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Is pickling paste ruining your stainless steel product?
White smudgy marks, corrosion, pitting, rust…cracking…eeeek! Are any of these symptoms found on your stainless steel product after you’ve cleaned with pickling acid? Are you using pickling paste the wrong way? Is there a solution? Let’s find out…
Stainless steel has some awesome anti-corrosive properties and it looks great – you already know this, hence your use of pickling paste/gel/spray to clean and passivate.
You’re also aware of the dangers of using pickling acid (if not PLEASE read about it here ASAP: Why Pickling Paste Is So Dangerous).
In fact, you’re probably using pickling paste because it was either recommended to you or its what is used in your workshop. So let’s cut to the chase…
Why is pickling acid ruining my stainless steel fabrication?
Although the health hazards surrounding acid cleaning stainless steel are discussed considerably online, there is little information relating to when pickling paste goes wrong on your stainless steel fabrication, rather than your skin. Here are a few of the common issues that occur when pickling paste is used incorrectly:
White smudgy marks
Ever found that after you rinse off the pickling paste the stainless steel surface is left with a white hazy appearance that can’t be wiped clean? This could be due to a couple of things:
Answer 1: You’ve left the pickling paste on too long, or not long enough.
Solution: This is a common issue with many people thinking the white marks are just a “normal” part of using pickling acid. The truth is pickling paste is rather picky when it comes to timing. The optimum time for letting it do it’s thing depends on the type of weld (tig or mig), size of the weld, material you’re using and the amount of acid you put on. Left too long, or not long enough and you’ll end up with white marks that require scrubbing with the scotch brite pad to disguise, or worse, corrosion as mentioned below.
Answer 2: Application of pickling acid on a hot weld.
Solution: Allow the weld/fabrication to cool to touch before applying the stainless steel acid wash. White marks from acid cleaning stainless steel when hot may be permanent, and can not be removed by sanding.
Corrosion, pitting, rusting – oh my!
You put yourself in danger to use this hazardous substance in an effort to clean, passivate and prevent corrosion – but there it is…the beginning of some ugly orange rust marks.
Answer – The pickling solution was left on too long – or not long enough!
There’s even a name for this – over pickling. (Yes that could also have been how you described yourself when you saw the rust marks – So Over Pickling!) When the hydrofluoric acid contained in pickling paste is left on too long it can eat into the stainless steel surface, thinning the metal and allowing pitting to occur. If this is not cleaned properly, the stainless steel will not passivate and will be left open to further corrosion and long term rust.
At the same time, if pickling paste is not left on the surface long enough, the stainless steel may not have enough time to passivate properly. This will also leave the fabrication open to contamination and corrosion.
Always follow the supplier instructions of individual pickling pastes for acid contact times and rinsing procedures. Contact times may vary for different grades of stainless steel, and it is very important to rinse off all traces of pickling acid, pickling residue and any contaminant parts from the stainless steel to achieve a fully corrosion resistant fabrication. As we mentioned above, there is no “standard” rule for how long you should leave pickling paste on for optimum results. It will depend on the type of weld (tig or mig), size of the weld, material you’re using and the amount of acid you use. If the fabrication is placed in a pickling bath it should be rinsed immediately once removed.
Is that a crack in my stainless steel?
Yep, she’s a bit more than a scratch, and a lot worse than a bit of rust… Pickling acids expose your stainless steel to heat and hydrogen which can lead to hydrogen embrittlement. What is hydrogen embrittlement? It’s where the hydrogen released from the pickling acid reacts with the surface of the stainless steel making it brittle and causing cracks.
Solution – Keep your pickling acid concentrations and solution temperatures under strict control.
Always follow the instructions provided by the supplier of the pickling solution you are using. Do not assume all pickling solutions are the same. If used at high temperatures, evaporation affects the solution and you will compromise your pickling results. At a minimum this can cause an uneven effect and rinsing difficulties. At worst you end up with hydrogen embrittlement and your fabrication will be ruined. To prevent this from happening ensure your stainless steel fabrication is not pickled at temperatures above 45°C or in direct sunlight.
Pickling paste – is there an easier solution?
For a long time pickling was the best way of weld cleaning and passivation. Well, the error of pickling paste is over and it’s now time for electrochemical cleaning to make a stand.
Electrochemical cleaning systems are not a new concept. Actually they’ve been around for a while. This has lead to a few misconceptions being formed (read about the 9 Common Misconceptions About Stainless Steel Weld Cleaning Machines here.) However these machines have been continually improving until we can finally say there are machines out there that perform better, work faster, and are easier to use than pickling paste!
What is electrochemical cleaning?
Electrochemical weld cleaning is an alternative to pickling paste which has been proven to produce a better result. Most electrochemical cleaning systems will apply an electric current coupled with a mild electrolyte to the stainless steel surface in order to cause the preferential dissolving of surface rust, iron contamination and various other forms of impurities. As a result, the stainless steel is left surgically clean.
Studies have proven that electrochemical cleaning stainless steel is able to provide the same if not better results than picking paste when cleaning welds. Where pickling paste is able to restore the natural corrosion resistance of stainless steel post welding, electrochemical cleaning is able to restore and enhance the corrosion resistance. On top of this, the mild chemicals used in electrochemical cleaning provide no significant health hazards, providing a safer work environment.
Electro-cleaning benefits:
While not all electrochemical cleaning machines are equal in quality or ability, a good industrial quality machine will:
- Bring the weld back to the natural finish of the stainless steel
- Remove blemishes
- Access small jobs
- Quick set up
- Fast and easy clean-up
- No shadowing around the weld
- Have long lasting consumables – the brushes are made to last!
- Be used on different thicknesses
- Can clean jobs without needing to dismantle parts
Do all electrochemical cleaning systems have the same results?
The performance of electrochemical systems will depend on your usage requirements and the specifications of the system you choose. As with any equipment you purchase, it is an investment, and you want a system that is going to be most effective for your needs. When choosing a system for your business keep the following in mind:
- How often do you need to clean welds? If you are using the system all the time, invest in equipment that is guaranteed to last the distance and improve productivity.
- Do you need to clean in hard to reach spaces? If so, make sure the machine you choose includes a brush that will allow you to do this. That way you can get rid of pickling paste once and for all!
Some older, or cheaper electrochemical cleaning models lacked features and power that make modern machines performance superior to pickling paste. So if you are considering investing in an electrochemical cleaning machine, do your research, or even ask for a trial to make sure it will work for your needs.
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