Plan 74 Mechanical Seal complicated Issue

[Abdullah GS]

Hello all,

We have a pump which is sealed with double mechanical seal with gas seal with 74 seal plan. the problem that we are facing is this seal had a repeated failures for unknown reason.

The MTBF for this seal not exceeding 20 days.

We increase the seal pressure to 8 Barg even the needed is 4 Barg to ensure that the process will not go into the seal.

We are still suffering repetitive failure for this seal.

Have any one experience this issue before? Any idea may help to make the seal perform well?

The seal is double mechanical seal with lip seal and expeller or screw.

 

[JJPellin]

I assume you have examined the failed seals to see what sort of damage was present. What services is this running in? What are you defining as a failure? Leakage above some value? Inability to maintain target differential pressure? External leak of pumped product? From my experience, these are the most likely causes of poor reliability for a seal with this flush plan:

Incorrect procedures for decommissioning or commissioning allowing the liquid process to get between the seal faces.
Running backwards.
Slow rolling when not in service (steam turbine driver).
Design error such as faces cut for incorrect rotation.

Pictures of the failed seal faces and a drawing of the seal would allow us to do more than just guess about potential causes.

Johnny Pellin

 

[Abdullah GS]

Thanks Johnny.

To make it more clear for you. we are running these pumps with TDI and Tar and from the picture of the inspection it is define that this seal loss the barrier pressure but from the trends nothing change.

 

[JJPellin]

I don't know what "TDI" refers to. You did not answer my questions. Without additional information, I cannot help you. I would generally not recommend this piping plan for hot tar service. Perhaps you should consider a different plan.

Johnny Pellin