Design, Development and Testing of Inconel Alloy IN718 Spherical Gas Bottle for Oxygen Storage
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JMEPEG DOI: 10.1007/s11665-017-2996-9
Design, Development and Testing of Inconel Alloy IN718 Spherical Gas Bottle for Oxygen Storage S. Chenna Krishna, M. Agilan, G. Sudarshan Rao, Satish Kumar Singh, S.V.S. Narayana Murty, Ganji Venkata Narayana, A. P. Beena, L. Rajesh, Abhay K. Jha, and Bhanu Pant (Submitted May 24, 2017; in revised form September 3, 2017) This paper describes the details of design, manufacture and testing of 200 mm diameter spherical gas bottle of Inconel 718 (IN718) with nominal wall thickness of 2.3 mm. Gas bottle was designed for the specified internal pressure loading with a thickness of 2.9 mm at the circumferential weld which was brought down to 2.3 mm at the membrane locations. Hemispherical forgings produced through closed-die hammer forging were machined and electron beam welded to produce a spherical gas bottle. Duly welded gas bottle was subjected to standard aging treatment to achieve the required tensile strength. Aged gas bottle was inspected for dimensions and other stringent quality requirements using various nondestructive testing techniques. After inspection, gas bottle was subjected to pressure test for maximum expected operating pressure and proof pressure of 25 and 37.5 MPa, respectively. Strain gauges were bonded at different locations on the gas bottle to monitor the strains during the pressure test and correlated with the predicted values. The predicted strain matched well with the experimental strain confirming the design and structural integrity. Keywords
electron beam welding, hammer forging, Inconel 718, proof pressure testing, spherical gas bottle
1. Introduction Gas bottles are one of the important subsystems of the launch vehicle and primarily used for fluid management (storage of pressurized fluids) (Ref 1). Gas bottles with different configurations and designs are used in launch vehicles considering lightweight and effective storage of pressurized fluids (Ref 2). Different metallic materials used in the fabrication of gas bottles are Ti-6Al-4V, CP-Ti, Ti-5Al2.5Sn, stainless steel and Inconel 718 (IN718) in view of their high specific strength, compatibility with fluids, good formability and weldability (Ref 3-6). Spherical gas bottles are used for storage of fluids like helium, hydrogen and oxygen at high pressure because of smaller surface area per unit volume and even distribution of stresses both internally and externally. The spherical gas bottles investigated in the present study are envisaged for oxygen storage. IN718 was selected as a material for oxygen storage based on the best balance between ignition characteristics, oxygen compatibility, weldability, and
mechanical properties. Typical values of certain characteristics are as follows: heat of combustion: 1575 Cal/g, combustion rate at 90 bar: 20 mm/s, ignition temperature (particle impact at 40 bar): 149 C, threshold oxygen pressure (for sustained combustion): 70 bar (Ref 7, 8). Further, tests performed to determine the effect of 30 day high-pressure (690 bar) oxygen exposure on the notched and un-notched
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