4 replies to this topic

[ankur2061]

Is blanketing inert gas (Nitrogen in my case) purity of 97% acceptable where the application is to provide blanketing for the pupose of preventing a flammable atmosphere in the tank rather than prevent chemical oxidation of the tank contents.

The actual consumers would be oil/gas separators and gas/liquid scrubbers.

Is there a criteria which says that a volume percent of less than 8% oxygen in any enclosure (tank) would correspond to an inert atmosphere preventing ignition.

regards,
ankur2061

[proinwv]

ankur2061

We need more information.

What composes the 3% of your gas?

I find it unusual to have a 97% N2. What is the source of this mixture?

The relationship between %O2 and the possibility of ignition depends upon your product's flammability characteristics.

I invite some of our ChE's to address the last issue also.

[oldliar]

Ankur2061,

The 97% purity is typically provided for the naval vessel such as product carriers etc. I guess the system is made up of N2 membranes and that if you want a higher purity (99,9% N2), you would not meet the required flowrate unless you use a lot of membranes and have a hughe capacity on your instrument/service air compressors. The 8% is given in the SOLAS rules (ref IMO), whereas most suppliers of these systems will say 3% O2 max or 97% N2 min.
This is the rule of thumb for all crude vessels, product carriers, FPSO's, FSO's etc who fall under the IMO/SOALS rules as well as the selected classification society. If you look at Bureau Veritas rules (www.veristar.com) and search for "nitrogen" you will find the applicable rules and oxygen limits.

However, I guess you shouldn't mix the phrase "blanketing" and nitrogen as 97% nitrogen is, by these rules, consideres inert whereas the gas used for blanketing is by far considered inert (at least not by discussing with the vendors supplying this kind of equipment).

I hope this made some sense?

[proinwv]

Sort of....and the question is then?

[oldliar]

The question is clear and the answer is yes. There is a requirement as long as your installation is offshore and non-fixed so that the IMO/SOALS rules are applicable.