Flow Assisted Corrosion (FAC)

[plantintegrity]

Has anybody got any info on FAC rates of CrMo - We are looking to change the MOC from C/S to CrMo (tubes)in a fixed shell and tube heat exchanger (steam on the shell side)3.5Barg / 100 Deg C aprox

 

[EdStainless]

The place to look is ASME either IJPGC or Nuc Reliability conf. procedings. There is a lot of info out there, just that I don't need it so I don't have it at hand.
Even small amounts of Cr help a lot. I have seen reheat lines fail from FAC. Sections of pipe with 0.15%Cr are fine and ones with 0.05% are eroded.
The T21 and 22 alloys are an order of magnitude better than plain CS.

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Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[unclesyd]

A little more information will be a great help to get assistance with your problem.

Where is your FAC occur ing and what is the media on the tube side?
What your flow velocities in the area of concern?


Your temperature is rather suspect on having several different problems with boiling or condensing.

I have never seen any difference in the behavior of the two materials in respect to corrosion and flow problems.

 

[eyec]

so far FAC has not been a concern for heat exxchangers but more on the reheat and economizer systems.

it is correct that a higher amount of Cr is better for areas suseptable to FAC.

i also believe that FAC is also more prevalent (where low Cr is used) just downstream of elbows (approx 1.5X the dia of the pipe).

 

[EdStainless]

Any transition can be an issue. I have seen it where pipe of two different walls were joined leaving and internal step.

Yes, Cr helps a lot in improving resistance to FAC. Even the normal variation in Cr seen in CS pipe can have an impact.

There are many factors in FAC, water chemistry is important and velocities. The worst cases involve two phase conditions. The wet steam in Nuc plants is real bad for FAC.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[stanweld]

SA-213 T2 tubes will be your most economical choice to mitigate FAC. It's a pity that the similar pipe grade was discontinued long ago. Maybe with continued concern regarding FAC, the old pipe grade can be resurrected in the ASME Code. It certainly has cost considerably more when replacement of CS must be done with P11 and P12 pipe.