Pipeline Vibrations – Measurements Under Difficult Conditions
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In many technical applications pipelines are used for transport of potentially flammable or hazardous gases and liquids. Dynamic issues at pipelines often depend on the volume flow. Vortex shedding is a typical result for flow induced pulsation and may also result in severe piping vibration and failures. Another kind of critical pulsation excitation or enhanced vibration is the use of compressors or pumps due to their unsteady working principle. Measurements of pulsations and pipeline vibrations are important for the assessment of dynamic material loadings. They often allow a comprehensive root cause analysis in case of elevated vibrations. Sometimes, it is not possible to install standard measurement equipment at the area of concern. Therefore specialized measurement technics and detailed investigation methods must be used. These different methods are presented in the two case studies. The first case study deals with a flow induced vibration problem at a grid gas manifold. Obvious vibrations occurred randomly during high volume flow in winter time. A long-term measurement has been used to determine the characteristic behavior. Spectral analysis and volume flow correlations have enabled a precise characterization of the critical vibration phenomenon. On this basis a simple well working mitigation measure has been identified and realized. In another case study elevated vibrations occured in the reactor bay of a chemical plant, where a hyper compressor is used to compress ethylene with a discharge pressure up to 3,000 bars. It is not possible to install extensive measurement equipment during compressor operation due to the hazardous conditions inside of the reactor. Therefore a laser vibrometer has been used to detect piping and steel construction vibrations from outside of the bay with distances of 100 meters. Means of measurement positions permitted detailed analysis of the vibration phenomena. Finally a measure has been derived to improve vibration behavior.
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