Anti-Icing Tubes Pitting Corrosion Problems

[daviwy]

There's known issues about pitting corrosion occuring on our anti-icing tubes on the air intake heat exchanger units fitted on our gas turbines. These operates at above 420degC.

Before i kick off this into a big project in replacing all our tubes with materials with better Pitting Resistance Equivalent number (PRE). I have done my own initial research and drafted the following;

Corrosion source/type: sulphur from neighbouring plant polution, atmospheric assisted corrosion.


Questions:
. Is coating/painting a suitable remedy for these tubes?
. As anyone experienced same issues and how did they deal with it?
. How do you mitigate against sensitization?
. What material is best for tubes operating over 420degC to resist sensitization and has high PRE?

Deduction
My deduction was items with high melybdenum and chromium content i.e. one of the following:
SA-312 TP316L : 16Cr-12Ni-2Mo (Pipe)
SA-213 TP316L : 16Cr-12Ni-2Mo (Tube)
SA-268 SA4735 : 29Cr-4Mo (Tube)
SA-249 SA4400 : 18Cr-2Mo (Tube)

Please advise

Thanks

Please do drop more information or knowledge you have on this subject they will all be taken in and appreciated.


David O.
Mechanical Engineer
Graduate as of: 2007
Oil, Gas & Power

 

[rmw]

I have read the OP several times and I have the following questions. What is the metallurgy of the current anti-icing tubes that the sulphur attacked? Are they bare tubes or finned tubes? Is your heat source for the anti-icing fluid exhaust heat or another source?

Are you more worried about the pitting due to the sulphur or sensitization due to temperature?

Does your anti icing fluid have to be at 420C? What is the fluid?

What is your minimum operating ambient temperature?

Give us some more information so we can try to help you.

Meanwhile, see thread338-233266 for some good background reading on what you are asking. I gave a link to a good article by Plymouth Tubing in that thread and others had good links posted as well.

rmw

 

[daviwy]

Rmw thanks for your comments, I am awaiting those information myself from our operators and but I can at least answer a few

we are not worried bout sensitization but more about pitting corrosion from Chlorides and sulphur.

the anti-icing fluid is not at 420degC but to my understanding, sensitization is prone to metals above that temperature. Although it's not our key concern now, my thought was that we might as well mitigate against it instead of waiting to see if it becomes an issue.


Thanks for the link and once I get more information which might be over a week due to the festive period, I will get back to you. Cheers


Please do drop more information or knowledge you have on this subject they will all be taken in and appreciated.


David O.
Mechanical Engineer
Graduate as of: 2007
Oil, Gas & Power

 

[rmw]

You never did answer as to what the current tube material is.

rmw

 

[daviwy]

The current tube material is SS 304, bare tubes
operating at less than 1.5barg and at about 140degC and the fluid is steam from the LP line

One of the method of replacement we are considering is thermal spray of SS 316 on the existing 304 to reduce cost.

Please do drop more information or knowledge you have on this subject they will all be taken in and appreciated.


David O.
Mechanical Engineer
Graduate as of: 2007
Oil, Gas & Power