Upon reading the attached documents, there does not appear to be a possibility of pump damage when loosing the barrier fluid nitrogen pressure. However, it is up to you and your plant colleagues to determine if there is a risk of the pumped fluid leaking to the atmosphere and the risk associated with this instance.
Sorry, I will add to say that there could be some leakage of the process fluid into the seal faces and possibly shorting the life of the seal. Again, this is up to you and your plant colleagues to decide about the risk. It may also depend on the specific seal purchased.
Certainly operation of the pump cannot continue endlessly without the proper seal buffer. For how long? Up to you again.
To be honest, there will be no pump damange, but there will be seal damange. The seal has springs that hold the seal faces together. This tensions is adjusted based on the pressure differential across the seal and the size of the seal faces (i.e. the seal application) to ensure that proper fluid lubrication exists between the seal faces.
If the pressure on the exterior of a plan 53 is lost, then the only thinkg holding the seal faces together are the springs in the seal, itslef. I would think that you would see seal failure rather quickly (depending on the pressure differential).
GHartmann is correct when he says that you need to consider the containment issues. The plan 53 was selected (probably) to limit exposure of the liquid to the atmosphere (because the whole idea is that nitrogen is pushed into the process when a seal fails, as opposed to process fluid being push to atmosphere when a seal fails).
Seal damage can easily lead to pump shaft damage from the heat, or if the seal locks up it will spin the sleeve and damage the shaft. You may end up having to cut the shaft to remove the seal... Not fun.
