A requirement that a crack penetrate apressure boundary and produce a detectable leak before unstable fracture. A simple screening comparison uses critical crack size versus wall thickness, but the result depends on crack geometry and on whether stress or pressure is held fixed.
A conservative material-screening upper bound obtained by requiring wall penetration before fast fracture even at a stated yield-limited stress. Substituting a thickness-dependent pressure stress instead yields a different fixed-pressure inequality; the two comparisons must not be conflated.