# Analysis of the Causes of Excessive Noise and Vibrations of Live Steam Pipelines
## 7 Summary and Conclusions  
Based on the performed tests and numerical FEM calculations for the live steam pipeline in one of the power units, it can be stated that the likely cause of the phenomenon of high-frequency vibrations, which generates the maximum noise of 101-107 dB, is as follows:  
* A change in the geometry of the pipeline elements resulted in a change in the parameters of the broadband noise generated in one of those elements. * Parameters of acoustic transmission were on the border of effective sound transmission, and as a result of the change, the effective frequency of transmission (957 Hz) overlapped with the range of generated noise. The results include an effective reinforcement of lateral vibrations of the steam column, pipe resonance, and effective transmission of sound into the environment. * Vibrations are probably generated in the vertical segment near the nozzle and probe. They are propagated effectively for both Y-pipes. Further propagation in steam is very difficult; this frequency is strongly dampened, but vibrations may propagate in the pipe material and above the vertical segment due to the fact that the value of natural frequencies in all these pipes is approximately 957 Hz. As the distance from the 508 mm \(\times\) 55 mm pipe increases, the vibration waves in the pipe material disperse, and the level of noise decreases [10; 13; 14; 20; 21]. Based on the analysis of the live steam pipeline, the potential source of noise might be one of the following four elements, listed according to decreasing probability of vibration generation:  
* The nozzle located near the level of 17 m and the probe located near the nozzle;
* The Y-pipe at the level of 42 m;
* Steam valves located in pipeline branches above the top Y-pipe;
* The Y-pipe at the level of 9 m.  
The maximum amplitudes of pipe vibration were recorded at the level of 17 m. At the same level, the sonometer recorded the maximum level of noise. Measurements with an acoustic camera also point to the source of noise being above the level of 12 m. This indicates that the nozzle or probe are the most probable source of noise. The frequencies generated on the probe located near the nozzles, calculated for the full range of Strouhal numbers, ranged from 372 Hz to 872 Hz. This does not mean that it could not generate vibrations with a frequency of 957 Hz. It is sufficient that the 957 Hz frequency is a multiple of the whirl generation frequency. Moreover, in reality, the nozzle does not generate a single frequency but a certain range of frequencies, which increases the possibility of exciting vibrations. It is proposed to exchange the nozzle for an identical one to the nozzle in power unit B. Another potential source is the Y-pipe at the level of 42 m. Its geometry is different in comparison to unit B, which could cause a different band of noise generation through whirls. A change in the diameter of the pipes from \(\O\)355.6 \(\times\) 40 mm to \(\O\)406.4 \(\times\) 50 mm substantially changed the character of steam flow through the Y-pipe. In the case of the solution with two \(\O\)355.6 \(\times\) 40 mm pipes entering the Y-pipe, the sum of the sections of both these pipes (A = 119.310 mm\({}^{2}\)) was approximately equal to the section of the vertical pipe (A = 118.237 mm\({}^{2}\)), whereas in the new solution, the sum of sections of pipes entering the Y-pipe was equal to A = 147.468 mm\({}^{2}\), which is approximately 25% larger than the section of the (vertical) exit pipe. Therefore, the flow speed in the vertical pipe increases, and surges occur in the Y-pipe. What makes the top Y-pipe an unlikely source of vibration is the lower levels of noise and measured vibrations of the pipe wall in the top span of the vertical 508 mm pipeline. Additionally, the steam valves were mounted in a piping span whose diameter was reduced from 406 mm to 355 mm. This could potentially cause noise-generating whirls, butthe level of noise measured near the valves was significantly lower than that in the lower span of the vertical 508 mm pipe.