PSI - Issue 68

Eduard Navalles et al. / Procedia Structural Integrity 68 (2025) 1105–1114 Eduard Navalles et al. / Structural Integrity Procedia 00 (2025) 000–000

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After UTS, necking promotes cracks formation at the inner surface of the hollow specimen (Konert, Wieder, et al., 2024), which propagate faster in H 2 than in Ar environment. Hence, hydrogen is solely reducing the ductility and toughness, but not influencing the tensile strength of the steels. In general, it may be concluded that both steels are resistant to hydrogen embrittlement at the testing conditions. From Table 2, the reduction in ductility due to hydrogen of both steels is established. The ferritic-pearlitic suffers a reduction about 30 % in strain and 43 % of reduction of area when comparing specimens tested in H 2 and Ar environment. On the other hand, for the bainitic steel, less reduction in ductility and reduction in area was observed, 21 % and 31%, respectively. For the bainitic steel was also observed that leakage was delayed after reaching the UTS in comparison to the ferritic-pearlitic steel for which the leakage occurs rather soon after reaching the UTS. However, it should be also mentioned that for the bainitic steel larger spread in the strain to leakage exists for the three hydrogen tested specimens compared to the ferritic-pearlitic steel. The reason for such behaviour is unclear, and further investigation to understand this behaviour is in progress. The values in Table 2 obtained for the relative reduction in elongation and reduction in area of both steels indicate that the bainitic steel is more resistant to hydrogen embrittlement than the ferritic-pearlitic steel. Table 2. Mechanical properties of the investigated steels tested under 200 bar pressure in argon and hydrogen environment at room temperature using strain rate of 10 -6 s -1 . Including the relative ratio hydrogen gas against inert environment test. Figure 3. SSRT stress-strain curves of tested hollow specimens using Ar (black) and H 2 (red) pressurized at 200 bar at room temperature conditions for both steels.

Relative RA (H 2 /Ar)

Relative Strain (H 2 /Ar)

Time to leakage [h]

Yield strength [MPa]

Relative UTS (H 2 /Ar)

E [GPa]

Strain [%]

UTS [MPa]

RA [%]

Steel

Environment

Ar, 200 bar, RT

364 ± 4

512 ± 5

34 ± 0.3

206 ± 2

64 ± 4

141 ± 1

Ferritic pearlitic

1

0.7

0.57

H 2 , 200 bar, RT

363 ± 3

517 ± 8

24 ± 2

206 ± 6

37 ± 2

98 ± 7

Ar, 200 bar, RT

510 ± 6

592 ± 3

33 ± 0.2

215 ± 1

73 ± 1

113 ± 1

Bainitic

1

0.79

0.69

H 2 , 200 bar, RT

512 ± 2

595 ± 2

25 ± 4

216 ± 4

51 ± 2

90 ± 13

To understand if hydrogen/steel interaction occurred during the SSRT testing, some of the specimens were used to analyse the hydrogen content with the thermal desorption spectroscopy with mass spectrometry (TDMS). Figure 4 shows TDMS curves recorded for both steels. The red curves on both graphs represent the specimen tested under hydrogen gas, while the grey curves represent the specimen tested under pressurized argon gas. The black curves represent specimen in as-received state of the steels, i.e., reference specimens not subjected to any testing and environment. The total hydrogen amount in weight parts per million (wppm) calculated from the area below the curves is also displayed in the plots. The shape of the red curves and their significant difference in size compared to the argon and reference specimens, indicate that hydrogen/steel interaction during the SSRT test occurred. The hydrogen contents show that about 2.5 times higher hydrogen content was absorbed in the ferritic-pearlitic than in the bainitic steel. This result agrees with