Ultrasensitive technique for detection of hydrogen emanating from steel and other solid surfaces

Abstract

Measurement of diffusible hydrogen in steel by destructive testing is, in many cases, impractical. A new non-invasive surface measurement technique is presented, whereby hydrogen emanating from a well defined steel surface is captured in a stream of air and analysed in situ. The apparatus embodying the technique is evaluated with respect to critical measurement parameters, indicating, for a high sensitivity version, flux resolvable to <2 pL cm^-2 s^-1 hydrogen at 298 K and 1013 mbar, and linear measurement of flux to 1000 pL cm^-2 s^-1. Flux measurements were obtained under ambient conditions by magnetically attaching the apparatus to one face of coupons expected to contain a low and uniform concentration of hydrogen, and 2 mm steel plate cathodically charged at the opposing face. The results suggested that hydrogen emanated into air at a rate of 50–30 000 pL cm^-2 s^-1, and was controlled by hydrogen diffusion through the steel bulk. The reproducibility and responsivity of the technique is also illustrated.