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Removing scale from welded stainless steel

I have heard of a process in which weld scale and heat patina can be removed from stainless steel by using electrically charged acid. Our tests with diluted hydrofluoric (muriatic) were a failure. I am now told that phosphoric acid is the solution. However, I am not sure which grade and concentration of phosphoric acid to use. Any input into this matter would be greatly appreciated.

Robert C Wiley
welding - Columbus, Ohio
2005

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Muriatic acid is a dilute hydroCHLORIC acid and is NOT hydroFLUORIC! Big difference!

I might suggest you look into electropolishing to remove heat scale, you get the added benefit of passivation with this process.

Bill Grayson
- San Jose, California, USA
2005

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1st of two simultaneous responses--

There are many options available for removal of heat tint and weld scale on stainless steel. Electropolishing would yield the best finish but may be cost prohibitive. Pickling pastes are commercially available and effective. They are primarily nitric/hydroFLUORIC acid based. You can have the entire assembly pickled by immersion, spray, or fill. Try ASTM A380 recommended practice for more information. To address your question more directly, yes, there are many machines on the market that remove weld scale and discoloration by using an electrically charged acid solution. Just try a Google search for "electronic weld cleaner" or something like that. Hope that helps.

Joseph Lockrem
- Indianapolis, Indiana, USA
2005

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2nd of two simultaneous responses--

Weld scale or heat tint requires mechanical removal, and electropolishing is the best method as suggested by Bill. The use of weld pastes(available through welding suppliers or Avesta) contain hydrofluoric acid and will etch the weld to remove the heat tint, but leave the surface more rough. Passivation after removal is required.

Daryl L. Roll
Costa Mesa, California, USA
2005

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As mentioned, there are a variety of ways and chemistries to eliminate the weld scale. Electropolishing is certainly excellent if you can afford it and if you can get the unit into an EP bath. Wand electropolishing is very effective and can be done with relatively safe chemistries if the right devices and currents are used.

There are also ways to immerse the unit in a bath and use low voltage DC electric current in commercially available products. This process is fast and effective. Not sure that I should mention specific companies here, but you can contact me if you would like references to companies who do this.

We have a number of companies using one of our products, but there are other excellent products and systems that we can refer you to.

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois

2005