ANALYSIS OF HYDROGEN – METAL INTERACTION
Characterization of hydrogen-metal interactions is fundamental to prevent the risks of hydrogen embrittlement. Consequently, this permits to avoid undesired and unpredictable failure in components during production and operative life. To achieve this goal, our R&D team typically recommends specific tests. The main tests include permeability tests to assess the diffusion of hydrogen and solubility tests to measure hydrogen concentration in metals. Furthermore, in order to evaluate the embrittlement effect caused by the presence of hydrogen, our team can conduct a series of mechanical tests. Additionally, we closely associate the test results with the corresponding diffusible hydrogen content. Notably, the measurement of hydrogen concentration in metals is accomplished using the hot gas extraction method as outlined in the BS EN ISO 3690-2012 Hydrogen Content in Welds.
Hydrogen Permeability through Metals
Evaluating effective hydrogen diffusivity proves valuable for comparing different metals. Moreover, effective hydrogen diffusivity defines hydrogen charging duration or evaluates the barrier effect of various coating layers.
Furthermore, our team has the capability to conduct hydrogen permeation tests using electrochemical techniques with reference to Standard ISO 17081:2014 and ASTM G148 through HELIOS 2. We can perform permeability tests at room temperature and controlled temperatures up to 50°C on both bare and coated metals.
Electrochemical hydrogen charging and solubility test
Our R&D Team can expose samples to electrochemical charging to introduce hydrogen, for both solubility tests and preceding mechanical tests.
Additionally, we can adjust charging conditions to achieve various hydrogen contents. The main parameters to consider are the electrolyte, the recombination poison concentration, and applied current density.
In this way, the approach allows to estimate the hydrogen solubility in steels by conducting a series of hydrogen charging on samples, in the condition of interest, followed by hydrogen measurement using HELIOS 3. Permeability tests to evaluate diffusivity through the specimen material are suggested.
Temperature programmed desorption (TPD)
Thermal analysis monitors physical parameters in a solid-gas system as a function of temperature. It serves as a frequently utilized experimental method for studying interactions in such systems. Our team regularly performs Temperature Programmed Desorption (TPD) to characterize hydrogen trapping systems within specific metal lattices. Hydrogen trapping systems influence the permeability through the material.
After a preliminary hydrogen charging, we heat some coupons with varying heating rates. We then analyze desorption curves, extracting information about the activation energy of each trapping site. These results are subsequently compared to Transmission Electron Microscopy (TEM) investigations for comprehensive identification.
Mechanical tests
Evaluate the susceptibility to hydrogen embrittlement by comparing the behavior of a metal in a hydrogen-free state and in the presence of various hydrogen contents. Preliminary hydrogen permeability tests are suggested before mechanical tests.
SLOW STRAIN RATE TESTS
Our Team can perform Slow Strain Rate tests according to ASTM G129 to correlate hydrogen absorption with resulting degradation in material’s mechanical properties. Carry out these tests on pre-charged specimens with the ultimate goal of determining the critical hydrogen concentration for the metal under investigation. Typically, use a strain rate of around 10-4 ÷ 10-5 mm/s to allow sufficient time for hydrogen-induced embrittlement.
FOUR POINT BENDING TESTS
An alternative test we can propose is Four-point bending tests, conducted under constant load or incremental step loading following ASTM F1624 standard. TConduct tests on both hydrogen pre-charged specimens and specimens in a corrosion condition with samples immersed in a test solution. The 4PB equipment is designed to ensure symmetrical loading, using four ceramic cylinders for both sample support and load.
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