Residual Stresses in Layered Pressure Vessel Nozzles

Abstract The National Aeronautics and Space Administration (NASA) has hundreds of non-code layered pressure vessel (LPV) tanks that hold various gases at pressure scattered across their various space centers across the US. Many of the NASA tanks were fabricated in the 1950s and 1960s and are still in use. An agency wide effort is in progress to assess the fitness for continued service of these vessels because vessel replacements costs are high. Layered tanks typically consist of an inner liner/shell (often about 12.5 mm thick) with different layers of thinner shells surrounding the inner liner each with thickness of about 6.25-mm. The layers serve as crack arrestors for crack growth through the thickness. Most tanks have between 4 and up to 32 layers. Cylindrical layers are welded longitudinally with staggering so that the weld heat affected zones do not overlap. The built-up shells are then circumferentially welded together or welded to a header to complete the tank construction. A prior effort published in the 2022 ASME PVP conference provided results which consider weld residual stress and fracture assessment of some layered pressure vessels. This paper adds to that effort by presenting results for the nozzle welds that attach to the layered pressure vessels. Weld residual stresses are the most important driver in the fracture response of the tanks because the toughness of the materials is rather low. In this paper, the WRS fields for three different nozzles are presented. The first nozzle considered, labeled V267-270, is a 1,530.35 mm (60.25 inch) inner diameter nozzle welded to a 15-layer tank and summarizes the WRS fields produced. The second nozzle considered here is a nozzle welded to a 1524 mm (60-inch) inner diameter 8-layer tank. The third nozzle weld considered is a 50.8-mm (2-inch) small nozzle weld. Both the residual stress fields are presented along with discussion of the potential fracture response of the nozzle and tank interface. Finally, the effect of repair welds in the nozzles are presented also.