Volume 37, Issue 3 (May 2009)
Improvements in the Mercury Displacement Method for Measuring Diffusible Hydrogen Contents in Steels
The mercury displacement method, also known as the eudiometer method, is one of the most widely used, reliable, and low cost techniques of determining hydrogen quantities in steels. This is one of the few direct and simple techniques for measuring diffusible (mobile) hydrogen quantities. It was originally developed for measuring hydrogen pickup in steels as a result of the welding process, ANSI/AWS A 4.3 standard. However, it is often applied in a more general sense to the measurement of mobile hydrogen in steels as picked up from a wide variety of sources. The main limitation in using this technique is one of safety concerns in handling mercury and controlling the mercury fumes that are given off. This paper describes and suggests a number of modifications and improvements that have been developed from experience over the past couple of years. The modifications increase the accuracy and significantly enhanced the level of safety. The system can be run at moderately high temperatures up to 180°C with minimal mercury vapor loss.