174 Y-Y Ma et aL/Engineering Failure Analysis 47(2015)162-177 crack propagation Fig. 11. Appearances of the sample B: (a the overall morphology of the crack on the sealing surface of the flange, (b) two corresponding cross sections. (c)and(d) fatigue crack propagation. Table 4 Recommended preparations Type of preparation Cross section gex,阝 Gap b(mm) Thickness of Depth preparation h(mm) 40°≤≤60°1≤b≤3 Flange to cylindrical body K-preparatic 35°≤B≤60°1≤b≤4 As for the process of fatigue crack on the weld joint includes two important stages, i. e crack initiation and crack propa- gation. So the total life(N,)of weld joint consists of the crack initiation life (N)and the crack propagation life(Np), which can be express However. in this event. there are twe LOPs in the weld joint, which act as the pre-existing crack-like imperfections in the weld joint, so it is normally co to eliminate the so-called crack initiation stage of fatigue life. Therefore, the mphasis of the fatigue assessment could be focused on the crack growth stage of the fatigue life in some conditions. Fatigue crack growth rate is usually analyzed in terms of fracture mechanics by using relations involving stress intensity factor. The most accepted approach to the analysis of fatigue crack propagation by linear-elastic fracture mechanics using a semi-empir- ical power law was Paris'formula 35: da/dN=C(△KAs for the process of fatigue crack on the weld joint includes two important stages, i.e. crack initiation and crack propa￾gation. So the total life (Nt) of weld joint consists of the crack initiation life (Ni) and the crack propagation life (Np), which can be expressed as: Nt ¼ Ni þ Np ð3Þ However, in this event, there are two obvious LOPs in the weld joint, which act as the pre-existing crack-like imperfections in the weld joint, so it is normally considered to eliminate the so-called crack initiation stage of fatigue life. Therefore, the emphasis of the fatigue assessment could be focused on the crack growth stage of the fatigue life in some conditions.Fatigue crack growth rate is usually analyzed in terms of fracture mechanics by using relations involving stress intensity factor. The most accepted approach to the analysis of fatigue crack propagation by linear-elastic fracture mechanics using a semi-empir￾ical power law was Paris’ formula [35]: da=dN ¼ CðDKÞ m ð4Þ Fig. 11. Appearances of the sample B: (a) the overall morphology of the crack on the sealing surface of the flange, (b) two corresponding cross sections, (c) and (d) fatigue crack propagation. Table 4 Recommended preparations. Location Type of preparation Cross section Angle a, b Gap b (mm) Thickness of root face c (mm) Depth of preparation h (mm) Flange to flange Double-V preparation 40 6 a 6 60 1 6 b 6 3 62 t/2 Flange to cylindrical body K-preparation 35 6 b 6 60 1 6 b 6 4 62 t/2 or t/3 174 Y.-Y. Ma et al. / Engineering Failure Analysis 47 (2015) 162–177