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ISO 3690:2011 specifies the sampling and analytical procedure for the determination of diffusible hydrogen in martensitic, bainitic, and ferritic steel weld metal arising from the welding of such steels using arc welding processes with filler metal. The techniques specified in ISO 3690:2011 include collection of diffusible hydrogen via displacement of mercury or collection into a headspace filled with an inert gas such as argon. The amount of hydrogen collected is determined by measuring the displaced volume in the former and by, for example, thermal conductivity in the latter. The temperature for collection of diffusible hydrogen is controlled to avoid thermal activation of non-diffusible hydrogen.