The External Review Board (ERB) for xLPR (eXtremely Low Probability of Rupture) has raised questions regarding the possibility of non-LBB (Leak-Before-Break) conditions for several scenarios of crack growth. There are essentially two areas of concern that need to be addressed regarding this issue. The first is with regard to the effect of weld residual stresses (WRS) on through-wall crack growth where the axial WRS field has high values of compression near the mid thickness region. In this case, the crack growth in the depth direction will slow down when the crack reaches the compressive WRS field especially if the service bending loads are relatively small. However, the crack growth near the inner diameter (ID) surface may continue and possibly become very large and even possibly a 360-degree crack prior to leakage. This may lead to a non-LBB situation which the xLPR code needs to address. The second area of suggested study recommended by the ERB is related to the effect of WRS fields on through-wall crack (TWC) growth and its effect on crack opening displacement (COD) and therefore leak rate. This paper summarizes the efforts taken to address the ERB comments.

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