# Analysis of the Causes of Excessive Noise and Vibrations of Live Steam Pipelines
## 3 Measurement of Vibrations of the Live Steam Pipelines  
Experimental tests were performed by means of a Polytec PSV-400 scanning laser vibrometer (Polytec GmbH, Waldbronn, Germany), which allows for direct non-contact measurements of vibration velocity and displacement. The basic parameters of the measuring system were as follows:  
- Bandwidth range from 0.1 to 250 kHz;  
- Maximum scan speed--100 points per second;  
- Vibration velocity range--1 \(\upmu\)m/s to 10 m/s;  
- Displacement range--1 \(\upmu\)m to 160 mm;  
- Laser type--633 nm (red) He-Ne laser, with power lower than 1 mW;  
- Scanning range \(\pm\) 20\({}^{\circ}\) about X, Y;  
- Angular resolution \(<\) 0.002\({}^{\circ}\). Vibration measurements were taken on power unit A, in which the live steam pipeline vibrated and generated noise at the level of 105 dB. For the purposes of comparison, vibration measurements were taken in the almost identical power unit B, where such problem did not occur. Vibration measurements of both pipelines were taken by means  
Figure 4: Live steam pipeline from the turbine to the upper Y-pipe. of a laser vibrometer. In order to measure the vibrations directly in both pipelines, holes were made in the thermal insulation at the following three levels of power unit A: 12 m, 17 m, and 36 m and at the level of 12 m in the control unit B, where excessive vibration and noise does not occur. The locations of the measurement points/levels were dictated by the expected structural modal vibrations modes and were selected to avoid vibration nodes. The exact height of the measurement levels (12, 17, 36) was dictated by the floor level of the building in which the pipeline was installed. Examples of measurement points are shown in Figures 5-7. The holes were spaced at 0.40 m vertically and 45\({}^{\circ}\) around the circumference. Figure 6 shows the laser vibrometer system during vibration measurements. The following parameters were measured:  
* The velocity and the RMS values of vibrations at individual measurement points;
* Mode shapes at individual levels [8], where measurements were taken;
* Amplitude-frequency spectrums for individual measurement points in order to evaluate if the structure does not operate in the resonant bands. For the time of the measurements, the control operation was responsible for keeping the operational parameters of the installation at the unchanged level to secure the stationary character of the vibrations. Figure 5: Holes in the insulation for measuring pipeline vibrations. Figure 6: The laser vibrometer system during vibration measurements. Table 1 lists the results in the form of RMS values of vibration velocity at individual measurement points, recorded at subsequent working levels in power unit A. The results of measurements taken at the level of 12 m in unit B are also included for comparison. Figure 7 shows the labels for measurement points used in Table 1.  
Figure 8 shows the amplitude-frequency plot for vibrations at the operating levels where measurements were made. The analysis also included the calculation of mode shapes, which are described in detail in [8], where it was concluded that they are of variable character similar to that of a sinusoidal waveform. The amplitude-frequency plot for vibrations of the live steam pipeline (Figure 8a) shows that in unit A, the dominating vibration frequency is 957 Hz, which was registered at all levels of unit A. On the other hand, the measurements taken on a