Corrosion on painted AL

Realtrucker56,

I'm not disputing anything you say.

Could you expand on, "Anything else and you risk Osmosis in the near future." I understand osmosis and I understand how moisture can be transmitted through polymers. Moisture vapor transmission rates are widely published and known. I guess it's the selection of abrasives that puzzles me and how that promotes osmosis.

Thanks.

I can expand certainly.

Your last sentence says it all.......the selection of abrasives is the primary key to all that follows. If you have any contamination from dirty abrasives or those types of abrasives deemed not to be neutral, both in their primary unused state and as the material changes in its use, you run the risk of cleaning the substrate and in the process re-contaminating it with new undesirable agents.

These "agents" can lay undetected in miniscule amounts, for varying periods of time, trapped between the substrate and the primer coat. As the chemicals begin to react either with the parent substrate or with other agents left around in the vicinity the result will be "bubbling" between the paint films. This is professionally known as Osmotic Blistering. You only need one to make a mess of your shiney new pride and joy.

The only answer is to start by carefully selecting clean washed abrasives (preferably washed Garnet) and be "clinical" in the entire process from start to finish.

The same applies to the paints and solvents (Chloride free every time)

Do not forget the very tools used to prepare and apply. This includes everything from your hands (sweat salts) The compressed air used......no oil (obvious), and definitely no water....water traps are practically useless especially in humid climates, so use a full bank of progressive air treatment starting with a simple "Cyclone" then include a chiller (to remove most of the condensation). Then go through a rack of filters and finish off with a good quality Coalescing filter to finish off the purification process to "breathing quality" which is sufficient.

I hope this explains everything in enough detail?

Please come back to me if in doubt.

Hmm, learn something new every day! I wasn't aware that surface contamination from abrasives were that big an issue. I can certainly see how it could be however, just never thought about it much I guess... but then again painting aluminum is usually not that big a deal for us in the oilpatch. The only aluminum parts we use are explosion proof junction boxes.

Unfortunately the same applies to stainless steel and carbon steel especially in a saline environment.

Osmosis is bad enough on land, but when you put the same story on the Ocean or in the Middle East it is x100.

The worst case I ever dealt with was an insulated stainless potable water tank on an oilrig.

The reason it was insulated was to maintain the temperature of the water.

This created the most awful microclimate between the insulation and the substrate.......Swiss cheese in 18 months!!

I designed a paint system which kept it in one piece.

Same principle.........washed garnet.........chloride free solvent wash......but the primer was replaced by Surface Tolerant Epoxy. Second coat the same. No need for a top coat as it was under insulation.

I also made another solution to SRB attack on the inside of Fuel Oil tanks.

After a full blast and solvent wash, the bottom, and first 2 foot of the tank walls were painted with 2 coats of SOLVENT Free Food Grade Epoxy, no primer just one over the other......then spark tested to check for pinholes. End of problem!!

:)

Hi Real,

I made "vinyl wash-primer with phosphoric acid" for years and we don't have any corrosion problem with the system containing 2-pack, solvent based epoxy as intermediate and finish coats. We use iso-propanol @ 99% with 2 to 3% of phosphoric acid in to wash the surface just before painting with the wash-primer.

Thanks for the precise explanations and I learned from you. Thanks from Gil.

Thanks. I agree. Nothing is more important than a pristine surface for adhesion.

step one, replace all the aluminum with steel. Aluminum will be a long term corrosion headache even if you do all the stuff suggested above. it is what it is.

Step two get thee out of the north and move to the south where we don't need road salt and we actually have jobs to boot. Last one out of Detroit, turn out the lights!

The corrosion phenomenon mainly seems to be of anionic chlorides, sulphates, carboxilated deposits on metal surfaces along with moisture of air, a live acid vapour rain possible.

This can be attributed to the following reasons.

*possible static charges developing on metal plate surfaces due to travel air friction.

*cationic attraction sites caused by resins in paint mixtures.

*Improper curing of paints.

*possible amino based low temperature curing catalysts in the paint formulations.

Suggestions;

Go for heat curing paints.

Add possible silicon components to get a hydrophobic surface

Add antistatic agents in the paint formulations

You may do some small scale R&D trials and conclude by yourself.

Good chemistry lesson, but means nothing if you dont take good care of the application process.

Any quality paint material is a worthless expense if the preparation and application is not taken care of.

Amen

Hi Real,

This is, the lack of or completely forgetten surface preparation. Why is this happen so often? Also, they blame everyone except the surface preparation.

