Piping vibration

Forces of Piping on Process Machinery and Piping Vibration. 10-133... 

FORCES OF PIPING ON PROCESS MACHINERY AND PIPING VIBRATION... 

This is an important practical problem area, as piping vibration can cause consider le downtime or even pipe failure. 

Reciprocating compressor pulsations were covered in Chapter 3, but neeti to be mentioned with the discussions on reliability. Problems with reciprocating compressor pulsations and the potential for acoustic and mechanical resonances are very similar to those experienced with helical-lobe compressors. The significant difference is the frequencies are much lower and the number of discrete frequencies per compressor aie much less. However, piping vibrations can occur and there is always a... 

To minimize pipe vibrations it is necessary to design pipe runs so that the "acoustic length of the pipe run does not create a standing wave that... 

Mechanical vibration of pipe is handled in the same manner as for reciprocating pumps (Volume 1, Chapter 12). Normally, if the pipe support spacing is kept short, the pipe is securely tied down, the support spans are not unifoiTn in length, and fluid pulsations have been adequately dampened, mechanical pipe vibrations will not be a problem. It is good practice to ensure that the natural frequency of all pipe spans is higher than the calculated pulsation frequency. The pulsation frequency is given by ... 

Design suction and discharge bottles for an ethylene compressor. Suction drum is to be sized for an orifice meter a short distance upstream. Discharge drum is to be sized for prevention of piping vibration. 

EveretP discusses pulsation associated with reciprocating compression and presents several points of analysis and diagrams primarily related to the pipe vibration. 

Figure 13-23 suggests recommended pulse level (peak-to-peak) pressure pulsations for acceptable pipe vibration. Figure 13-24 presents allowable machinery and pipe vibration at safe limits and damage levels, and Figure 13-25 presents allowable pressure pulsations for various pipe spans between rigid supports when a 5 mil peak-to-peak vibration is allowed at the center of the pipe spans for the pipe sizes noted. 

Figure 13-23. Recommended pulse level for acceptable pipe vibration (assumes adequate pipe support and anchors). (Used by permission Everett, W. S. Hydrocarbon Procession and Petroleum Refiner, V. 43, No. 8, p. 117, 1964. Gulf Publishing Company. All rights reserved.)...

Group B powders can be troublesome (e g., severe pipe vibrations) if high solids/gas loadings are contemplated. 

However, the PVC powder was tested in a 52 mm internal diameter pipeline, 71 m in length, and found to exhibit unstable plugging in the vicinity of saltation or minimum pressure (i.e., prior to the fluidized dense-phase region). That is, dilute-phase transport was only possible on this test rig. Also, solids/gas loadings were quite low (e.g., max m 20). Note that the unstable plugging was accompanied by sudden increases in pressure and severe pipe vibrations. 

These unexpected results were confirmed by the Group B classification ofDixon (1979,1981), (i.e., could be troublesome in dense-phase and produce severe pipe vibrations). 

For existing equipment a vibration measure survey should be undertaken or examination of piping suspected of being under stress. Critical examination of connection points should be made where the induced piping vibration stress is the greatest. For new designs a stress analysis can be prepared on the pipework by specialized consultants. 

Pipe vibration is caused by f. Internal flow (pulsation)... 

To prevent mechanical pipe vibrations, the pressure pulsation should be less than 3 %. Since the CFM is based on the evaluation of mechanical swinging inside the measuring device, it is sensitive to fluid pulsations with high frequencies (> 50 Hz) [5-6]. At frequencies above 50 Hz no appreciable shares of pulsation should be presented. 

It certainly is desirable to have precise values of Reynolds numbers for laminar, tran.sitional, and turbulent flows, but this is not the case in practice. This is because the transition from laminar to turbulent flow also depends on the degree of dislurbatice of the flow by surface roughness, pipe vibrations, and the fluctuations in the flow. Under most practical conditions, the flow in a tube is laminar for Re < 2300, fully turbulent for Re > 10,000, and transitional in between. But it should be kept in mind that in many cases the flow becomes fully turbulent for Re > 4000, as discussed in the Topic of Special Interest later in this chapter. Wlien designing piping networks and determining pumping power, a conservative approach is taken and flows with Re > 4000 are assumed to be turbulent. 

FRNL < 1.0, PULSE FLOW, and may result in pipe vibration FRNL > 1.0, NO PRESSURE GRADIENT... 

Flow is pulse and this may result in pipe vibration. Line is selfventing. Therefore no vibration problems are expected. Line is selfventing. Therefore no vibration problems are expected. 

FLOW IS PULSE AND THIS MAY RESULT IN PIPE VIBRATION... 

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