Welding SS2205 - Duplex Stainless steel to 316L

Question

Welding SS2205 - Duplex Stainless steel to 316L

Gears6580 (Mechanical)

(OP)

22 Aug 24 22:40

Hi All,

I am looking to see if there is a potential risk of galvanic corrosion when welding a 316L nozzle to a 2205 duplex pipe with E2209 electrode. I understand that there is a risk of SCC and may even accelerate the SCC at the welds but ignoring that for now, will there be any galvanic corrosion?

Medium - filtered water
Temp - 98 degree Celsius

Thanks in advance.

EdStainless (Materials) · Answer 1 · 2024-08-23 16:02:56

You would need conditions which would be attacking the 316L anyway.
Why bother with 2209 for filler? Why not just use 316L?
The welds will barely be duplex if you have equal dilution.
And yes SCC of the 316L adjacent to the welds is a real possibility.
The 2205 has much lower CTE, so in addition to weld stresses you will have thermal stress issues.

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Gears6580 (Mechanical) · Answer 2 · 2024-08-28 00:23:49

Thank you EDStainless.

Can you please elaborate on the conditions for attacking the 316L?

EdStainless (Materials) · Answer 3 · 2024-08-29 20:47:58

If we assume an aqueous environment and a starting point of 120F, 100ppm Cl, and pH=7
If you raise Cl, temperature, or lower pH then pitting corrosion becomes nearly assured.
SCC in 316L is possible at temperatures above 100C even with low Cl levels if the stress is high enough.
The higher the temperature and the lower the pH the faster it will initiate.
I have entire books written about SCC in austenitic stainless steels.

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mfgenggear (Aerospace) · Answer 4 · 2024-08-30 17:28:15

Once corrosion starts it is difficult to remove. My opinion it has to be mechanically removed.

EdStainless (Materials) · Answer 5 · 2024-08-31 16:15:55

Once corrosion starts the parts remaining life is measured in days or weeks, not years.
You can remove corrosion, but I have never seen someone remove enough material to actually stop it.
Pitting and cracking in SS is very small and localized. And usually very deep.

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mfgenggear (Aerospace) · Answer 6 · 2024-08-31 16:20:08

Ed
Agreed if not immediate action is taken.
Generally I should say still in the manufacturing cycle. Once past that.
Then it depends.
Never had luck with chemical removal even passivate or pickle.
On the other hand of tolerance allowed I have had success mechanically removing. But ya not always 100%

dik (Structural) · Answer 7 · 2024-08-31 17:08:38

CTE?

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EdStainless (Materials) · Answer 8 · 2024-08-31 18:19:00

Coefficient of thermal expansion
Near RT 316L will be 8.9/F and 2205 will be 7.2/F, roughly a 25% difference.

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P.E. Metallurgy, consulting work welcomed

dik (Structural) · Answer 9 · 2024-09-12 17:27:40

Thanks...

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So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

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Welding SS2205 - Duplex Stainless steel to 316L