When analyzing vacuum elements (with input negative operation pressure), the local stability of pipe cross-section under external overpressure Pop, as well as longitudinal forces N, transverse forces Q and bending moments M, must be analyzed. Analyses are performed according to GOST .
Total stability margin factor under combined forces of Pop, N, Q, M must be less than 1:
where Pop - external overpressure (absolute operation pressure value for a vacuum element), N - value of effective axial force in element, Q - absolute value of effective transverse (shearing) force in element, M - absolute value of effective moment in element, [P] - allowable external pressure based on stability conditions, [N] - allowable axial force based on local stability conditions, [Q] - allowable transverse (shearing) force based on local stability conditions, [M] - allowable moment based on local stability conditions. All allowable values are determined according to GOST 32388-2013 + rev. 1 and 2.
If the above stability conditions are not met, the corresponding cell in the table will be highlighted in red.
To increase stability under external pressure Pop, various types of stiffening rings can be inserted at set intervals along the pipe axis. To consider them in the analysis, select the ring type number in the "stiffening ring type" field. Clicking on one of the stiffening ring property cells will bring up a dialog window, where properties can be input (fig. 2).
Fig. 2. Dialog windows for inputting stiffening ring type and properties
After analysis: Output > Pipe Wall Buckling Check