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API 618 – 619 and AIV-FIV studies

Pressure pulsations are generated by the reciprocating motion of the compressor piston and are amplified or weakened by the acoustic response of the piping system. Pressure pulsations produce oscillating forces that are called unbalanced forces. These forces, applied to a more or less flexible pipe system, generate vibrations that can lead to fatigue failure when the cyclic stresses are too great.

Other problems are also linked to pulsations: compressor performance, inaccuracies in flow measurement, the behaviour of non-return valves and safety valves, etc.

What are the applications ?

Air handling and ventilation system inlets and outlets

Machine acoustics (air conditioning, ventilation, etc.)

Pulsation and vibration

The pulsatory study

During the acoustic study, pressure pulsations and unbalanced forces are controlled using the following techniques:

Acoustic filters such as empty volume or volume with internals
Frequency separation by optimising pipe cross-sections and/or lengths
Addition of resistive elements such as orifice restrictions

In accordance with API 618, the acoustic study provides information on :

Pulsating pressure
Unbalanced forces induced by pulsations
Pressure losses
Flow and power deviations

Study of mechanical response

The mechanical response study helps to optimise vibration and cyclic stress conditions by improving the design of pipe and boilerwork supports.

In accordance with API 618, the mechanical study provides information on :

Natural frequencies
Forced response vibrations and cyclic stresses