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Water Treatment Laboratory Corrosion 5

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bimr

bimr

Civil/Environmental
Feb 25, 2003
9,369
Does anyone have an explanation for this corrosion?

This application is a remodel of a water treatment laboratory. The equipment is all new. The trough sampling sinks are made from Gauge 316L-2B stainless steel. The other items like the drawer pulls and safety eyewash are 316 stainless steel.

The trough sinks are used for water quality control and the water runs continuously. The trough sinks have the worst corrosion. As you move farther away in the room, the corrosion on the other fixtures lessems.

October 2020, photos were taken of new rusting stainless-steel products in the Control Lab. New stainless-steel eyewashes, new stainless-steel tub sink, and new stainless-steel cabinet handles were all showing significant signs of rust.

March 8th – 10th, 2021 the new stainless steel trough sinks were installed and were not cleaned or polished at that time. Within a week, these items began showing signs of
rusting.

On April 5th, 2021, the new stainless steel trough sinks were cleaned and polished along with other existing stainless-steel products. Within a week, they began showing signs of rusting again.
On May 27th, 2021, Owner polished the new stainless-steel trough sinks. Within a week, they began showing signs of rusting again and photos of the current condition of the new stainless steel trough sinks are included.
 
 https://files.engineering.com/getfile.aspx?folder=f49c19b1-32e1-463d-b644-a5da2f2f7fbb&file=lab.docx
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How are they polishing?
Have they acid cleaned (passivated) everything?
Why on earth didn't they use non-metallics?
This room is 100%RH 100% of the time with water being splashed on items carrying whatever is in it.
I am sorry that someone told them that 316 would stand up to this.



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P.E. Metallurgy, consulting work welcomed
 
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You can pickle in place with gel solutions such as Wonder Gel. It would be worth trying it before tossing everything. Wash with a caustic cleaner first to remove residues from the polishing compounds.

The pickling will give significantly more corrosion resistance but the procedure may have to be repeated occasionally over the lifetime, ideally just spot repairs.

Do you use chlorides in your water treatment?

Your application is indifferent from a natatorium of which there are many resources for design and maintenance.

 
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EdStainless (Materials) said:
How are they polishing?
Have they acid cleaned (passivated) everything?
Why on earth didn't they use non-metallics?
This room is 100%RH 100% of the time with water being splashed on items carrying whatever is in it.
I am sorry that someone told them that 316 would stand up to this.
Click to expand...

Polished with with Bar Keepers Friend Stainless Steel Cleaner & Polish and Iron Out Rust Stain Remover.

Don't know if acid cleaned (passivated) everything.

The laboratory is air conditioned, don't know what the RH is. New HVAC system.

The laboratory was remodeled. The stainless steel backsplash was 50 years old and the reused backsplash is not rusting.

The inside of the trough sink is not exhibiting rust like the outside.

This water is potable drinking water from a clarifier. The water has been treated with alum to remove solids, plus chlorination. The water is fresh water from Lake Michigan and is considered to be good quality, low TDS water.

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Does the 316L-2B stainless steel need to be passivated prior to use?

The other components (eye wash, faucet, and hood) are 316 and also show rust, but not as bad as the trough sink.

The 316L-2B stainless steel was supplied by Outokumpu.
 
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any high chloride concentrations?


Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik
 
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dik (Structural) said:
any high chloride concentrations?
Click to expand...

Chloride averages 20 mg/L.
 
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Start here, I implore you:


The price seems to have skyrocketed, I paid the same for a full gallon last year. But it's a cheap test. Passivate the metal and if the corrosion doesn't come back your problem is solved.

Also, make sure nothing stays in contact with any surfaces for more than a few hours (don't leave containers standing on the surfaces) and rinse everything down with water regularly. As the water evaporates it concentrates the chlorides so regular rinsing will help prevent corrosion. Treat it like a commercial kitchen.
 
