Pickling Treatments: Healing the Damage of Heat Exposure with Chemical Means

Methods for eliminating scaling and oxide degradation due to welding, heat treatment, and other means

Basic maintenance can improve the appearance and life of your stainless steel. However, there are specialized cleaning and maintenance routines that offer benefits in specific scenarios as well.

We’ve already discussed stainless passivation treatments in a previous guide. However, passivation is often best used for whole parts and won’t account for scaling or contaminants present on the surface of stainless steel.

What can you use if you need a little more control or precision?

Pickling provides a flexible means of addressing scaling, removing contaminants, applying spot treatments, and restoring the surface of stainless to like-new condition.

Available as pastes, gels, and baths, this treatment provides flexibility in maximizing the corrosion resistance of welded or heat treated steels.

What is Pickling?

Pickling solutions come in a variety of forms. However, they all use acid to accomplish their goals.

Unlike passivation, pickling removes a thin layer of chromium-depleted steel to both clean and restore an exposed surface with the same characteristics as the raw metal.

Common components of pickling solutions include nitric, hydrochloric, and hydrofluoric acids in various concentrations.

However, many specialized pickling products use alternative or proprietary ingredients to enhance performance, protect certain grades of steel, or increase safety.

When Should You Consider Pickling Steel?

Pickling solutions have a variety of uses. Common uses include:

• Removing mill scalings

• Removing oxides from heat treatment or welding

• Removing impurities

• Removing stains

Available in a variety of forms--from bathing liquors to thick pastes--pickling solutions are ideal for full submersion and spot treatment alike.

One of the most common uses for stainless pickling is to remove discolouration from welding.

By applying paste or gel to the welds, a cleaner appearance is attained and corrosion resistance restored.

However, it’s important to note that pickling removes the chromium-depleted layer, so the pickled surface might not match in finish and visual brightness to the untreated, raw or polished surface of the surrounding steel.

For this reason, you might combine both pickling and passivation—either in separate or combined processes—to ensure an even appearance and further encourage a strong passivation layer.

Applying Pickling Solutions

As pickling solutions are highly acidic, care must be taken during both the pickling process and while disposing of any wastewater or resulting products. The acids can also create fumes, leading to breathing hazards on top of poisoning and burn concerns.

ALWAYS consult the MSDS data and manufacturer recommendations before using a pickling solution as concentrations and ingredients can vary between products.

In general, pickling liquors are used in baths for full submersion of fabricated stainless steel items.

Gels and pastes provide more flexibility when it comes to application. Most are compatible with brushes, rollers, and even sprayers. However, when using sprayers, be sure to observe any additional precautions required—such as respirators or ventilation.

Most products require treatment for 15 to 60 minutes.

It’s also important to thoroughly clean and degrease the surface you intend to pickle as the acids are not designed to remove oils, greases, and other similar contaminants.

At the least, pickling a contaminated surface will cause poor performance. At the worst, it could create a reaction that further damages the steel or increases personal injury risks.

Disclaimer: Pickling products rely on acid to restore the passive layer of your steel. This comes with risks of both personal injury and damage to the steel if improperly applied or used. The information in this guide is intended to serve as a general overview of the benefits and concerns regarding stainless steel pickling. Always consult a professional, engineer, or pickling product manufacturer before using pickling pastes, gels, or baths. Consulting MSDS data for any chemicals involved and disposal information will further minimize risk to persons, materials, and the environment.

A Quick Review

• Choose the pickling solution best suited to your application needs

• Always follow recommended safety and disposal protocols

• Consider following pickling with passivation treatment for further improvement of both appearance and oxide layers

• Thoroughly clean and degrease the surface you intend to pickle before starting

• Follow any post-treatment instructions to halt the pickling process and ensure safety