The factor is used when calculating dynamically loaded springs (cyclic fatigue load for life N > 10 5 working strokes). It is given by a ratio between the endurance limit of spring and the torsional stress of spring material exposed to full load, that is, k f ≈τ e / τ 8 . For standard operating conditions, the recommended value of safety factor at fatigue limit k f is recommended to be in the range of 1.1 ... 1.5. In general, higher kf values must be used for springs working in corrosive environment, at high temperatures or under impact loads. The effect of a corrosive environment has a serious influence on the spring fatigue strength, since it can reduce the spring loading capacity down to one fifth, depending on the material and type of corrosive environment.