Delayed fracture and H embrittlement

Delayed fracture and H embrittlement

Diffusion tests

H diffusion testing

Hydrogen permeation test, performed by electrochemical technique, is useful to determine hydrogen effective diffusivity and other hydrogen diffusion related parameters.

Tests can be carried out also on coated sheet metals to evaluate the barrier effect of specific coating layers.
Hydrogen permeation tests are performed by using HELIOS 2 PERMEATION equipment with reference to ASTM G-148.

Temperature Programmed Desorption Test (TPD)

Thermal analysis, associated with monitoring physical parameters as a function of temperature, is an experimental method frequently used to study the interactions in solid-gas system.

In the sheet metal sector, TPD tests are useful for characterising hydrogen trapping systems present in a certain metal lattice. After a preliminary hydrogen charging, some metal coupons are heated with different heating rates. Then, the elaboration of desorption curves can provide information on the activation energy of each trapping site.

These results can also be compared to TEM (Transmission Electron Microscopy) investigations for full identification of trapping sites.

H measurement by Hot Gas Extraction

Measurement of diffusible hydrogen content in metal samples by hot extraction methodology, that consists in heating the sample in order to enhance hydrogen diffusion out of the metal for a quick measurement.

Tests will be executed with HELIOS 3 equipment.

Mechanical tests

Slow Strain Rate Test (SSRT)

Uniaxial tensile slow strain rate tests on notched or unnotched specimens based on the guidelines of ASTM F-519/ ASTM G-129 standards. 

Samples are charged with different diffusible hydrogen contents before testing.
Average diffusible hydrogen concentration is measured at the end of the test via the hot gas extraction method to correlate mechanical performance and relative hydrogen content.

Critical diffusible hydrogen concentration can be determined with reference to ASTM STP 962 in correspondence of a reduction of the 30% of a significant material’s property in comparison with hydrogen-free sample.

Four Point Bending Tests

The four-point bending test can be performed on notched or unnotched sheet metal specimens, by bending loading fully in the elastic range of the material.

This test can be both carried out on pre-charged specimens or in aggressive media (stress corrosion cracking). It is useful to realize a fracture map of material’s behavior in presence of different hydrogen conditions (concentration or environment respectively) and load levels.

Four-point bending tests can be also executed by step loading as per standard ASTM F1624. Load can be increased according to a defined time schedule. This standard establishes a procedure to measure the susceptibility of steel to a time-delayed failure due to hydrogen embrittlement.

Step load test

This test method is based on standard ASTM F1624 and establishes a procedure to measure the susceptibility of steel to a time-delayed failure due to hydrogen embrittlement. The test consists on increase incrementally the load applied to the sample until its failure.

Stress corrosion
cracking evaluation using the constant load test

The constant load test is a method that estimates the hydrogen content threshold at which a steel does not fail due to hydrogen embrittlement under a constant load. The steel is considered not susceptible to hydrogen embrittlement if the failure doesn’t appear at 150h or 240h.