Good morning all,

During a PSL compressor inspection, we observed corrosion spots on the tertiary seal, which is supplied with instrument air produced by service air dryers.
We suspected the quality of the instrument air supplied by the air dryers was a problem.
Thank you for helping us with how to check the air dryers and how to perform preventive maintenance, monitoring to ensure the production of moisture-free instrument air.

Best Regards

 

You can use permanent dew point sensors downstream of dryers and at critical control panels.
Integrate with your SCADA/PLC system to log data and set alarms.

 

Corrosion on a dry-gas-seal tertiary (separation) seal fed from instrument air usually points to the air reaching its dew point somewhere in the line. A practical approach:

1. Verify the spec. Instrument air should meet ISO 8573-1 class 2 or better for water (pressure dew point -40 °C or lower), or at least 10 °C below the lowest ambient temperature the piping sees. Make sure you compare pressure dew point, not atmospheric dew point.

2. Measure at the point of use, not only at the dryer outlet. Take a spot check with a portable dew point meter (aluminium-oxide or polymer sensor, ideally verified against a chilled-mirror reference) at the seal panel inlet. Leaks, wet dead legs and failed drains downstream can add moisture after the dryer.

3. Check the dryer itself. Desiccant dryers: confirm purge flow and cycle timing, check the switching valves for leaks, look for desiccant dusting or oil fouling, and replace desiccant at the interval the manufacturer gives. Refrigerated dryers can only reach about +3 °C PDP, which is not good enough for seal gas. Check the condensate drains and pre-filters (coalescing filter differential pressure).

4. Monitor continuously. Install a fixed dew point transmitter downstream of the dryer, alarm at around -30 °C PDP, and trend it in the DCS so dryer degradation shows up before corrosion does. Calibrate the sensor every 12 months.

Also confirm there is no oil carryover from the compressor. Oil fouls desiccant and can make the corrosion worse.