Issue 61

E. Entezari et alii, Frattura ed Integrità Strutturale, 61 (2022) 20-45; DOI: 10.3221/IGF-ESIS.61.02

C

 C C

dc

da

 

t b C

t

h

t





(21)



dt

dt

D

D

where λ D denotes the length of the diffusion zone, a represents the crack length, and τ D is diffusion time. C t represents hydrogen concentration at the crack tip, and C h indicates the hydrogen concentration for the stationary crack when t>> τ D , and C b is the hydrogen concentration for fast crack propagation [110].

Figure 8: Comparison of experimental and predicted results of HIC growth of an API 5L X52 steel plate by cathodic charging and a synthetic sour medium. Hydrogen transport through the hydrogen trapping mechanism was modeled by MC-Nabb and Foster [111] and is represented by Eqn. (22).



 T θ = KC 1- θ - θ t    T L T

(22)

where C L is hydrogen concentration in normal interstitial lattice sites, θ T denotes the coverage of trapping sites, K represents the hydrogen capture rate, and  is the hydrogen release rate. It should be noted that the above model describes the threshold hydrogen concentrations at the crack tip. Balueva [112] proposed a phenomenological model based on determining the time to grow delamination (t) under hydrogen pressure, given by Eqn. 23:

2 β 1 a 1 - a + β 2 2

a

t=2 α (a-

β arctan(

))

(23)

β

where α and β are defined as:

π G

C 0 eff

α =

(24)

6RTC D

2 C 0 β =8B 2G D

(25)

G c is the critical energy release rate specified as:

36