LBB Nozzle Transition Parameter Variation and Plasticity Influence

Abstract

In the framework of the R6 development programme on leak before break NRG investigated a circumferential through wall crack in a pipe with nozzle. A range of crack angles (3–180°), radius over wall thickness ratios (Ri/t = 5, 10, 20, 50 and 100) and nozzle divergence angles (0, 5, 10, 20, 30 and 40°) have been investigated in order to investigate parameter sensitivity. The stress intensity factor (KI) and the Crack Opening Area (COA) are compared for the nozzle and pipe models. The nozzle investigation is performed using a longitudinal force (100 MPa). It can be concluded that with larger nozzle divergence angles, the resulting maximum KI nozzle factors are higher. The larger nozzle divergence angles have a suppressive effect on the crack opening resulting in a lowered COA nozzle factor. The influence of plasticity has been investigated by a number of analyses including plastic behaviour. The geometry variations are five Ri/t ratios (5, 10, 20, 50 and 100) and eight different crack angles (3, 10, 30, 50, 75, 100, 140 and 180°). A 30° nozzle angle was selected for plastic analyses. The plasticity investigation is performed using longitudinal force (100 MPa). In general the results for KI are higher with the inclusion of plasticity. However, since the inclusion of plasticity has a stress relieving effect on the pipe/nozzle transition, the resulting maximum KI nozzle factor is lowered. The COA results for the individual analyses are overall higher due to the inclusion of plasticity. The COA nozzle factor is lowered, because the relative influence of plasticity is lower on the stiffer nozzle.