Electrolisys

[Note title correction.]

Electrolysis would be more likely to show up as metal loss (similar to corrosion) at or near joints of dissimilar metals, rather than in the middle of a span of all the same material. [I think, without being totally sure.]

Chlorides in the water, such as salt or sanitizing bleach, can also cause pitting from corrosion. Maybe some further advice will appear from persons more familiar with details than this brief comment.

Thank you for the reply. I need to go back and conduct more test however I don't want to go back too many times because the customer is getting impatient with the process. It is taking a long time for a resolution and the big question is who is going to pay for all this. The unit has passed its initial warranty, but the wholesaler has agreed to pay for another visit. Politics!

If the manufacturer knows what causes the problem, he should have found a solution for it. Did he recommend any solutions for the metal loss?

Electrolysis can only occur with an electrical potential present and a conductive solution to carry it. Bond all the various parts together and properly ground the equipment and it should not continue. Or, find a non-conductive cleaning solution.

Thanks Lyn for the comments. Unfortunately the manufacturer doesn't have a solution. It's why I am turning to you guys.

This unit is a commercial dishwasher that cleans dishes in a restaurant. It is limited to using water and detergent (sodium hydroxide).

I will go back and verify grounding.

I've never seen this happen...Can you describe the hole characteristics...how big? smooth on both sides? What is the age of the equipment? Does the hole look like it was worn, punched, corroded, if it was corrosion there should be signs elsewhere..Something metallic may have been touching that spot for a long time and removed...

...and worn a hole in it mechanically. Without seeing the area of the hole there are a range of possibilities.

During my first visit, the hole was patched with silicone sandwiched between a dime and a penny. No kidding. It seems to have blocked the hole temporarily.

When I go back I will remove the patch and take pictures.

Something metallic, as you say, may have caused this. usually cutlery left at the bottom will leave a rusty contour of the offending piece. It could be some other piece of metal also.

I should return this week.

Hi

I have taken some pictures. just follow the link

http://www.flickr.com/photos/marsolais77/sets/72157628196376367/

let me know what you think

Robert

On a hunch I took a close look at my decidedly noncommercial dishwasher. The pullout baskets run on rollers on pullout rails. The rollers have protruding head screws for axle. When pushed home, these are always parked at the same spot. Sheetmetal and screws and axles are normally made from compatible, but not identical stainless steel material. The machining requirements usually iust too different.

Bent sheetmetal's flat parts always bulge a bit in or out.

Now, if the basket rolls on 3 rollers, the center one is parked on the centerline, and maybe over the spot in question. If the sidewall (always or under liquid load) bulges inward, you may have a sliding contact between it and the protruding head of the axle. Two different metals = electrocorrosion. When you open the door and pull out the basket, you see nothing.

I did write this note simply as a possible scenario. One has to see the machine in question, to work up other possibilities on the mechanical side.

Hi

Here are some pictures.

http://www.flickr.com/photos/marsolais77/sets/72157628196376367/

see what you think..

Robert

GA

You beat me to it.

Alfa had similar problems with many of their cars in the '70s in the UK.....rust in the middle of panels without rhyme or reason....

Either way it is the manufacturer's problem, unless the guarantee has run out......then it's the customer's problem.

Two stainless steel washers (either side of the hole), with a stainless nut, bolt (through the hole), a spring washer and a dab of silicone sealer should fix it forever.....

Good repair method. Only thing I would add is to use the same type of SS as the drum if possible.

Leveles and IBGrizzly are Both spot on. If something scratches the surface it can start the corrosion process. I had some 316ss that had an arc drawn to it. That started a corrosion point that eventually destroyed the part. It was operating in dilute NaOH solution. Once the corrosion starts you must remove all signs of corrosion before replacing into service and check back often to remove all signs. Thanks IBGrizzly for the info on the process.

If the customer has used a high salt content cleaner, or tipped a significant amount of salt into the washer this could have started the pitting, combined with the heat of a commercial steam wash.

I did some tests here to compare 304 (our standard material) with 316 (used in our marine applications) and found that when road salt is applied, 304 looses most of its "stainless" properties.

Combined with damage or a permanently wet spot as hypothised by others, this may be the cause.

Hello,

Just notice your post and have not read the replies.

A simple answer is when two different metals come in contact with each other that are not compatible, example steel and copper connections attributed with flow of water will speed up the electrolysis process. This is a common occurance in appliances when installers don't use proper fittings.

The detecting of 'stray' current should be detectable by providing a solid earth ground and can be caused by not properly grounded equpment and their counter parts. I have removed many a dryer, 220 volts with a 120 volt motor with excessive rusting sometimes completely through on the side of a well grounded washer,residential and commercial. and the cut ground on washers has been found to cause of rusting and pitting. Many vending machines in areas not galvinized and located in areas where no earth ground was possible. Remedy was to change the part or relocate the machine or properly ground.

Addendum to this.

some pictures

http://www.flickr.com/photos/marsolais77/sets/72157628196376367/

I could not detect any stray voltage. The unit is grounded.

Robert

Those photos tell the story quite well.

The pitting is just plain corrosion. For electrolysis to work you need to have a dissimilar metal interface and that is not evident (except at that coin patch where it is really very evident)

Not surprising for 304 stainless.

The holes can be repaired by drilling out, deburring, applying suitable sealant, fitting a stainless steel rivet or a nut, screw and washer set in the prepared holes.

This is going to be ongoing. Apart from the corrosion is the machine still serviceable?

How old is this machine?

Thank you for your reply.

I have sealed three holes so far in this unit in the manner you describe. I have done this in the past and works really well.

I wasn't sure if it was corrosion. The machine is serviceable. This unit is about 2 years old. I am submitting a report with recommendation. I will tell them (the manufacturer) should replace the tank. Life expectancy of this kind of equipment is 5 years, it used to be 10.

We'll see what happens.

Thanks again

Why on earth are you messing about on this blog? if the machine is only two years old, get it back to the retailer and demand that they get it fixed, to have that much damage in such a short period is a fault in manufacture, let every one know what make it is so we can all avoid buying the same machine.

BAZZER

In Europe you are dead right, in the USa guarantees are often much shorter time wise......

It depends upon what the "service" guarantee is from the OP's company, but I would guess that the buck stops there....

The repair seems to work well, does not take much time (but could be applied to both sides for better security), and gives the customer a good feeling.

I would check up for possible problem areas and seal them before they break through.

My personal take is poor quality steel from possibly the far east......

I appreciate the feedback. Indeed warranties are different in north america. We'll see what they decide next.

You guys have been a lot of help. Again thank you

If dishwasher Stainless is made in Certain parts of the World the Quality of the Specs may not match the Quality of the Materials

A minor amount of carbon steel or other impurity would be the focal point for electrolisis.

IE: more conductive.

Such as the sacrificial Anodes on an Ocean Vessel Minute electrical currents will remove material one molecule at a time until a hole appears

Certain minerals in the Water Supply can accelerate these effects such as salt softened water.

Check salinity/acidity etc of water supply Check Steel for composition is it 304 s/s grade or a cheap knockoff?