Aluminum Particles in the Discharge of Steam Turbine

Hi. I am used to check oil samples from jet turbines, and this is a similar issue. By what you wrote, it seems that there are more aluminum particles comming from the inside of the turbine than what could be present as contaminants at the inlet, am I wright?

Check for the following:

1- Was any component replaced recently whose failure could deliver aluminum to the system?

2- Did any failure occur that could release some amount of aluminum to be traped somewhere inside the equipment?

3- Check all seals, plugs, threads, spacers, that could be worn and release aluminum. Also, if you have a not-so-good bearing that didn't fit well in its housing, it can vibrate and wear the housing (see item 1).

4- Be sure there's no aluminum contamination outside of the unit.

5- Many equipment have plugs for inspecting delta-P across seals, to detect leakage and wear. This is usually a usefull source of information.

First, check the manual to note which parts are aluminum. If blades are cast aluminum for some reason, shut 'er down immediately and start looking for metal fatigue and blade replacement candidates. If you are multi-stage, then take off samples and check each stage to save opening them all.

Mark

Yeah, definitely and first of all, check the manual and determine which parts are made of aluminum.

Assuming we have here a permanent working cycle, are you able to do vibration measurement (this including check the current measurement against a historical pattern)?

Regarding blade fatigue, it can be caused mainly if you have problems in operational conditions (stall, surge, oscillations in load) or mechanical conditions resulting in a blade tip rub against the stator. Check all those possibilities. You can have by now only a tip rubbing, but it can progress to a blade loss.... Not good at all have a first stage turbine blade loose and breaking all the downstream stages...

Is the turbine brand new?

Are you certain the particles observed are aluminum, or do they just look like it? Have the metallurgy of the particles examined carefully, since this will tell you much. Don't rely on guesses!

Many turbines utilize "abradable seals", where a thermal sprayed coating is applied on the interior of the housing. As the turbine reaches operating speed and has expanded due to the high temperatures, the blades create their own tight fitting seal by literally wearing a groove into this abradable coating. The (hard) blade tips create an optimal seal at operating conditions by "machining" it themselves. This would produce particulates of the seal material and would be expected during initial running, and perhaps to a lesser extent after certain maintenance operations, otherwise seal particles would be indicative of bearing wear, or some other factor needing looking into.

As stated by others check the manual, but also by all means contact the manufacturer. But make sure you analyze the metallurgy of the particles, this is standard procedure for large, and/or expensive equipment!