Analysis of Samples Cleaning Methods Prior to Hydrogen Content Determination in Steel

There are multiple references to sample cleaning methods prior to hydrogen content determination, or hydrogen spectroscopy analysis, but there is still no unified criteria; different authors use their own “know-how” to perform this task. The aim of this paper is to solve, or at least clarify, this issue. In this work, the most commonly used sample cleaning methods are compared. Then, five different methodologies are applied on certified hydrogen content calibration pins and on high strength steel concrete-prestressing strands and the three main situations regarding hydrogen content in the microstructural net (non-charged, charged, and charged and uncharged) are studied. It was concluded that the HCl solution C-3.5 cleaning method recommended by ASTM G1 introduces large amounts of hydrogen in the samples; but can be useful for eliminating superficial oxides if necessary. The rest of the methods had similar results; but the more complete ones that involve ultrasounds and last longer than 8 min are not appropriated when important diffusion may occur on the samples during their application. Simple methods that involve acetone or trichloroethylene and last around 1 min are preferable for almost all situations as these are faster, easier, and cheaper. As a final recommendation, as trichloroethylene is toxic, the simple acetone method is, in general, the most convenient one for regular hydrogen content analysis.