Welding Tips and Tricks

Hey guys.

I got a question for ya, there is a large commercial/industrial dishwasher that I take care of, it has multiple sections to it and each has it's own pump and heating system, it's called a flight type as the belt runs continously around, transporting stuff through it.

The entire machine is 304 S.S, now the oddity is that in the very last section of the machine which can also be the hottest, (water gets up to 190-200*F in that section) the stainless is getting a goldish tint.

Based on the below article it's related to temp and oxide layer which makes sense, I think we all know what a good TIG weld looks like in all it's different colors but I've never seen it on something this "low temp".
https://www.bssa.org.uk/topics.php?article=140

It's not necessarily bad or wrong, I'm just curious, it's the entire interior, but any other section of the machine is regular stainless color.

Maybe a reaction to not only the temp but the water over a long period of time? The water isn't pure so perhaps the high temp is staining the stainless? Can you post a pic?

Probably more to do with the minerals in the water

it also can be from oxidants from dishwasher powder/liquid, not necessarily direct contact but also air borne.

tweake wrote:it also can be from oxidants from dishwasher powder/liquid, not necessarily direct contact but also air borne.

Quite likely.. Stainless is definitely not impervious to everything. Eg. chlorine compounds will attack it as well as caustic environments, which is probably exactly what's happening with strong cleaning agents used in such a machine. This will damage/strip the nickel oxide layer and expose the steel which basically rusts..

If the latter part were made from 316 it would probably fare a little better in such environments, but probably too expensive and even from 304 the machine likely will work fine for the designed lifespan, but just not lok as nice

Some late-night reading on stainless and corrosion:

https://www.parrinst.com/wp-content/upl ... n-Info.pdf



Bye, Arno.

Sorry it took so long to get back to you guys.
Interestingly enough, only the 2 last rinse tanks are what's affected, nothing else.

The way the machine is laid out, left to right.

Load, 120-140*F Scrapper, 120-140*F Scrapper, 150-165*F Wash (detergents), 160-180*F Rinse 1, 160-180*F Rinse 2,185*F - 200*F Final rinse (a sanitizing spray), unload. The end.

The 2 rinse tanks are turning gold.
Hopefully this gives you guys some idea of what I'm seeing.

They apparently tried delimer, soak tank and some other chemicals used in the kitchen, nothing worked.

I just went and tried delimer myself, doesn't do anything. It REALLY looks like a heat tint, but how did it get there? Temps are nowhere near 500*F, all kinds of stuff would melt before we got there.

Olivero wrote:They apparently tried delimer, soak tank and some other chemicals used in the kitchen, nothing worked.

I just went and tried delimer myself, doesn't do anything. It REALLY looks like a heat tint, but how did it get there? Temps are nowhere near 500*F, all kinds of stuff would melt before we got there.

I think the answer has already been pointed out, and as you said the last 2 tanks saw the highest temps (not implying heat tint)

Perhaps, discussing it with my chemical rep he originally thought it might be iron oxide as someone else mentioned, delimer supposedly removes it, but didn't work.

Perhaps I missed the answer? Water is softened, if it was ONLY due to chemical reaction in the water, I imagine it would be all of them.

If it was due to chemicals, I imagine the tank containing it would be gold.

Only other thought is the rinse aide going into the rinse tanks (they share water) and perhaps it's doing it?

I'll try to get the MSDS's for the chemicals and post them, perhaps it says something.

If clr of a similar chemical didn’t remove it. Then I’d guess Arno is correct. It’s either the chlorine in the water or soaps. Or from the strong oxidizers often used in cleaning chemicals.

As a test you could try a small section of the stainless and do a picking and then a passivation step on it. Eg. using some gel:

https://www.materials.sandvik/contentas ... iumres.pdf

That should give you a 'bright' area and you could see if it develops the same discoloration again.

Could also be that the discoloration is some other dissolved mineral in the water (eg. copper/iron salts) precipitating out and either reacting or depositing/adhereing onto the metal surface.

Chemistry can be funny in that some reactions between compounds don't happen at high concentrations (eg. in the wash stage) but only kick off when diluted enough to ionise some of them which would possibly happen at the rinse stages.

As you say the temperatures are way too low for it to discolor from pure heat (would probabvly be warped like crazy too ). I'd also expect the outside to discolor in that case. If that doesn't happen then it's pointing to some form of chemical reaction either with the metal or it's something that gets deposited onto the metal from the water, detergents and such.

Bye, Arno.

Arno,

Makes sense what you are saying, I think you are right.

I just don't know how to make it so it won't happen again, without pinning down exactly why and how the color came to be, it'll be difficult to prevent.

Per some stuff I Read online, that goldish color could also be from the oxide layer growing thicker and the way the light is reflected back changes, thereby changing the color, but that was talking about when it gets up to 500*F and the oxide layer generation is sped up.

The oxidizers in the soaps will speed up the oxidation of the metal even with out the temperature changes. I’ve seen it on boiler chemical injection systems.

Poland308 wrote:The oxidizers in the soaps will speed up the oxidation of the metal even with out the temperature changes. I’ve seen it on boiler chemical injection systems.

Okay, but these 2 tanks have the least amount of chemical in them, they have a rinse aide which helps evaporate water off the washware, which is not directly injected into it but any runoff the washware would go in that tank, the rinse aid is sprayed along the final rinse spray.

The tank with soap has no gold tint.

Olivero wrote: Okay, but these 2 tanks have the least amount of chemical in them, they have a rinse aide which helps evaporate water off the washware, which is not directly injected into it but any runoff the washware would go in that tank, the rinse aid is sprayed along the final rinse spray.

