This paper describes an investigation of the explosion of a combustion chamber shell in an aeroengine. Metallographic analysis, mechanical calculation and fatigue life estimation have been performed to determine failure causes and to make a proposal for preventive measure. The analytical results show that the poor quality of the roll welding seam is the fundamental cause of failure added to which a crack in the seam had not been discovered during a second overhaul. The effective design improvement is argon arc welding instead of roll welding in fabricating new shells. The effective preventive measures for old shells are to raise the strength of the seam by additional melt welding at overhaul, and to perform rigorous nondestruction inspection.