Comparisons of creep constraint and fracture parameter C* of different types of surface cracks in pressurized pipes

Abstract

The surface cracks in pressurized pipes include internal axial crack (IAC), internal circumferential crack (ICC), external axial crack (EAC) and external circumferential crack (ECC). The unified creep constraint parameter Ac and fracture parameter C* for ICCs, EACs and ECCs have been calculated by three-dimensional finite element analyses. The Ac solutions for ICCs with high aspect ratio (1.2 ≤ a/c ≤ 2) have been obtained, and the estimation method of Ac for EACs and ECCs are given. The Ac and C* of the four types of pipe cracks have been comparatively investigated. The results show that the four types of cracks have similar distributions of Ac and C*, and the order of the constraint level and C* from high to low is IAC > EAC > ICC > ECC. Among all pipe cracks, the IACs and EACs with larger depth a/t and lower aspect ratio a/c have the highest constraint and C* levels, thus they are the most dangerous cracks. The ICCs and ECCs with smaller a/t and higher aspect ratio a/c have the lowest constraint and C* levels, hence they are relatively safer cracks. The IACs and EACs should be avoided as far as possible in manufacturing and service of high-temperature pipes.