How can we estimate the safety valve opening phenomenon? We have three options: static analysis using a maximum DLF of 2.0, dynamic analysis using the response spectrum method, and dynamic analysis using the response history method. Both dynamic analyses yield lower stress values that are not as oversized as in static analysis.
The DLF (dynamic load factor) can be determined according to Annex II of ASME B31.1 and used in static analysis. An excessive but frequently used simplification is to assume a maximum DLF value of 2.0. The DLF obtained in one way or another is a multiplier of the PSV recoil force, obtained from the manufacturer or calculated independently.
The spectral response method is used to evaluate the system's response to vibrations at different frequencies. The responses at a given frequency are combined into the overall system response using the SRSS method.
The response history method allows the load to be scheduled at any time and place with the use of damping.
Below is an interesting video generated by Cesar II showing how the entire system behaves.
