failure
Hydrotesting uses ambient-temperature water; thermal stresses from hot process fluid can open small flaws or loosen tube-to-tubesheet joints that held during the cold hydrotest.