Well, presumably you have the wall vibrating at some frequency, and the pipe vibrating at some other frequency/frequencies, which can cause the nozzle and any other connections, e.g. wall supports vibrating at any other frequency/frequencies, all in competing fashions.

You can (probably) assume the vessel wall won't fail, since they're calling you in, so it's really a pipe failure and nozzle failure issue.

But you can't really do anything until you have a grasp on what information you presently have and that's if it's sufficient for the analysis.