I would prefer a Plan 53A for that service. But, I would consider the 31/52 combination to be an acceptable alternative that should produce good reliability.

Johnny Pellin

thanks a lot about your answer.
but I have a concern about seal pot in API plan 52. if we have any leakage in here, Benzene will be in liquid phase in the seal pot and the seal pot level will increase. it is unlike services like propane that the fluid goes to flare because of its high vapor pressure in atmospheric pressure. Is it necessary to have a high level switch in this plan? What about changing the buffer oil? after a certain period of time because of high level alarm, it will be necessary to lower the oil level. Is it safe or not?
This despite the fact that we do not have this issues in pressurized API plan 53A or 53B.

I want to know if you have ever had any experience with Benzene pump with non-pressurized API plan 52?

Yes. We have pumps in high Benzene service with Plan 52. We do not have a high level alarm. Operators monitor the level at least four times per day. We do not typically see any increase in level. We do not need to routinely remove fluid to maintain level. We replace the fluid once per year. I feel this is safe.

Johnny Pellin

Thanks a lot for your feedback

mkfe3005,
The use of API PLAN 31 is a standard for Sundyne as the cyclone separator is built into the pump casing (not all models but most 300 series OH6s).
The use of an unpressurized dual seal, API PLAN 52 meets the minimum HSE requirements due to the presence of Benzene.
This sealing approach is common practice in the industry and meets the minimum requirements from a safety or RAGAGEP standpoint.

Since Benzene is a chronic carcinogen, short term exposure during the buffer fluid replacement should not be a concern, especially with the proper PPE (AND with proper procedures, exposure should be almost 0 and well below OSHA, other other local, limits).
The Seal pot should be piped to a closed drain header and drained without any possible exposure during a routine PM to change out the buffer fluid.

JJPellin is correct in replacing the buffer fluid, not just draining off the excess. The rate of change in level of the seal pot (going up or down) will determine if the change is due to normal seal leakage (seal's always leak - have to work properly) or if you have an actual seal leak that requires a repair.

If you plan on using a pressurized dual seal, API PLAN 53 A or B, suggest you work with the process licensor to determine an appropriate barrier fluid that is compatible with the process so that you do not inadvertently pick something that could contaminate a finished product stream, impact a downstream unit or poison catalyst. If you have already purchased the pump and seal, you will also need to work with the seal vendor since the API PLAN 52 may not have the reverse pressure capability to allow it to function as a pressurized dual seal.