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Mechanical seal failure

We are facing multiple seal failures (NDE side seal) in one of our multistage NGL pump . When opened the seal we found water, some black paste, one of the shaft O ring disintegrated, other O rings elongated  etc after only 6 month in service. The seal is from  Flexibox with API plan 53C . The O ring is Viton and supplied by OEM.  The symptoms begins with loosing the barrier seal which required frequent top up.

We suspect   pump product is entering inside seal due to O ring issue and causing spring hangup . Another doubt is assembly error during seal refurbishment. But as per the maintenance who refurbish the seal ( Replacing all parts except casing with new spares) there is no chance for any fitting error as it is a cartridge type seal and passes  the static test every time.

My question is how can we test the O ring in a practical way whether it is compatible for this service. Please bear in mind DE side also uses same components.

Is there any way the product can come to seal other than through secondery seals as the barrier pressure is always high

Is there any error during seal assembly is possible and if yes please explain

Any other thoughts are welcome


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