Good point again, Gil.

just to add something useful to the discussion, i think this page can give some good info:

http://aluminium.matter.org.uk/content/html/eng/default.asp?catid=181&pageid=2144416708

S

corrosion & rust control

"just to add something useful to the discussion"

Are you implying that nothing useful has been presented until your contribution?????

sorry.. maybe my english is so so so so so so so so so bad that you undrstand something i didn't mean...

the meaning is "to add something useful to the discussion" " to give my little help" "to help the discussion" "to add something that maybe you didn't know"...

now you understand or is not clear?????

i didn't imply ANYTHING ....

hope this help u

S

My MY,

You certainly take offense easily. Next time I'll be sure and include a bunch of

Thanks for the information, it was enlightening.

Hi Lyn,

Actually, are you in the two-engine airplane with the failing one engine? Let crash the airplane and become unsensitive to opinions. They are good or bad but they are just opinions with words on the screen, nothing else! Have an enjoyable weekend, Gil.

Hi Linch

I'm sorry i didn't want to be polemical.. maybe i've exaggerate...

All the best

S

Hi Rider,

I would like to change in your sentence "to add something that maybe you didn't know"... the word "maybe" to "for sure", with your permission to follow the protocole of politeness in the world of blogging. I saw the 119 good answers! Who allocate good or bad rating to a post? I see many out of context without any negative signs.

However, we have to protect Aluminum from cathodic attacks because anodic charm cannot be used.

My suggestion is a good wash with IPA @ 99% with 2 to 3% H3PO4 just before using a wash-primer with the same acid, let dry for 2 hours at room temperature, and follow with two coats of 2-pack solvent (only IPA) containing polyamid-adduct or one coat of 100% solid epoxy coating with amine-adduct hardener.

I hope I was clear enough to follow the recipe because I don't want to be responsible of any mix ups by someone else than me, Gil.

Hi Rider,

Thanks for the web-sites, instructive! Oh, I practically forget. Watch went you open your mouth because some people see you and others, including myself as dangerous when we have some idea. Don't worry, we will grow up one day, Gil.

C'mon Guys,

Its not about growing up.

We are all Engineers, Technicians, Graduates, Hobbyists, Scientists........whatever.

We have to learn from each other......and each others mistakes and triumphs.

This is called evolution. From the Stone age to the Atom Bomb there have been many benefits and downfalls.......but there has been progress.

I hope my simple comments on this subject have been of benefit to all. I have been as straightforward as possible as a comprehensive detailed description would have resulted in a small encyclopedia.

As I am neither a Scientist nor a Graduate, I pride myself in being a Student of experience. No University on earth can provide the learning I have gained in the last 45yrs especially in Corrosion Control and Coating Technology.

Alongside this, I have also learned the in depth Engineering requirements for Construction of Powerstations, Desal plants, High Rise Towers, OHL Transmission Lines, Marine Installations, etc etc.

My current position as Project Coordinator is a result of the above.

One day soon I will be ready to hand over the experience to others.

Any question gladly answered.

Brian

Good morning Brian,

I don't want to argue with you but it's about growing up. Mainly, how we arrive to the end. I explain: I work in the coating industry for over 54 years, and I consider my knowledge as "limited". Many things I don't know because I don't wanted to know or I just missed but still learn today. When someone talk about what I should know, I shut up, listen, and learn. There isn't any argument that I promote.

One thing I learned well is not react to others' opinions, sayings, and critics. Everyone has the right to tell what they want, except unsanities. It doesn't hurt. It hurts only the "ego". I live with a small ego and pass through life without stress.

This is important for me! The rest, I can let flowing with the flow of life because I cannot deviate too much. It could be too much deviation to match my volonty or desire and get too many opposition. Sorry for the funny wording but it's better for me, I can smile or eventually laugh a moment. Actually, I am retired by years, I still help people, my few customers to solve their absolute and major problems, Gil.

Hi Gil

I want to apologize if i have made a polemic into a forum where we should only give suggestion to people that is looking for help.

English is not my mother tongue, ok i think that you realized that ..., sometime when i write something i think in italian an translate in english and the result is that the meaning could be different.. i didn't wanted to be pedantinc or arrogant

all the best, forget the polemics and let's start to talk about corrosion and science..

S

Hi S,

No! No! You are fine. No one ask for apology on the polemic introduced into the forum as you tell us. The important was that you helped to solve someone's problem, and it was done.

If another person tells something different, we have two things to do; Accept for truth or refuse as false or failure in the case of corrosion. Nothing other. The reality is the users' decision. Hers/his solution is solved or not!

English is my third language and yours is good too, Gil.