Leak-Before-Break: What Does It Really Mean?

Leak-before-break (LBB) is a term that has been used for decades in reference to a methodology that means that a leak will be discovered prior to a fracture occurring in service. LBB has been applied to missile casings, gas and oil pipelines, pressure vessels, nuclear piping, etc. LBB also has several technical definitions. For instance, LBB can occur for an axial flaw in a pipe where the penetration of the wall thickness will result in a stable axial through-wall crack. This is LBB under load-controlled conditions. LBB could also occur for a circumferential crack in a pipe with high thermal expansion stresses. This might be LBB under compliant displacement-controlled conditions. Finally, LBB might occur when the flaw is stable under normal operating conditions and remains stable when there is a sudden dynamic event (i.e., seismic loading). This might be a time-dependant inertial LBB analysis. These analyses are deterministic, and could be extended to probabilistic evaluations as well. This paper describes some of the technical LBB approaches, applications, and significance of the methodology used in the applications. [S0094-9930(00)01603-6]