The tank with soap has no gold tint.

The amount of chemicals may not be the deciding factor, just the particular chemical

This is the final rinse chemical.
https://external.stateindustrial.com/MS ... 98_SDS.pdf

This is the detergent.
https://external.stateindustrial.com/MS ... 60_SDS.pdf

304 stainless can have galvanic reactions to minerals in the water, and it seemed to be enhanced in water with especially low amounts of entrained oxygen. It happened to 304-grade components on submarines based in fresh water river ports with low oxygen content. Not only discoloration, but galvanic rot on submerged 304.

Hot water has less ability to retain oxygen. That's why the minnows in a bait bucket gulp air at the surface when the bait bucket gets warm.

Dipping to get an acid etch is likely the only thing that will restore the silver coloring. Passivating might help, but both of these seem like overkill. The discoloration has no reason to cause any health concerns that I know of.

Jim_D wrote:304 stainless can have galvanic reactions to minerals in the water, and it seemed to be enhanced in water with especially low amounts of entrained oxygen. It happened to 304-grade components on submarines based in fresh water river ports with low oxygen content. Not only discoloration, but galvanic rot on submerged 304.

Hot water has less ability to retain oxygen. That's why the minnows in a bait bucket gulp air at the surface when the bait bucket gets warm.

Dipping to get an acid etch is likely the only thing that will restore the silver coloring. Passivating might help, but both of these seem like overkill. The discoloration has no reason to cause any health concerns that I know of.

Makes sense, fair enough,

So far there is no sign of rusting, I cleaned a section of it with Barkeepers Friend and it hasn't returned, so perhaps it was a one time deal, regardless, it seems like it's not an issue.

Olivero wrote:Hey guys.

I got a question for ya, there is a large commercial/industrial dishwasher that I take care of, it has multiple sections to it and each has it's own pump and heating system, it's called a flight type as the belt runs continously around, transporting stuff through it.

The entire machine is 304 S.S, now the oddity is that in the very last section of the machine which can also be the hottest, (water gets up to 190-200*F in that section) the stainless is getting a goldish tint.

Based on the below article it's related to temp and oxide layer which makes sense, I think we all know what a good TIG weld looks like in all it's different colors but I've never seen it on something this "low temp".
https://www.bssa.org.uk/topics.php?article=140

It's not necessarily bad or wrong, I'm just curious, it's the entire interior, but any other section of the machine is regular stainless color.

What you are seeing is iron in the water that is depositing in the machine. Only one product that I know that will remove it and its called “ultra lime away” from ecolab, in a machine that large you might need up to 1/2 gal per tank, let it run for 15-20 mins. The final rinse end will most likely need to be done manually, put it in a bottle and spray it on, rinse it off. The discoloration wont affect the machine, or sanitation, its just cosmetic. I see this on a daily basis. If you need a contact to get some let me know and ill get you connected with someone.

Ive been reading this forum forever, just actually joined to help you with your issue.

Olivero wrote:Hey guys.

I got a question for ya, there is a large commercial/industrial dishwasher that I take care of, it has multiple sections to it and each has it's own pump and heating system, it's called a flight type as the belt runs continously around, transporting stuff through it.

The entire machine is 304 S.S, now the oddity is that in the very last section of the machine which can also be the hottest, (water gets up to 190-200*F in that section) the stainless is getting a goldish tint.

Based on the below article it's related to temp and oxide layer which makes sense, I think we all know what a good TIG weld looks like in all it's different colors but I've never seen it on something this "low temp".
https://www.bssa.org.uk/topics.php?article=140

It's not necessarily bad or wrong, I'm just curious, it's the entire interior, but any other section of the machine is regular stainless color.

What you are seeing is iron in the water that is depositing in the machine. Only one product that I know that will remove it and its called “ultra lime away” from ecolab, in a machine that large you might need up to 1/2 gal per tank, let it run for 15-20 mins. The final rinse end will most likely need to be done manually, put it in a bottle and spray it on, rinse it off. The discoloration wont affect the machine, or sanitation, its just cosmetic. I see this on a daily basis. If you need a contact to get some let me know and ill get you connected with someone.

Ive been reading this forum forever, just actually joined to help you with your issue.

mmonti wrote:

Olivero wrote:Hey guys.

I got a question for ya, there is a large commercial/industrial dishwasher that I take care of, it has multiple sections to it and each has it's own pump and heating system, it's called a flight type as the belt runs continously around, transporting stuff through it.

The entire machine is 304 S.S, now the oddity is that in the very last section of the machine which can also be the hottest, (water gets up to 190-200*F in that section) the stainless is getting a goldish tint.

Based on the below article it's related to temp and oxide layer which makes sense, I think we all know what a good TIG weld looks like in all it's different colors but I've never seen it on something this "low temp".
https://www.bssa.org.uk/topics.php?article=140

It's not necessarily bad or wrong, I'm just curious, it's the entire interior, but any other section of the machine is regular stainless color.

What you are seeing is iron in the water that is depositing in the machine. Only one product that I know that will remove it and its called “ultra lime away” from ecolab, in a machine that large you might need up to 1/2 gal per tank, let it run for 15-20 mins. The final rinse end will most likely need to be done manually, put it in a bottle and spray it on, rinse it off. The discoloration wont affect the machine, or sanitation, its just cosmetic. I see this on a daily basis. If you need a contact to get some let me know and ill get you connected with someone.

Ive been reading this forum forever, just actually joined to help you with your issue.

Okay cool, I can have them give that a shot, we currently use ecolabs products so I'll check and see if they have some of that, thanks for the offer.

& Thanks for replying.