The stability of a circumferential crack in a pipe

A simple procedure is currently used to determine the effective pipe length associated with the instability of circumferential crack growth in a piping system. This procedure involves a separation of the complete piping system into two elastic parts at the cracked cross-section, the application of equal and opposite moments M to the cut faces, and the equation of the effective pipe length with EI/phi//M where phi is the rotational discontinuity generated at this section, E is Young's modulus and I is the second moment of area of the pipe at the cracked section. It is presumed that the pipe-ends remain fixed, i.e. they are built-in, throughout this operation. This paper shows that this procedure refers to the stability of a crack in a piping system which is subject to either a fixed displacement or a fixed rotation at a built-in end. The viability of the simple procedure is therefore underscored by the present paper's analysis. (author)