PSI - Issue 60

Rohan Nair et al. / Procedia Structural Integrity 60 (2024) 93–114 Rohan Nair / StructuralIntegrity Procedia 00 (2023) 000–000

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1. Introduction

Toroidal shaped water storage tanks are used in earth storable stages of liquid rocket engines of launch vehicles. These water tanks tanks are used to generate steam to drive the turbine as well as to feed water to moderate the temperature of gas servomotor and cool fuel (unsymmetrical dimethyl hydrazine) pump bearing during engine operations. These tanks were initially realized from high strength aluminium alloy AFNOR 7020 (Al-4.5Zn-1.5Mg) aluminium alloy, which possessed good strength and weldability. In view of the susceptibility of AFNOR 7020 to stress corrosion cracking [1,2], it was decided to switch over to AA 6061, which had comparatively lesser specific strength but was immune to stress corrosion cracking [3]. The water tank is toroidal in shape having mean toroidal diameter of about 2000 mm and internal sectional diameter of ~350 mm. It is made in 8 segments (45° each). Four segments are welded using an interconnecting (IC) rings of the same material and is made into a sub-assembly. Two such sub-assemblies are joined together by flanged joints using fasteners to form the final tank assembly. There are 4 nozzles in the tank each one for pressurization, overflow, fill/drain and feed. Out of these, one nozzle weld has a diameter of ~150 mm and the remaining three nozzles have a diameter of ~100 mm. The working pressure also known as MEOP (Mean Effective Operating Pressure) is 5.1 bar (g) and the design pressure (Ultimate Pressure) is 6.4 bar (g). The temperature encountered during flight on the water tank is from ambient to ~45 o C. This paper describes the procedures adopted to develop and qualify [4] an alternative source for fabrication of AA6061 water tank and the qualification tests carried out as a part of inducting the hardware into launch vehicle program. The test article is a quarter model of the water tank with similar sectional dimensions and shape (toroidal) with a nominal thickness of 2mm which is fabricated out of AA6061 aluminum alloy. It comprises of 2 segments which are longitudinally welded out of 2 formed half toroidal shells. The segments are circumferentially welded with an interconnecting ring (IC) made of AA6061 in between and segment ends are welded with flanges which are bolted by closure plates. Two adaptors are welded on one of the toroidal shell segment for filling fluid and mounting pressure gauge. The IC ring has an anti-slosh baffle riveted onto it from within the toroidal shell. The total volume of the test article is 172 L. Fig. 1 shows manufactured test article. Fig. 2 shows the entire water tank in which highlighted blue segment corresponds to the test article. Fig. 3 & Fig. 4 shows sectional images of anti-slosh baffle and IC ring respectively. 2. Test Article:

Fig. 1: Photograph of the test article