Consulting Services/Expertise/Pulsation Analysis

API 674 Analysis For Reciprocating Pumps

Pulsation analysis for reciprocating pumps (according to API 674) and centrifugal pumps

Reciprocating and centrifugal pumps are used to raise the pressure of a liquid medium. As with compressors, the oscillations from a reciprocating pump or the blade passing of a centrifugal pump will lead to pulsations in the flow upstream and downstream of the flow. The vibrations and dynamic loading due to these pulsations can lead to excessive loading and fatigue issues in the piping.

Dynaflow Research Group (DRG) can offer a complete range of solutions to assess how critical a pump is for the operation of your system. Our assessments can be used to assess a concept at the design stage or to solve a pulsation issue observed during operation.

The API 674 Design Code for Reciprocating Pumps

Typically reciprocating pumps will lead to significantly larger amplitude pressure pulsations than centrifugal pumps. Within the industry-standard API 674 design code, it is stated that the piping around a reciprocating pump should be analyzed to ensure that the piping is capable of withstanding the pulsations. For bespoke systems, where an identical version is not already in operation, this assessment should take the form of a calculation.

The API 674 design code provides guidelines for acceptable pulsation levels in the piping connected to a reciprocating pump.

If the pulsation amplitude remains within these levels, then experience has shown that the dynamic stress levels within the piping will not lead to fatigue issues.

The allowable pulsation amplitude according to the API 674 is dependent on the frequency. Thus, to determine the suitability of a system, it is necessary to assess all of the pump harmonics individually using a discrete Fourier analysis.

API 674, Flow station, pulsation studies
API 674, CFD, Computational Fluid Dynamics, Pulsation Analysis

Computational Fluid Dynamics

To reduce pulsation levels at the exit of a pump to within the allowables according to the API 674, it can be useful to understand the cause of the pulsations within the pump. This level of detail requires the analysis to go beyond a one-dimensional analysis and instead, the complete 3-dimensional flow field needs to be resolved within the component.Through an understanding of the 3-dimensional flow and thermal fields, design changes and strategies to improve the component efficiency and reduce the pulsation amplitudes can be evaluated.Computational Fluid Dynamics (CFD), in which the governing equations of fluid flow are solved numerically, is a highly cost-effective tool to enable the designer to decipher the flow field and evaluate the impact of their design changes. CFD offers the designer of pumps and compressors, as well as other flow components, the opportunity to reduce their component development costs.A CFD study, given the approximations in the analysis, is not a straightforward undertaking. DRG, with extensive experience in using CFD for industrial applications, is capable of helping you take advantage of CFD in the design of your pump or compressor.

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Case Study: Removing Vibrations in a Flow Station

Dynaflow Research Group (DRG) was asked by one of our clients to reduce the excessive, potentially fatigue-inducing, vibrations they were observing at one of their oil flow stations. These were seen in the suction and discharge headers for the reciprocating pumps, and the pump recirculation line.

To find the cause of the observed vibrations and to determine what measures were required to rectify the problem, DRG performed a pulsation analysis combined with a mechanical response analysis. DRG worked with the client to obtain the information necessary to build a model of the system piping using the CAESAR II piping stress software. This model was used first to perform a scoping static stress assessment to verify if the existing pipe-supporting design was adequate.

To perform the pulsation analysis, a model of the fluid path within the flow station was then generated in BOSpulse. Here pulsations, according to the maximum amplitudes given in the API 674 design code, were applied at the location of the pumps. Using BOSpulse it was possible to calculate the pressure amplitudes within the downstream piping and determine if any acoustic resonance modes were being excited.

The pulsations due to the reciprocating pumps led to unbalanced forces within the piping system. These forces were used as an input for the mechanical response study. As a result of the analysis, it was found that the observed vibrations were likely to cause a fatigue problem. Consequently, DRG developed a revised supporting layout to ensure that all the piping could withstand the pulsation levels conforming to the API 674 design code

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