Copper Pickling Question?

[Gmccabe]

I am using a 10% Muriatic pool acid 90% water pickle solution and noticed that after a short 5 minute pickle and good water rinse that the copper seems to be possibly still reacting to the pickle? It looks rusty and when I rub my hands over it they have a copper residue on them. Even after a long water wash when I go to towel dry the copper the towel has a copper residue on it.

Is this normal, should wash in a neutralizer after each wash? What is the ratio of baking soda to water, or other neutralizer to use?

[steamin10]

You have to mechanically loosen the products on the copper, toothbrush, 3-0 steel wool, 3M pad, or some such. Neutralizing with Amonia or soda, will leave a chemical salt that will still be active with humidity, and the level of that salt will determine the 'clean' stability of the copper in air.

[Gmccabe]

Thank you for the quick response, I scrubbed with a wire brush while in the pickle, but not after/with the water rinse. Are you saying that I need to scrub during the rinse? What happens once I start to close up the boiler and cannot scrub the inside after pickling?

[SteveR]

I'm thinking that you should use sulfuric acid, not hydrochloric (muratic) acid. See for example in: http://en.wikipedia.org/wiki/Pickling_(metal). Must be more references on this board or Kozo's book, but I'm pressed for time.
good luck.
SteveR

[steamin10]

Yes it will work. But Hydrochloric is milder on shop tools, hands and everything else. We are talking pre assemble pickle here. When in service, the natural calcium hardness in waters will kill off any acids that decompose out of the salts, and reform. That is what blowdowns are for, to keep the TDS in boilers to a managable level. (Total Dissolved Solids). Not blowing down while running is a mistake commonly made, that will sediment and shorten the life of any boiler.

Full sized railroads went in for periodic inspections, washouts, that cleaned the waterside of the tubes, and minor service at regular intervals. Reflues, and major repairs were grouped as needed. Much of the mechanical wear was controlled by bearing adjustments, and flues were inspected for the purpose of integrety, and fuel efficiency.

[Kimball McGinley]

I always use a green scotchbrite pad and Comet cleanser or similar. Buy a new pad - don't use one that has ever been in the kitchen due to cooking oils.

[Gmccabe]

Thank you all for the great information. One thing I did not mention is I am pickling between brazing process as I am assembling the boiler and I am using the Harris Black Flux.

[steamin10]

Buy a handfull of brass and stainless tooth brushes. the flux is sometimes stubborn, and can be picked at with an ice pick when cleaning. I have several that are straight and hooked for various problems. These are handy for silver that keeps a small hole, you can scratch in while flowing.

[Harold_V]

Yes it will work. But Hydrochloric is milder on shop tools, hands and everything else.

Wish I could agree, although I do with most of your comments.

I worked with hydrochloric (muriatic) acid, along with nitric and sulfuric acids, for years, refining precious metals. It was purchased by the 55 gallon drum.

HCl is the worst of the three, where fumes are concerned. Granted, it's not very hard on skin (although exceedingly damaging of lung tissue), at least when it's dilute, but if it is used in the machine shop, fumes will rust everything (ferrous) in sight. I do not recommend its use unless it is a requirement, which, for copper, is clearly not the case. Nitric is not suited to this application in that it readily dissolves copper, silver, and zinc, and converts tin to metastannic acid.

Sulfuric acid, by sharp contrast, isn't much of an issue where fumes are concerned, although it is very aggressive when making contact with skin and most fabrics. It also does NOT dissolve copper when dilute, but dissolves copper oxide with a vengeance, so it's a perfect choice for pickling.

Harold

[steamin10]

Harold , your comments are very true, and right on.

My issue here is safty. When scrubbing with a brush, it is often little droplets that spray out. HCL, will not harm the eyes for some minutes, and allows the treatment of water flush. The same amount of sulfuric could result in immediate damage that would progress until flushed or used up. The hydrochloric is more like bleach, and forms copper chloride, a simple salt, in use. it is not particularly aggressive with copper, but much safer for any contact.

Sulfuric, unless highly concentrated, does not cast much fume. Hydrochloric, is a gas, dissolved in water, up to saturation of 33%. It ALWAYS casts the gas, especially when heated, as heated water always gives up disolved gasses.

The fact that HCL loves to rust iron is a widely stated fact, I have warned about on this board. It will react with iron with only humidity for available O2. Ferric chloride is hygroscopic by nature and attracts moisture, (as does table salt, another Chlorine agent) and will continue to degrade clean iron, unless treated to arrest the cycle.

Nitric is nasty stuff to work around, and I have little experience with it.

[Bruce]

Is there any way to neutralize sulphuric acid? I'm working in a shop with ecological concerns, they're requesting that I pickle my copper with Muriatic acid and neutralize it with soda? Muriatic does not sound good from what I read here.

Has anybody used the citric drain cleaners to pickle that question was not answered.

Thank you.

[Bob D.]

I use a friendly solution of 1 gallon white vinegar mixed with 1 lb of table salt to pickle copper for silver soldering. Works very well and is cheap. Afterwards it can clean your sink drain or go on your salad or make pickles. Brass pickles well too but if the solution is used for copper it will give a coppery color to the brass. I keep the solution in an old plastic cooler jug and have had it for years.
Bob D.
Disclaimer: don't actually ingest the stuff, I doubt it will hurt you though.