Acceptance of general corrosion

[MaxCarb]

I have problems with the presence of some points of general corrosion in the Air-Intake conduit of a gas turbine.
The material is 304.
Is there an international standard or norm or something like this that regulate the presence of this points of general corrosion? i mean something like a "density" of points per m2?

Thanks

 

[metengr]

MaxCarb;
What I believe you are asking is for some type of condition assessment method to evaluate the extent of pitting corrosion in the air intake duct work, correct?

 

[EdStainless]

If it is at points then it is not general corrosion. We usually use the term general corrosion to talk about uniform material loss.
If you are having pitting on an intake duct I suggest that you look at it from an integrity point of view. Will you have leaks or will you be at risk of structural failure.
Sometimes because of the way that the unit was fabricated the pitting will be concentrated near supports and you risk having it collapse.

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Plymouth Tube

 

[rmw]

Is this pitting due to the atmosphere that passes through the duct or due to sloppy fabrication (use of carbon steel tools and brushes) when it was built?

Is it localized to a certain section or portion of the duct, or uniform around the entire periphery of the duct?

Do you have inlet chilling, evap cooling, fogging or deicing or other contributors to the presence of corrosive agents?

rmw

 

[unclesyd]

Can you post a picture?

 

[MaxCarb]

Same pictures of the situation.
Now we are brushing and pickling.
But i think it's not crevice corrosion. It seems to be general corrosion due to atmospheric attack.

 

[stanweld]

It appears to be corrosion due to irom contamination.

 

[EdStainless]

Certainly from surface contamination.
You say that you are brushing? Use abrasive flap wheels and make sure that they are new.
And also make sure that you rinse the pickling paste off very well.

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Plymouth Tube

 

[TomEun]

I also think the root cause is an iron contamination, such as by grinder wheel which was used for carbon steels. As far as I know there are no specifications for corrosion and the acceptance categories of conduit and its structure in the industrial standards. Only owner’s company standards may be applicable.

For the repair, you may do the acid cleaning per ASTM A380 and repair welding as well as making drain holes (diameter 1/4”) at the water pocket/stagnant areas.

Thomas Eun