The structural analysis of the material resulting from the destruction by explosion of a compressed air cylinder

Abstract

In this paper is presented the structural analysis carried out on samples from a compressed air cylinder subjected to explosion. The air cylinder was mounted on public transport bus. The risk that the incident would repeat with other similar cylinders carrying compressed air required a detailed study regarding the causes that led to the catastrophic degradation. The research by micro and macro structural analysis has highlighted several factors that have increased the damage. The optical micrographs are obtained using an Olympus metallographic microscope equipped with a digital camera, with the possibility to automatically assign the microstructure magnification and with automatic software for linear measurements. The research regarding the appearance of the inner surface of the compressed air cylinder container has highlighted an accentuated corrosion process, developed in the thickness of the cylinder wall with a non-uniform thickness. The break occurred near the welding, known as thermal influence zone (the analyzed cylinder being welded longitudinally). The research has shown that inter-crystalline corrosion associated with pitting (punctiform) corrosion developed between the dendrite branches leads to an intense metal degradation in the wall depth and, in limited cases, causes perforation of the metal wall, increasing the explosive fracture development. A factor that influenced the corrosion process in the ZIT area was the mounting of the compressed air cylinder with the welded area at the bottom of the component.