A gas chromatograph is designed to analyse a representative gas sample. When liquid enters the sample path, the sample composition and flow behaviour can change immediately, often causing poor repeatability, contamination, or distorted peaks.
Liquid carryover is therefore both a reliability issue and a measurement-quality issue.
How it develops
Carryover usually begins when pressure and temperature conditions allow heavy hydrocarbons or water to condense in the transport line, regulator, filter, or sample hardware. In some systems, slugging occurs only during certain process conditions, making the issue easy to miss.
Intermittent liquid presence is often harder to diagnose than constant liquid presence.
Typical warning signs
Common symptoms include unstable readings, drifting calibration, contaminated filters, blocked components, slow recovery after process changes, or sudden changes after shutdown and restart.
Where liquids collect, the sample history begins to influence the current reading.
Prevention by design
Good prevention uses correct take-off location, adequate heating margin where needed, suitable pressure reduction strategy, drainage points, fast bypass flow, and hardware selected for the actual sample conditions.
The best liquid problem is the one prevented before the analyser ever sees it.
Field response
If liquid carryover is suspected, inspect filters, drains, regulators, and low points in the tubing. Check whether the sample conditions remain single phase through the full transport path.
Cleaning the symptom without correcting the phase problem only creates repeat failures.
