Water Treatment Laboratory Corrosion 5

[bimr]

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.

 

[EdStainless]

Give some of the worst area an abrasive cleaning (flap wheel or scotchbrite) and see how deep the pitting is.
If there is not deep pitting (only a few thousandths of an inch) then cleaning properly (abrasive, caustic, acid, rinse) should work.
Be careful with the alkaline cleaner though, and commercial pre-packaged ones have corrosion inhibitors in the intended for use on steels. Residue from these will interfere with the passivation.
I agree with your conclusions that the splashing is what makes it worse. This is common with SS.
At least inside the sinks get rinsed off.

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P.E. Metallurgy, consulting work welcomed

 

[bimr]

You did not mention passivation?

The sampling sinks are supposed to be made of 316SS. There is a smaller sink fabricated from 430SS. 430SS seems to be more suitable for a commercial food establishment than a laboratory.

 

[TugboatEng]

The passivation should occur naturally after the acid wash provided and the surface is clean and exposed to air.

 

[bimr]

The passivation should occur naturally after the acid wash provided and the surface is clean and exposed to air.

This is a 24/7 operation. How long does this equipment have to sit idle for passivation to occur naturally?

 

[EdStainless]

Passivation of SS means to acid clean in order to remove embedded iron on the surface.
The forming of a passive surface film is a natural process in these alloys and does not need any chemical assistance beyond a good clean surface.

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P.E. Metallurgy, consulting work welcomed

 

[bimr]

Thanks everyone for the comments, have a good weekend.

 

Aside from the corrosivity issues, better drainage would help matters.

I basically agree with EdS though, 316SS is not up to the task of resisting everything flowing over it in a lab like this one.

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

 

[bimr]

There are test procedures to determine if there is contamination. Would you have to remove the rust spots before you do this contamination test?

 

[TugboatEng]

Ed may have something else to say but as far as I know there are no procedures to test. This is a case where you need to follow the procedures to prepare the surface. Everything with stainless is about processing and handling. The damage can be done at any step and it won't become apparent until the material is placed in service.

I implore you, get a container of the pickling gel. McMaster stocks it and will have it in your mailbox within 24 hours. Use it on a small area. You're risking all of $100. I think you'll be pleased with the results.

 

[bimr]

I wish it were so simple. I am representing the Owner. I have an engineering who specified this mess. I have a Contractor who installed it.

The problem is that the existing stainless steel fascia has performed well for over 40 years with scant rust. This new stainless steel rusted and stained within a week. I don't know the specifications on the existing material.

One of the things that I have to determine is if there is contamination of the new stainless steel. There is e Ferroxyl test to do this. ASTM A 380 Ferroxyl Test for Free Iron.

The first thing that I need to do is to positively identify the problem. The problem is likely the contamination, but that needs to be confirmed so that I can provide the path forward.

 

[TugboatEng]

You are fortunate that your problem shows itself in such short time. That will help identify and prove the solution rapidly. You can do the acid cleaning tomorrow and have results in a week. That's likely faster and more conclusive than any lab test. I understand the desire to follow the more traditional route but the cause of your problem seems very obvious (assuming the correct alloy was used).

As this seems to be warranty work, and you're providing the solution, perhaps the engineer will cover the cost of the solution as well as your time finding it? I know it never works this way, insurance makes nothing simple.

 

[dik]

It'll be done before you have the lab results... no harm trying... just hit 'petty cash'.

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

-Dik

 

[EdStainless]

It could also be related to the surface getting smeared when they did the final 'polish' and trapping stuff in the smears. Anything that traps moisture on this surface will aggravate this issue, in addition to iron contamination.
I always recommend that people do an abrasive treatmetn first, it helps open up any smears and it helps remove other surface contamination.

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P.E. Metallurgy, consulting work welcomed

 

[mrfailure]

I'm going to throw out something totally different: When I've seen damage like that in 316, I've found the corrosion is really from stress corrosion cracking that formed from chloride exposure. The SCC exhibited in the form of localized pitting when observed macroscopically. I note that the sink outside surface as well as all of the new hardware all exhibit significant corrosion damage while the inside is largely free of it, probably from the constant rinsing away of the sink interior during use.

An alternate explanation is the grade of steel is not 316L but a grade much less resistant to pitting corrosion in a water lab. Given the degree of damage, is it possible to remove some of the corroded material and send it to a lab to investigate? They could examine corrosion mode (i.e. SCC or pitting, for example), look for contaminants like chlorides that would drive corrosion, and confirm base material.

 

[bimr]

I'm going to throw out something totally different: When I've seen damage like that in 316, I've found the corrosion is really from stress corrosion cracking that formed from chloride exposure. The SCC exhibited in the form of localized pitting when observed macroscopically. I note that the sink outside surface as well as all of the new hardware all exhibit significant corrosion damage while the inside is largely free of it, probably from the constant rinsing away of the sink interior during use.

An alternate explanation is the grade of steel is not 316L but a grade much less resistant to pitting corrosion in a water lab. Given the degree of damage, is it possible to remove some of the corroded material and send it to a lab to investigate? They could examine corrosion mode (i.e. SCC or pitting, for example), look for contaminants like chlorides that would drive corrosion, and confirm base material.

This is potable water with 20 mg/L of chlorides. Not significant chlorides.

Mill provided information that shows this material is 316L.

Somebody kept telling me that the original sink that was installed for 60 years did not have corrosion like this. I wasn't here so I went back and found some pictures. Well surprise, surprise.

EdStainless mentioned it in his first post. Not a good application for stainless. Why would a consultant specify the same material when it is clearly not suited for the application?

 

[TugboatEng]

This is potable water with 20 mg/L of chlorides. Not significant chlorides.

The issue with exposed surfaces is that as the water evaporates away, the concentration of chlorides increases substantially.

 

[EdStainless]

As TBE said, the spots that form when water drops evaporate will be 26% salt. Wet/dry is the killer application for SS.
There are special aggressive corrosion tests where you warm the sample and then apply drops of low concentration salt water, waiting just long enough so that it almost drys between drops.
If there are visible scratch lines in the polish they should run up and down to assist drainage.
I have seen people wax SS to prevent this, but it takes maintenance. I don't know how one of the newer hydrophobic auto polishes with ceramic in it would work. It should help.

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P.E. Metallurgy, consulting work welcomed

 

[mrfailure]

Take note of what Ed and Tugboat said. Easiest way to know if you do have high chloride content is to have a lab do EDS analysis on a removed sample, if you can spare one.

 

[stevenal]

Did it rust through in those 60 years, or is this a cosmetic problem? In my experience, stainless steel is miss-named. It stains easily, but resists serious corrosion.

 

stevenal,
The 'steel' component of stainless steel came from the Engineering Dept.
The 'stainless' component came from the Marketing Dept.

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