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Can you do the same with a nitric acid wash?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik
 
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From my project notes:

STAINLESS STEEL
-ALL STAINLESS STEEL SHALL CONFORM TO AISI [S304L | S316].
-STAINLESS STEEL BOLT SPECIFICATION TO ASTM A193, GRADE 8B CLASS 2. NUTS SHALL CONFORM TO ASTM A194, GRADE 8. WASHERS SHALL CONFORM TO AISI S 304L. THREADS CAN BE INCLUDED IN THE SHEAR PLANE.
-STAINLESS STEEL WELDING SHALL CONFORM TO ANSI/AWS D1.6-2017.
-WELDING ELECTRODES MAY BE 308L.
-IN THE ABSENCE OF FACTORY PASSIVATION, ALL STAINLESS STEEL WELDING SHALL BE PASSIVATED BY IMMERSION IN A 20% SOLUTION OF NITRIC ACID FOR 4 HOURS. ATTACHMENTS SHALL BE FLUSHED CLEAN AND DRIED.
-INSTALLATION OF STAINLESS STEEL FABRICATIONS SHALL USE NON-FERRIC TOOLS.
-WELD MATERIAL CHARACTERISTICS SHALL MATCH THE PROPERTIES OF THE BASE MATERIALS.


Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik
 
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I don't believe nitric acid alone posseses the properties to passivate the more corrosion resistant alloys such as 316. There needs to be some hydrofluoric acid in the mix to pickle type 316. If immersion is possible, the passivation can be done using citric acid and electrical current.
 
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Thanks... will look into this.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik
 
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Straight Nitric will passivate fine at 30-40% concentration.
First a light cleaning with a fine abrasive, like the abrasive ScotchBrite pads.
Then wash with a caustic degreaser (make sure that it doesn't have any corrosion inhibitors in it).
And then acid wash.
If we were worried about heat tint or scale then we would want to pickle. That is where you need HF in the acid solution.
All that we are concerned about is removing embedded iron from the surface, and straight Nitric will do that. There are also systems that use a brush or pad with a DC power supply. They are often used to descale welds, but with weaker solutions work great for passivation.
I suspect that in production (or more likely fabrication) iron (steel) has been embedded in the surface of this material.

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

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik
 
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For clarity, I always emphasize the caustic cleaning first because acids can't penetrate through oil residues that maybe present on surfaces.
 
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Thanks, Tug... I've added the caustic cleaning to my project notes... It's a 400K text file with information added to it over the last 3 decades that I use for project notes for projects. The last edition to this part of the notes was the inclusion of using Head and Shoulders 'white' shampoo for trace iron content.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik
 
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I was called into this project at the punch list stage representing the owner.

The lab supervisor stated that the previous sinks were all some type of stainless steel and didn't exhibit the corrosion stains. As stated previously, the stainless steel backsplashes haven't been changed nor the faucets. Don't know why the trough sinks were changed.

The room humidity is 67%
 
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Thanks, bimr... I'm not into materials, but that is some of the worst SS corrosion, I've seen.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik
 
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EdStainless (Materials) said:
I suspect that in production (or more likely fabrication) iron (steel) has been embedded in the surface of this material.
Click to expand...

Do you think that this equipment can be saved or is it recommended to propose non-metallic sinks? The trough sinks with the worst corrosion are used as just potable water sampling with no other reagents used. 70% of the inside of the sinks have no corrosion. The worst corrosion is on the outside. It looks like the splashing water may be evaporating leaving salts behind or the splashed surface is absorbing corrosive fumes from the lab. The lab does clean glassware with HCl but not in these trough sinks. The lab uses other chemicals such as sulfuric acid.

The lab supervisor stated that the previous sinks were all some type of stainless steel and didn't exhibit the corrosion stains. As stated previously, the stainless steel backsplashes haven't been changed nor the faucets. Don't know why the trough sinks were changed. For the most part, the backsplash and faucets do not have extensive corrosion, but do have some water scale on them.

This operation operates 24/7. Can the chemical treatments for passivation be conducted safely in a working laboratory?






 
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If your corrosion were concentrated around the welded areas I would suspect carbide precipitation and that would likely require replacing the equipment. This does not seem to be your case. In 2 of your pictures there appears to be blisters of rust which indicates pitting so you may want to replace those pieces (only if they fail again after cleaning).

The acid cleaning an be done online, the process takes minutes. Just work small areas at a time. This will minimize the fumes produced. Ventilation and respirators will allow workers to be in the space during the cleaning process. The gel type cleaners can be applied by brush and may help facilitate online cleaning. The same gel cleaners can be used to touch up future corrosion areas that may arise.
 
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