Abstract: During Leak-Before-Break assessment,it is of great importance to predict thelimit-load of the ligament at a surface crack.The current limit-load formulas are mostlyoverconservative.By using them in LBB assessment,the actual transient length of throughcrack at penetration will be underestimated with unsafe assessment results.In this paper,anew collapse model of the ligament at a surface crack is propsed.The derivation of relevantnew limit-load formula of ligament is briefly presented.Finally,in terms of diag...