Page 289 - Pipelines and Risers

262 Chapter 15

Test RatiotiD crm GI Ratioalt L2c Ratio 0-118) P-(19) Pet Ratio
No: MPa nun DdD Mpa MPa MPa P,Jp
1 .0366 556 63 0.0 0.0 0.0 556 40.7 46.0 1.13
2 .0366 556 63 0.0 0.0 0.28 556 40.7 34.7 0.85
3 ,0366 556 63 0.0 0.0 0.12 556 40.7 42.0 1.03
4 .0221 600 63 0.03 810 0.18 178 7.8 7.4 0.94
5 .0219 600 63 0.01 810 0.18 583 25.5 23.6 0.83
6 .0213 600 63 0.0 810 0.18 600 25.5 27.0 1.06

Note: Mean value and COV of predicted burst strength pO.92, COV=O.I 1
From the comparison shown in Table 15.1, it is observed that the agreement between
prediction and test results is quite good, demonstrating the approach presented in this chapter
is quite rational and practical.

15.3 Fracture of Pipes with Circumferential Cracks

It is assumed that the stressconcentrator is a notch located at the deepest point of the dent, it
is continuous (infinite length, constant depth) and has circumferential length 2c and depth, a.

15.3.1 Fracture Condition and Critical Stress
Based on PD6493, the equation of the fracture failure assessment curve is given by:

(15.20)

in which:

(15.21)

where:
p plasticity correction factor
KI Stress intensity factor, determined from the following equation:
KI = Yo& (15.22)

where Yo is divided to primary stress term and secondary stress term as:
Yo = (Yo), + (Yo), (15.23)