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Digital Acoustic Pulsation Analysis

Digital pulsation analysis applies to any positive displacement pump or compressor. Many pumps and compressors are purchased with pulsation dampening equipment to reduce the pulsation levels. When these are selected by the pump/compressor supplier or damper manufacturer, general sizing rules are used based on desired pulsation levels. However, as suggested by API 618 and API 674, these sizing rules don't have the ability to consider the acoustical response of the header/manifold or the associated plant piping system. These acoustical responses can easily amplify the pulsation amplitutes to dangerous levels.

One of the main benefits of digital acoustic pulsation analysis is to guarantee that the fluid pumping system can operate safely over possibly variable speed ranges or with different fluids. Properly designed systems result in fewer pump failures and greatly reduce the failure of pump valves. In addition, piping vibration is limited to known safe values as provided in a number of enginering standards.

API 618 Digital Pulsation Studies

API 618 is a common design specification referenced for reciprocating compressors designs. This standard includes descriptions of the various design approaches that are available for reciprocating compressors.

For Design Approach 2 studies, we use digital pulsation modeling software to calculate the pulsation forced responses. This tool allows modeling of a number of reciprocating compressor cylinders with a range of compressor characteristics and cylinder timing. Once an acceptable acoustical design has been finalized that meets customer requirements and/or API pulsation criteria, basic calculations are used to determine maximum piping spans and verify that vessel natural frequencies are above a safe limit.

Design Approach 3 studies are similar to Design Approach 2 studies, except that a detailed mechanical models are used to calculate the natural frequencies and forced response of the compressor cylinder, compressor pulsation suppresion devices, and associated piping. We use ANSYS to create finite element models of the compressor cylinder and compressor pulsation devices. Finally, we use Bentley Systems AutoPIPE to model the piping system response. Using all of these tools effectively proves the most realistic model of a reciprocating compressor's acoustic and mechanical dynamic response.

API 674 Digital Pulsation Studies

API 674 is a common design specification referenced for reciprocating plunger and diaphragm pump pulsation designs. This standard includes descriptions of the various design approaches that are available for reciprocating pumps. Kelm Engineering, LLC performs a number of Design Approach 1 and 2 studies for a variety of OEM’s and end users. For the API 674 methods, the common equipment analyzed is limited to reciprocating plunger and diaphragm pumps. We have modeled a wide range of fluids including molten sulphur, liquid nitrogen, water, oils, numerous hydrocarbons, ammonia, etc.

For Design Approach 1 studies, we use a variety of proprietary acoustical design tools as well as simplistic acoustical response analyses to review damper selection for proper sizing. Piping system supports and natural frequencies are estimated and reviewed based on the layout of the piping system.

For Design Approach 2 studies, we use digital pulsation modeling software to calculate the pulsation forced responses. This tool allows modeling of a number of reciprocating pump cylinders with a range of pump characteristics and cylinder timing. Once an acceptable acoustical design has been finalized that meets customer requirements and/or API pulsation criteria, the calculated pulsation amplitudes are transferred to Bentley Systems AutoPIPE for evaluation of piping system natural frequencies and forced responses.