Dear Experts,
We are operating a gas turbine model Frame 5. After completing a Hot Gas Path inspection, the unit was successfully returned to service and has accumulated approximately 6,000 operating hours since of this HGPI. we make borescope inspection, we observed minor dents on the First stage turbine buckets also observed some powders, along with slight discoloration in some areas.
It is important to note the following:
The Turbine Running normally, all parameters within the range.
The turbine is operating on treated/neutral gas fuel.
The filter house has been thoroughly inspected, and all filters are in good condition with no missing or damaged elements.
The gas scrubber/filter system has also been checked and is functioning properly with no abnormalities detected.

By the way Both nozzles with buckets stages replaced with new sets.

Given these conditions, we would like to understand:
What could be the possible causes of dents on the first stage buckets & some powders despite proper filtration and good fuel quality?

Any insights regarding potential sources such as foreign object damage (FOD), upstream component degradation, or operational factors would be highly appreciated.


Thank you in advance for your support.

 

@Ali Kadum,

As you've been a member of this forum since 2021 and made several posts you are aware this is primarily a controls-related forum. YES--we do from time to time cover some mechanical issues as they relate to controls and control schemes and control devices.

There may be some readers/members which have some experience with the issue you are inquiring about as there are some "mechanical department" types who lurk on control.com and occasionally provide insights and the benefit of their experience.

You would do well to provide information about the source of the nozzles and buckets (OEM or otherwise), and whether or not they were new parts or refurbished parts to get the best responses possible. You might also explain "...treated/neutral gas fuel..." (as that's probably a new term for most of the readers here). If the machine has any "unusual" operational factors (frequent starts/stops; frequent trips from load; DLN-I combustion system; etc.) it would be most helpful to describe these as well.

You should also tell if the fuel nozzle tips were checked with the borescope at the same time as the nozzles/buckets, and if the combustion liners were also looked at with the borescope during this same inspection. And, have you considered borescoping the axial compressor and IGVs (or has that been done during the same inspection?)? Lots of unknowns and the information could trigger someone's memory or experience that might provide useful responses.

But it more than likely has to be some kind of FOD, or upstream component degradation.

Best of luck with your investigation!