Abstract
The National Aeronautics and Space Administration (NASA) operates roughly 300 non-code layered pressure vessels (LPVs) constructed of steels that are at a risk of cleavage fracture during operation. NASA is currently assessing the continued fitness-forservice of these vessels and is employing computational analysis of the critical initial flaw size (CIFS) in key regions in the LPVs, such as the circumferential welds, to guide non-destructive evaluation (NDE) inspections. The NASGRO fatigue crack growth and fracture mechanics software is being used to perform the CIFS analysis. Cleavage fracture toughness varies as a function of crack-front length, but standard procedures for computing the CIFS in NASGRO assume fracture toughness is invariant to crack-front length. Thus, the CIFS analysis procedure in NASGRO was modified to account for a fracture toughness value that is dependent on crack-front length and a varying aspect ratio during the CIFS computations. This paper describes the CIFS analysis approach for cleavage fracture in circumferential welds using NASGRO and provides an example of the analysis for a postulated flaw in the shell-to-shell circumferential weld of a 9-layer exemplar vessel within NASA’s LPV fleet.
