Hydrogen Assisted Cracking is an undesirable an unpredictable defect in a weld: it causes a reduction in the mechanical properties, and thus poses a potential threat towards the structural integrity of the weldment. HAC can occur at ambient temperatures, and appears also hours or days after the completion of welding and the component cracks often remains undetected while in service. The hydrogen content assessment in the weld is considered as the best way of reducing the risk of HAC. This can be achieved according to the methodology described by the Standard ISO 3690:2012


HELIOS 3-WELDING is an innovative solution to get fast, precise and repeatable measurement of diffusible hydrogen content in welding samples.

The most common technique for the diffusible hydrogen measurement is described by the standard ISO 3690:2012. 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.

Moreover the measurement requires inert gas and chemical substances restricted by the current REACH norm. HELIOS III Welding overcomes these limits and it is able to perform test substituting mercury by heating the sample using a furnace.

Once acquired, the signal is processed by proper mathematical codes (by means of a dedicated panel PC), in order to return the diffusible hydrogen content.

Letomec offers a customized solution in function of customer sample dimensions.


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