Summary
- Why Pulsations Threaten a Reciprocating Compressor
- Why API 618 Mandates Pulsation Study from Design
- Our Method: Design, Simulate, Validate
- Network Acoustic Simulation, Rather Than an Analytical Approach
Why Pulsations Threaten a Reciprocating Compressor
Pulsations generate dynamic forces on piping. When they encounter acoustic or mechanical resonance, they produce vibrations capable of cracking nozzles, welds, and supports.
A reciprocating compressor intermittently draws in and discharges gas. This chopped flow creates pressure pulsations at the machine’s rotational frequency and its harmonics. These propagate through the network and amplify if a piping length enters into acoustic resonance with one of these frequencies.
At elbows, reducers, vessel heads, and closed ends, these pulsations transform into unbalanced forces. These forces excite the piping and its supports. If a mechanical natural frequency is close, the vibration escalates: fatigue of small nozzles, leaks, breakage, unplanned shutdowns.
Why API 618 Mandates Pulsation Study from Design
API 618 mandates the pulsation study during design because it is the only time when every correction can be made on paper. Once the package is built, corrections cost significantly more.
API 618 is the American Petroleum Institute standard for reciprocating compressors in the petroleum, chemical, and gas industries. Its paragraph 7.9 sets calculation and design requirements aimed at controlling pulsations and vibrations in the compressor and piping system.
In design, there are many levers: volume and internals of pulsation bottles, orifice plates, line routing, support positions. On an already assembled package (compressor, bottles, piping, and auxiliaries on a skid), the same corrections require rework of fabrication, modification of pressure vessels, or adding supports, often at the cost of a shutdown.
Depending on the level of study chosen (DA1, DA2, or DA3), the analysis ranges from pulsation bottle sizing to the mechanical response of the system. We detail these levels in our article on pulsation bottle sizing.
Our Method: Design, Simulate, Validate
SIM Engineering has a dedicated team for API 618 studies. It handles all three aspects of the pulsation study, from damper sizing to mechanical integrity validation.
- Sizing of pulsation dampers. Pulsation bottles and their internals are sized precisely to need. They form the first level of attenuation, closest to the cylinders.
- Acoustic simulation of the complete system. Compressor, bottles, and piping are modeled together. The simulation verifies three criteria: pulsation levels, unbalanced forces, and pressure drop. This last point is important: every added attenuation (orifice, internals) consumes pressure, thus reducing performance.
- Validation of mechanical integrity. The natural frequencies of the manifold and piping are compared to excitation frequencies, then the mechanical response is evaluated to rule out any risk of fatigue.
What this means for you: the pulsation risk is identified and addressed during design, pulsation bottles are sized, the design is validated by simulation, and the package complies with API 618 requirements. Details of our services can be found on our API 618 study page.
Network Acoustic Simulation, Rather Than an Analytical Approach
SIM Engineering is one of the few engineering firms that addresses pulsation through network acoustic simulation. This allows us to locate the actual resonances of your installation, not just those of an isolated bottle.
An analytical approach sizes a pulsation bottle using formulas, independently of the lines surrounding it. It therefore does not detect resonances created by the actual piping layout. Simulation, however, reproduces the acoustic behavior of the complete system. This is why we design our pulsation bottles using simulation, even when the DA1 level only requires an analytical method.
This rigor is based on nearly 30 years of field expertise and on our OPQIBI and MASE qualifications, which authorize our teams to work on industrial sites, including Seveso sites. As an independent engineering firm, we have no equipment to sell: our recommendations aim for compliance with precise needs.
Reciprocating Compressor Pulsation Study: Key Takeaways
A reciprocating compressor pulsation study is not a mere regulatory formality: it’s the assurance that a package will not vibrate upon startup. Conducted during design, it allows for sizing pulsation bottles, verifying the complete network through simulation, and validating mechanical integrity before construction. Do you have a new compressor package to validate? Contact a SIM Engineering engineer during the design phase, when every correction can still be made on paper. Contact Us