API High Speed Balancing Acceptance Criteria and Pedestal Dynamics

LectureAcceptance criteria for high-speed balancing of turbomachinery are specified in API standards based on either pedestal velocity or shaft displacement. In addition to performing balancing, the measured displacements can also be used for verification of the unbalance response analysis. Since the pedestals are relatively soft, their dynamics need to be considered in the analysis. In this paper, multiple modal tests were conducted on 3 different pedestals. Different torques on the pedestal bolts were used to study the effect on the measured FRFs. The added-mass method was applied to DH7 pedestals. The calculated modal mass and stiffness were compared to values identified from the measured FRFs. Unbalance verification of some shop orders is compared to the predictions with different ways of characterizing the pedestal dynamics: rigid, mass and stiffness, and the FRFs

Torsional Rotordynamics of Machinery Equipment Strings

Short Cours

Predicting, Understanding and Avoiding the Ekofisk Rotor Instability Forty Years Later

LectureThis famous machine is re-examined to assess how well (or not) current design and analytical methods have evolved to avoid shaft whip instability. In addition to reviewing the compressors history and design evolution, the rotordynamic performance of a newly configured machine, based on todays technology, is compared against the original design

Torsional Rotordynamics Of Machinery Equipment Strings

Short CourseOne of the foremost concerns facing rotating equipment users today is that of torsional vibration. In contrast to lateral vibration, torsional vibration is rarely monitored. As a result, torsional failures can be especially heinous since the first symptom of a problem is often a broken shaft, gear tooth, or coupling. In the past, torsional vibration problems were considered to be rare; however the number of torsional field problems has markedly increased recently with the advent of higher power, higher complexity variable frequency drives (VFDs). The increased risk plus the difficulty of detecting incipient failures in the field makes the performance of a thorough torsional vibration analysis an essential component of the turbomachinery design process. There are three primary objectives to this Short Course. First, it will provide users with a basic understanding of steadystate torsional vibrations, their potential for generating problems, and methodologies that are commonly used to analyze and avoid these problems. This portion of the course is aimed at younger, less experienced users, although veteran users will probably also benefit from the review. Second, it will provide users with some understanding of the more complex issues related to transient torsional vibration and acceptance based on stress analysis. Third, it will educate users on how VFDs work, and why they are a concern from a torsional standpoint. This portion will be beneficial to all users since modern VFDs are not well understood, especially by mechanical engineers. The course will be based on practical examples starting from the simple to the complex with some material based on a tutorial the lead author presented at this very show in 1996, Practical Design Against Torsional Vibration. Among the topics that will be discussed include description of torsional vibration, modeling, undamped analysis, Campbell diagrams, excitations generated by various mechanical and electrical components, steady-state and transient analyses, synchronous motor startups, and fatigue life analysis. At the conclusion of this portion, the user should have a good grasp of the fundamentals of this topic. A significant portion of time will be spent on VFDs. Topics covered will include VFD types, excitation frequencies generated by various VFDs, typical excitation amplitudes, control loop instabilities that can lead to problems, coupled electro-mechanical analyses, and design procedures for preventing VFD-related torsional issues up-front. At the conclusion of this course, all users should have sufficient understanding of the relevant concepts so that they should be able to take the proper steps to prevent torsional vibration problems from occurring in their equipment, even when their system contains a VFD

Lubrication: Fluid Film Bearings: Operation, Maintenance, Troubleshooting

Discussion GroupTurbomachinery bearings: Sleeve and tilting pad journal bearings, Thrust bearings, Babbitt bearing failures Bearing upgrades: Clearances, preload, offset, Installation, Oil Specific questions: Journal bearing fit – loose? Line on line? Or some crush?, Discuss API temperature sensor placement:Journal – how many per bearing? Axial locations? Thrust – how many? TPJ No. of pads & orientation – LOP or LBP? TPJ Pivot design Experience with pivot wear? Experience with Ball & Socket pivots? Locking issues? Alarm and shut down values Bearing temperature Rotor movement Varnish experiences? Solutions? Oil types – who is using synthetics and why

API High Speed Balancing Acceptance Criteria and Pedestal Dynamics

LectureAcceptance criteria for high-speed balancing of turbomachinery are specified in API standards based on either pedestal velocity or shaft displacement. In addition to performing balancing, the measured displacements can also be used for verification of the unbalance response analysis. Since the pedestals are relatively soft, their dynamics need to be considered in the analysis. In this paper, multiple modal tests were conducted on 3 different pedestals. Different torques on the pedestal bolts were used to study the effect on the measured FRFs. The added-mass method was applied to DH7 pedestals. The calculated modal mass and stiffness were compared to values identified from the measured FRFs. Unbalance verification of some shop orders is compared to the predictions with different ways of characterizing the pedestal dynamics: rigid, mass and stiffness, and the FRFs

PNEUMATICALLY ACTUATED CONTROL VALVES IN OIL SYSTEMS: HARDWARE RECOMMENDATIONS AND TUNING CONSIDERATIONS

TutorialsWell designed and properly commissioned auxiliary systems are crucial to the reliability of rotating equipment. This paper addresses the upfront hardware selection and commissioning of pneumatically actuated control valves when applied in oil systems. Either improper selection and tuning of these valves or improper system design can cause poor reliability of the oil system resulting in spurious trips that can adversely impact turbomachinery and plant operation. Common problems are addressed

Development and Application of Very High Flow Covered Stages for Process Centrifugal Compressors

LectureFor process centrifugal compressor applications, achieving higher flow rates through a given sized compressor can reduce capital cost while still meeting process requirements. Key technologies for enabling such higher flow rates are high flow coefficient (design ϕ > 0.12) and very high flow coefficient (design ϕ > 0.20) aerodynamic staging featuring covered impellers. Since the 1990s the prevalence of high flow coefficient stages has only increased in LNG, Ethylene, and some other compression services. The overall trend has been towards higher flow coefficient stages that push beyond existing experience limits. Applications involving what can be termed as very high flow (VHF) coefficient staging have only first been applied since around 2010. The present work describes the development and application of a family of very high flow (VHF) stages with nominal design flow coefficient of 0.24 and moderate to high Machine Mach Number (Mu) of 0.88. The design is essentially a constrained optimization where the stage aerodynamic performance (range and efficiency) is optimized while still meeting targets related to mechanical robustness and rotor dynamic usability. The first part of the paper describes the aerodynamic design focusing on the features that help address the aerodynamic performance requirements. As the design flow coefficient increases, both the efficiency and the available stable operating range become further challenged, especially as the inlet relative Mach number increases. The presented aerodynamic stage design solution consists of an impeller with both full and splitter blades having unique features and a return channel system that also features three-dimensional Copyright© 2021 by Turbomachinery Laboratory, Texas A&M Engineering Experiment Station 2 blading, which extends into the cross-over section. Subsequent parts of the paper discuss the mechanical design, single stage aerodynamic rig testing, selection examples, and a case study involving results from a tested shop order

Torsional Rotordynamics of Machinery Equipment Strings

Short Cours

Lubrication

Discussion GroupSuggested Topics: Introduction Plant Wide Maintenance and Problems Effective Maintenance Programs Best Practices Oil Varnish Oil / Grease Type and Selection Testing and Maintenance Including Frequency Mixing and Compatibility Lubrication Systems and Auxiliaries API 614 Systems Oil Mist Systems Grease System