Abstract
Hydrogen (H2) technologies are extremely important in reaching the goal of a fossil-free society. Applications promoting this include for example replacing coal with H2 gas in steelmaking, H2 fuel cells and gas turbines running on pure H2 gas. Storage and transportation of H2 will also be crucial for this transition, and successful use of these technologies requires that the material-H2 interactions are known. Hydrogen embrittlement (HE) is a potential threat since it may lead to catastrophic failures in equipment used in H2 environments. To design and build H2 gas safe equipment, correct information about material behaviour in relevant environment including low or high temperatures and high gas pressures is necessary. The conventional HE testing methods, such as tensile testing, constant load, slow strain rate testing, three- and four-point bend testing, also combined with cathodic hydrogen charging, cannot directly be used for evaluating the effect of hydrogen gas on metals. Testing in H2 gas is complex as it involves high pressure levels that require autoclaves and special safety measures are needed to avoid explosive hazards. There is an alternative method, known as hollow specimen test method (HSTM) that can offer a safer, simpler, and less costly approach than the autoclave method to test the behaviour of metals in H2 gas. HSTM involves a tensile test specimen with a hole which is filled and pressured with Ar or H2 gas and usually strained in tensile direction with a certain strain rate. Compared to the autoclave method, the main advantage is that a small volume of hydrogen is used reducing the complexity of the test method as well as the testing costs.
In this work the HSTM was used to evaluate the effect of H2 on carbon-steel and austenitic steel under Slow Strain Rate Testing (SSRT). Testing was conducted at ambient temperature in both Ar and H2 gas at 200 bars pressure. The strain rate used was 5x10-5 s-1. The specimens after failure were stored in liquid nitrogen and analysed using thermal desorption spectroscopy with mass spectrometry (TDMS) for presence of diffusible hydrogen. Moreover, the fracture surfaces were also analysed with Scanning Electron Microscopy (SEM) to reveal indications for HE. The obtained results from the HSTM and the respective hydrogen and fractography analysis showed that the HSTM is potential method for assessing the risk of hydrogen embrittlement when metals are exposed in H2 gas at high pressure combined with mechanical load.