PSI - Issue 54

Florian Konert et al. / Procedia Structural Integrity 54 (2024) 204–211 Author name / Structural Integrity Procedia 00 (2023) 000–000

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Fig. 2. SSRT test machine and drawing of the hollow specimens

4. Results and discussion

The influence of hydrogen on the mechanical properties has been evaluated in terms of embrittlement index and elongation loss by comparing the test results in hydrogen and argon. Fracture area, embrittlement index, elongation at failure, and elongation loss are reported in Table 2 for each test. In addition, the force-displacement curves are plotted in Fig. 3. Tests conducted in H 2 gas and Ar are marked with red and blue lines, respectively. All drilled samples tested in 6 MPa H 2 showed a loss in elongation compared to those tested in 6 MPa Ar. The values range from 5.90% to 41.93% (i.e., 21.97 ± 18.33%), indicating significant scattering. Similarly, greater fractured areas were measured in H 2 , thus resulting in embrittlement indexes from 14.88% to 38.67% (i.e., 27.76 ± 12.02%). The same e ff ect was observed for the reamed samples tested in hydrogen. In this case, the elongation loss ranges from 7.33% to 25.80% (i.e., 16.45 ± 9.24%) and the embrittlement index from 6.39% to 23.75 % (i.e., 13.37 ± 9.17%). In this sense, not only the average elongation at failure of reamed specimens is higher compared to that of the drilled ones, but also the scattering is lower. Therefore, it is concluded that a smoother inner surface with fewer notches and grooves results in lower susceptibility to HE. Surface defects might act as crack initiation sites in hydrogenated environments, constituting prefered paths for hydrogen uptake and di ff usion, thus accelerating the specimen’s failure (Michler and Ebling, 2021). In contrast, both the elongation at failure and the embrittlement index of the reference samples are similar for drilled and reamed specimens. Hence, surface finishing has a negligible influence on the tensile properties of X65 steel in inert environments.

Table 2. Results of the SSRT tests in hydrogen and argon ID Type Environment

Fracture area

Embrittlement index

Elongation at failure

Elongation loss

[mm 2 ]

[%]

[mm]

[%]

AR D 1 AR D 2 H2 D 1 H2 D 2 H2 D 3 AR R 1 AR R 2 H2 R 1 H2 R 2 H2 R 3

Drilled Drilled Drilled Drilled Drilled Reamed Reamed Reamed Reamed Reamed

6MPaAr 6MPaAr 6MPaH 2 6MPaH 2 6MPaH 2 6MPaAr 6MPaAr 6MPaH 2 6MPaH 2 6MPaH 2

7.98 8.46

- -

5.99 6.17 4.98 3.53 5.72 6.12 6.01 5.08 4.50 5.62

- -

13.09 14.56 10.86

29.73 38.67 14.88

18.07 41.93

5.90

8.13 8.04 9.73

- -

- -

9.96

16.23 25.80

12.01

23.75

9.14

6.39

7.33