My question is with regards to a surge analysis calculation that I am currently dealing with:
According to Process data, there is a pressure wave transition throughout the pipe run; the time period between the "peaks" of the waves are about 20 msec and the whole spectrum lasts about a minute (there are only five or six force peaks -all positive- in the whole scenario though).
since the natural radial frequency of the pipe spool is about 30 rad/sec and the frequency of the applying force is about 300 rad/sec
can I conclude that because the forcing frequency is significantly larger than the natural frequency, DLF would approach to zero (flexible criteria) thus, those forces-regardless of their significance- can create no response in the system?

thanks in advance

Your system has more than one natural frequency. There is a chance, then, that your forcing frequency response will be amplified by your system.

you are right Dave however, in my situation the closest natural frequency to the inducing one occurs in mode 22! is it not far enough to yet conclude the above statement?

I would expect little response from your 22nd mode but...
what if you had a small bore, pig tail connection (e.g., a pressure gauge that just happened to be that 22nd mode and your applied load activates this shaking?
Your conclusion is probably correct but it may not be.