Issue 41

A.S. Chernyatin et alii, Frattura ed Integrità Strutturale, 41 (2017) 293-298; DOI: 10.3221/IGF-ESIS.41.39 297 I NTERSECTING CRACKS IN PIPELINE WITH RESIDUAL STRESS racture mechanics parameters for intersecting surface cracks in the weld joint of pipeline are analyzed bellow. The pipe has the following dimensions, namely, outer diameter is 325 mm; wall thickness is 16 mm. The material is corrosion-resistant austenitic steel. The circular crack (crack A) with depth of 6 mm is assumed to be formed on the inner side of the pipe in the plane of welding zone. The semi-elliptical crack is located in the meridional section (crack B). These cracks are intersected perpendicular each other (Fig. 4). Dimensions of the elliptical crack are 8 mm (crack depth) and 12 mm (length). Figure 4 : Intersecting cracks on inner surface of the pipe. The active circumferential stress is 67.6 MPa and axial stress is 108.8 MPa (taking into account not only pressure, but other loading factors). In addition, there are residual stresses occurred during the welding process. It is assumed that the axial residual stress is linearly varying through the pipe thickness. The residual stress reaches the yield strength on the inside surface near the weld root and a similar value with the opposite sign on the outer surface. The circumferential residual stress is also equal to the yield strength and this stress is constant through the thickness (they are varying along the pipe). a) b) Figure 5 : Distribution of K I , T xx , T zz along the crack front A (a) and crack front B (b) under different loading conditions. The computed results are summarized in Fig. 5. Note that s A and s B are dimensionless local coordinates (Fig. 4) transiting along a front of the crack A and B, respectively. Distributions of the T zz -stress [9] as well as the SIF and the T xx -stress are determined by means of the program "Williams" for only active external stress ("act") as well as in combination with the residual stress ("res"). An analysis of fracture mechanics parameters allows concluding the following. The axial crack (B) has a great influence on the T xx - stress and the T zz -stress. The values of T xx and especially T zz are decreasing (staying more F