corrosion - what / who's to blame!

[chav666]

Hi Guy's,
Hopefully someone can help me out here. I've spent ages searching the forum and can't find the info I require. So here it is: -

I supply Detergents / Disinfectents to a Food Manufacturer (Processed Veg, Fruit). They have identified severe corrosion of the aluminum evaporator fins in their Air Conditioning Units in the Roof Void. The units extract air from the factory and mix it with air drawn in externally. Air is pocket filtered before going through the heat exchange. They have previously had issues with drainage in the unit, and there is evidence of SEVERE corrosion at the base of the units main body.

Depsite this, the engineering manager thinks it must be cleaning chemicals used in the factory being carried over onto the fins?? They have an industrial traywasher using 0.2% Sodium Hydroxide.

They have an identical unit with no drainage issues and ZERO corrosion...

Any ideas? I have no engineering experience (obviously) so am trying to get educated!

Thanks for any help.

[Brian_UK]

Hi and welcome, an interesting choice of forum name you have gone for, are you a satanic east coaster ?

Anyway, back to your question - where abouts in the country is the site, is it by the coast? Salt laden air....

Poor drainage equals water laying inside ductwork which corrodes the metalwork.

When you say that they have an identical unit - is it in the same area or serving a different product?

[chav666]

The names supposed to be ironic - but I just use it now so that I dont have to remember loads of usernames! Although I get the odd occasion of 'username taken'... so, not the only moron!

I'm in the Midlands. So no salt air. The other unit services another area - yes. The damaged unit services an area where fruit is processed - so maybe the acid content in the fruit?

The undamaged unit services an area where vegatables are cooked n blanched.

Am I right in assuming that aluminium shouldnt be affected by moisture alone?

If condensate is allowed to collect, can it's Ph be raised / lowered over time, depending on the factory environment?

Thanks for your swift reply by the way.

I am of no use to you for evaporators - but If you need any hygiene / cleaning advice PM me anytime.

Cheers

[Electrocoolman]

Does Ethylene attack Aluminium?

[NH3LVR]

Having left the trade for the most part, I have taken a job with a major fruit and vegtable processor. (Fresh cut, no cooked product)
We have copper coils with aluminum fins in the process and storage rooms. They rot away and have had to be replaced in the past.
I have not studied the issue yet, but suspect the onions.
I believe someone mentioned this in a eariler thread.
I can tell you from experience if you get sodium hydroxide on aluminum evaps they get eaten away very quickly.

[cakabo28]

hı chav666,
yes you are right,moisture has a big factor on corrosion.But aluminum evaporator fins must have covered rustless coat.If you want to understand what casued this corrossion,I can advise you to make salt spray test on fins.First of all take two pieces fins and then apply your detergent on one of them not the other.Make a salt spray test on both of them at the same time about 200 hours If the corrosion occurs only on fin that you applied detergent,yes it will be related with your detergent,If you don't observe any corrosion after test,you can be relax,problem is not your detergen

[The MG Pony]

If your product is sodium hydroxide based then yes it will most certainly attack aluminium (We use this to prep aluminium for Anodizing, as it removes a layer from the metal chemicaly), how ever this alone is nothing, it must get to the fins in the fist place then it must be left there to work on the metal.
The last two points puts the issue solely on the hands of the processors, their application method, & the failure to rectify the drainage issues has A: Allowed the carry over of the detergent & B: Has allowed the detergent time to chemically act on the evaps.

The product its self will add to this due to the standing water.

Personally I think their site engineer is using you as a scape goat to redirect attention to his failure to maintain good drainage and failure to check up on the evaps and clean them! As to me this would seem to be his duty to keep an eye on such things.

Solutions would seem some what obvious, Fix the drainage issue/ See about ways of applying detergent that minimize misting, Coating the coils with a protective substance.

[chav666]

Thanks guys. Your input is much appreciated. I took this info back to my client and they have now gone quiet on the issue.

Thanks Again!

[gwapa]

hı chav666
Some time the problem is located in the air inself. You are talkig of fruit storaged .
Normaly the fruit aand vegetable produce CO2 during breathing
THe co2 wil combine with the condensated water in the evaporator.
This mixsure could produce carbonic acid that will atack the aluminium of the fins

You should provide fresh air to keep the co2 at low levels

[The MG Pony]

Well this would be a good thing in the presence of sodium hydroxide as the carbonic acid would neutralize it.

But again, you must have standing water for the ions to work in, thus no standing water little can happen as no hydrogen ion exchange can readily take place to react with the metal, thus had the drainage issue been resolved there would be no major corrosion, just minor surface corrosion.