왕복동 펌프의 맥동 설계 기준 (Pulsation Study, API 674)

왕복동 펌프의 맥동 설계 기준 (Pulsation Study, API 674)

 

왕복동 펌프(Reciprocating Pump)의 Pulsation study 진행 시 고려되는 설계 기준은 API 674에 언급되어 있는 Pulsation level, Cavitation, Pressure reliev valve 설계 사항을 검토합니다.

 

 

 

* API 674 3rd 2010, Positive Displacement Pumps-Reciprocating

 

1. Maximum Allowable Pulsation Levels

For Analysis Approach 1 or 2, the peak-to-peak pulsation levels in the suction and discharge piping systems beyond the pulsation control devices shall not exceed the levels calculated by below Equation, which specifies the allowable peak-to-peak pulsation level of each individual pulsation frequency component.

 

 

- P1: the maximum allowable peak to peak pulsation level of the individual pulsation frequency components, expressed in kPa (psi), (suction and discharge pulsation levels also must be limited to values that will not cause cavitation or relief valve lifting),

- ID: the inside diameter of line pipe, in millimeters (in.)

- f: the pulsation frequency, in Hertz, derived from the following equation

 

 

- RPM: Pump speed

- n: corresponds to the fundamental frequency and harmonics of the pump speed.

 

 

 

 

[ Pulsation Study, Reciprocating Pump ]

 

 

 

2. Inlet Pressure versus Liquid Vapor Pressure

Unless otherwise specified, the minimum value of the suction complex pressure wave Pmin at the inlet reference point shall not be lower than the highest liquid vapor pressure with a margin of 10 % as shown in below Equation.

 

Pv: the highest liquid vapor pressure or the gas dissolution pressure, expressed in kilopascals (pounds force

per in.2.

 

[ Cavitation Review, Suction Pipe ]

 

 

3. Pressure-Limiting Valve Protection

Unless otherwise specified, the margin of separation between the positive peak of the pulsation complex wave at the relief valve and the relief valve setting shall be 5 % of the maximum specified discharge pressure or 165 kPa (25 psi), whichever is greater.

 

- Pd: the maximum specified value of average discharge gauge pressure, expressed in bar (psi);

- Pp: the positive peak of pulsation complex wave, expressed in bar (psi).

- Prv: the required relief valve setting in gauge pressure, expressed in bar (psi).

 

[ PSV Set-pressure Review ]

 

 

 

4. Separation Margin Requirement for Piping Systems

Unless otherwise specified, to ensure that separation requirements are met, both of the following guidelines are to be used together to avoid coincidence of excitation frequencies with mechanical natural frequencies of the pump, pulsation suppression devices, and the piping system.

 

1) The minimum mechanical natural frequency of any manifold or pipe system element shall be designed to be greater than 20 % above the significant frequency of the unbalanced forces and cylinder stretching loads (RPM x Number of Cylinders) plus the inertial loads at 1 and 2 times RPM. In certain pump configurations, there can be significant excitation energy at higher orders of running speed and the system design shall take this into account. When the minimum mechanical natural frequency guideline is not met, or when there is significant excitation energy at higher orders, the separation margins as defined in 2) shall be maintained.

 

NOTE The intent is to prevent the mechanical natural frequencies of the piping system being excited by forces generated by the pump.

 

[ Separation Margin Review for Piping System ]

 

2) The predicted mechanical natural frequencies shall be designed to be separated from significant excitation frequencies by at least 20 %.

 

NOTE The intent is that at least 10 % separation for the actual system is achieved and, due to modeling limitations, if 20 % is used for predicted designs, then 10 % for the actual system will generally be attained.

 

 

 

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