COMPRESS considers numerous vessel conditions for the purpose of determining the required thickness based on longitudinal stress. These include:

All conditions are investigated for the corresponding pressure condition combined with weight (and other external loads) combined with wind or seismic load (wind and seismic loads are not combined).

The "hot shut down" conditions correspond to cases where the vessel is at operating temperature but internal pressure is "0". Normally, the compressive forces resulting from weight and wind acting on the leeward side of the vessel are partially resisted by the tensile force from internal pressure. In the hot shut down case the loss of the tensile force may result in very high compressive stress on the leeward side of the vessel. In design mode COMPRESS will increase the nominal thickness of the shell components to compensate for this condition. If hot shut down is not applicable because of the process design then this condition can be switched off in the Set Mode Options dialog, Calculation tab.

COMPRESS will further investigate the effect of vortex shedding on the required thickness of the vessel shell components. This investigation must be initiated by the designer: click the "Vortex Shedding" button on the Wind Code dialog, then "check" the conditions to be investigated. COMPRESS calculates the critical wind speed and compares to the design wind speed. If the critical wind speed is greater than the design wind speed then no further calculations are performed because the vortex shedding condition is not experienced. But if the critical wind speed is less than the design wind speed then further calculations are performed to obtain the additional loading on the vessel due to the vortex shedding loads; these are combined with the basic wind loads acting on the vessel at the critical wind speed. In this case the following three conditions are reported for the purpose of determining the required thickness based on longitudinal stress.