ESDU 88022 provides graphical data and introduces a program in Fortran@ provided on disc (uncompiled) in the software volume as ESDUpac A8822@ for the estimation of the natural vibration characteristics of non-rigid planar piping systems@ either empty or running full. The program calculates natural frequencies and corresponding mode shapes@ and normal-mode generalised masses and stiffnesses of the transverse bending and axial modes of vibration@ up to a chosen cut-off frequency. Lumped masses@ to model in-line valves for example@ and externally-acting elastic restraints in the plane of the system may be treated. The effects of bend flexibility may be included. The pipes may vary in cross-section@ or be of different materials@ but the fluid is assumed of constant density. The graphical data allow the estimation of the fundamental frequency of a single pipe@ or of configurations with up to three right angle bends@ subject to additional idealisations over those imposed by the computer model. Worked examples illustrate the use of both methods. The program is also provided compiled to run under PC DOS in the ESDUview user-friendly shell that prompts for the input data.