Stainless steel in chloride environment 9

[Meysamsh]

Hello everyone.
I have little problem.
We have a potable storage tank that hase been made by stainless steel 304.
But the concentration of chloride is about 130 ppm. Corrosion is start in near the welding.
That was design problem, and we cannot change the material.
What is the solution? Can we paint the inside the tank? Or can we use the cladding?
Thank a lot..

 

[EdStainless]

There are correct SS alloys for service up to concentrated brine, but you have to careful, and ready to pay the price.
What let this application down is the weld quality. Making fine, smooth, and clean welds in SS is not the same as making sound strong ones. Shielding and pickling are critical.
The other thing is that when you are in environments like this it is wise to over alloy the filler, 317L wire would have made sense.
130ppm Cl with neutral pH, ambient temp, and no biological activity should work for 304L. But we are back to the welds....
The biggest issue with SS isn't the Cl level, it is temp, pH, and biological activity.Two pH more acidic or 10C hotter is roughly the same as 10x the Cl level in impact.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[Meysamsh]

@Edstainless
You say the building-up the welds, didn't works?

 

[Meysamsh]

@0707
As i know, we can not use hydro test limits for in service condition. Because we have many tensions in hydro test.

 

[0707]

Meysamsh

please clarify I don´t understand your question.

luis

 

[EdStainless]

The difficulty is that larger welds will cool slower and have more segregation in them. This lowers their corrosion resistance.
And the shielding needs to be perfect. I watch welders turn out welds where I have to strain to see the ripples and there is zero discoloration on either side. On the backside the weld bead width is less than the material thickness and very flat.
Design plays a role also, no corner welds, no traps or dead spots, and if you can do it no welds in the very bottom.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[gtaw]

I just saw the photograph.

I suspect MIC. By chance, is there little to no flow where the leaks occurred? By chance are the leaks close to, but adjacent to the weld in what we call the HAZ? Did this happen after the tank was newly installed and leak tested using the "fresh" water? Was the water completely drained after the leak test or was the tank allowed to set flooded with water while the piping, pumps, etc. were installed?

The iridescent green color is what makes me suspect Microbiologically Induced Corrosion (MIC).

If you have access to the inside of the tank, look for small mounds of "brown jello" that look like small ant hills along the welded seams. The mounds are excrement from the bacteria that I suspect is the culprit and cause of your problem. You will find that "clean" water isn't all that clean, even if it is chlorinated.

Attached is a photograph of MIC I discovered on one of my failure investigations. Doesn't it look familiar? I will post another photograph to look at.

Best regards - Al

 

[gtaw]

Here's a photograph of the "mound" typical on the wet side of the tank. It is the excrement from the bacteria and microbes causing the leakage.

I could see the mounds of excrement through a few feet of standing "clean" water.

Best regards - Al

 

[gtaw]

I seem to be having a problem uploading a photograph of the "dry" side of a leak caused by MIC, so I'll give it another try.

Best regards - Al

 

[gtaw]

The tank involved was a brand new installation that was leak tested by the owner. The tank was allowed to sit with the water in it for about 90-days when they noticed the tanks dripping water. At that point, the plant was still under construction. They wanted to blame the fabricator for the leaks, but it wasn't the fabricator's fault the owner tested it with "dirty" water and allowed it to stagnate.

Best regards - Al

 

[CheemaJ]

Just thought I'd add to this discussion. We have recently experienced issues with MIC on newly installed process pipework in 316 stainless. This was using UV treated towns water that was left in the pipework for only a few weeks during commissioning. Almost all of the corrosion sites were on or around the heat effected zone. We are now having to replace a large quantity of this pipework.

From now on I will be ensuring heat tint oxidation is kept to an absolute minimum and welds are pickled and passivated wherever possible. Also wherever water is to be left stagnant for a prolonged period employ use of a biocide.

 

[TugboatEng]

Treating the water with sodium nitrite prior to shut down will prevent the issues associated with stagnation. In fact, it will prevent corrosion in all piping systems of all materials.

 

[EdStainless]

The problem with water standing stagnant for a few weeks is twofold.
First the biocide is not persistent enough. We deliberately use biocides that decompose so that they do not impact the environment (we can't use the Cr and Mo compounds any more for this reason).
So hyprchlorite or hydrogen peroxide work fine (peroxide is nice because you can't use too much) work, but are not persistent. Hypo will last for a week or so, H2O2 will only last a day or two.
The other issue is that when you have no flow if you do start getting local corrosion you will likely also have local oxygen depletion. Since SS relies on CrO2 for its passive film the low O2 will make re-passivation more difficult.
In SS the problem with bio growth isn't the growth itself, the bacteria does not eat the SS. It is the fact that it is forming a crevice condition which is more severe, and that it will die and release decay products which are often corrosive.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[TugboatEng]

I'm just curious as I'm more of a general fleet operations guy but is sodium nitrite used for offline systems? It's the corrosion inhibitor in engine cooling systems. At 3000-6000 ppm it seems to prevent nearly all corrosion and microbe growth even in systems that may sit for periods of time. It's a film forming additive so it will not work on dirty surfaces. Disposal may or may not be an issue.

 

[EdStainless]

I know that sodium nitrite is used in curing meat, so it does have some biocide effects.
And it is very effective at inhibiting corrosion on carbon steels. I have seen it used for treating freshly sand blasted to prevent rust blush. It was also the primary inhibitor used in cross country gasoline pipelines.
I know that it also has some inhibition effect with SS and Cl solutions, but the effects seem to be limited to a range of pH, temp, and concentrations.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[Meysamsh]

@gtaw
Those pics were amazing.
It seem we have a same problem. I'll send more photo from inside of the tank. Before and after cleaning.
There are many mounds of brown jello.

Now i have little problem with sending photo. I'll be send them as soon as i can.
Best regards.

 

[gtaw]

My client refused to believe the issue was caused by microbes, "The water is so clean!" I even included a few articles on MIC, but it wasn't what they wanted to hear. They wanted new tanks from the manufacturer.

In my younger years a consultant told me, "To be successful, you have to learn to tell the client what they want to hear."

I was a poor student, told him he was a whore and I would find a different line of work if that was the case. He's gone, but I'm still here. I've never been accused of being diplomatic. I did have a client tell me, "I don't always like hearing what you have to say, but I know what you say is your honest opinion and I can take it to the bank."

 

[Meysamsh]

@gtaw
May i have your email address?

 

[gtaw]

We can't give it out on this Forum.

Go to the website for the American Welding Society and find the library for Inspection Trends, you can find a number of articles I've written and my email there if you are serious.

Best regards - Al

 

[EdStainless]

Yes Al.
I just got done giving a deposition in a damages case. "You know if they had washed the dirt off this equipment once in a while it would corrode less" was not the diplomatic response, but it is the truth.
I used to work in Hygienic service applications. Their problem is that they forget that the cleaning solutions are also corrosive.
I have never had a shortage of consulting work. For some reason users don't get much smarter as a group.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

For some reason users don't get much smarter as a group.

That jibes with my observation-based theory that on aggregate, humanity is getting stupider just slightly faster than it is getting smarter. The differential seems to have widened since 2016 though.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."