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I'm looking for a liquid that can remove copper corrosion (oxides and basic carbonates - the black and green stuff) off copper piping.

The corrosion will be located on the inside of the pipe, in hard-to-reach areas, so ideally I should be able to just pour the liquid in, leave it for a while, and just flush it out with water. It will be practically impossible to scrub the corroded areas.

Additionally, the piping is brazed or soldered together with an unknown filler metal.

I've read around, and it seems people commonly use acetic acid (vinegar) or hydrochloric acid for this. Is this correct?

However, I'm interested in if any acids (or other liquids) that can be stored as solids can be used for this instead. Mainly because it's easier to store and transfer solids than liquids. (As far as I'm aware, acetic and hydrochloric acid are only readily available in liquid forms)

Some common solid acids that seem to be effective on rust (iron oxide) that I can buy off Ebay include citric acid, oxalic acid, and sulfamic acid. But will these also be effective on copper corrosion, and keep the byproducts in solution?

Additionally, will I need to use any corrosion inhibitors, to prevent the acid for eating away from the raw metal itself? If so, what should I use, and what acids are they compatible with? I'd like to avoid anything that would leave phosphates/silicates/etc coated on the metal.

TL;DR: What (stored-as-solids) acids/liquids can clean corroded copper, that will leave the byproducts in solution? Do I need to use any corrosion inhibitors?

Note: I do not have access to chemical suppliers, so only things commonly available on Ebay and the like please. Additionally, I do not have fume hood, so no toxic fumes too.

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    $\begingroup$ Google is your friend. When typing "Copper cleaning" on Google, you will find a lot of different recipes for cleaning oxidized copper surfaces. In the majority of these processes, vinegar is used, usually with some slat. There are plenty of videos about each recipes. And I can tell you, that vinegar will not corrode any other metal (tin alloys usually) used for soldering. Of course, sulfuric acid may also do the job. $\endgroup$
    – Maurice
    Commented Oct 3, 2020 at 12:04
  • $\begingroup$ Yes, I'm aware of vinegar (as mentioned in the question), but I don't have any so I would have to go out and buy some anyways. In which case I would rather buy something stronger like HCl instead. But I also want to know if there are any stored-as-solid alternatives readily available $\endgroup$
    – 小太郎
    Commented Oct 3, 2020 at 16:48
  • $\begingroup$ See patents.google.com/patent/US5468303A/en $\endgroup$
    – DrMoishe Pippik
    Commented Oct 5, 2020 at 1:31
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    $\begingroup$ Try sodium bisulfate. It is cheap: used to lower pH in swimming pools. Readily available. $\endgroup$
    – Ed V
    Commented Oct 29, 2021 at 1:29

3 Answers 3

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Per a source to generally clean copper metal surface, to quote:

A few hard rainstorms may clean the surfaces sufficiently to start operations. However, it is always advisable, particularly if the coloring is to be done immediately after installation, to go over the surface with a commercial chemical metal cleaner. Cleaners of the trisodium phosphate type should be satisfactory. Avoid cleaners which leave a coat of oxide on the copper surface.

However, assuming one has already a basic copper carbonate, the application of an acid, like HCl or more friendly acetic acid, is likely suitable, especially with the addition say NH4Cl or NaCl to increase the activity coefficient of the acid (so less strong acid may be employed).

However, a review of the cited source notes that these reagents are the very agents suggested to create a patina coating (which can be characterized as electrochemical based corrosion) occurring in the presence of air/oxygen.

So, do limit air/oxygen exposure by immersing the copper surface to be cleaned in say a HCl/NH4Cl mix.

Also, employing the concept of a sacrificial anode, experiment with performing the latter cleaning in the presence of a more anodic metal (say a small piece of Aluminum metal in acetic acid and NaCl), especially when the requirement of limiting air exposure could be difficult to implement. This may prove to be actually beneficial in avoiding surface oxidation.

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Sulfamic acid is a standard for cleaning pipes. Typical use is to remove blockage by carbonate and rust scale, not green film on copper. But it will clean copper. Why do you want the remove the film ? Do you have a corrosion problem that you want a protective coating for ? Solder is lead + tin, or just tin if it is newer, after the lead hysteria started. Caution , do not use any ammonia compounds on copper- severe corrosion potential.

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Two common acids that can be used to clean corroded copper are:

Vinegar (Acetic Acid): Vinegar is a weak acid that can effectively dissolve tarnish and corrosion from copper surfaces. Soak the corroded copper item in vinegar or create a paste with vinegar and salt to gently scrub away the corrosion.

Lemon Juice (Citric Acid): Lemon juice contains citric acid, which can also be used to clean corroded copper. Apply lemon juice to the corroded area and use a cloth or sponge to gently scrub away the corrosion.

Always exercise caution when working with acids, even weak ones, and wear appropriate protective gear such as gloves and safety goggles. Additionally, ensure proper ventilation when using these cleaning solutions. For more information us on - https://goo.gl/maps/CzTRuLaAi5h1Mxe46

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