In-Situ Hollow Sample Setup Design for Mechanical Characterisation of Gaseous Hydrogen Embrittlement of Pipeline Steels and Welds

Abstract

This work discusses the design and demonstration of an in-situ test setup for testing pipeline steels in a high pressure gaseous hydrogen (H2) environment. A miniature hollow pipe-like tensile specimen was designed that acts as the gas containment volume during the test. Specific areas of the specimen can be forced to fracture by selective notching, as performed on the weldment. The volume of H2 used was minimised so the test can be performed safely without the need of specialised equipment. The setup is shown to be capable of characterising Hydrogen Embrittlement (HE) in steels through testing an X60 pipeline steel and its weldment. The percentage elongation (%El) of the base metal was found to be reduced by 40% when tested in 100 barg H2. Reduction of cross-sectional area (%RA) was found to decrease by 28% and 11% in the base metal and weld metal, respectively, when tested in 100 barg H2. Benchmark test were performed at 100 barg N2 pressure. SEM fractography further indicated a shift from normal ductile fracture mechanisms to a brittle transgranular (TG) quasi-cleavage (QC) type fracture that is characteristic of HE.

Hydrogen Embrittlement of Inconel 718 Manufactured by Laser Powder Bed Fusion Using Sustainable Feedstock: Effect of Heat Treatment and Microstructural Anisotropy

“…To characterise the effect of gaseous hydrogen on Inconel 718, the sample design developed by Boot et al [40] (shown in Figure 3) for slow strain rate tensile (SSRT) test was used. This design has the advantage that the sample acts as the gas containment volume throughout the experiment, thus avoiding the need for autoclaves and sophisticated equipment.…”

“…The degree of hydrogen embrittlement is measured as the relative reduction of area of samples tested in nitrogen (%RAN2) and hydrogen (RAH2) environment [40]: The SSRT tests were performed in both nitrogen (N 2 ) and hydrogen (H 2 ) environments, with a pressure of 150 bar at 25 • C. Two repetitions were performed for each testing condition for repeatability. For the hydrogen tests, the samples were additionally charged for 48 h before the test to allow for hydrogen diffusion within the sample.…”

“…After the SSRT tests, the area of cross section after failure (A f ) is determined at the fracture location using Keyence VHX-5000 digital microscope. The percentage reduction in area (RA) is found by comparing it with the initial cross sectional area (A 0 ) [40]:…”

Hydrogen Embrittlement as a Conspicuous Material Challenge─Comprehensive Review and Future Directions

“…This procedure is based on a tubular specimen exposed to high-pressure H in the inner machined hole; it was firstly proposed by Chandler and Walter 818 and has been also adopted by other authors. 819,820 The comparison with conventional tensile specimens can be hindered by the inner surface roughness 821 and by the different necking mechanisms during ductile failure. 748,822 The small punch test (SPT), which is commonly used as a screening tool for nuclear materials, requires a simple procedure to test miniature specimens, 10 × 10 × 0.5 mm 3 approximately, and it has been recently standardized (ASTM E3205-20 or BS EN 10371:2021) for metallic materials.…”

“…For example, to circumvent the need of an autoclave containing a high volume of gaseous H 2 at high pressure, hollow specimens have been proposed as a safer and simpler alternative. This procedure is based on a tubular specimen exposed to high-pressure H in the inner machined hole; it was firstly proposed by Chandler and Walter and has been also adopted by other authors. , The comparison with conventional tensile specimens can be hindered by the inner surface roughness and by the different necking mechanisms during ductile failure. , …”