Measuring and Modeling Vertical Crosshead Vibration in API-618 Reciprocating Compressors
Abstract
Reciprocating compressors constructed to API-618 standards find application in refineries, petrochemical plants, and pipelines around the world. These compressors are constructed with a force-fed lubricated crosshead that drives a double-acting piston via a piston rod. Looseness in the running gear (piston assembly, connecting rod assembly, and crosshead assembly) results in knocks (impulse events) that are usually detected at the crosshead guide with accelerometers and, in some cases, with proximity probes measuring the piston rod vibration at the pressure packing case. Crosshead guide accelerometers have proven successful in detecting and preventing catastrophic failure; however, the alarm set points for the vibration levels have been derived heuristically because no model exists that relates forces and impacts within the running gear to the vibration of the crosshead guide. This paper presents a model of the crosshead system that estimates the vibration response of the crosshead and crosshead guide in reaction to the forces and impulses in the running gear. The model incorporates the oil-film behavior including non-linear, position-dependent stiffness and damping. The paper also examines the system response in the time domain and the complex plane (eigenvalue migration). The numerical model results are validated by comparison with data acquired on operating machines in known conditions of distress. The results show good agreement between the model and crosshead and piston rod vibration data, both in the timing and amplitude of vibration. Using the results of the model and historical data collected from operating reciprocating compressors the paper concludes with guidelines for filtering of crosshead accelerometer signals and alarm thresholds.
Description
LectureSubject
TurbomachinesCollections
Citation
Howard, Brian; Hatch, Charles; Yonker, Gregory; Philips, Kevin (2015). Measuring and Modeling Vertical Crosshead Vibration in API-618 Reciprocating Compressors. Turbomachinery Laboratories, Texas A&M Engineering Experiment Station. Available electronically from https : / /hdl .handle .net /1969 .1 /162188.