PSI - Issue 42

Snezana Kirin et al. / Procedia Structural Integrity 42 (2022) 351–355

353

3

Author name / Structural Integrity Procedia 00 (2019) 000–000

Figure 3. Prototype with artificial defects, [23], defect 1.75 x 26 mm in cross-section C-C is analysed in this paper Analytical assessment of structural integrity is based on calculation of the stress intensity factor and stress ratio, with an aim to define the corresponding point in the Failure Analysis Diagram (FAD), [23]. In order to calculate K I and S and to compare with K Ic and S c , and get the corresponding point in FAD, following data for service pressure p=10 MPa is used:  Circumferential stress S=pr/t=100 MPa for design pressure (10 MPa),  Cross section reduction (1.75x26)/(6.98x702)=0.009,  Net circumferential stress S net =100/0.991=101 MPa,  Critical stress, taken at midpoint between Yield and Tensile Strength, S c =(537+585)/2=563 MPa, [21]  Abscissa for the new material S net /S c =101/563=0.18. Stress intensity factor for surface edge crack in a cylinder can be obtained using different methods for geometry factors, depending on crack size. According to procedure explained in [24]: F total =2.71, K I =1100 MPa √ mm for 2c=26 mm and a=1.75 mm, while K Ic =3836 MPa √ mm. Therefore, coordinates for service point in FAD is (0.18, 0.29), and (0.4, 0.64) for the testing pressure, Fig. 4.

Figure 4. FAD points: (0.18,0.29) for design pressure, (0.4,0.64) for testing pressure Corresponding risk levels are defined in Table 1, indicating the low risk level for design pressure and high risk level for testing pressure.

Table 1. Position of assessment points in the risk matrix Consequence category

Risk legend

1 – very low 2 - low

3 - medium

4 - high

5 - very high

≤ 0.2 very low 0.2-0.4 low 0.4-0.6 medium 0.6-0.8 high

Very low

p =10, MPa 0.33

Low

Medium

p =22, MPa 0.73

High

Probablity category 0.8-1.0 very high

Very High

3. Structural life assessment According to the results of FCG rate, one should expect significant reduction of fatigue life of corrosion damaged material. To evaluate this detrimental effect, Paris law was used for both analytical and numerical calculation: � � � � � �����√ � � where Y(a/W) is the geometry factor depending on crack geometry. Paris law can be integrated directly if one neglects dependency of geometry parameter Y on crack geometry, or numerically if dependency is taken into account, as was done here by dividing range of crack depth growth: 1.75; 2.44; 3.13; 3.82; 4.51; 5.2; 5.89; 6.58; 6.9 mm. Coefficients C and m are used for new and used BM, as given in Table 5. The geometry coefficient Y(a/W) was in the range from 2.39 to 4.29, also affected by different crack