How to know that the white metal of an oil seal is damaged?

[Hamza1988]

Hi I am a maintenance engineer, been working with my company for a couple of years now. I was measuring the inner diameter of an LP seal ring (oil seal) the other day using a bore gauge for some clearance checks before installing the seals on a multistage compressor when suddenly I realized that I might have scoured the white metal surface of the seal in the axial direction as I had to slide the bore gauge slightly in an out of the seal ring.

My question is, how would I know that the seal ring is scratched and cannot be used. Is there a certain check we can perform to know that the scratch is deep enough to consider the seal as damaged or mild/light enough to deem the seal ring usable.

Thanks for the help in advance and apologies if the question sounds a little stupid or very basic as I am new to maintenance.

 

[gerhardl]

'Stupid' is a label reserved for technical people NOT asking questions after trying in vain to find an answer!

For scratches on sealing surfaces visual inspection and evaluation based on experience, and even a very light polishing by fine polishing paper is quite common. There is a large 'but' attached: only practical when experience tells this is suitable based on non-leakage requirements, fluid, pressure, geometrical requirements, requirements for surface exactness and microscopic surface condition etc. etc.

Even hairline scratches can under circumstances (cavitation, supersonic speed through the crack) lead to serious leakage and damage.

Conclusion: Even if all parameters above can be technically measured, there is no simple way by a given application to find the border limit between clearly to much and probably to small scratches to matter, any way than by experience. Leakage must after all be measured under test conditions, not by examination of single parts before the total assembly.

The general quality rule of maintenance of important parts is easy: to be replaced by new parts if suspicious.

Seems you are on the right track, and sorry for the 'non-answer'! You can perhaps try again with more detailed information and pictures in the forum for sealing technology. Good luck!

 

[Hamza1988]

Thanks 'gerhardl'. Your response was very helpful. The seal rings were inspected by an expert and he said they were fine but suggested to avoid such scenarios one can reduce the force of spring of the bore gauge by using the smallest extension possible to avoid too much compression of the spring when inserting the bore gauge in the seal ring.