OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk Learning by Mistakes - Using Hydrochloric Acid

So I had some very rusty/oily bolts and nuts. Vinegar was not up to the task, so I went to the hardware store and got some "good old" hydrochloric acid. Found a container in the shed which I thought was stainless steel. Dropped in bolts. Mixed some strong hydrochloric and poured it over the bolts. Then I thought, gee that's strange, the solution instantly turned bright green. Then all hell broke loose. Turned out the old oily container I found in the back of the shed was actually made of aluminum. (Mental note for future: ALWAYS double check the container before pouring the acid!). Then came the inevitable grey/black clouds of billowing smoke and the noxious fumes which sent me scurrying. Nothing I could do but wait for the reaction to subside and then went in with the garden hose to dilute the mess. Poor old container looks like its been zapped with a ray gun. Good thing I had enough smarts to mix it outside of the shed and not inside, or I would have had a hell of a mess. Another good thing, all of the rust was gone from the nuts and bolts!

Wow !!!!!!!!

That's why acid like this shouldn't be available for general sale to the public.

Hydrochloric in the first instance is the incorrect acid to use and at the strength you've suggested it's basically a lethal BOMB.

You are so lucky that you didn't do yourself some serious burns.

Sulphuric acid is the normal de-rusting acid that's used in industry. It's known as a Pickle Bath and it should be around 5 to 15% in strength. Also oil is not to be induced into the bath as it acts as a barrier at that percentage. Oil must always be removed from the items prior to immersion. Also the solution should be heated and not cold.

One last thing, there's an old saying when mixing acids etc.

"Do what you oughta and add acid to water" never the other way round as that will cause an instant explosion which will cover you with serious acid burns.

Why do I know all this you ask ? well I was an apprentice Electroplater and worked in one of Australia's best plating shops in South Australia and safety was something our maintenance guy "Bill Topper" (now deceased) whom I worked with for months on end was always paramountly insistent of. Yes I nearly blew myself and the shop up and had people running when I broke the golden rule. So you're not alone in that department.

BTW I'm not trying to be a smart arse, but I can't stress enough the safety factor when playing with acid and alkaline solutions.

Cheers,
BB.

Also known as Muriatic acid and used to clean mortar off bricks. Many years ago I burnt potatoes rather badly when I forgot they were on to boil and could not remove the mess from the pan so decided some muriatic might just do the trick since it is basically the same as the acid in your stomach that dissolves food so well. What was left of the aluminium saucepan was a sight to behold but gee it gave off such lovely clouds of billowing white smoke before it ate right through. I also did it in the middle of the lawn which took some time to recover. But hey, that was over 40 years ago so I think I have been forgiven by now.

Funny enough on my Facebook page the other day someone asked for the best way to make old corroded Aluminium go nice and clean again. Then some bloke comes along and says "use hydrochloric acid, best way". We said no and then he replied back "I am right, I have worked in the industry for 20 years, I am sick of you back yarders telling me what to do"

Lets just say he isn't on the page anymore

Hi Kye and AT,

In the anodising process of Ally, again a very diluted Sulphuric acid is used to strip off any previous anodising. I've never heard of Hydrochloric acid being used anywhere in the Aluminium processing department. It's really only used in the brass refreshing process if my memory serves me correctly. We had a Hydro bath next to the Pickle bath and it was always bypassed unless you had a brass component going down the plating line. Nitric Acid (now there's some lethal stuff) was also used as a quick brightener of brass or copper.

Cheers,
BB.

It was a good day because:

1) I learnt a very valuable lesson.

2) I got the bolts and nuts clean.

3) I did not die.

Yes indeed, it would make the corroded Aluminium turn a dull, scorched, grey colour.

I guess as it's past tense you are spot on in that evaluation.

Good to see you're still with us. Sadly some aren't from not applying dot point 2.

Cheers,
BB.

I would have to say that for a product that can be purchased over the counter, the warnings on the label are pretty mild. I am opposed to "Nanny State" thinking that sets out to ban every product that could hurt somebody, because it is hard to know where to draw the line. You get to the stage where bleach and toilet cleaners must be banned just in case someone might wash their hands in them or drink them. But I must say the warnings on the HCl label were very understated for such a potentially dangerous product. At least I remembered my basic high school science of always adding the acid to water and not vice versa. But they did not even put that simple rule on the label.

Hi VM,

I guess it's not so much about what it is meant for but rather what it shouldn't be used for in todays twisted world, thus why I'm a bit surprised that its still just an over the counter product. It's used in swimming pools to lower the Ph but generally it's already in diluted form for that purpose and not "neat" as we call it at 99.9%

I'm seeing that Hydrochloric is now been used as the weapon of choice opposed to Sulphuric in production line pickling. The problem with this process is what is called "Hydrogen Embrittlement" which is induced into the steel and thus weakens things like nuts and bolts severely if the exposure is not monitored correctly and also if the concentration of acid is too high, thus it's not the best thing for hobbyists to use.

Here's a good page that explains it much more precisely.

http://www.columbiachemical.com/reprints/Reprint%20A%20Practical%20Approach.pdf



This rapidly becoming a chemistry lesson I feel so from here I'll stop as it's probably way over some people's heads.

Cheers,
BB.

BB doesn't the hydrogen embrittlement dissipate by itself over some time and can also be gently heated in a home oven to release the trapped gas?

Hi SB,

We used to heat treat parts in an industrial oven that were going to be required for torsional strength, but yes a home oven can also be used.

Cheers,
BB.

BB any idea of the temperature required and soak time?

Hi SB,

If I recall correctly it was at around 100 degrees C for a couple of hours time wise to be totally safe.

Yes you could easily do that in a domestic oven.

Cheers,
BB.

Thanks BB.

You could almost do that on our front lawn lately, just with a sheet of black metal placed out in the sun for a few hours.