Passivation refers to the process by which the surface of a material can be altered so that the material can no longer be as reactive as it would have been. This article discusses why inexperienced fabricators should ensure that they passivate stainless steel products after fabricating them.
Contamination from Tool Parts
As you machine stainless steel, some particles of iron may break away from your tool and embed themselves within the stainless steel part. Such fragments can cause rust spots to develop within the stainless steel products. Those rust spots can reduce the corrosion resistance of the stainless steel because they break the oxide layer on the surface of the stainless steel. This reduced corrosion resistance can affect the performance characteristics of the fabricated components. Passivation in this case can involve dipping the machined part in an acid solution so that a uniform oxide layer can form on the surface of the part.
Contamination from Shop Air
Do not imagine that iron particles will not get into the stainless steel parts just because you are using tools that aren't made from iron. The air inside your fabrication shop may contain iron particles. Such particles can drop onto the machined stainless steel and cause corrosion to develop on its surface. Passivation is vital in removing such surface contaminants that may have found their way onto the stainless steel as you were machining it.
Problems of Exposed Suphides
Steel mills at times add sulphur to stainless steel in order to increase the ease with which that stainless steel can be machined. The sulphides make it easy for chips to form during machining processes, such as grinding or cutting. The machining process exposes those sulphides to the extent that they can react with air. Those reactions can cause the stainless steel to show signs of corrosion. Passivation helps to treat the surface of the stainless steel so that an oxide layer shields the sulphides from being exposed to agents of corrosion, such as moisture.
Remember that improper passivation may also encourage the corrosion of stainless steel. You should therefore ensure that you follow all the recommendations provided for the passivation of different kinds of stainless steel. For instance, ensure that the passivation solution is of the appropriate concentration so that flash attacks of the stainless steel don't take place. Flash attacks are characterised by etching or darkening of the stainless steel component. Consult experienced stainless steel fabricators in case you have any queries about any of the steps needed in order to passivate stainless steel components.