Coking Barrier Fluid

[sinbj1]

I have an application where an API plan 54 is used. A recent failure had heavy coke build-up on the atmosheric side of the mechanical seal. The barrier fluid is Synturian Six at 100psig and 4gpm. The process is heavy gas oil at 700 degF. The first thing that pops in my head is...The plan 54 circulator was not operating properly. The seal support system is under further evaluation. I have two questions...

1.) At what temperature does barrier fluid coking on the atmospheric side of the seal become a concern?

2.) Can coking on the atmospheric side of the seal create a slip-stick condition that could potentially crack a face when the pump is started?

 

[flexibox]

Without looking at the seal drawing it will be a little difficult to answer your question no 2. The first thing to consider in Plan 54 is the seal design self venting? ensure venting is addressed. I believe that you have sufficient flow within the system but what is the cooling capacity? What is the barrier temperature? If you are using water cooling check for fouling. I will assume that in order to get coking you will be operating the barrier fluid over 260F. Check the cracking temperature of the oil. Sounds like your face temperature is high install an LP steam quench if you have room to fit a connection on the atmospheric side of the seal. This problem sounds like wrong barrier fluid or insufficient cooling. For these temperatures you will have a Metal bellows design. These seals are prone to Slip Stick however I believe that Coking is the not the cause of the damaged face. Check to see if you have any fretting on the bellows drive rings at the front of the seal near the face. If this is serverly fretted then Slip Stick may be a cause of failure then I would check Barrier fluid and viscosity. Check the setting lengths of the seals too. You barrier fluid has a flash point of 280F, you may need to change your barrier fluid.

trust this helps