Corrosion in Duplex stainless steel pipes 3

[Salmet]

Dear Members,
After 3 months of Untreated sea water service at ambient temperature, 65 Bar pressure, Radiographic testing of welded duplex stainless stainless UNS S32205 with ER2209 TIG filler wires, severe corrosion pits have been observed. Please refer to attached snaps of RT films. Please share your expert opinion. Should S32205 be used for Un treated sea water service?

Thanks in advance.

Salmet

 

[EdStainless]

No, I would not expect 2205 to survive in untreated seawater.
I have seen 2205 used successfully in higher Cl environments, but those were free from all biological activity and they were below ambient temp.
Have you sent a camera inside these? I'll wager that there is significant biological growth, especially along the welds and this has resulted in crevice corrosion of the weakest material.

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P.E. Metallurgy

 

[Salmet]

Thanks Ed Stan. I am sharing here a video of a corroded Flange joint adjacent to pump. I would request your expert opinion on it.

https://drive.google.com/file/d/1iIukuxi1Yj9k54Ziy4qSKjIB0dnM40Fi/view?usp=drivesdk

Other radiograps are showing uniform distribution of corrosion pits on and around weld joint (over base metal). I would request elaboration of biological activity here.

THANK YOU

 

[EdStainless]

Salmet, Let's back up a little here.
When this was fabricated you required S32205, correct?
You also required A923 testing?
Did you require A923 as part of the weld qualification?
Did you require that the ID of the welds be free from discoloration?

And, is this pipe full of water at all times?
Does it ever sit static or allowed to partially drain?

You have a major issue. Perhaps the easiest and least costly alternative is to look into resin lining the existing pipe. You likely have places in this line will be leaking withing the next month or so otherwise.

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P.E. Metallurgy

 

[weldstan]

In addition to Ed's statements and questions, did you hydrotest with seawater and did you leave the hydrotest water in before commissioning?

 

[Salmet]

Thanks Ed and WeldStan,

1) We were asked to weld install S2205 Lines i.e. Materials selection was at clients end.
2) ASTM A923 was not considered a part of procedure qualification, but Ferrite Number Analysis was. The PQR test coupon and weldments had delta ferrite number within limits.
3) Most of these joints were shop welds, with controlled parameters and the textures of welds were normal.
4) These pipes usually remain pressurized with untreated sea water and occasionally drained for maintenance purpose. During past three months, pipes were drained 3-4 times.
5) These lines were not hyro statically tested, instead were put to service after RT.

In my point of view, resin lining cannot with stand 65 BARS pressure. Please specify if any resin lining can.

Please suggest, What should be the course of investigation. Should I go for the analysis of black slug as visible in the video. What haunts me the most, is the deterioration of root passes within a span on 3 months, and that the base metal and weld metal had uniform distribution of corrosion pits.

 

[EdStainless]

A plastic liner installed inside of this pipe (after good cleaning) would have the same pressure rating as the metal pipe.
What about the color of the welds? Was there any heat tint? Were they even inspected?
If the seawater was filtered and chlorinated then these pipes might have a chance, that is if the welds were free from heat tint and would pass an A923.
But in the long run 2205 is not robust enough for this service. That is why people use superaustenitic (6%Mo) or superduplex pipe for raw seawater service. And corrosion testing needs to be part of the weld qualification process.

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P.E. Metallurgy

 

[SJones]

Just to get things wrapped up: what was the ambient temperature of the exposure?

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[Salmet]

Thanks Ed and SJones,
The color of welds were normal, as were welded under strict supervision, Root passes were visually inspected by qualified inspectors.
The ambient temperature at service is between 30 to 40 degrees celcius.
Usually, weldments, if done properly, have superior metallurgical and mechanical properties,so was our case. The most effected joint was the one between reducer and pipe. Can stress concentration due to thickness mismatch at hight pressures, play catalytic role?

 

[SJones]

"30 to 40 degrees Celsius" - say no more.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[EdStainless]

What plays a role is a series of things;
1) there IS metallurgical damage to the base metal adjacent to the weld
2) any slight imperfection on the ID of the weld (miss-match, lack of fill, splatter, slag, heat tint) will be a place that is much more easily corroded
3) because the weld metal does not match the base metal (it never does, even in autogenous welds there is always a difference) there will be small corrosion currents. These currents tend to attract and promote biological growth.

So the place in the pipe that has the least corrosion resistance will see the most biofouling. If the alloy selection is at all borderline this assures crevice corrosion starting in or along the welds.

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P.E. Metallurgy

 

[weldstan]

As Steve implied, at those temps, there is no chance of success in mitigating corrosion in the stated environment. 2205 is simply the wrong choice.

 

[MagBen]

You will need an alloy with PREN > 40. 2205 has only about 36. Super duplex 2507 should work better (PREN 43), or if you can use MP35N (PERN =52) or C-276 (PERN 75) that are superior.

 

[Salmet]

Thank you very much Edstainless, weldstan and Magben, for your valuable suggestions. EdStainless, if you can please refer me some literature or link regarding your point no.3, I will be extremely thankful.

 

[SJones]

If you are stuck with the 2205, there might be something left in last chance saloon:

https://forcetechnology.com/no/abou...about-cathodic-protection-of-stainless-steels

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.