Is it true that passivation of stainless steel should be done before NDT (Non Destructive Testing)? What is the reason for that? Does it help to find the possible defects in the stainless steel?
Passivation is the formation of an oxide layer that can be protective. A non-destructive test, as its name says, is one that does not damage steel.
Yes Ricardo. I am aware of that. Passivation is done to make and strengthen the Cr3O2 layer on the stainless steel. As you know, the stainless steel is categorized as CRA (Corrosion Resistance Alloy) due to content of Cr which is above 9-10 percent.
NDT is a Non Destructive test which is done to detect the defects on the material. Defects could be on the surface or under the surface.
We know these two. But the question is that why NDT should be done after passivation? How NDT could detect the defect better after passivation?
some NDT methods such as Magnetic particle inspection (MPI) require pre cleaning processes to ensure a surface free of debris or foreign particles, may be this why passivation is requires prior to the NDT. so I don't think passivation here means to add cladding layer or protection layer to the surface rather than cleaning issue.
Pssivation is done through for example acid picling to activate the Cr-Oxide layer on the stainless steel surface. Yes. I think it helps to detect the defects through applying non- volumetric NDT such as Magnetic Particle or Visual Examination through providing more clean surface.
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