Pulsating pipes

Shemer, L., Investigation of the Turbulent Characteristics of a Pulsating Pipe Flow, Ph.D. thesis, Tel-Aviv University, Tel-Aviv Israel (1981). 

A. Z., 2002. Convective heat transfer characteristics of laminar pulsating pipe air flow. Heat Mass Transfer, 28(3) 221-232. 

A pulsating pipe penetrating a non-watertight bulkhead should be passed through a cut hole 1.3 cm (0.5 inch) oversize, and the clearance sealed with a sealing compound. 

Space needs to be provided for the auxiliaries, including the lube oil and seal systems, lube oil cooler, intercoolers, and pulsation dampeners. A control panel or console is usually provided as part of the local console. This panel contains instmments that provide the necessary information for start-up and shutdown, and should also include warning and trouble lights. Access must be provided for motor repair and ultimate replacement needs to be considered. If a steam turbine is used, a surface condenser is probably required with a vacuum system to increase the efficiency. AH these additional systems need to be considered in the layout and spacing. In addition, room for pulsation dampeners required between stages has to be included. Aftercoolers may also be required with knockout dmms. Reference 8 describes the requirements of compressor layouts and provides many useful piping hints. 

Software packages are commercially available for simulation of hydrauhc transients. These may be used to analyze piping systems to reveal unsatisfactoi y behavior, and they aUow the assessment of design changes such as increases in pipe-wall thickness, changes in valve actuation, and addition of check valves, surge tanks, and pulsation dampeners. 

Flow Low mass flow indicated. Mass flow error. Transmitter zero shift. Measurement is high. Measurement error. Liquid droplets in gas. Static pressure change in gas. Free water in fluid. Pulsation in flow. Non-standard pipe runs. Install demister upstream heat gas upstream of sensor. Add pressure recording pen. Mount transmitter above taps. Add process pulsation damper. Estimate limits of error. 

Nimitz, Walter W., Pulsation and Vibration, Part I. Causes and Effects, Part II. Analysis and Control. Pipe Line Industry, Part 1, August 1968, pp.. 6-79. Part II, September 1968, pp.. 19 2. 

Safriet, B, E., Analysis of Pressure Pulsation in Reciprocating Piping Systems by Analog and Digital Simulation, ASME 76-WA/DGP-3, New York, NY American Society of Mechanical Engineers, 1976. 

Screw compressors of the dry type generate high frequency pulsations that move into the system piping and can cause acoustic vibration problems. These would be similar to the type of problems experienced in reciprocating compressor applications, except that the frequency is higher. While volume bottles will work with the reciprocator, the dry type screw compressor would require a manufacturer-supplied proprietary silencer that should take care of the problem rather nicely. 

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... 

When a cylinder end is deactivated, the pulsation levels in the piping system can increase significantly. If a cylinder may be operated with... 

Because of the reciprocating action of the piston, care must be exer-ci.sed to size the piping to minimize acoustical pulsations and mechanical vibrations. As a rule of thumb, suction and discharge lines should be sized for a maximum actual velocity of 30 ft/.sec (1,800 ft/min) to 42 ft/sec (2,500 ft/min). Volume 1 contains the necessary formulas for determining pressure drop and velocity in gas piping. 

For smaller, high-speed compressors the piping sizing rules of thumb discussed above, in conjunction with pulsation bottles sized from Figure 11 -24, should be sufficient for individual field compressors. These niles of thumb can also be used for preliminary sizing of piping and bottles in preparation for an analog study. 

Pipe length from scrubber to suction pulsation dampeners... 

Pipe length from discharge pulsation dampeners to cooler... 

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 ... 

Never use malleable iron fittings or pipe unless the fluid is nonhazardous and the pressure not greater than 25 psig. Always use a pressure rating at least four times that of the maximum system pressure. t lso, never use cast iron or malleable iron fittings or valves in pressure pulsating systems or systems subject to physical shock. 

A general appreciation of some of the effect of gas pulsation on the performance and impact on the compressor pulsation drums, their nozzles, the piping system, and the cylinder valve performance, as well as possible other effects in some unique systems or items of equipment, can be discovered by examining the cylinder performance using an indicator card. This examination (see Chapter 12) can reveal acceptable and unacceptable performance in terms of pressure variations within the cylinder as the piston passes through its cycle. Hicks presents a helpful analysis see Figures 13-3 and 13M. 

Figure 13-6A. Influence of pulsations on valve behavior. (Used by permission Compressor and Piping System Simulation, Southern Gas Association s Gas Machinery Research Council.)...

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. 

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

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