The nature and reasons of two cases of premature failure of engineering products are investigated (metal-composite cylinder for moto fuel and metal rod of bulldozer's hydraulic cylinder). By methods of metallography and fractography with using the basic provisions of metallurgy, physics of metals, physics of strength and fracture we have identified the localization of initial cracks, the micromechanisms of their formation and subsequent development, and described the general picture of failure. It is shown that the main physical and mechanical causes of cylinder's failure are connected with coarsening and heterogeneity of intermetallic phase distribution in an alloy and the increased roughness of internal surface processing on the metal liner. It is established that the reason of the rod failure was unsatisfactory quality of metal caused by errors of heat treatment before chrome plating. As a result, there are structural inhomogeneities (ferritic banding, non-metallic inclusions) in the hardened layer and in the transitional zone to the core area which initiated the fatigue cracks. The main mechanism of failure of the automobile gas tank and bulldozer's hydraulic-cylinder rod is metal fatigue that evolves in time and is induced by manufacturing processes errors.