Seal Failure

[A_123]

I have some inquiry about Mechanical Seal in Petrochemical.

most pump that we have 2 for each Tower(under Vacuum) one running another one standby. My Question
What is the best practice for standby pump that has Gas Seal (N2). Seal Plan 74
1- Keep N2 online all the time.
2- Isolated N2 during standby.


If there is any passing from discharge valve for the standby pump (it has common header) how that will affect on the standby mechanical seal.
What we have to do to protect mechanical seal from Failure?

 

[JJPellin]

In our refinery, we do not use any dry gas seals (Plan 74) in vacuum services of the types you are describing. But, we would normally keep the N2 in service all the time for the standby pump. If the standby pump has leakage across the check valve or has a warm up flow (drilled check valve or bypass line for warm up flow), there will be a small backward flow of hot product through the pump. The normally tiny amount of N2 leaking past the seal will pass up the suction line of the off-line pump and enter into the running pump. For a Plan 74 on the running pump, I would not expect this to have any affect on the seal of the running pump. It would also have no expected affect on the seal in the not-running pump. As long as the seal gas it maintained at least 30 psi higher pressure than the seal chamber pressure (static or running), liquid product will not get between the seal faces.

Johnny Pellin

 

[russcalub]

Normally, N2 quench will be kept open even during standby period. It helps quench out minimal weepage from seal faces to avoid accumulation under the seal. This could build up under the seal faces and solidify. During start up, the solidified product at seal faces ID or OD may break the seal faces. The accumulated or solidified product under the seal could also cause hung up of dynamic oring near the area. In cryogenic application, N2 prevents icing on seal faces.