What is Passivation?
Passivation refers to the corrosion resistance of stainless steel. We all know that stainless steel does not generally rust. In high performance environments such as the manufacturing of pharmaceuticals or food beverages. A small amount of oxide is not acceptable. Koslow manufactures testers that evaluate stainless steel surfaces for corrosion resistance. For a more thorough discussion please feel free to contact a Koslow technical representative.
The Technician's Guide to Stainless Steel Passivation
Testing is the only way to verify the passivity of stainless steel, and it is imperative to perform passivity tests at regular intervals and after installing or replacing equipment. Verifying passivation, in addition to validating the effectiveness of passivation bath procedures, will satisfy quality expectations of control engineers and end-users.
Technicians can use passivation test meters on 300 series, 400 series, 17-4PH and 17-7PH stainless steel. The meter’s volt measurement is based on the metal’s surface potential under carefully controlled conditions of constant pH. Surface potential is strongly affected by free iron particles, which form a momentary, active corrosion coupling. Measuring the voltage potential across any active corrosion allows for an immediate determination of the metal’s passivity.
Following a metal passivation bath, passivation meters can also be used 1) to determine whether a passive film has fully formed on the metal’s surface and 2) to establish how long to wait for a chrome oxide layer to fully develop. Stainless steel is typically passive after several hours after the bath, though some alloys and environments will require waiting up to 24 hours. A quick passivity test will determine whether more exposure time is required. By recording test data and time intervals, technicians can use passivation tests to develop and optimize production timelines.