Pickling is the most common chemical procedure used to remove oxides and iron contamination. Besides removing the surface layer by controlled corrosion, pickling also selectively removes the least corrosion-resistant areas such as the chromium-depleted zones.

Fume reduction during pickling

The toxic nitric fumes generated during pickling have a number of harmful effects on health and environment. By using modern pickling products such as our BlueOne^TM pickling Paste 130 and RedOne^TM Pickling Paste 140, the toxic fume levels can be reduced by up to 80%.

This procedure is carried out in a manner similar to pickling. The passivator, applied by immersion or spraying, strengthens the passive layer. Because the passivator also removes free iron impurities from the surface, the treatment is more important after mechanical cleaning and operations involving a risk of iron contamination. It is for this reason that the method can also be referred to as decontamination.

Electropolishing normally produces a surface that guarantees optimal corrosion resistance. It does not selectively remove areas of inferior corrosion resistance, but polishes micro tips from the surface. The material gains a fine luster and, most importantly, an even micro profile that meets extremely stringent hygiene requirements. For these reasons, electropolishing is normally used as a final treatment after pickling.

• Inspect the surface to be treated and ensure that all non-stainless material has been protected.
• Using an acid-resistant pump (Avesta SP-25), spray the product onto the surface. Apply an even layer that covers the entire surface. Do not apply in direct sunlight
• Allow the product sufficient reaction time, but avoid letting it dry. If the contaminants are stubborn (difficult to remove) and in thick layers, mechanical brushing with a hard plastic or nylon brush will help
• Preferably using a high pressure water jet, rinse thoroughly with clean tap water. To reduce acid splashing, prewashing at tap-water pressure (3 bars) is recommended. Ensure that no residues are left on the surface. Use deionised water for the final rinsing of sensitive surfaces.
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• Inspect the surface to be treated and ensure that all non-stainless material has been protected.
• Using an acid-resistant pump (Avesta SP-25), spray the product onto the surface. Apply an even layer that covers the entire surface. Do not apply in direct sunlight
• Allow the product sufficient reaction time, but avoid letting it dry. If the contaminants are stubborn (difficult to remove) and in thick layers, mechanical brushing with a hard plastic or nylon brush will help
• Preferably using a high pressure water jet, rinse thoroughly with clean tap water. To reduce acid splashing, prewashing at tap-water pressure (3 bars) is recommended. Ensure that no residues are left on the surface. Use deionised water for the final rinsing of sensitive surfaces.

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• Inspect the surface to be treated and ensure that all non-stainless material has been protected.
• Pretreat oxides, slags and weld defects mechanically. This should preferably be done while the welds are still warm and the weld oxides less hard.
• After any welding, give the area to be pickled time to cool down to below 40°C.
• To remove organic contamination, degrease using Avesta Cleaner 401.
• Before using, stir the spray gel well.
• Using an acid-resistant pump (Avesta SP-25), apply the product as a spray. Gently apply an even layer of acid that covers the entire surface. Do not pickle in direct sunlight!
• Allow the product sufficient pickling time.
• Desmutting is necessary if dark areas appear on the surface. Apply either more solution or Avesta FinishOne™ to these spots until they disappear. This must be done when the surface is still wet (i.e. “wet on wet”), just before the pickling spray is rinsed off. Spraying Finish One™ on top of the pickled surface also reduces the production of NOx gases.
• When pickling, the pickling spray must not be allowed to dry. Drying may cause discoloration of the steel surface. This means that at high temperatures, and when prolonged pickling times are required, it may be necessary to apply more of the product after a while.
• Preferably using a high-pressure water jet, rinse thoroughly with clean tap water. To reduce acid splashing, prewashing at tap-water pressure (3 bars) is recommended. Ensure that no pickling residues are left on the surface. Use deionised water for the final rinsing of sensitive surfaces.

