PICKLING

Pickling is the process that uses chemical means to remove oxide flakes that are formed during hot processing in the presence of atmospheric oxygen: the final result is a product with a regular surface and uniform grey colour, in preparation for any subsequent passivation or electropolishing treatment.

Pickling is the simplest and cheapest method to obtain a decontaminated and homogeneous stainless steel surface that can guarantee the characteristics for which this alloy was used. The formation of the particular protective film that distinguishes stainless steel can only be formed correctly in the absence of the oxides and contaminants that pickling eliminates. Contaminated stainless steel that has not been pickled will corrode sooner or later - guaranteed!

Pickling and passivation treatments can be performed in accordance with ASTM A480 and ASTM 967 standards by immersion or spray using gels or liquids, with products completely free of or containing nitric acid, according to the customer's specifications.

DECONTAMINATION
The decontamination treatment eliminates ferrous and other metal contaminants from the surface of the stainless steel. The presence of these foreign materials on the surface interferes with the formation of the protective film, favouring potential corrosive triggers. The immersion or spraying of special solutions allows the complete removal of these pollutants without altering the original appearance of the product; compared to pickling, there is practically no material removed.

Decontamination always has a beneficial effect on the stability of the passivation of stainless steel and for this reason it is often improperly defined as passivation. Decontamination can be verified with specific reagents, compliant with the reference ASTMs, or with a cycle of wetting repeated over 24 hours .

However, when only small areas need to be treated,

such as in the vicinity of a weld, pickling pastes and gels applied by brushes can be used.
When you want to decontaminate a stainless steel surface from particularly tough oxides, you can use a product that allows complete removal, without however significantly altering the colour of the treated surface. A clean stainless steel surface without contamination will autonomously generate its own passive layer of chromium oxide when placed in contact with the oxygen in the air.
It is precisely this passive surface layer that gives this material its excellent characteristics of resistance to chemical attacks and corrosion in general. It is however possible to use chemical passivation to accelerate the formation of this protective layer.

Chemical passivation is not always necessary

but it is certainly recommended where the surfaces do not have abundant ventilation, such as inside pipes or in hermetically sealed reactors.
Our chemical pickling and passivation treatments are compliant with ASTM A380/06 and ASTM A967/99.
Passivation on an electropolished surface is not necessary due to the excellent surface oxide formation after the electropolishing step (ASTM 912/02).
Delmet has a wide range of plants, products and equipment to carry out steel pickling treatment, both automatic and manual, with a dedicated contract service at its production plants or through the creation and supply of customised plants at the customer's premises.

Delmet offers an efficient contract pickling service for stainless steel pickling in two different production plants, equipped with the most innovative equipment and using the most suitable treatments for your stainless steel: immersion pickling, spray pickling and localised manual treatment for small parts.
Pickling is carried out on steel objects and manufactured parts - up to 10 tons and 15 meters in length - with an express service, thanks to the processes that operate up to 24 hours a day, 6 days a week, but a contract service is also available at the customer's premises.
You also have the option to follow the progress of the work on the products remotely through our digital monitoring platform.