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PASS/NOZZLE-FEM 3.5. Program Manual | |
The maximum shear stress theory (Tresca criterion) is used to calculate equivalent stress [p. 4.1, 7]:
$$ \displaystyle\sigma_e = \max\left\{|\sigma_1-\sigma_2|; |\sigma_1-\sigma_3|; |\sigma_2-\sigma_3|\right\}, $$where σ1, σ2, σ3 - the principal stress at the considered point.
The allowable stress $S_m$ is used for assessment general membrane stresses $P_m$ [Tab. 5-1, 7].
Except the bolt materials, the design stress intensity $S_m$ of general steels shall be the minimum of the following values [p. 3.6.5, 7]:
a) 1/2.6 of the lower limit value of the standard tensile strength under the normal temperature;
b) 1/1.5 of the yield strength $R_{eL}$ ($R_{p0.2}$) under the normal temperature;
c) 1/1.5 of the yield strength $R^t_{eL}$ ($R^t_{p0.2}$) under the design temperature.
As for the components made of austenitic stainless steels, according to the application parts, 90% of the yield strength $R^t_{p0.2}$ under the design temperature may be adopted for the components for which slight permanent deformation is allowable, but the design stress intensity must not exceed 1/1.5 of the yield strength $R_{p0.2}$ under the normal temperature. This requirement is not applicable to the flange or other components for which slight deformation will cause leakage or fault.
The allowable stress $S_{PL}$ is used for assessment local primary stresses $P_L$ or $P_L+P_b$ [Tab. 5-1, 7]. This limit value is calculated as follows:
$$ S_{PL} = 1.5 K S_m, $$where $K$ - load combination factor for occassional loads given in table 3-3 [7].
The allowable stress SPS is used for assessment secondary stresses $P_L+P_b+Q$ [Tab. 5-1, 7]. This limit value is calculated as follows:
$$ S_{PS} = 3S_m. $$The general membrane stress $P_m$ is assess as follows [p. 3.7.1, 7]:
$$ P_m \le 0.9 R_e. $$where $R_e$ - yield strength $R_{el} (R_{p0.2})$ at the normal temperature.
The local primary membrane stress plus bending stress $P_m+P_b$ is assess as follows [p. 3.7.1, 7]:
$$ P_m+P_b \le \left\{ \begin{array}{ll} 1.35 R_e, & P_m \le R_e/1.5, \\ 2.15 R_e-1.2 P_m, & R_e/1.5 \lt P_m \le 0.9 R_e. \end{array} \right. $$Other allowable stresses and strength assessment are provided in according to ASME BPVC VIII.2 [4].
PASS/NOZZLE-FEM 3.5. Program Manual
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