Acid Pickling

Question:

I am a metallurgical engineer working in a private firm. I have a problem during welding with filler wire. My filler wire for TIG welding is corroded due to atmospheric humidity. Filler wire composition is C = 0.15%, Si = 1%, Cr = 1%, Mo = 0.5%

Please advise which acid (or combination of acids) to use for pickling/rust removing of above-mentioned alloy. Thanks. A.A.

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Answer:

It is somewhat dependent on the level of rust on the product. Ideally, you would only use as strong an acid as necessary to remove the corrosion product. For light rust that would be generated from a short in-process storage of wire in a humid environment, there may be limited rust to be removed. In that case, an organic-acid-based cleaner may be effective at rust removal. The next strongest acid for moderate rust removal would be a phosphoric acid. For heavy rust removal, sulfuric acid may be necessary.

Regardless of the type of acid, it is advisable to contact a chemical supplier for a compounded or mixed product that can also provide other benefits. Rather than just using a straight acid, they can add components such as an inhibitor that will still allow you to remove the rust, but minimize base metal attack on the weld wire. Additionally, they could add surfactants or wettings agents that will allow more uniform rust removal since it lowers the surface tension and allows hydrogen bubbles to float away from the surface.