The durability calculation represents an important stage in designing of the thick wall cylinders, due to avoid the fatigue failure during the operating process. This paper presents aspects regarding the stress state from cylinders loaded with high pressure and it is indicated the important role of stress behaviors in initiation and propagation of the fatigue crack. The paper presents a case study, analyzed using the NASGRO 5.0 simulation software, hereby is determined the critical length of the fatigue crack and the conformable number of cycles.