PSI - Issue 35

Kpemou Apou Martial et al. / Procedia Structural Integrity 35 (2022) 254–260 Kpemou A. M. et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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5. Results and Discussion 5.1. Influence of hydrogen embrittlement on transition temperature

To highlight the influence of hydrogen on the value of transition temperature, Charpy impact tests were carried out on two types of specimens, and both with (H2) and without hydrogen (Air). Experimental data were fitted according to Eq. 2 and parameters of the ‘S’ -shaped curve obtained were determined. These parameters are reported in Table 4 for all the specimens tested. D CV represents the transition temperature. The comparison between curves with and without hydrogen embrittlement was made by Fig. 3a and Fig. 3b for the two types of specimens. Regarding the small shift induced by HE, it considered whether this shift was due to the dispersion of the results. To answer this question, an estimated scatter band was drawn. The real scatter band is not available, as it requires many tests. Knowing the coefficient of variation (COV) of the yield strength of API, 5L X65 steel (5.25%) [17] the upper and lower limits of COV for C CV and D CV are estimated to be 10%. These values are used to draw the associated scatter band in Fig. 3a and 3b. One notes that the correlation coefficient is similar of each curve however the number of specimens is reduced for HE tests (Table 4). Nevertheless, in order to ensure the reliability of the results for ½ Charpy, a test campaign will complete the data concerning this type of specimen.

Table 4. Parameters A CV , B CV , C CV , and D CV for ½ mini-Charpy specimens with and without HE . A CV (J) B CV (J) C CV (K) D CV (K)

R²

Standard without HE Standard with HE ½ Charpy without HE ½ Charpy with HE

137.7

132.4 143.5

4.3

180 177 149 132

0.83 0.82 0.88 0.84

145 16.7 17.7

5

17.3 17.4

7.1

5.17

One notes a shift of 17 K of the transition temperature D CV for ½ mini-Charpy specimens and a shift of 3K for Standard Charpy specimens

Fig. 3. (a) Curves Charpy energy versus temperature for ½ Mini-Charpy with and without HE; (b) Curves Charpy energy versus temperature for Standard-Charpy with and without HE.

The DBTT shift for ½ Mini - Charpy is greater than the width of the scatter band. It reveals that HE influences this type of specimen. For Standard Charpy, the shift (3K) is included in the scatter band. One concludes that HE has no effect on DBTT for this type of specimen. This result is similar to those obtained by Fassina et al. [18] on the same