Obtaining corrosion rates from hydrogen flux

Acid corrosion generates hydrogen activity just under the corroding internal surfaces of service steel pipes and vessels. The hydrogen flux which permeates the steel depends on this hydrogen activity, the steel thickness and the hydrogen permeability, which in turn is very temperature dependent.

It has been shown that crack susceptible and crack resistant steels and other variously prepared steels do not vary significantly in their hydrogen permeability. It is also now well demonstrated that flux varies inversely with steels of >5 mm thickness. Therefore, from a flux measurement, steel thickness, steel temperature and permeability data, we can work out hydrogen activity, ‘normalised’ for thickness and temperature, and thus potentially closely correlated with crack risk and corrosion rate.

The scientific basis for the correlations are presented in the document converting hydrogen flux to corrosion rates and hydrogen crack risk. Please download for more information.

Please note, data relating to Hydrosteel use presented by Ion Science on this website and elsewhere is intended for indication purposes only, on the basis of correctly carried out hydrogen flux measurement with calibrated Hydrosteel equipment. No responsibility can be accepted by Ion Science Ltd for damage or injury caused by use of information contained herein.

It is likely that correlations of corrosion rate in HF and specific sour scenarios will be further refined.

Ion Science welcomes your comments regarding the information contained in the document.

Hydrogen flux is not particularly sensitive to pH or concentration of sulfide in the liquid phase.  This is evident from measurements of quite significant hydrogen flux due to corrosion under salt deposits, eg in sour gas lean amine lines.  Also, the correlation applies to cyanidic ammonium bisulfide, which occurs in overhead streams from  hydrodesulfurization columns, hydrotreaters and catalytic crackers, where hydrogen cyanide is present from high nitrogen containing feedstock.