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• Pretreat oxides, slag and weld defects mechanically.
• After any welding, give the area to be pickled time to cool down to below 40°C.
• To remove organic contamination, degrease using Avesta Cleaner 401.
• Check the bath temperature.
• Immerse the object in the bath. Typical pickling times are shown in table 2. Avoid overpickling. This can produce a rough surface.
• Allow the product sufficient pickling time.
• If dark spots appear on the surface, desmutting is necessary. Apply either more solution or Avesta FinishOne™ to these spots until they disappear. This must be done when the surface is still wet (i.e. “wet on wet”), just before the pickling spray is rinsed off. Spraying FinishOne™ on top of the pickled surface also reduces the production of NOx gases.
• When lifting the object, allow time for the bath solution to flow off above the bath
• Rinse thoroughly using a high-pressure water jet. Ensure that no pickling residues are left on the surface. Use deionised water for the final rinsing of sensitive surface.
• Collect the waste water so that it can be neutralised. Find here more information about neutralisation and waste treatment.
• As the pickling acid in the bath is being constantly consumed and metals precipitated, analysis of bath contents is important. Bath contents affect the pickling reaction.

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• To passivate after mechanical treatment, first use Avesta Cleaner 401 to preclean the surface. Next, rinse with water and apply the passivator “wet on wet”. Leave it to react for 3 – 5 minutes.
• To desmut or avoid smut formation during spray pickling, the passivator must be applied before rinsing while the surface is still wet (“wet on wet”). Leave it to react for 10 – 15 minutes.
• To use for fume reduction after bath pickling, lift the object over the surface of the bath and spray FinishOne™ as a mist on the object’s surface (“wet on wet”).
• To passivate after spray pickling, first rinse off the pickling spray and then apply the passivator. Leave it to react for 20 – 30 minutes. n Using an acid-resistant pump (Avesta SP-25), apply the product as a spray. Apply an even layer of acid that covers the entire surface.
• Using an acid resistant pump (Avesta SP-25); apply the passivator as an even layer that covers the entire surface.
• Preferably using a high-pressure water jet, rinse thoroughly with clean tap water. Ensure that no acid residues are left on the surface. Use deionised water for the final rinsing of sensitive surfaces.
• There is no need to neutralise the waste water (it is neutral and acid free).

• Stirring all the time, add the neutralising agent to the rinse water (e.g. our Neutraliser 502).
• The neutralising reaction takes place instantly.
• Using litmus paper (for example), check the pH of the mixture. Precipitation of the heavy metals is optimal at pH 9.5.
• When the waste water has reached an acceptable pH value, wait for the sludge to sink to the bottom and for the water to become clear. Adding a special settling agent improves the precipitation of heavy metals.
• If analysis shows that the treated water satisfies local regulations, it can be released into the sewage system. To increase the degree of treatment, an extra filter can be inserted before the water reaches the sewage system.
• The sludge contains heavy metals and must be sent to a waste-treatment plant.

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• Pickling chemicals must only be handled by persons with a sound knowledge of the health hazards associated with such chemicals. This means that the material safety data sheet (MSDS) and the product label must be thoroughly studied before the chemicals are used.
• Eating, smoking and drinking must be forbidden in the pickling area.
• Employees handling pickling chemicals must wash their hands and faces before eating and after finishing work.
• All parts of the skin that are exposed to splashing must be protected by an acid-resistant material, according to MSDS. This means that employees handling pickling chemicals (including during rinsing) must wear protective clothing as stipulated in the MSDS for the product in question.
• A First Aid kit containing calcium glucontate gel, Hexaflourine® (Avesta First Aid Spray ) or other products suitable for an immediate treatment/rinsing of acid splashes caused by pickling products, should be easy available. For more information check the MSDS for the Avesta Pickling Products.
• The pickling area must be ventilated.
• To avoid unnecessary evaporation, the containers/ jars must be kept closed.
• To minimise the environmental impact, all pickling residues must be neutralised and all heavy metals separated from the process water and sent to a waste treatment plant.