Effect of Degassing on pH? 2

[Corroneer]

Hi Everyone,

I am looking for a reference that clearly shows that taking a sample from a line/vessel under pressure will yield wrong pH measurements because of degassing.

Regards,
Corroneer

 

[3DDave]

Google lists a number of them. The first hit is about CO2 removal, which would be carbonic acid in an aqueous solution. There are others:

https://dl.sciencesocieties.org/publications/sssaj/abstracts/55/5/SS0550051456?access=0&view=pdf

 

[EdStainless]

Instead or wrong maybe you should think different. It depends on weather you want the pH in the process or the pH of the product.

https://water.usgs.gov/nrp/jharvey/pdf/Choi et al- j hydro 1998.pdf

https://www.imwa.info/docs/imwa_2011/IMWA2011_Geroni_363.pdf

CO2 in water will be the most common one that you find. As I recall at high pressure CO2 dissociates more and you can drive the pH down to ~3.3, But if you degas that sample it will be 7. Again, it depends on which information you need.

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P.E. Metallurgy

 

[SJones]

Draft NACE Report, ―Prediction of Environmental Aggressiveness in Oilfield Systems from System Conditions‖ (to be reviewed) states:

"The reported pH in a water analysis is often useless for corrosion prediction, as it is usually measured at atmospheric conditions after depressurization. This gives no information about the actual pH in the pipeline, which is calculated from the CO2 partial pressure, temperature, bicarbonate content in the water and ionic strength."

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[Corroneer]

Thank you guys for the references.
Much appreciated.