Consulting Services/Expertise

Pulsation Analysis

Pulsations, caused by reciprocating equipment, such as pumps and compressors, are a common cause of vibrational problems in piping systems. Reciprocating equipment and to a lesser extent positive displacement equipment, cause a pulsating flow in the system that can cause the system to vibrate. Several API standards from the American Petroleum Institute can be used to ensure that the vibrating system does not exceed any limit that can cause failure in the system. API 674 concerns reciprocating pumps, API 675 positive displacement pumps, API 618 reciprocating compressors, and API 688 positive displacement compressors.

A pulsation analysis typically consists of a damper pre-study or damper check, acoustic simulation, and a mechanical review. To avoid vibrational problems in your reciprocating system, good system design is key and here DRG can be your perfect partner.

Design analysis per API 674 / API 675

The API 674/675 code for reciprocating pumps provides two different design approaches. Depending on the requirements of the client, the most suitable design approach can be conducted.

  • Design Approach 1 of API 674 sets limits on pulsation levels (C.1.5), minimum pressure (C.1.6), and maximum pressure (C.1.7). Conformance with these criteria is meant to be shown through empirical techniques. The mechanical review is limited to good design principles and empirical data. Empirical data is often not available, which limits the applicability of design approach 1. This also applies to API 618/688 for compressors.
  • Design Approach 2 of API 674 also sets limits on pulsation levels (C.1.5), minimum pressure (C.1.6), and maximum pressure (C.1.7). In design approach 2 the conformance with these criteria is shown through an acoustical simulation. In addition, a mechanical review of the piping system including restraints is included. The piping system mechanical analysis is performed using span tables and a modal analysis of the piping system.
    Beyond the coverage of API 674, design approach 2 can be extended with a forced mechanical response study. In that case, the piping with restraints and supporting steel is included in a piping analysis. A forced mechanical response study may be required when the frequency separation criteria of the API cannot be met.

The design approaches according to API 618 and API 688 for reciprocating compressors are similar to the design approaches in API 674/675. Design approach 2 of API 618/688 however only includes an acoustic simulation. The modal analysis and forced mechanical response (when necessary) are included in design approach 3 of API 618/688.

Benefits

+35 years of experience

DRG has more than 35 years of experience and knowledge of all the code vibration rules and mechanical response studies.

In-house software solutions

DRG uses an in-house developed software package BOSpulse to conduct acoustic simulations and mechanical reviews according to API.

Applications

DRG can assist in the design of dampers and Pulsation Suppression Devices (PSD). The acoustical performance should be determined at an early stage in the design of the system to prevent unnecessary and costly changes to the PSD at a later stage in the project.

The acoustical performance will be determined through modeling of the pump or compressor and damper in BOSpulse without explicitly including the connected piping system.

This way the damper can be efficiently designed to avoid excessive pressure peaks or cavitation problems at a later stage in the design. This is done through damper layout and volume calculations. Both gas-filled (pre-charged) dampers and liquid-filled dampers can be considered for the analysis.

The mechanical performance of the damper from both a static and dynamic perspective can be included. The mechanical design is done using Finite Element Analysis according to the applicable code (ASME VIII division 2 or EN13445).

Application 1 - pulsation damper

An acoustic simulation can be performed with our in-house developed pulsation analysis package BOSpulse. The acoustic analysis covers all possible operating conditions including changes in temperature, pressure, pump speed, pump operation, and changes in suction/discharge lines.

At the start of the analysis, a pre-study of the damper and pump is conducted, neglecting the effects of the connected piping. This allows for an initial verification of the damper’s performance and can prevent project delays due to changes to the damper at a later stage in the project.

The acoustic simulation then covers all piping from the pump up to an appropriate boundary condition and includes the damper and potential other inline equipment such as filters. The appropriate boundary conditions will be determined in consultation with the client. Boundary conditions can include large-diameter vessels, injection locations, or long gas transportation lines.

The acoustic simulation seeks to capture the acoustic interaction between the reciprocating equipment, damper, and associated piping. It also considers pulsation effects on the equipment and acoustic shaking forces in the damper.

Required changes for conformance with the API 674 / API 675 or API 618 / API 688 limits, when applicable, are discussed in close consultation with the client. 

The mechanical review is part of most pulsation analyses. Both the separation margin check and the forced mechanical response analysis can be performed by DRG.

The separation margin check is conducted using span tables or a modal analysis of the system. The span tables contain a list of the maximum restraint span per pipe diameter based on the separation margin requirements from API. The maximum allowable span is based on the maximum operating speed of the reciprocating equipment.

In a forced mechanical response analysis, in the acoustic simulation, calculated shaking forces are applied to the system using the ANSYS plugin in BOSpulse to evaluate the vibration levels and fluctuating stress levels.

During commissioning or after changes to the operating conditions, operational vibration levels may become critical because the Eigenfrequencies changed and moved closer to the excitation frequencies. In these situations, DRG supports its clients using a high pace vibration assessment, root cause analysis, and mitigation. A client-specific approach is proposed typically including vibration measurements and acoustic and mechanical simulations. 

Conducting these in sync means DRG can quickly determine whether the system is safe to operate or at risk of failure with continued operation. The root cause, whether acoustic or mechanical, of the vibrations can also be resolved quickly. Finally, DRG can propose the most effective way to mitigate the vibrations based on the acoustic and mechanical simulations.

Application 2 - mechanical review

Discover how we can support your Pulsation Analysis related projects

Software Solutions For Pulsation Analysis

BOSpulse

Our in-house developed professional software solution BOSpulse is a comprehensive software solution for performing pulsation analyses of piping systems involving reciprocating equipment such as reciprocating compressors (API 618) and reciprocating pumps (API 674).

It enables engineers to model both common and custom reciprocating equipment and the attached piping, perform pulsation analyses, check the results against the allowable pressure and shaking force amplitudes prescribed by the API standards, and assess the impact of the shaking forces on the structural response of the piping system.

Learn more about BOSpulse