PSI - Issue 41

4

Mohamed Amine Belyamna et al. / Procedia Structural Integrity 41 (2022) 372–383 Mohamed Amine Belyamna et al. / Structural Integrity Procedia 00 (2022) 000–000

375

  I





  I Log t 0.3081 

Log t

3.10 4.21 Log D    

Mean value of

and Standard deviation of

(1)

IG SCC

IG SCC D  represents the effects of loading, environment and material variables on IG

The damage parameter

SCC and is given by



 

 7 C

 





C C

C

C

2 5 8 D C Pa O exp C T 273 log C C            3 6 IG SCC 1 2 4

(2)

9

Where Pa is a measure of degree of sensitization, given by Electrochemical Potentiokinetic Reactivation in C/cm 2 , O 2 is oxygen concentration in ppm, T is the temperature in degrees centigrade, γ is water conductivity in μs/cm, and σ is stress in MPa. In the above equations, C i are constants whose values depend on the type of material. Values for these constants are presented in (Harris, 1992). The growth of very small cracks that have just initiated can't be treated from a fracture mechanics standpoint. Therefore, an initiation velocity V 1 (inches/year), is assigned to newly initiated cracks, and given by:     1 IG SCC Log v J GLog D    (3)

Where J is normally distributed and G is a constant. Fracture mechanics based crack growth velocity, V 2 (inches/year), is given in (Harris, 1992) by     2 14 15 12 2 13 Log v C C (C Log f environment C K)       

(4)

Where K is the stress intensity factor, C 12 , C 13 and C 15 are constant and C 14 is normally distributed. Values for these constants are presented in (Harris, 1992). In their work (Priya et al., 2005; Guedri, 2012) concluded that equations used in PRAISE to calculate the stress intensity factors in order to simulate crack propagation need modification. In our modified PRAISE (M-PRAISE) (Guedri et al., 2012; Guedri, 2013a-b) this modification has been accomplished using well-accepted expressions given in (American Society of Materials, 1996). All cracks considered by M-PRAISE start out as semi-elliptical interior surface cracks, generally circumferentially oriented. 2.2. Multiple Cracks and Their Coalescence Circumferential welds are divided by PRAISE into multiple segments of 50.8 mm in length. Each segment has only one corrosion critical location, where a crack can initiate. The multiple cracks that may be present can coalesce as they grow. Linkage of two cracks takes place if spacing between them is less than the sum of their depths. After coalescence of two cracks, the dimensions of modified crack are given by (5) Where l 1 and l 2 are lengths of two cracks under consideration, a 1 and a 2 are crack depths and d is the distance between them. Cracks in neighboring segments may link to form larger cracks. The entire weld is assumed to be inspected at the time of each scheduled inspection. If a crack is detected in the weld, the weld is repaired, and the entire weld regains its integrity (perfect repair). Length l l d l and Depth , a a or a , which is greater 1 2 1 2  ,   