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Chemical residual analysis after pipeline passivation

Sodium hydroxide and nitric acid is used in degreasing and passivating pipes. it is use in cleaning in place. Sodium hydroxide is added with hot water and then circulated in the pipe. and then rinse with water.rinsing is continued until nth times until no traces of chemical present. the drained water is analyzed for chemical residual of sodium hydroxide. the same procedure is used for passivation using nitric acid. what is the procedure to determine the chemical residual analysis of nitric acid and sodium hydroxide? so that we will know if the rinsing process is okay.

Joya Camp
researcher - Canada
November 3, 2009

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Sodium hydroxide residuals can be determined by a simple pH measurement.

For nitric acid, you would need to test for nitrates; if you do not want to send the samples out to a lab, I suggest the chromatropic acid method; it's excellent when you have just one or two samples. See "Standard Methods For the Examination of Water and Wastewater."

What you should not do is use a Hach Nitrate kit. Their method has horrible reproducibility, it's an exception to the usual excellence of their products.

Dave Wichern
Consultant - The Bronx, New York
November 5, 2009