Team Stressman was engaged to assist a client with a vibrating piping system. During testing of the high pressure (HP) mud pumps, some of the piping near the pumps was shaking.
The reason for the shaking was due to pressure pulsations from the HP manifolds was hitting the natural frequency of the piping system.
Stressman Engineering modelled the entire system in CAESAR II (pipe stress). Each of the 170 pipe supports was modelled and the stiffness from these supports was included in the CAESAR II analysis. This was done to estimate the natural frequencies of the piping system as good as possible.
The piping model was then exported to BOSPulse (pulsation software). The pumps was modelled in detailed and several cases was evaluated. The unbalanced forces in the piping was exported and imported into the CAESAR II dynamic model.
The results from CAESAR II showed the same results as what was observed. Stressman Engineering then suggested alternations on the pipe supports to shift the frequencies. No additional pipe supports had to be inserted, just changing their type. Also, no changes to the piping system had to be made. This was great since the piping already had been built, checked and the hydrostatic pressure test had been performed.
Since the pipe support types had changed, all the static load cases was also re-run. The stresses in the pipes was checked with API-6A and ASME B31.3 Chpater IX. The support members and welds were checked in accordance with Eurocode 3.