Particularly, high-strength steels with a tensile strength over 800 - 1000 MPa tend to hydrogen-induced delayed cracking. The reason for such material damages is a certain concentration of diffusible hydrogen existing in the metal matrix. The analysis of this hydrogen content is therefore necessary for a safe application of a high-strength component.
There are several destructive and non-destructive methods to evaluate the hydrogen content. Every method has its advantages and disadvantages relating to sample preparation, applicability or measurement accuracy.
Conventional methods are the „Carrier Gas Melt Extraction” to determine the total (and partially harmless) hydrogen content or the „Carrier Gas Hot Extraction“, where the results depend on the chosen temperature. A low temperature of 200 to 300°C detects the diffusible (harmful) hydrogen content but has a low accuracy.
The industrial standard to analyse the diffusible hydrogen content is the “Thermal Desorption Analysis (TDA)” or “Thermal Desorption Spectroscopy (TDS)” wether the detector is a thermal conductivity cell or a mass spectrometer. This method is widely used for diverse applications with a temperature range up to 900°C. Samples with a diameter up to 30 mm can be measured with a high accuracy. The measurement provides just integral data of the whole measured sample volume, a local accumulation of hydrogen is not detectable.
That is where the local and non-destructive “Local Hydrogen Analysis” comes in. It is a mobile application, which measures the diffusible hydrogen content in a surface near region, where in general, the harmful hydrogen is accumulated. This electrochemical measuring method reveals that the diffusible hydrogen content can be determined by non-destructive measurements and correlates with exact measurement techniques.
In general, it is necessary to know in which way the hydrogen content is determined to interpret the results in a correct manner.