Characteristics of allowable axial cracks for pressurized pipes governed by limit load criteria

Abstract

When axial cracks were detected in pressurized pipes, failure stresses for high-toughness ductile pipes are estimated using the Limit Load Criteria. The allowable stresses for the cracked pipes are derived from the combination of the failure stresses and safety factors. Then, the allowable sizes of crack depths and lengths are determined from the allowable stresses. From the comparison of the allowable and failure stresses for through-wall cracks, the allowable cracks are not uniform. The allowable crack sizes can be separated into different characteristics of leak-before-break (LBB) and crack growth stability. Inspectors and users should pay special attention to allowable cracks with non-LBB and crack growth instability characteristics to prevent unexpected failure, particularly for thin-wall pipes. The boundaries of allowable crack depths and lengths that require special attention can be expressed by appropriate equations.