Oil and Gas Upstream

All,

In my head, the corrosion limit for O2 affecting the corrosion rate of carbon steel is between 20 and 50 ppm. I am looking at some pipeline tariffs and seeing numbers of up to 1 mol % allowed which seems more of a flammability limit than a corrosion limit.

What do you consider to be a safe level of O2?  Does that vary with partial pressure? What drives your response, general corrosion, inhibitor performance, interactions with H2S, flammability concerns? 

All thoughts welcome.

Krista

Hi Krista.  Rule of thumb is normally 20-50ppb, so 1000x less for oxygen concentration and where it can see an affect on corrosion rates. 1% mol would be huge and agree not likely the right number when thinking about corrosion rates. There are numerous corrosion inhibitor and lab studies done with synbrine fluids and Linear Polarization Resistance probes that show how the rates can increase from a baseline condition where no oxygen is present to when oxygen starts flowing into the autoclaves.  

The issue with oxygen, is that in general it is very difficult to find a corrosion inhibitor that will protect against oxygen corrosion.  They do exist, but are fairly specialized in my experience therefore any off the shelf corrosion inhibitor should be questioned to the chemical supplier on what its resistance/protection is against oxygen corrosion.  

The question to ask is where the oxygen could be coming from in a Sales Oil system and try to stop the oxygen from getting in before it becomes a larger problem. Leaking valves or sales oil pumps?  If not yet present or measured and just overall concerned by a spec for the oil, then normally you would not be seeing oxygen in it. 

In general a good pigging program to ensure the water keeps moving along and doesn't drop out at a low spot helps. If oxygen is a threat, then it is normally the first few hundred meters of a steel line that will see the most damage as the oxygen gets consumed fairly quickly when in contact with carbon steel (I've seen that a few times in pipelines that I've managed where you think a crude sales line should be relatively good from an internal corrosion perspective and then find swiss cheese on the first km of the pipeline related to some continuous oxygen that has been sucked in by venturi affect.

Hope that helps on some of the questions.  Others can chirp in for the H2S/flammability concern.

Evan Bloomfield

All,

In my head, the corrosion limit for O2 affecting the corrosion rate of carbon steel is between 20 and 50 ppm. I am looking at some pipeline tariffs and seeing numbers of up to 1 mol % allowed which seems more of a flammability limit than a corrosion limit.

What do you consider to be a safe level of O2?  Does that vary with partial pressure? What drives your response, general corrosion, inhibitor performance, interactions with H2S, flammability concerns? 

All thoughts welcome.

Krista

All,

In my head, the corrosion limit for O2 affecting the corrosion rate of carbon steel is between 20 and 50 ppm. I am looking at some pipeline tariffs and seeing numbers of up to 1 mol % allowed which seems more of a flammability limit than a corrosion limit.

What do you consider to be a safe level of O2?  Does that vary with partial pressure? What drives your response, general corrosion, inhibitor performance, interactions with H2S, flammability concerns? 

All thoughts welcome.

Krista

Hi Krista, In my experience, we have observed O2 values ​​of up to 20 ppb and have had corrosion rates exceeding 3 ppb. We have corroborated these measurements using various techniques. Regarding corrosion control, what hasn't worked best has been the oxygen scavenger. Corrosion inhibitors rarely reduce corrosion rates better than a scavenger. We are currently using ammonium bisulfite as a scavenger with excellent results, reducing the concentration from 1 ppm to values ​​of 20 or 0 ppb. A good treatment should consider temperature, injection point, potential O2 ingress zones, and the correct stoichiometric balance to calculate the O2 scavenger dosage.

All,

In my head, the corrosion limit for O2 affecting the corrosion rate of carbon steel is between 20 and 50 ppm. I am looking at some pipeline tariffs and seeing numbers of up to 1 mol % allowed which seems more of a flammability limit than a corrosion limit.

What do you consider to be a safe level of O2?  Does that vary with partial pressure? What drives your response, general corrosion, inhibitor performance, interactions with H2S, flammability concerns? 

All thoughts welcome.

Krista