Guidelines in Pulsation Studies for Reciprocating Compressors

While new gas compression in pipeline service tends to be dominated by centrifugal machines, reciprocating compressors still have a significant place in the industry. Specific dynamic design is required to ensure reliable and efficient operation of all reciprocating compressor installations. This requirement is particularly significant in pipeline installations, because the compressor is intended to be in service for many years, and because high efficiency is important for economic reasons. It is widely recognized that the design of these types of installations should include a “pulsation study”. A pulsation study involves analysis of the proposed installation to predict pulsation, vibration, and stress levels. Further, a pulsation vibration control scheme is developed as part of the overall design. The objective is to ensure that predicted pulsation and vibration levels meet guidelines while limiting associated pressure drops and horsepower losses to acceptable levels. Various guidelines have been used in these studies, but the most commonly used standards are in API 618. While this standard was not originally intended for pipeline service, in reality it represents the best design standard available for high specification reciprocating compressor installations in any application. Recently, work has been done to upgrade the API 618 design standard. One of the changes in the proposed new 5th edition is the addition of unbalanced force guidelines to the existing pressure pulsation guidelines. Much discussion occurred regarding the need for and the advisability of making the addition. Real examples show designs in which a reduction of pressure pulsation is accompanied by an increase in unbalanced forces, illustrating the need for an unbalanced force guideline. It is also shown that problems can occur due to unbalanced forces in parts of the piping system not currently addressed by the pulsation guidelines in API 618. The paper compares the current 4th Edition versus the draft 5th Edition. Comments are made on the applicability of the various guidelines. While API 618 is the best available design document, the addition of force guidelines will help API 618 do a better job for industry.