Seal Leak in Atmopsheric side Cold Service Pump

[Jungpao]

Hi Folks,

I am experiencing leak on the atmospheric side of mechanical seal on some pumps more specifically on cold service pump. We are using double pressurized mechanical seal for all the pump mentioned. The pump and seal operating condition as below :

1. Pump A1/B1
Pump type : OH2 Centrifugal Horizontal Pump
Liquid : Hydrocarbon
Temperature : -30 deg F (can reach -50 deg F)
Flow : 80 usgpm
Discharge Press : 440 psig
SG : 0.49
Vapor Pressure :360 psig
Seal Configuration :3CW-FF
Seal Face : Carbon / Sil-car (both product and atmospheric side)
Seal Ring : PTFE + Alloy
Seal Flushing : Plan 53B
Barrier fluid : 2-Propanol

2. Pump A2/B2
Pump type : OH2 Centrifugal Horizontal Pump
Liquid : Hydrocarbon
Temperature :-69 deg F (can reach -78 deg F)
Flow : 120 usgpm
Discharge Press : 450 psig
SG : 0.53
Vapor Pressure : 385 psig
Seal Configuration : 3CW-FF
Seal Face : Carbon / Sil-car (both product and atmospheric side)
Seal Ring : PTFE + Alloy
Seal Flushing : Plan 53B
Barrier fluid : 2-Propanol

The leak is visible only when pump standby and icing is defrosted (icing reach mechanical seal during standby).
Has anyone experience something like this? Also, is there any chance that the barrier liquid might need to be changed to other liquid (ethanol, propylene glycol, etc.)

Any suggestions or opinion would be very helpful. Thank you for your help!

Best Regards,
Jungpao

 

[georgeverghese]

Bladder pressure should be higher than suction pressure by 20psi or so at all times, including shutdown - standby. During standby mode, is pump suction valve closed ? If so, pump casing can get blocked in, casing pressure can rise well beyond plan 53B bladder pressure with ambient heat input, and cold hydrocarbon can leak into LP side of seal into atm.
2propanol seems to be suitable for this service, since melting point for this barrier fluid is much lower than -80degF.

 

[FMJalink]

Hi Jungpao,
As you mentioned it occurs only during de-icing, it seems to have to do with still cold internals and heating up of the casing outside. Could be something as the seal bellow is still cold and the casing already extensioned (locally), having the bellow not providing sufficient pressure on the sealing surface. Could also be something with the material properties. PTFE seems OK for this temperature, but most likely the rings will not be in solid PTFE. Best advise I can give is, contact your seal supplier and explain the situation. If that does not lead to the desired results, you can contact another mechanical seal supplier/manufacturer. They often know the strengths and weaknesses of their main competitors. Keep in mind that the mechanical seal and the pump (construction) should be suitable for de-icing/cold service.
Success