Piping, vibration stress failure

As von Nimitz points out, only cyclic stresses are directly related to failure probability. These stresses are often produced by pulsations in the fluid system, by mechanical vibrations produced by the mechanical movement of certain equipment components, and as a result of the fluid pulsations. Figure 13-8 lists the sequence of events that leads to most failures of equipment and piping. 

Piping failure at compressor due to vibration induced stress. Combustible gas detection system inoperability contributed to loss. 

Two other specific problems complicate the process of sealing pipelines with adhesives. One is that gas in gas mains is transported under 70-75 atmospheres pressure, and noticeable increase of gas main diameter is observed under this pressure. Thus, on the adhesive-metal interphase boimdary heavy internal stresses occur, which can lead to strength reduction or to failure of the adhesive joint. Joint failiu-e will also be promoted by vibration, which occurs with passage of fluid or gas through a deformed section of the pipe. 

Repair of underwater pipelines. Failures of underwater pipelines are observed most often because of damage by ships or anchors. In rivers with strong currents, scours may appear beneath pipelines the pipelines sag, and as a result of the vibration and stresses generated, cracks may appear, most often observed in the weld area. The pipe... 

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