Etudes Industrielles de vibrations sous écoulement dans des réseaux de tuyauteries

Industrial vibration studies on flow in pipe networks

Electricité de France, Direction des Etudes et Recherches, Clamart

Abstract

To improve the allowance mode in the design stage for vibratory phenomena affecting main lines and nozzles under operating conditions have led Electricité de France to develop special engineering codes and study methodologies. The basic aim of the various actions undertaken has been to locate the causes of fractures of cracking of piping in auxiliary circuits, exomine the corrective actions taken, and define industrial vibration prevention practice.

So far, vibration problems have been detected during start-up tests. As regards nozzles, the cracks sometimes oppear rapidly, and are in this case treated during the installation testing period, as called for by the RCC-M. Further more, the problem posed by vibration fatigue is hard to solve, because the operating configuration that gave rise to the problem must be known.

Evolution of EDF's acceptance guide involves incorporation on the vibration acceptance criterion for piping systems.

Knowing the operation of the circuit, we predict the dynamic Ioads generated by the flow, to predict the vibratory behavior of the piping, in particular that of nozzles, and so estimate the design margins with respect to the vibration risk either using the current acceptance criteria or a damage analysis. Two methodologies based on the modeling and calculation options of the CIRCUS code are proposed. One concerns studies based on operating design data and the other studies based on the operating diagnostic. The latter is based on an opproach combining numerical modeling and on-site tests.