Chemical cleaning of steel as a finishing step boosts corrosion resistance and prepares the part for field use. A two-step cleaning process, known as pickling and passivation, removes impurities and imperfections from the steel’s surface such as oils, free iron, and scale. The resulting metallically clean surface allows for the protective chromium oxide layer to form. Stainless steel often requires pickling and passivation, but carbon steel can also receive the process. For carbon steel, the pickling process happens much less frequently, and passivation stabilizes the remaining free iron.
Omaha Steel adheres to the ASTM A380 specifications when performing pickling and passivation, ensuring your products are always to code. Additional testing can be performed to measure the effectiveness of the process if your specifications require it. The process of pickling and passivation is critical in many duplex, super-duplex, and super-austenitic stainless steel applications. Omaha Steel understands the required processing and the necessary controls necessary for achieving the metallurgical integrity for your castings to operate successfully in these service environments. If you need additional corrosion testing to confirm the foundry processes, Omaha Steel provides testing to the ASTM standard A262 for the detection of susceptibility to intergranular corrosion.
Pickling and passivation offer several advantages for steel castings and parts:
Pickling removes scale and other impurities from the steel’s surface, and is done by swabbing, spraying, or submerging the steel casting in an acid solution, typically sulfuric acid. The chemical bath removes the corrupted chromium oxide layer on stainless steel. Pickling is a much more aggressive process than passivating.
During passivation, the steel goes through another type of chemical bath, using less abrasive acids such as nitric or nitric-hydrofluoric acid. Many surfaces, including machined surfaces, can be passivated with a less aggressive citric acid solution. Passivation usually only treats the surface of the steel and does not go deeper or change the chemical makeup or mechanical properties of the steel.
We’re your partner for ensuring the metallurgical integrity of your steel castings and parts. We can manage the preparation and finishing of parts for reliable and long service life. Talk to us today about managing pickling and passivation steps for your castings.
Seeing in person how we implement our processes, and how they contribute to quality castings, can go a long way towards making the right decision. Schedule a tour with Omaha Steel, and we’ll give you an in-depth look at our commitment to quality.