There are four key reports for a relief valve analysis:
Mass Participation Report - Shows how sensitive each of the piping system’s modes is to the relief valve firing. High modal participation factors indicate that the mode is easily excited by the applied dynamic forces. If subsequent displacement, restraint, or stress reports indicate excessive dynamic responses, then the modes having high participation must be dampened or eliminated. After a particular mode is targeted as being a problem, it can be viewed in tabular form using the mode shape report or graphically using the animated mode shape plots.
Displacement Report - Shows the maximum possible positive or negative displacement that can occur at some time during the relief valve’s firing. Values in this report are always positive.
Restraint Report - Shows the maximum dynamic load for which the support should be designed. The top value is the maximum support reaction. The second value is the largest support reaction due to any one mode. The last number on the left indicates which mode.
Stress Report - Shows the maximum dynamic stress due to the relief valve firing. Stresses from a dynamic shock load case should be combined with the sustained stresses from a static analysis and the result compared with the code defined occasional stress for the material.
Participation Factor Report - Shows which modes tend to be excited by the applied dynamic load.
The following Stress report shows element stresses due to the dynamic relief loads. The top value is the maximum stress due to the interaction of all the system modes. The second value is the largest stress due to any one mode. The bottom number on the left indicates which mode.
In the following examples, the maximum stress at node 5 is 1481 psi. The stress at node 5 due only to mode #1 is 1280 psi.
The maximum stress at node 40 on elements 40-50 is 6430 psi. The stress at node 40 due to mode #4 is 3982 psi. Mode #4 is the largest contributor to the stress at node 40.
Support reactions due to the combination of the static sustained and the dynamic solutions are shown in the following two report samples:
This stress combination can be compared to the B31 code allowables for occasional stresses.