PSI - Issue 60

Varsha Florist et al. / Procedia Structural Integrity 60 (2024) 614–630 2 Varsha Florist, Santhoshkumar R, A. Vamsi, Sajju V, Sarath Mohan, Sanjeev Kumar, Dhanoop A, Venukuttan C, M.K. Sundaresan, SVS Narayana Murty / Structural Integrity Procedia 00 (2024) 000 – 000

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Keywords:: 15-5 PH stainless steel; burst test; pressure vessel; structural integrity

1. Introduction During the initial ascent phase of a launch vehicle, the attitude (pitch and yaw) is adjusted through a thrust vector control. For this purpose, an aqueous solution of strontium perchlorate and pressurized N 2 gas are stored in a pressure vessel. The pressure vessel consists of a cylindrical shell with tori-spherical end domes with openings in the Fore End and Aft End. These vessels are currently made from AFNOR 15CDV6 material by sheet rolling & welding with three-layer internal coating of resin (Epoxy 1061) sealed aluminium for corrosion resistance. The existing 15CDV6 pressure vessels are designed with a MEOP (maximum expected operating pressure) of 7.85 MPa with a proof factor of 1.5 (proof pressure is 11.77 MPa) and design ultimate factor of 2.0 (design ultimate pressure is 15.70 MPa). In order to reduce number of weld joints and thereby improve reliability, reduce the lead time for realization as well as to dispense with multi-level internal coating an alternate material and state-of-the-art realization method was identified. Accordingly, 15-5PH stainless steel, which is chemically compatible with strontium perchlorate has been identified as a superior alternative. Based on the compatibility of the working medium, 15-5PH steel is selected for the revised proof and ultimate factors of 1.25 and 1.5. These factors are reduced due to introduction of remote fill and drain system. This material which has simple heat treatment, superior mechanical properties and flow forming technique was selected for realization of cylindrical portion of the tank to avoid multiple welds. The 15-5 PH pressure vessel was configured with flow formed cylindrical shell and shaped integral dome forgings to avoid sheet rolling and welding. This paper presents the design of pressure vessel and feasible reduction in load factors. The first qualification tank was successfully realized and was subjected to a series of pressure tests including burst test for ensuring the structural design margins 2. Design of the pressure vessel Configuration and design procedure of 15-5 PH pressure vessel is similar to the one using AFNOR 15CDV6 steel, except for the reduction in overall length, from 4591.5 mm to 4224 mm where the length for 15-5 PH pressure vessel was trimmed considering the reduced loading of strontium perchlorate due to changes in the mission requirements Dennis R Moss, Diamantoudis (2005). Owing to excellent corrosion resistance and compatibility with injectant, 15-5 PH stainless steel at H1025 condition having UTS 1070 MPa and 0.2%YS 1000 MPa was selected as replacement of AFNOR 15CDV6. The new pressure vessel is configured with three major components, namely cylindrical shell, tori-spherical aft end and fore-end domes. The tank design is based on yield strength of the material and tank specifications are tabulated below as Table-1.

Table 1. Specification of the pressure vessel. Sl. No.

Pressure vessel specifications

1 2 3 4 5 6 7

MEOP, ksc/Mpa

88/8.63

Proof pressure = 1.25*MEOP, ksc/Mpa

110/10.792 132/12.94

Design Ultimate Pressure = 1.5* MEOP, ksc/Mpa

Inner radius, mm

344 0.45 3660

Allowable mismatch for cir-seam, mm Cylindrical shell length considered, mm Cylindrical portion int. volume, litre

1360.65