Metallurgical Analysis of Cracked Redundant Valves for Propellant Flow Control in the Attitude Orbital Control System of a Satellite
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Attitude Orbital Control System (AOCS) thrusters, used in Indian satellites employ Latchable Series Redundant Valves (LSRV) for propellant flow control. The valve body has a major component called bobbin, which comprises four parts, three parts made of AISI 304L stainless steel and one part of AISI 446 stainless steel. About 150 bobbins were electron beam welded and one, from a group of thirty bobbins, developed a crack in the HAZ of one of the face welds. Detailed analysis revealed that the crack was due to stress-assisted cracking phenomenon. The stress induced by press fitting of a part in between other two parts of valve was primarily responsible for the cracking.
KeywordsStress-assisted cracking Press-fitted components
The authors express their sincere thanks to Dr. P. P. Sinha, Deputy Director, VSSC (MME) for technical guidance and encouragements during the research study. They are indebted to Dr. K. Radhakrishnan, Director, VSSC for permitting us to publish the article.