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Analysis of the constraint levels and the creep crack initiation times for pressurized pipes with long surface cracks
Abstract The constraint levels and the creep crack initiation (CCI) times for pressurized pipes with four types of long surface cracks and different geometrical sizes were investigated by using 3D finite element (FE) method. The C*–Q* two-parameter approach was also applied to estimate the CCI times for different conditions. For each type of long surface cracks, it could be found that the larger crack depth (a/t) was associated with the larger constraint and shorter the CCI time. Furthermore, for the same crack depth (a/t) and pressure, the order of constraint levels was axial internal crack > circumferential internal crack > axial external crack > circumferential external crack, while the CCI times were in contrary sequence. Generally, long external surface cracks were less dangerous than long internal surface cracks no matter they were axial or circumferential surface cracks. Additionally, the fitting formulae between CCI times and crack depth ratio a/t and pressure (or stress intensity factor) were developed and verified to be effective. The power law relation between the CCI times and constraint parameter Q* was also established and validated. Finally, the suitability of the transient prediction models in C*–Q* two-parameter approach was verified by comparing results of the two-parameter theoretical analysis and simulation. What's more, it was known that for long internal surface cracks (axial or circumferential), the K-RR solutions were more accurate than the HRR-RR solutions when pressure is below 10 MPa, while the HRR-RR solutions would be better for higher pressure. As to the long external surface cracks, the critical pressure between these two solutions was about 12 MPa.
Highlights The crack-opening stress and load-independent constraint parameter Q* ahead of the crack front are investigated for the pressurized pipes with different long surface cracks. The creep damage accumulations and the CCI times are investigated considering the effect of the crack depth ratio a/t of the long surface cracks. The empirical relationships between the CCI times and crack depth ratio a/t are obtained. The effectivity of the empirical equations is verified. The exponential law relation between the CCI times and constraint parameter Q* is extrapolated. The two-parameter C*-Q* approach could conservatively and effectively characterize the CCI times.in CCI times prediction. For long internal and external surface cracks, critical pressures between K-RR and HRR-RR were 10 and 12 MPa, respectively.
Analysis of the constraint levels and the creep crack initiation times for pressurized pipes with long surface cracks
Abstract The constraint levels and the creep crack initiation (CCI) times for pressurized pipes with four types of long surface cracks and different geometrical sizes were investigated by using 3D finite element (FE) method. The C*–Q* two-parameter approach was also applied to estimate the CCI times for different conditions. For each type of long surface cracks, it could be found that the larger crack depth (a/t) was associated with the larger constraint and shorter the CCI time. Furthermore, for the same crack depth (a/t) and pressure, the order of constraint levels was axial internal crack > circumferential internal crack > axial external crack > circumferential external crack, while the CCI times were in contrary sequence. Generally, long external surface cracks were less dangerous than long internal surface cracks no matter they were axial or circumferential surface cracks. Additionally, the fitting formulae between CCI times and crack depth ratio a/t and pressure (or stress intensity factor) were developed and verified to be effective. The power law relation between the CCI times and constraint parameter Q* was also established and validated. Finally, the suitability of the transient prediction models in C*–Q* two-parameter approach was verified by comparing results of the two-parameter theoretical analysis and simulation. What's more, it was known that for long internal surface cracks (axial or circumferential), the K-RR solutions were more accurate than the HRR-RR solutions when pressure is below 10 MPa, while the HRR-RR solutions would be better for higher pressure. As to the long external surface cracks, the critical pressure between these two solutions was about 12 MPa.
Highlights The crack-opening stress and load-independent constraint parameter Q* ahead of the crack front are investigated for the pressurized pipes with different long surface cracks. The creep damage accumulations and the CCI times are investigated considering the effect of the crack depth ratio a/t of the long surface cracks. The empirical relationships between the CCI times and crack depth ratio a/t are obtained. The effectivity of the empirical equations is verified. The exponential law relation between the CCI times and constraint parameter Q* is extrapolated. The two-parameter C*-Q* approach could conservatively and effectively characterize the CCI times.in CCI times prediction. For long internal and external surface cracks, critical pressures between K-RR and HRR-RR were 10 and 12 MPa, respectively.
Analysis of the constraint levels and the creep crack initiation times for pressurized pipes with long surface cracks
Wu, Dongquan (author) / Xu, Lianyong (author) / Zhai, Wei (author) / Jing, Hongyang (author) / Zhao, Lei (author) / Han, Yongdian (author)
Thin-Walled Structures ; 153
2020-04-15
Article (Journal)
Electronic Resource
English
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