Flux measurement frequency

A frequent question about the  measurement of hydrogen flux is how often flux needs to be measured in order to trend an episode of corrosion.  The short answer is to be found in the illustration below.

Depending on the thickness an temperature of a steel, the time required for 90% of the steady state flux caused by a step increase in corrosion is indicated.  To indicate such corrosion changes promptly, flux should be measured at an interval no less than one tenth of the time indicated for 90% stabilisation. In most circumstances though, the monitoring interval will be extended, to take into account the episodicity of corrosion.  If corrosion changes are expected over hours, then a minimum sampling interval of an hour is required.  If corrosion changes over weeks, then measurements a few times per day are sufficient.