PASS/NOZZLE-FEM 3.5. Program Manual

5.8.6. GOST 34233.6-2017 (from cyclic loading)

Fatigue analysis is not performed if the total number of loading cycles over the entire service life does not exceed 1000 cycles for steel vessels and its components.

When calculating, the principal stresses in the most loaded nodes are determined. For each load type, the range of individual stress components is calculated $\Delta\sigma_х$, $\Delta\sigma_у$, $\Delta\sigma_z$, $\Delta\tau_{ху}$, $\Delta\tau_{xz}$, $\Delta\tau_{уz}$ as the difference between the stresses of both loaded states included in the cycle. The principal stress range $\Delta\sigma_1$, $\Delta\sigma_2$, $\Delta\sigma_3$ is calculated as the principal stresses under action in the selected coordinate system of stresses equal to the ranges of individual stress components [15].

The stress amplitude at each point and for each cycle is calculated by the formula (6) [15]:

where $K_{\sigma}$ - fatigue strength reduction factor, which is set by the user for each weld seam or calculated automatically based on other factors:

where factor ξ are defined as per tab. 1 [15]; factor ρ equal to 1.0 for polished weld surfaces, and 1.1 for unpolished weld surfaces; φ - weld strength factor that is defined as per GOST 34233.1 [15]:

The allowable stress amplitude is calculated by the formula (12) [15]:

where $C_t$ factor, $A$ and $B$ parameters, depending on the material properties, are determined by table 3 [15]; $n_N$ and $n_{\sigma}$ factors assums following values:

The allowable number of loading cycles is calculated by the formula (13) [15]:

If $\displaystyle\sigma_a\le\frac{B}{n_{\sigma}}$ then the number of cycles is not limited and their influence is ignored.