PSI - Issue 59

Ihor Dmytrakh et al. / Procedia Structural Integrity 59 (2024) 74–81 Ihor Dmytrakh et al. / Structural Integrity Procedia 00 (2024) 000 – 000

80

7

a

b

c

a/ a/ a/

1000000

a/c=0,25 a/c=0,50 a/c=0,75

70000

70000

a/c=0,25 a/c=0,50 a/c=0,75

60000

Ст Ст Ст

60000

Степенной (a/c=0,25) Степенной (a/c=0,50) Степенной (a/c=0,75) 100000

Степенной (a/c=0,25) Степенной (a/c=0,50) Степенной (a/c=0,75) 50000

50000

y =

40000

40000

3

y = 18761x -0,3238 R 2 = 0,8797 y = 24975x -0,3242 R 2 = 0,8802 10000 N f , cycles

R

y = 17233x -0,3237 R 2 = 0,8796 y = 22936x -0,3238 R 2 = 0,8798 y = 31129x -0,3237 R 2 = 0,8796 10000 20000 30000 Nf, cycles

3

3

30000

2

y =

N f , cycles

2

2

R

20000

y =

y = 33936x -0,3244 R 2 = 0,8806

1

10000

1

R

1

1000

0

0

0 1 2 3 4 5 6 C H , ppm

0 1 2 3 4 5 6 CH, ppm

0 1 2 3 4 5 6 C H , ppm

Fig. 7. Residual durability N f of a pipeline ( D 2 =1 220 mm; t 1 =14 mm) versus hydrogen concentration C H in the metal in the case of a longitudinal semi-elliptical crack at the outer surface (a); a longitudinal semi-elliptical crack at the inner surface (b) and a circumferential semi-elliptical crack at the inner surface (c): 1 – a / c =0.25; 2 – a / c =0.50; 3 – a / c =0.75. As it can be seen (Figs. 6 and 7) for both pipeline sizes the N f values significantly decrease with the increase of the hydrogen concentration C H in the metal. At the same time, the residual durability N f of the pipeline changes with the change of the defects ’ shape, namely: the increase of the a/c ratio leads to the increase of the N f . Therefore, the defect shapes with the low a / c ratio can be considered as the most dangerous defect among others. Here it should be also marked that the N f values are the lowest in the case of the circumferential semi-elliptical crack at the inner surface of the pipe. It is seen for both sizes of the pipelines. It was found that all plots presented in Figs. 6 and 7 can be successfully described by the power function as follows:

m

H ( )

,

(4)

f N B C 

where B and m are some constants, which characterize the “material–environment” system and the conditions of the tests.

4.3. Comparative assessment of different defects types danger in the pipeline a b

1 2 3

1 2 3

1000000

1000000

Степенной (3) Степенной (2) Степенной (1)

Степенной (3) Степенной (2) Степенной (1) 100000

100000

y = 8832,9x -0,9346 R 2 = 0,9985 y = 18761x -0,3238 R 2 = 0,8797

1

y = 29386x -0,6926 R 2 = 0,9877 y = 31734x -0,3115 R 2 = 0,8568 10000 N f , cycles

1

Nf, cycles

10000

2

3

2

y = 17233x -0,3237 R 2 = 0,8796

3

y = 29562x -0,3122 R 2 = 0,8582

1000

1000

0 1 2 3 4 5 6 CH, ppm

0 1 2 3 4 5 6 C H , ppm

Fig. 8 Fig. 8. Comparative assessment of residual durability N f of pipelines with D 1 =610 mm; t 1 =11 mm (a) and with D 2 =1 220 mm; t 1 =14 mm versus hydrogen concentration C H in the metal in the case of a longitudinal semi-elliptical crack at the outer surface (1); a longitudinal semi-elliptical crack at the inner surface (2) and a circumferential semi-elliptical crack at the inner surface (3) with the constant crack shape ( a / c =0.25).

Fig. 8