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Ted Mooney, P.E. RET

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Excessive passivation of plant piping

We do passivation (Re-circulation of 7 % HNO3 at 45 Deg. C for 30 min) of SS pipe lines of plant using the CIP tanks as a source of preparation of passivation solution, as all routes are getting connected through these tank. In this process CIP supply and return line comes in passivation cycle more than 4 to five times. I want to know to what extent multiple / prolong passivation is harmful. In past we have observed pin hole on passivated pipe line. Could this be one of the reason?

7% nitric acid is not a passivation process that can be used. At this concentration it is a reducing acid and can be quite harmful to the surface of the steel depending on the process.

Yes it true. For hygienic industries like Stainless Steel Milk equipments and pipelines you should be using Biodegradable Chelant Passivation Chemical available which is non-toxic, non-hazardous and mainly best suitable for SS pipelines & equipments to get contamination & sterile particle free passive surface.

This will not give the problems that you are facing and will increase life of your SS plant & pipelines.

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