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PASS/NOZZLE-FEM 3.5. Program Manual | |
EN 13445-3 allows to determine equivalent stress in two ways: the maximum shear stress theory (Tresca criterion) and the maximum distortion energy yield criterion (Mises criterion). PASS/NOZZLE-FEM uses von Mises equivalent stress given by eq. (C.4.1-3) [6]: $$ \displaystyle\sigma_e = \frac{\displaystyle 1}{\displaystyle \sqrt{2}} \sqrt{(\sigma_1-\sigma_2)^2+(\sigma_1-\sigma_3)^2+(\sigma_2-\sigma_3)^2}, $$
where σ1, σ2, σ3 - the principal stress at the considered point.
The allowable nominal stress $f$ is used for assessment general membrane stresses $P_m$ (tab. C-3 [6]). The allowable nominal stress is defined as per table 6-1 [6] that shown in table 5.12 below.
| Table 5.12. Maximum allowable nominal stress | ||||||
| Steel designation | Normal operating loadcases | Testing loadcases | ||||
| Steels other than austenitic, A < 30%% |
$\displaystyle f_d = \min\left\{\frac{R_{p0,2/T}}{1.5}; \frac{R_{m/20}}{2.4}\right\}$ | $\displaystyle f_{test} = \frac{R_{p0,2/T_{test}}}{1.05}$ | ||||
| Austenitic steels, 30%% ≤ A < 35%% |
$\displaystyle f_d = \frac{R_{p1.0/T}}{1.5}$ | $\displaystyle f_{test} = \frac{R_{p1,0/T_{test}}}{1.05}$ | ||||
| Austenitic steels, A ≥ 35%% |
$\displaystyle f_d = \max\left\{\frac{R_{p1.0/T}}{1.5}; \min\left(\frac{R_{p1.0/T}}{1.2}; \frac{R_{m/T}}{3.0}\right)\right\}$ | $\displaystyle f_{test} = \max\left\{\frac{R_{p1.0/T_{test}}}{1.05}; \frac{R_{m/T_{test}}}{2.0}\right\}$ | ||||
| Cast steels | $\displaystyle f_d = \min\left\{\frac{R_{p0.2/T}}{1.9}; \frac{R_{m/20}}{3.0}\right\}$ | $\displaystyle f_{test} = \frac{R_{p0.2/T_{test}}}{1.33}$ | ||||
Nomenclature for this table 5.12 is as follows:
| A | = | minimum rupture elongation. |
| Rp0.2/T | = | 0.2% proof strength at temperature T. |
| Rp1.0/T | = | 1.0% proof strength at temperature T. |
| Rm/20 | = | tensile strength at temperature 20°‘. |
| Rm/T | = | tensile strength at temperature T. |
The PASS/NOZZLE-FEM performs stress analysis of all loadcases based on user loadcases. The table 5.13 summarizes the assessments that based on table C-3 [6].
| Table 5.13. Assessment criteria | ||||||
| Loadcase | Assessment | Description | ||||
| $WGT$ | N/A | Only weight (dead) loads. For design and operating loads. It is only used to calculate range stress. | ||||
| $T$ | N/A | For operating loads. It is only used to calculate thermal stress for allowable loads. | ||||
| $P+P_s$ | $P_m \le f$ | Only pressure and hydrostatic pressure. For design loads. It is only used to assess general membrane stressess. In nozzle junction is not considered in the case. | ||||
| $P_L \le 1.5f$ | It is only used to assess local membrane stressess. | |||||
| $P_d+P_s+WGT$ | $P_L+P_b \le 1.5f$ | Pressure plus dead loads. For design and operating loads. It is only used to assess local primary stressess. | ||||
| $max\left\{\sigma_1; \sigma_2; \sigma_3\right\} \le R_{p/T}$ | For design loads. If suitable flag is enbaled then this checking is performed and for operating loads. Limitation of primary stresses in case of tri-axial state of stress to avoid brittle failure caused by the limited ductility. | |||||
| $P+P_s+DSG$ | $P_L+P_b \le 1.5f$ | Design pressure plus design loads. It provides protection against plastic collapse. | ||||
| $P_L+P_b+Q \le 3f$ | If suitable flag is enbaled then this checking is performed and for design loads. | |||||
| $P+P_s+OPE$, $P+P_s+OPE+T$ |
$P_L+P_b+Q \le 3f$ | Operating pressure plus operating loads plus thermal strains. It provides protection against ratcheting. | ||||
PASS/NOZZLE-FEM 3.5. Program Manual
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