Oxygen concentrations after inerting
Oxygen concentrations after inerting
(OP)
I have a question with respect to residual oxygen concentration in a process unit, vessel etc after inerting.
The usual limit of oxygen (in nitrogen) I have usd in refineries are 0.5 or 1.0 vol% after an inerting step. The the inerting is regarded to be complete and accepted. However looking at figures such as LOC combined with LEL/HEL this figures is about 11-12 vol% oxygen.
In my past I have been accustomed to use the 1.o vol% limit without giving it much consideration. however I cannot find a god explanation why such a low number should be used. Pratically I can buy into using a margin from e.g. LOC to cover for uncertanities in sampling/analyses and that all part of a unit/system that has been subject for the inerting havent mixed ideally. Naturally if hydrogen can be present I an see a reason for a lower limit, but in the case there is no hydrogen present, should the limit be this low?
The 1.0 vol % seems to be an industry practice. Is there anything I forget, overlook here.
Would be very much interested to hear others view on this subject.
Thanks
The usual limit of oxygen (in nitrogen) I have usd in refineries are 0.5 or 1.0 vol% after an inerting step. The the inerting is regarded to be complete and accepted. However looking at figures such as LOC combined with LEL/HEL this figures is about 11-12 vol% oxygen.
In my past I have been accustomed to use the 1.o vol% limit without giving it much consideration. however I cannot find a god explanation why such a low number should be used. Pratically I can buy into using a margin from e.g. LOC to cover for uncertanities in sampling/analyses and that all part of a unit/system that has been subject for the inerting havent mixed ideally. Naturally if hydrogen can be present I an see a reason for a lower limit, but in the case there is no hydrogen present, should the limit be this low?
The 1.0 vol % seems to be an industry practice. Is there anything I forget, overlook here.
Would be very much interested to hear others view on this subject.
Thanks





RE: Oxygen concentrations after inerting
You may find some answers by visiting thread798-33615: How to Calculate Flammability of gas mixture and thread135-116595: Flammability limits in oxygen and the links therein.
RE: Oxygen concentrations after inerting
Some degradation mechanisms due to O2 are difficult to predict before hand and the designers assumed an O2 free environment. That could also be a reason why the industry standard is to get the O2 level down as far as possible before introducing process fluids.
Some examples of damage due to "higher" levels of O2, I can think of: degredation of MDEA - corrosive products will manifest themselves after months; pitting if there are Cl ions.
RE: Oxygen concentrations after inerting