10 ppm Oxygen

[zdas04]

I was at a NACE presentation by a vendor last week and the guy said that "everywhere in the country except ________ the limit on oxygen is 10 ppm in gas transmission lines" (I think he said "except Michigan where it is 1,000 ppm", but I can't be certain that is what I heard). After the meeting I called him on it and he said "that is the way it is and I don't have to provide references" (the guy was an idiot).

Looking through several state's regulations, I can't find a single one that mentions oxygen in natural gas at all. Looking at pipeline tarrifs, most of them have a 2,000 ppm (0.2%) limit (some are higher, some lower, didn't see any that were near 10 ppm).

I'm starting to see gas gathering companies try to slip a 10 ppm Oxygen number into new contracts. They seem to still be hungry enough to be willing to back off if you push-back hard enough, but it is becoming troubling.

Does anyone have any any idea where the 10 ppm number that is starting to be kicked around came from? I can't find any references that talk about gaseous oxygen being a problem lower than about 500 ppm (using Henry's law, 500 ppm at 50 psig and 60F will result in over 9 ppb dissolved oxygen in distilled water). I've only been able to find one NACE paper on the subject and it was long on arm waving and really short on data.

David

 

[dcasto]

The 10 ppm number was started by a company that contaminated their underground "water drive" storage with O2 a long time ago. The O2 got bacteria active and the bacteria started to create H2S. So they had lots of sour gas in storage. They switched to a lower tarriff amount (10 ppm) to try to stop the H2S. In the colorado front range they inject up to 10% air into the gas stream at 1000 psig going to TBS's. Again 2+% at 1000+ psig....

If the gas steam has no free water, then how can there be any corrosion. Similarly, why is there a limit on CO2 and N2 in a pipeline? And don't answer that second one with its an effiency thing. The piplines charge a tarriff on BTU's and a pipeline or compressor doesn't know a thing about a BTU, its MCF's that causes effiency or capacity constraints. Similarly with WOBBE numbers......

Inerts are becoming quite an issue, IMHO, but the pipeline hide behind their tarriffs when it suits them.

 

[zdas04]

The more I dig into this, the more I think that all of the parameters in the tarrif's gas quality language are just arbitraty. I can't find any reason for the magnitude of any of them.

I'd forgotten about utilities doping their sales gas with air in the communities north of Denver. Best I can remember they started that after they messed up and put 1,400 BTU gas into a bunch of older homes and burnt them to the ground.

The oxygen reaction that everyone is worried about in mild steel is a cathodic reaction where the oxygen raises the potential of the standing water in the line and the pipe acts as the anode. Seems to me that controlling the standing water and/or maintinaing the cathodic-protection system would be easier, cheeper, and more effective than arbitratially and unilaterally imposing stupid oxygen limits, but that involves spending their money instead of forcing the producers to spend theirs.

David

 

[dcasto]

Public Service Company presented a paper at several pipeline industry meeting title "To AIR is Human". We also added a lot of air in North Dakota and Montana in the 70's and 80's because we we paid on an MCF and not MMBTU basis.

 

[zdas04]

Is there any way to find a copy of that paper? I did a Google search on the string and got a bunch of "air guitar" links and global warming sites. It sounds like that paper is something I really need for a project I'm working on.

David

 

[unclesyd]

zd4as,
If dcasto doesn't have a copy of the paper you might try the Linda Hall Library.

http://www.lhl.lib.mo.us/

 

[dcasto]

The last time Isaw it presented was a Gas Processors Association meeting in Denver in about 1998. It was by Excel (the old Public Service Company of CO).