Introduction to the PFA Module

What is the PFA Module?

Steady-state pressure and flow dynamics, henceforth referred to simply as “pulsation”, is a common problem, which can cause high vibration, fatigue failures, frequent maintenance outages, and flow uniformity or product quality problems.

The PFA Module helps engineers identify and avoid resonant frequencies in systems. Problems can arise when the frequencies that are excited by pulsation are at or near the acoustic resonant frequencies of a fluid system. The module is used to calculate the acoustic resonance frequencies that could damage system equipment.

The PFA Module can also be used to check compliance with the peak-to-peak pressure limits defined in the API 618 standard for reciprocating compressors.

How Does the PFA Module Work?

The Pulsation Frequency Analysis (PFA) module is used to determine resonant frequencies that could damage system equipment by calculating the acoustic resonance.

The general steps of pulsation analysis involve the following:

The piping and process equipment system is first modeled.
At run-time a pulse is generated to determine excitation frequencies, and generate the forcing function. This forcing function is then placed in the transient data of the junction at which the pulse is applied.
The model is run with the forcing function to generate the Acoustical Frequency Analysis graph, providing information on the resonant frequencies in the system.
Replace the pulse transient with a transient at the frequencies of interest in the reciprocating compressor and turn on the API 618 evaluation option.
When the model is run xStream will show warnings if API 618 is violated.

Using the PFA Module

The user has the option of activating or not activating the PFA module when AFT xStream first loads. After AFT xStream is loaded, the PFA module can be activated or deactivated for use from the Tools menu. Whether or not PFA is activated impacts the Analysis menu and Graph Results window.

If the PFA module is active, the user can still run models without pulsation. This is selected under Pulsation Frequency Analysis on the Analysis menu. Hence there are three possibilities for the PFA module.

PFA is not active
PFA is active and pulsation is disabled
PFA is active and pulsation frequency analysis is performed