Creep crack growth prediction and assessment incorporating constraint effect for pressurized pipes with axial surface cracks

• Creep crack growth assessment based on single-parameter C∗C∗ is unduly conservative.
• It is strongly recommended to incorporate constraint effect by two-parameter C∗–R∗C∗–R∗.
• Benefit from two-parameter assessment increases with decreasing initial crack sizes.
• Crack growth profile may be correctly predicted by the two-parameter assessment.
• The C∗C∗ calculation of the reference stress method leads to extra conservativity.

Creep crack growth life is firstly predicted and assessed by two-parameter concept to incorporate constraint effect for pressurized pipes with inner axial surface cracks. The prediction and assessment results are compared with those based on conventional single-parameter C∗ and finite element calculations. For shallower and shorter cracks, the life assessments based on single-parameter C∗ are excessively conservative. To reduce excess conservativity, it is strongly recommended to incorporate constraint effect. With decreasing initial crack sizes, the benefits gained from two-parameter assessments increase. The crack growth profile may also be correctly predicted by two-parameter calculations. The C∗ calculation of reference stress method leads to extra conservativity.