ANALYSIS OF H-METAL INTERACTION

Characterization of hydrogen-metal interaction is fundamental to prevent the risks of hydrogen embrittlement in components during production and operative life. All test can be associated with correspondent diffusible hydrogen content. Hydrogen concentration in metals is measured by hot gas extraction method (BS EN ISO 3690-2012 Hydrogen Content Welds).

 

Metals permeability and diffusivity evaluation.

Evaluation of effective hydrogen diffusivity is be useful to compare different metals, define hydrogen charging duration or evaluate the barrier effect of different coating layers.

Permeation tests by electrochemical technique can be carried out with reference to Standard ISO 17081:2014 and ASTM G148 by means of HELIOS 2. Tests can be performed at room and controlled temperature up to 50°C, on bare and coated metals.

Electrochemical hydrogen charging and solubility test.

Samples can be subjected to electrochemical charging to introduce hydrogen both for solubility tests and prior to mechanical tests.

Charging conditions can be varied to reach different hydrogen contents, main parameters are the electrolyte, the concentration of recombination poison and applied current density.

It is possible to estimate the hydrogen solubility in steels by performing a series of hydrogen charging                                                                                              on samples, in the condition of interest, followed by hydrogen measurement using HELIOS 3.

 

Temperature Programmed Desorption Tests (TPD).

Thermal analysis associated with monitoring of physical parameters in a solid-gas system as a function of temperature, is an experimental method frequently used     to study the interactions in said systems. TPD are useful to characterize the hydrogen trapping systems present in a certain metal lattice.

After a preliminary hydrogen charging, some coupons are heated with different heating rates. The elaboration of desorption curves can give information on activation energy of each trapping site. These results can be compared to TEM                                                                           investigation for full identification.

 

Mechanical tests.

The susceptibility to hydrogen embrittlement can be evaluated by comparing the behaviour of a metal in a hydrogen-free status and in presence of a various hydrogen contents.

SLOW STRAIN  RATE  TESTS

Slow Strain Rate tests can be performed referring to ASTM G129 in order to correlate hydrogen absorption and resulting degradation in material’s mechanical properties. Tests are carried out on pre-charged specimens and the final goal is to determine the critical hydrogen concentration  for metal under investigation. Typical strain rate is around 10-4 ÷ 10-5 mm/s in order to give hydrogen time enough to lead to embrittlement phenomenon.

FOUR POINT BENDING TESTS

Four-point bending tests can be performed under constant load or incremental step loading with reference to ASTM F1624. Tests can be carried out both on hydrogen pre-charged specimens and in corrosion condition with samples immersed in test solution.

The 4PB equipment is designed to ensure symmetrical loading. Four ceramic cylinders are used for sample support and load