API674 and API618 are both specifications issued by the American Petroleum Institute that cover the examination of piping systems for pressure pulsation and mechanical response (modal vibration). attached to reciprocating power pumps API674 covers power pumps dealing with liquids, whilst API618 deals with gas compressors.
In both specifications pressure pulsation analysis means the examination of the piping system for resonances and harmonics of the frequency at which the pump, or compressor, discharges slugs of liquid, or gas, into the piping system.
Whilst mechanical response means the examination of the piping system for its modal, or frequency response, sometimes referred to as natural frequency and the higher order modes of vibration. The mechanical response analysis is not just a dry simulation of a hammer, or knock, test to find the natural frequency of a piping system, but rather it is a full simulation including fluid in the piping, temperature effect and most importantly dynamic forces from the pulsation simulation.
Historically such analysis work was done using hand calculation methods, empirical formulae, nomogram charts as well as experience to establish the pumping frequency of the pump and then determine the natural frequency of the piping spans. Where the piping spans were found to have a low natural frequency then supports would be added, moved or deleted to achieve a suitable natural frequency for the system.
In addition to this similar techniques were used to examine the suction and discharge pressures to ensure that problems with acceleration head in the suction lines, or excessive pulsation in the discharge line do not cause problems either with the operation of the pump, or the operation of any PRV's on the line.
Today, whilst the task remains the same the advent of powerful laptop computers and user friendly software for both pressure pulsation within the pumped liquid, and mechanical analysis of structures has enabled greater detail modelling, usually in 3D, of piping structures and faster analysis.
API674 draws on this history, whilst at the same time considering the analysis techniques currently available and defines what must be examined, the way in which this may be done, and the expected minimum standards that must be achieved.
Flo-Dyne is able to offer full compliance with the requirements of API674, from empirical analysis to full computer aided analysis of the pressure pulsations, the mechanical response, and how they interact together.
Our analysis work has included pumping systems with multiple pumps, pumping glycol, oils, water and other hydrocarbons for both pressure pulsation analysis and mechanical response.
Not all examinations require the installation of a pulsation control measures, however where it is found that such equipment is necessary we may propose our own equipment, or if we cannot build what you need then we will provide sufficient generic information for you to procure the equipment on the open market.
When appropriate we offer site measurement services where we visit site, take pressure pulsation measurements and vibration readings, and cross refer these against our simulations.
Such site visits can be done simply as a before visit, to provide initial data to benchmark the simulation, or we can visit after the installation has completed to verify that the pulsation and vibration levels are as expected.
We are able to cross-refer our mechanical simulations as we run both Intergraph and Bentley software, to give added assurance that the mechanical analysis is correct.
Our engineering team has over 100 years of experience to call on, with our lead engineer having over 25 year of experience in pulsation control.
