Mechanical Analysis

The second main component of a pulsation study, after the acoustic analysis, is the mechanical analysis. During the mechanical analysis the dynamic mechanical response of the pipework is considered, to ensure that mechanical piping natural frequencies are not excited by the residual pulsation levels, causing excessive vibration levels and pipe fatigue failures.

Spectrum undertake full modal analysis and forced response stress and vibration analyses using ANSYS® finite element software. API Standard 618 includes recommended separation margins between the dominant acoustic pulsation frequencies and the mechanical piping natural frequencies, as well as recommended limits for piping vibration and stress levels.

Spectrum ensure that acceptable vibration levels are achieved and that residual stresses are kept well below the fatigue limits set in API 618.

The type of pipe supports used are reviewed and recommendations made to upgrade pipe supports where necessary to provide sufficient restraint to pulsation forces. Additional pipe supports are also recommended, where necessary, to detune mechanical natural frequencies. The stiffness of the pipe support structure is also considered, to ensure that the pipe supports provide adequate dynamic restraint.

Care is taken to minimise the impact of the recommendations, with consideration given to allowing thermal expansion of the pipework, whilst restraining the pipework in order to prevent pulsation induced vibration.