Testing vibration diagnostic method to detect fastening defects due to slackening

BACKGROUND: One cause of increased vibration in rotary equipment is the loss of clamp load between the bearing assembly and the foundation caused by fastening defects, including thread wear, slacking, corrosion, metal fatigue, etc. Such defects lead to increased vibration, reduced equipment performance, and its early wear. To prevent such negative effects, a method is used in vibration monitoring to identify defects in fasteners based on the analysis of factors; however, available sources indicate that there are no differentiated approaches to various types of fastener defects. AIM: The article examines the performance of this method to identify fastening defects occurring due to slacking of the fastener that connects the bearing bracket leg to the foundation. MATERIALS AND METHODS: There is no experimental data to support the performance of this method in identifying specific defects within the general category. The article examines the possible use of a vibration diagnostic method based on the analysis of factors to identify fastening defects caused by slacking of fastening screws. The study includes an experimental validation of the method based on the analysis of factors, i.e. the ratio of overall structure vibration of the bearing assembly and the foundation. RESULTS: During the experiments, the root mean square (RMS) value of vibration velocity was measured in three planes on various components of AP7000 simulation test bench using SD-21 analyzer and AP40 vibration sensor. The data were used to calculate factors characterizing the fastening health. The most insightful factors to identify defects in fasteners of rotary equipment include those calculated as the ratio of the bearing housing RMS to the foundation RMS in horizontal and vertical planes and the ratio of the bearing bracket leg RMS to the foundation RMS in the vertical plane. Only these factors allow to reliably identify fastening defects when the fastening screws are loose. CONCLUSIONS: The results confirmed that the considered method is useful in identifying fastening defects caused by screw slaking.