PSI - Issue 77

Olha Zvirko et al. / Procedia Structural Integrity 77 (2026) 484–489 Olha Zvirko / Structural Integrity Procedia 00 (2026) 000–000

487

4

No significant differences were observed between the strength and plasticity characteristics of the as-received and post-operated pipeline steels during tensile testing; only minor variations were noted in yield strength and plasticity parameters. The impact toughness for the operated X52 steel was slightly lower than for the as-received one. The operated X67 steel exhibited a significantly lower impact toughness value compared to the as-received steel: a decrease in KCV due to operation was 21%. Despite the decrease in impact toughness after operation, its value remained relatively high for the X67 steel. 3.2. Resistance to Hydrogen Embrittlement of Pipeline Steels Depending on Operational Degradation The values of indexes HES for the steels in different states are presented in Figure 1. Susceptibility to hydrogen embrittlement assessed as index HES was approximately 10% and 15.2% for the X67 steel in as-received and post operated states, respectively. A difference in index HES was more pronounced for the X52 steel depending on its states: HES was in more than 6 times higher for the operated metal compared with the as-received one.

Fig. 1. Hydrogen embrittlement susceptibility HES of the pipeline steels in as-received ( 1 ) and post-operated ( 2 ) states.

Therefore, the long-term operation of the pipeline steel caused an increase in the susceptibility to hydrogen embrittlement, especially for the X52 steel. 3.3. Effect of Hydrogen Pre-charging on Fracture Toughness and Fracture Behavior of Pipeline Steels Considering Operational Degradation The fracture toughness values J cr for the steels depending on the state and the influence of hydrogen, are presented in Table 2.

Table 2. Fracture toughness for the tested pipeline steels Steel strength grade Steel state Test condition

Displacement rate, mm/min

J cr , N/mm

Without hydrogen charging

0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5

72.3 54.6 81.4 66.0

API 5L X52

As-received As-received

Hydrogen pre-charged

Without hydrogen charging

Operated for 38 years Operated for 38 years

Hydrogen pre-charged

Without hydrogen charging

331.0 162.0 319.0 159.0

API 5L X67

As-received As-received

Hydrogen pre-charged

Without hydrogen charging

Operated for 34 years Operated for 34 years

Hydrogen pre-charged