MATERIALS TESTING IN GASEOUS HYDROGEN ENVIRONMENT

In case of high-pressure hydrogen application, the hydrogen embrittlement risk assessment should be carried out in  gaseous environment. Dedicated facilities to reach high-pressure and/or high-temperature are needed, in Letomec a series of tests are now available but testing services are constantly increased.

Typical hydrogen purity is 6.0.

Gaseous Hydrogen Permeation Tests

Gaseous permeations should be performed in the case of gaseous hydrogen applications, for the evaluation of effective hydrogen diffusivity in steels.

Tests can be carried out on bare and coated steels with general reference to ISO 17081 and ASTM G148. Limit conditions are T = RT ÷ 500 °C, P = 1 bar.

Test consists in exposing one side of a metal plate to gaseous hydrogen environment and put the other side is in contact with the HELIOS reading probe, able to measure the hydrogen flux permeating through the metal.

Moreover, it is also possible to perform permeation tests on a portion of real pipe filled with operative gas mixture at laboratory scale or directly on field!

Solubility and trapping investigation

In order to characterize hydrogen solubility in a metal, it is possible to perform a series of hydrogen measurements on coupons exposed to hydrogen gaseous environment.

Elaborating the results of hydrogen measurements, the constants of Sievert’s law can be estimated. Typical expousure conditions are T = RT ÷ 500 °C, P = 1 ÷ 200 bar.

Moreover, it is possible to estimate the effective hydrogen diffusion coefficient by indirect method based on Hot Gas Extraction.

Mechanical tests

Norms currently applied in energy sector suggest a series of mechanical tests including fracture mechanics and fatigue to correctly characterize new materials for gaseous hydrogen application. Static or quasi-static load tests can be useful to determine the durability, while fracture mechanics and fatigue tests can be useful to characterize the behaviour in presence of cracks with static or cyclic loads respectively.

Choose a test to learn more about what we offer:

Spring loaded tests

Spring load testing is quite interesting because a series of samples can be simultaneously tested, at various stress levels and directly in gaseous hydrogen environment, with a pass/fail result. Spring load thus can easily return statistical information on the behaviour of a certain material.

Test samples are sub-size tensile test samples with or without notch (effect of hydrogen stress-driven migration). After preliminary hydrogen charging, constant load is applied to the specimen by means of spring loading device (ASTM G49, NACE TM0177, ISO 16573‑1:2020) and exposed to gaseous hydrogen environment for 100 ÷ 200 h (ISO 16573). Maximum load 12 kN, T = RT ÷ 500 °C, p = 1 ÷ 200 bar.

Example of sample and spring load device with relative autoclave test chamber

Slow strain rate tests

Slow Strain Rate tests can be performed referring to ASTM F 519 and ASTM G129 in order to correlate hydrogen absorption and resulting degradation of mechanical properties, see Figure 14. Tests are carried out on specimens pre-charged in gaseous hydrogen environment (T = RT ÷ 500 °C, p = 1 ÷ 200 bar) and then subjected to tensile test in air with very low strain rate (strain rate 10-4 ÷ 10-5 mm/s). Diffusible hydrogen content is measured at the end of the test.

SSRT in autoclave with high-pressure gas environment and at room temperature may also be tested.

Low Cycle Fatigue (LCF) tests

Test samples smooth or with notch are pre-charged in gaseous hydrogen environment (T = RT ÷ 500°C, p = 1 ÷ 200bar) and then subjected to LCF test according to conditions of interest, with reference to ASTM E 606. Diffusible hydrogen content is measured at the end of the test for each specimen to correlate mechanical performance and H content in the metal.

Fatigue Crack Growth rate tests (FCGR)

Test samples smooth or with notch are pre-charged in gaseous hydrogen environment (T = RT ÷ 200 °C, p = 1 ÷ 200 bar) and then subjected to FCGR test according to conditions of interest, with reference to ASTM E 647. Diffusible hydrogen content is measured at the end of the test for each specimen to correlate mechanical performance and H content in the metal. Similarly, Jq and Kq tests can be carried out.

Fracture Mechanics: KI limit tests at constant displacement

Modified Bolt-Load Compact Test samples are eventually pre-charged in gaseous hydrogen environment (T = RT ÷ 200°C, p = 1 ÷ 200bar) and then subjected to mechanical test at constant displacement in gaseous hydrogen environment, with reference to ASTM E 1681. Diffusible hydrogen content is measured at the end of the test for each specimen to correlate mechanical performance and H content in the metal.

Hollow specimen tests

Hollow specimen can be used to perform tests with high-pressure gas, but using very limited gas volume and thus reducing the safety risk and needed precautions. Hydrogen embrittlement tests with Hollow specimens were already described in ASTM STP 543 (1972). Evaluation of the susceptibility of materials to the effects of high-pressure gas within hollow test pieces is carried out according to the Draft Standard ISO/DIS 7039.

Possibility of quasi-static (SSRT) and dynamic (fatigue) tests at room and high pressures (max 200 bar).

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