FAC in oxgenated environment

[maxer64]

My question is how it is possible for there to be single phase flow accelerated corrosion in an oxygenated environment?

I haven't seen anything about it in any of the EPRI documentation, and wondered if anyone here had any experience with this?

 

[metengr]

How? I have seen FAC for a boiler that has been converted to OT (oxygenated treatment). The typical location for FAC was within the deareator vessel itself (where oxygen and other gases are removed within the deareator) and oxygen is added downstream. We are evaluating replacing the deareator vessel with feedwater heaters because this is a once-through unit with polishers.

 

[EdStainless]

FAC hinges on two issues
The shear at the surface due to local flow velocity;
and how robust the surface film is.

Of course the flow shear is much greater in turbulent two phase flows, but even in single phase it can be rather high.

The surface film is dictated by more than just oxygenation. The pH, temperature and other species in the water can have a strong influence on the composition and morphology of the film. Just having plenty of oxygen does not assure that you will have the strongest surface films.

Carbon steels with little or no Cr can be very sensitive to this.
Metengr, your concept in in line with best practices these days. Many plants with DA between the LP FWHs and the HPs are running them differently than they used to. Your condenser should be your primary control on dissolved gasses and oxygen content in an OT system.

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Plymouth Tube

 

[SJones]

Corrosion Vol 63, (8), 2007 pp770-780

In an oxygenated environment, FAC should be reduced but not eliminated as the factors outlined by Ed (who may have read the same paper) are still present.

Steve Jones
Materials & Corrosion Engineer

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

 

[strider6]

WHAT IS FLOW ACCELERATED CORROSION?

Flow accelerated corrosion (FAC) may be defined as a process whereby a normally protective oxide coating dissolves into a rapidly moving water, or a water/steam mixture.? In the case of plain carbon steels, this process occurs under very specific, well-defined environmental parameters. Principal among these parameters are temperature, pH, oxygen content, and water velocity.

http://www.onepetro.org/mslib/servlet/onepetropreview?id=NACE-98721&soc=NACE

i suggest u to read this article. i think you can also dowload it from NACE:
98721 FLOW ACCELERATED CORROSION

http://web.nace.org/Departments/Store/product.aspx?id=dc9161e1-4bc1-41ff-aa0d-b8fbd626942a

S



Corrosion Prevention & Corrosion Control