Abstract: The leak before break (LBB) analysis is an advanced assessment technology for pipes. The key technology of LBB is the crack stability analysis, which decides the usability of the LBB approach. The crack stability analysis problem was studied based on the failure mode of the nuclear grade pipes in this paper. Advantage, disadvantage and application range of the modified J integral tearing modulus intersection method (J-T method), modified limit load method and twice elastic slope method were discussed. Finally, aforementioned methods were applied to an engineering example to verify their validity. Conclusions of this paper can provide some references for the application of the LBB approach to the nuclear power stations of China.