API PLAN

[LP ENGG]

Hi,
I received a query from a customer who has a vertical pump with a component seal and a labyrinth, with pressurized air supplied between the seal and labyrinth. He wants a dual seal to prevent any leakage to the outside (the fluid is water used in a nuclear plant). I have suggested a dual cartridge seal with a dry, non-contact seal on the outboard side. The suggested plans are API Plan 13 for the inboard side and API Plan 75 for condensed water collection, with API Plan 76 for vapor collection. Is it appropriate to use both plans simultaneously, particularly in vertical pumps? If not, would a combination of API Plans 72 and 75 be sufficient?

 

[BEMPE16524]

I feel that I have answered this somewhere. Anyway, this is not from me but from different sources which you can consider:

Using both API Plan 75 and API Plan 76 in combination with API Plan 13 may be excessive and complex, particularly in a vertical pump application. Here’s a breakdown of the appropriateness and possible alternatives:

1. API Plan 13 (Inboard Side)
   Plan 13 is suitable for vertical pumps, as it recirculates fluid from the seal chamber back to the pump suction, maintaining pressure balance. It is commonly used to control seal chamber pressure, and it works well with an inboard seal in a dual seal setup.
2. API Plan 75 and 76 (Outboard Side)
   • Plan 75 is effective for collecting and managing condensed liquid leakage from the outboard side, which is useful when dealing with water vapor that condenses.
   • Plan 76 is intended to capture vapor leakage from the outboard seal, venting it safely for applications where vaporized fluid may escape.
     In a vertical pump, both plans may add complexity without significant benefit, as typically only one of these would be necessary based on whether the leakage is expected to be liquid or vapor. In this case, if leakage is primarily condensed water, Plan 75 alone should be sufficient, simplifying the system without compromising containment.
3. Alternative Plan Combination: API Plan 72 with API Plan 75
   • Plan 72 provides an inert gas buffer (often nitrogen or air) to the outboard seal to prevent contamination. This plan is valuable in applications requiring strict containment and low-pressure environments.
   • Plan 75 would then handle any condensed water leakage effectively.
     This combination (Plans 72 and 75) should meet the requirement for preventing any leakage to the atmosphere, especially in a controlled environment like a nuclear plant where environmental containment is crucial. Plan 72 would act as a secondary barrier, and Plan 75 would manage any liquid leakage, making this setup both efficient and straightforward for a vertical pump.

Recommendation:​

For this application, combining API Plans 13 (inboard), 72 (air buffer for outboard), and 75 (condensed liquid collection) should suffice. This setup would prevent both liquid and vapor leakage effectively while minimizing unnecessary complexity.