Corrosion of SS304 while SS316 remains intact

[EmmanuelTop]

Good day to everybody,

I am not a corrosion engineer but there is a really weird case here. I would appreciate if somebody can give a hint.

We have production manifold equipped with SS 316 strainer mesh welded onto a CS perforated plate. Manifold is feeding 5 compressors in parallel, and each one of them is equipped with a conical strainer made of SS 304 welded onto CS perforated plate.

The manifold handles 2-phase flow consisting of sweet gas at 6 barg pressure, and produced water (pH~5.5 and 20,000 ppm Chloride). Compressor suction lines normally handle gas ONLY but this is the only point where corrosion has been observed.

Can you throw some light on this phenomena?

Many thanks in advance.

http://antwrp.gsfc.nasa.gov/apod/astropix.html

 

[TomDOT]

I don't know why it would be a weird case, 316 is more corrosion resistant than 304.

 

[EmmanuelTop]

Thanks for the reply. The confusing part is that 316 is exposed to liquid water whereas 304 sees wet gas only.

http://antwrp.gsfc.nasa.gov/apod/astropix.html

 

[EdStainless]

The conditions for the 304 are more aggressive.
With wet gas the conditions probably shift, sometimes wetter and sometimes dryer.
The result is that impurities (salts) can concentrate on the material. The residue on the surface of the 304 is likely saturated (25-30%) brine.

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Plymouth Tube

 

[EmmanuelTop]

Would it be OK to use 904L instead of 304? I'm asking because there is some amount of sand particles (<10 micron size) and wondering if 904L has better or worse resistance to erosion than 316?

http://antwrp.gsfc.nasa.gov/apod/astropix.html

 

[EdStainless]

It should be about the same.
I has slightly better pitting resistance.
If you have seen rapid attack of the 304 though I doubt that 904L is good enough.
A 6%Mo superaustenitic or even a NiCrMo (C type alloy) may be what it takes.

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Plymouth Tube

 

[Ripz]

316 SS is more corrosion resistant than 304 SS.

You didn't mention the CS Perforated Plate? I'm assuming since the 304 SS is being corroded, the CS plate should be destroyed by now.

 

[EdStainless]

The corrosion resistance difference between 304 and 316 is very small.
In most environments that attack 304, 316 will eventually corrode also.
It will take longer for the corrosion to start in 316.

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Plymouth Tube

 

[EmmanuelTop]

CS plate is of much higher thickness than the 304L mesh. It hasn't been destroyed but it had corroded as well. Visually it does not seem to be dramatic.

http://antwrp.gsfc.nasa.gov/apod/astropix.html

 

[EdStainless]

The CS will have general corrosion, so the attack will be spread out.
The SS will suffer localized pitting and crevice corrosion, it will have holes in it first.

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Plymouth Tube

 

[zdas04]

Do you have any pictures of the corrosion? In wet gas, the transitions that EdStainless talks about can give you phase change scale that can look like corrosion. Also at that pH, significant amounts of CO2 can cause either "mesa attack" or "acid attack" (the pH is at the boundary between the two modalities). Pictures and a gas analysis would be a big help to diagnose this.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[EmmanuelTop]

Photos attached.

http://antwrp.gsfc.nasa.gov/apod/astropix.html

 

[Ripz]

Are you sure that's corrosion and not some type of scaling? If 316 Stainless Steel got to that point, then your CS component should have been destroyed.

 

[Ripz]

In fact, all three strainers look to be made of Carbon Steel.