Heat exchange corrosion

[ozfish]

I have 50mm hollow 316 TUBE with 80-100 deg C air running through - on the outside of the pipe I have 17-20 deg C bore (ground) water low in calcium some iron and manganese running past the tubes. The Tubes are pitting on the outside and failing.

I considered teflon coating but this would restrict the heat transfer that I am after.

I considered SAF2205 but was too difficult to source.

Any ideas

 

[metengr]

Your source of corrosion could be chlorides in the ground water that result in pitting corrosion on the OD of the 316 ss tubes or during off-line periods of the heat exchanger your setting up conditions for microbiological influenced corrosion (MIC) attack.

Try to sample the ground water for chlorides and, if possible, see if you can extract a pitted tube for metallurgical analysis to confirm the corrosion mechanism before deciding on corrective actions.

 

[EdStainless]

When you a pull a tube for examination you will want to analyze the scale on the surface.
i believe that Metengr is right, you will find chorides. While 316 has decent pitting resistance it has poor crevice (under deposit) corrosion resistance.
The next most logical alloy option is 2205.
You should not have trouble sourcing 2205. It is made in both welded and seamless to ASTM A789. Either would be fine for you. You can also use a thinner wall then you are using now because of the higher strength.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[ozfish]

Thanks for the advice. I have been advised of this in the past. We do have some chlorides in the ground water. The 2205 is not readily available in Australia and I was advised by Sandvik in OZ that they could not import a small qty - I need around 20 x 6m lengths.

 

[EdStainless]

????? You need to find an alternate supplier. It is a standard heat exchanger tubing grade. Try some of the distributors, or even a fabricator.
I can help you if you need it.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[mthakur]

Thats true, Sandvik may not be interested in supplying smaller lot, but you can always approach the agents. Sanicro 28 is another option if you dont have superduplex available, they also have good pitting and crevice resistance in chloride environment.

 

[EdStainless]

S28 would cost an arm and a leg. It would be cheaper to use a 6%Mo like AL-6XN or 254sMO. I would guess that those arre overkill for you, but availabilty may dictate.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[ozfish]

EdStainless thanks for your info. Can I take you up on your offer to assist - supply?

How will I contact you?

 

[EdStainless]

via the link in my sig
tks

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[mcguire]

I think the forum meister gets a commission on these transactions. (Just kidding, Dave)

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[EdStainless]

I will find something appropriate

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm