Metallurgical failure analysis of the 560 mm dia 0.15C–1.25Cr–1Mo–0.25V steel pressure vessel

0.15C–1.25Cr–1Mo–0.25V steel, a high strength low alloy (HSLA) steel, is being extensively used in space programme. This alloy being a versatile material and its ease of fabrication and welding made it the most suitable for the fabrication of 560 mm dia pressure vessel for smaller rockets. During proof pressure test for 73 KSC, one of the pressure vessels burst opened at 71 KSC. Metallurgical analysis of the failed motor case was carried out to understand the causes of its failure. Observations indicated that a deviation in normal heat treatment resulted in low strength of material, which caused yielding and premature rupture at lower pressure than expected. This paper brings out the salient features of this analysis.