Mechanical Response Analysis is a computer based procedure that examines the geometry of a piping system in order to find the frequencies, and in some cases, the magnitude, at which the piping will resonate. This analysis, is not just a static analysis, but also takes into account the liquid, or gas, in the piping system and the dynamic pulsation forces that are introduced by any attached pump.
The procedure is a rigorous analysis which will lead to the correct positioning of supports and restraints along the piping system, something that, prior to the advent of easily accessible computers, was done using Nomograms and other hand calculation techniques to try and ensure that the frequency of the dynamic driving forces created by the pump do not either line up with the natural frequencies at which the piping would resonate and are less than the fundamental pumping frequency, and its initial harmonics.
Mechanical Response analysis takes the same approach as the original hand design did, in that it endeavours to provide a system where the first resonant frequency of the structure is both above the fundamental pumping frequency, and not coincident with either the fundamental pumping frequency, or the initial harmonics thereof. To do this the analysis will use pulsation simulation software to calculate pressure pulsation forces within the piping system, and then input these forces into CAE software to calculate the first natural frequency, and harmonics thereof, for the piping arrangement under that dynamic loading.
During the first examination of a piping system for its modal frequency it is often found that this first modal frequency is less than the fundamental pumping frequency, which means that the pump is almost certainly going to cause the piping to resonate as it operates. Therefore the initial approach is simply to identify the way in which the piping distorts and moves under the dynamic loading of the pressure source, and then either add in additional support or modify the piping runs. Usually the simplest solution that sufficiently raises the frequency of the first mode, or natural frequency, above the minimum frequency value to give compliance with API674 is additional guide type supports.
Whilst every effort is made to model the detail of a piping system, and every effort is made to position the first mode of vibration of the structure between the highest harmonic of the pumping frequency possible it is a fact that when any system is built in real life that the resonant frequencies of that system will not be exactly as predicted. It is also a fact that there are limitations to how much the first frequency of the first mode of vibration of the structure can be raised by additional support.
As with all engineered structures, when the real structure is built there will be differences and deviations from the design model. The impact of this in respect of API674 analysis is that the actual first mode, or natural frequency, of the system is unlikely to be where the design model says it will be, and so sufficient design margin must be allowed for this error.
Where piping runs are changed Flo-Dyne will check the mechanical integrity of the revised piping for static as well as thermal and dynamic stresses, such that any modification proposed back to the client has been fully evaluated prior to presentation.
If this detailed analysis is not done then piping supports and restraints can be miss-placed, which may result in undue vibration in the piping system, which in turn may result in mechanical failure of the pipe supports or structure, and in the very worst cases catastrophic failure of the pipe itself.
Flo-Dyne offers complete compliance with the most rigorous assessment required by API674 for pulsation analysis, mechnical response and stress analysis of piping systems. Unlike many companies, our results for the mechanical analysis can be cross-checked using either CEASAR or Bentley software.
