Steel manufacturers continually seek to reduce the hydrogen in steel which remains trapped upon cooling, as it embrittles steel, especially upon cold working, and onward steel processing – especially welding – re-mobilises the hydrogen, leading to SOHIC and embrittlement. Conventional measurements are taken of steel concentration in ppm H by weight, by destructive testing of steel, which is expensive and slow. The H content is then included in steel specifications for onward customers. Hydrosteel provides a very good in situ measure of mobile hydrogen exiting steel to at least 500 °C, and can also reduce expensive and time consuming ‘hot stacking’ of steel to drive out hydrogen at between 300 and 500 °C. Also Hydrosteel presents an attractive research tool to enable incidents and sources of high hydrogen to be identified. Target steel is usually at least 1 inch thick; at lower thicknesses the rate of hydrogen escape is usually too fast to cause problems.
Another large scale application for Hydrosteel under present scrutiny is welding. Large pipe weldments (pipe wall >1.5 in. thick) have been tested for hydrogen, indicating the value of the tool in determining conditions leading to hydrogen damage associated with welds, namely stress oriented hydrogen induced damage, or SOHIC. Hydrogen free welds are to be identified by flux measurements below specified thresholds, carried out within an hour of welding. In the case of multipass welding, the aim is to afford flux tests between passes to assure hydrogen does not become increasingly entrapped within successive new weld pass, leading to SOHIC.
Electrodeposition of metals such as zinc on steel can lead to high levels of hydrogen being occluded. The plating seals them in place and occasionally a whole batch of steel components cracks or fails. In one case a whole range of cars had to be recalled due to embrittled joints. The same issue can arise in pickling baths. Of interest as a possible future area for industrial research. Hydrosteel has been evaluated extensively in research, both as part of evaluations into its field use, and in evaluations of the corrosivity of various solutions and HIC susceptibility of various steels.
For more information please see Hydrogen flux literature.