Vapor Pressure Margin 2

[CaracasEC]

What is the minimum Vapor Pressure Safety Margin between the seal chamber pressure and vapor pressure of the process fluid. I am comparing whats best 53B or plan 11 + 52. Rated seal chamber pressure is 17.3 barg and vapor pressure is 16.61 bara. thanks

 

[Airsporter1st]

API 682 3rd Edition says a margin of at not less than 30% between seal chamber pressure and maximum fluid vapour pressure, or a 20 degC product temperature margin based on maximum process fluid temperature.

 

[CaracasEC]

Hi Airporter1st,
Thanks for these data, i will look again on the API 682 as this is the fact i'm looking now for almost 3 days and yet not found. Is it also a rule of thumb that the seal chamber pressure should be higher than 1 bar to the fluid vapor pressure?

 

[Airsporter1st]

Like many things in API 682, this particular statement appears where you would not expect to find it!!!

It is at the bottom of Page 25 of the 3rd Edition.

The rules of thumb I have used in the past were 25 psig higher for S.G. > 0.5 and 50 psig higher for S.G. < 0.5. I am not sure now whether they came from other standards, an earlier version of 682 or were just company standards.

For me, therefore, 1 barg margin would not be enough.

 

[CaracasEC]

Hi Airporter1st,
Thanks for the infos. I have now found the corresponding page....