Pulsation Analysis - Practical solutions for systems to last the long term

28 August 2026 by Elise Phoenix

A reciprocating compressor does not deliver gas as a steady flow. It delivers it in pulses, producing excitation at the running speed and its harmonics, with the relative magnitude of those components influenced by the compressor design and operating conditions.

These pressure waves travel into the connected pipework, and where the frequency of the pulsations coincide with an acoustic resonance in the system, the amplitudes grow. The resulting shaking forces act on bends, tees and closed ends, with the potential to excite mechanical natural frequencies in the piping system.

The consequences can be excessive vibration, fatigue failure, reduced compressor efficiency and accelerated valve wear.

For compressor manufacturers and engineering contractors, an early pulsation study reduces the risk of late package changes, fabrication rework, commissioning delays and costly responsibility disputes once the system is on site.

Spectrum Fluid Dynamics are specialists in pulsation analysis and we have undertaken over 550 pulsation studies over the last 35 years.

New build compressors: resolving the problem before anything is fabricated

For new compressors purchased to API 618, the pulsation study is an essential design tool. It identifies where the pulsation response in the proposed arrangement exceeds the standard’s limits while the design can still be changed.

Pulsation dampeners are the first line of defence, and the pulsation study will check the performance of the proposed vessels before moving onto the main study.

Spectrum’s own well established PIPAC® software predicts dynamic pressures and forces in complex connected pipe systems. Pulsation levels and net shaking forces are reviewed throughout the pipework, with particular attention paid to sensitive locations including pressure relief valves, non-return valves and flow meters. Pulsation levels at the cylinder flanges are checked separately, to protect the compressor valves and limit the effect on compressor efficiency.

The second part of the main pulsation study is mechanical analysis. Mechanical natural frequencies of the pipework system are calculated using the ANSYS finite element software, followed by a forced response analysis that predicts vibration and stress levels under the residual pulsation forces.

Paul Scourfield, Director of Spectrum Fluid Dynamics, comments,

“The serious problems occur when a mechanical natural frequency coincides with a frequency where there is significant pulsation energy. That is why both halves of the study matter. Pulsation levels within the API limits can count for nothing if the pipework responds at the same frequency.”

Where predicted vibration levels are too high, the cause is frequently an insufficient number of pipe supports, or supports that do not provide enough restraint. The support structure stiffness is also important. Pipework carried at height on beams will move with the structure if that structure is not stiff enough, even if there are a sufficient number of pipe supports.

”Part of our job is choosing practical solutions that a client can actually build,” Paul Scourfield says. “Changing the length of a pipe run has consequences for layout and for the process. Changing the diameter of a section of pipe can achieve a similar result with less disruption. When adding pipe supports to reduce vibration levels consideration has to be given to the impact on thermal expansion and stresses. It is often a compromise, and we work through it with the piping designers to find a solution that works in practice.”

Revamp studies: when system changes can invalidate the assumptions in the original study

A pulsation study is only valid for the system it was carried out on. Plenty of installations now operate well outside the conditions they were assessed against.

Revamp studies are necessary when systems are changed. Gas composition or operating conditions change, which moves the acoustic response of the whole system. Pipework is rerouted or extended. An additional compressor is installed, an existing machine is modified, or a cylinder design is changed. Control systems are upgraded, and while stepless unloading systems in particular give operators far better control over capacity, they can introduce significant pulsation problems.

Existing acoustic and mechanical models from previous studies are retained and can be adapted for revised operating conditions and piping systems.

“Often, clients tell us the pipework has not changed, so they assume the original study still stands,” Paul Scourfield says. “However, if the gas has changed, the acoustic response has changed. And re-evaluating with a revamp study before any modifications are committed costs far less than dealing with vibration on a live plant afterwards.”

Troubleshooting: measuring what the system is doing

Where vibration is already a problem on site or some pipework has failed in service, the work starts with measurement rather than modelling.

Spectrum Fluid Dynamics can attend site (often at short notice if resource is available) and measure vibration levels on the pipework and the compressor itself, using equipment including the SVAN 958 vibration analysis system.

The measured data is assessed against recognised standards and guidance including ISO 20816-8:2018 and the European Forum for Reciprocating Compressors guidelines. Acoustic and mechanical models of the system can then be built to develop and test a solution before anything is installed.

Typical outcomes are additional pipe supports, modifications to existing supports or support structures, and orifice plates to detune internal acoustic resonances.

Paul Scourfield comments,

“Often high vibration levels on site are caused by systems not being installed or designed correctly. For example, orifice plates haven’t been installed, pipe supports have been omitted or have been wrongly installed such that they are not providing the required dynamic restraint. There is no substitute for visiting site and seeing the system in operation, to identify the root cause of the problem.”

Case Study

Three reciprocating compressors installed at a refinery in India in 2004 were modified eleven years later to increase capacity.

Spectrum undertook analysis to review the pulsation response under the revised process conditions, acoustically and mechanically, and visited site before the work to measure vibration on the pipework and record baseline levels.

A flexibility study to ASME B31 assessed the effect of the revised conditions on pipework stress and vessel nozzle loads.

Click here to read more case studies

Why work with Spectrum Fluid Dynamics for your pulsation study

Spectrum Fluid Dynamics has undertaken over 550 pulsation studies over the last 35 years, for the majority of the world’s main compressor manufacturers and many of the leading engineering contractors and oil companies. Site troubleshooting has also been carried out worldwide.

For compressor manufacturers and engineering contractors, Spectrum Fluid Dynamics can support the system at every stage – design-stage API 618 pulsation studies for new packages, reassessment before a revamp is committed, and measurement-led troubleshooting when vibration is already affecting operation.

If you have a new compressor package in design, a revamp in planning, or a system that is already vibrating, we can help. Contact our team on 01767 318871, by email at enquiries@spectrumacoustic.com, or through the contact form on our website.