A relationship between dissolved oxygen and corrosion

[Dawoon]

Normally speaking, dissolved oxygen could act as an accelerating parameter of corrosion.

I want to know more details.

Is there a quantitative relationship like if D.O. is 1 ppm, the corrosion rate will go up twice?

Or is there a minimum guideline of D.O. to avoid corrosion?

If anyone has an experience, advise me plz.
Thanks for your kind answer~

 

[CoryPad]

The relationship between corrosion rate and dissolved oxygen is linear. There are multiple variables (fresh water vs. salt water, thickness of diffusion barriers (surface film/oxide), stagnant vs. flowing, etc. You should review books on this subject, such as those by Fontana, Jones, and Uhlig.

 

[zdas04]

Oxygen pitting is a cathodic reaction like MIC and CO2 corrosion. The dissolved oxygen is the cathode and the pipe is the sacrificial anode. There is a lot of published data on this subject that is collectively horrible science. In one often quoted study from PRCI (I'm not going to include the link since I don't want to propagate that dreck), they did their analysis with nitrogen as the carrier gas and the minimum gaseous O2 level was 100 ppm--then they concluded that 10 ppm was the maximum safe level of O2 without any experiments to support that number!

There are really two parts to this analysis: first, the gaseous oxygen has to dissolve into the standing liquid; second, the dissolved oxygen has to create a cathodic cell. Researchers have more agreement than disagreement on the affect of pressure on the rate that oxygen will dissolve in distilled water, but when it comes to the temperature and the TDS of the water the researchers cannot even agree on the direction of the change in the Henry's Law constant. Without that number you can't convert a gaseous O2 number into a dissolved O2 number.

When talking about how much oxygen can dissolve before a cathodic cell is created you have another can of worms. Looking at Pourbaix Diagrams I get a number around 150 ppb for API 5L grade pipeline steel, but others get numbers as low as 9 ppb without specifying the steel they are talking about.

This is a really hot topic right now since the natural gas gathering companies have latched onto the PRCI report and are writing contracts with a 10 ppm max--there is no science in the world that supports the concept that 1 ppm is better than 10, or 100 or 1,000, or 10,000.

At NACE Corrosion 2009 in Atlanta in March, the agenda was again amazingly short on any discussion of oxygen corrosion. There was a lot of discussion of Cathodic Protection, CO2, H2S, and MIC, but I didn't find anything on Oxygen when I was looking at the agenda trying to decide if I wanted to go (I didn't go). One big problem is that this topic is being addressed by any number of lawsuits and researchers seem to shy away from that sort of scrutiny.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

Remember, being ignorant isn't your fault; staying ignorant is.

 

[SJones]

You won't get a straight answer because it is totally dependent upon the specific system that you are dealing with. If you could elaborate upon the specific system: fluid, material, flow, pressure, temperature, etc you are considering we may be able to render more assistance. For industrial waters, see if you can find the following on the web:

I Andijani, S Turgoose, Prediction Of Oxygen Induced Corrosion In Industrial Waters

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[strider6]

if we talk about water with dissolved oxygen then the usual accepted limit to consider water as "non corrosive" is 10-20 ppb of oxygen. You can find reference for this value in NORSOK M001 (see water injection)

http://www.ivt.ntnu.no/ipm/und/fag/k_i/robmat/Forelesningsmatriell/13.10.2004 NORSOK M-001.pdf

there are also formulas that allow you to calculate the corrosion rate based on the DOD and also some graph, see the link below and look at page 20.

http://www.corrosionist.com/public/showthread.php?tid=29

S

Corrosion Prevention & Corrosion Control