A curious nucleus

AbstractI describe a simple construction that assigns a pre-nucleus and associated nucleus to each frame. The nature of this nucleus appears to measure the subfitness properties of the parent frame. I pose a few questions concerning this pair

Cast iron-base alloy for cylinder/regenerator housing

NASACC-1 is a castable iron-base alloy designed to replace the costly and strategic cobalt-base X-40 alloy used in the automotive Stirling engine cylinder/generator housing. Over 40 alloy compositions were evaluated using investment cast test bars for stress-rupture testing. Also, hydrogen compatibility and oxygen corrosion resistance tests were used to determine the optimal alloy. NASACC-1 alloy was characterized using elevated and room temperature tensile, creep-rupture, low cycle fatigue, heat capacity, specific heat, and thermal expansion testing. Furthermore, phase analysis was performed on samples with several heat treated conditions. The properties are very encouraging. NASACC-1 alloy shows stress-rupture and low cycle fatigue properties equivalent to X-40. The oxidation resistance surpassed the program goal while maintaining acceptable resistance to hydrogen exposure. The welding, brazing, and casting characteristics are excellent. Finally, the cost of NASACC-1 is significantly lower than that of X-40

REMAINING LIFE ASSESSMENT AND PERFORMANCE CHARACTERIZATION OF CENTRIFUGAL COMPRESSORS IN LNG TRAINS

LectureRasGas LNG Trains-1 and 2, comprising of three refrigeration centrifugal compressors each, were commissioned in 1999 and 2000, respectively. Three compressors have achieved 15 years of trouble free operation through risk based Predictive and Preventive Maintenance Strategies and surveillance program. None of these compressors’ major components such as the rotor, dry gas seals or bearings have been replaced so far except three cases due to design upgrades (Rotor Re-rate, Thrust Disk fretting issue). Industry and technical literature survey indicates that several hundred compressors have achieved service life of over 20 years. However, the frequencies of maintenance interventions are not common/standardized due to site specific variations, shutdown 3rd Middle East Turbomachinery Symposium (METS III) 15-18 February 2015 | Doha, Qatar | mets.tamu.edu Copyright© 2015 by RasGas Co. Ltd, Qatar, and Turbomachinery Laboratory, Texas A and M Engineering Experiment Station 2 windows and differences in applications. In the LNG business, major maintenance activities of these compressors are required to be aligned with Gas Turbine Driver’s 8 yearly Major-Inspection Cycles to avoid extended outages and very high adverse economic consequences. Train-1/2 compressors’ running life would exceed 23 years, well beyond API recommended service life of 20 years, when the next Gas Turbine Major-Inspection (MI) is scheduled. This Paper presents Engineering Studies on these six Compressors for the assessment of all potential failure modes, estimating remaining operational life and identifying requisite life-extension recommendations for meeting the challenge of achieving failure free operation for the extended period of 8 years. The compressor components are susceptible to low and high cycle fatigue, erosion, corrosion, creep, wear, and accumulated damages resulting in performance degradation and may eventually lead to failures. Review of rotor-dynamic design and performance, head/end wall O-ring life estimation, balancing drum condition review, and acoustic mapping were performed to evaluate the compressor train reliability and to benchmark the current system performance. To predict the static and dynamic stress distribution on compressor impellers (14 in total), detailed finite element (FE) models of the impellers are developed and validated using results from modal testing of spare impellers. The stress predictions using conservative estimates of alternating fluid pressure loads and rotor spin motion as forcing functions allow computing the impeller endurance limit, i.e., the stress limit corresponding to its infinite life. A stress based life prediction method, using Goodman diagram, was used to determine the impeller margin of safety. Aerodynamic excitations and structural resonant vibrations mostly contribute to the acoustic emissions. Non-intrusive acoustic and vibration measurements were performed near the compressors and piping to benchmark the current operating condition of the system, which will serve for future Condition monitoring and periodic system evaluation. Rotordynamic response measurements from bode plot, waterfall plots, and orbit plots was reviewed to identify the rotor critical speeds, sub-synchronous whirl, rotor misalignment, and rubbing. The compressor efficiency and pressure ratios are characterized and trends developed to evaluate historic performance. This study for the assessment of the remaining life of centrifugal compressors provides a reference for development of long term maintenance philosophy for all RasGas LNG trains and gas processing plants

Gestational Diabetes Mellitus: NICE for the U.S.?: A comparison of the American Diabetes Association and the American College of Obstetricians and Gynecologists guidelines with the U.K. National Institute for Health and Clinical Excellence guidelines

OBJECTIVE - To compare recent U.S. and U.K. guidelines on gestational diabetes mellitus (GDM)

Vibration Monitoring Of Turbomachinery.

Tutorialpg. 101-118The overall concept of vibration monitoring is presented based upon theory and the practical constraints of machinery construction, transducer characteristics and the cost/benefit ratio of available systems. General features of velocity, acceleration, and displacement measurements are considered. Machine malfunction characteristics, mechanical impedance ratio, and force versus restraints consideration are assessed with respect to selecting vibration transducers for measuring housing vibration, relative shaft vibration, and absolute shaft vibration. The construction, application, limitations, and comparison of available vibration transducers is discussed. Typical vibration monitoring protection systems for various types of rotating machinery (turbines, compressors, pumps, fans, electrical motors and gears) will be discussed. Data acquisition, data management and analysis, cost, and general capabilities of periodic and computerized on-line vibration monitoring systems are analyzed. A presentation of vibration data in the form of overall vibration, vibration frequency spectrum, bode, waterfall and trend plots is addressed. Description and identification of typical sources of vibration such as unbalance, misalignment, rubs, resonance, subsynchronous instabilities, and electrical problems is provided. Detection of blade related problems through the use of advanced techniques for defining vibration related machine malfunctions such as modal testing, strain gage, and radio telemetry are briefly discussed. Vibration severity limits for measurements on both machine housings and shaft relative to the housing are presented; appropriate correction factors are introduced to accommodate different machine designs, installations, and vibration sources. The use of these limits, and examples of vibration monitoring successes, is supported by reviewing the actual field case histories. The significant concepts presented are supported by the actual case histories data

Unique Fan Vibration Problems: Their Causes And Solutions

LectureOperating requirements for new fans demand that greater attention be given to the design of the total installation including everything from the foundation to the ducts. Rotor dynamic analysis without adequate consideration of the structural and foundation dynamics and of the fluid dynamics and acoustics of the entire system is often not sufficient to deal with fan vibration problems. This paper discusses a multi-disciplinary approach to evaluate existing fan system designs for root causes of overall vibration problems and the development of methods to solve them. Actual case histories are presented which cover the latest field instrumentation and evaluation techniques in the analysis of fan vibration problems

Exploring International Law: Opportunities and Challenges for Political Science Research

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/148360/1/1521-9488.00223.pd

REMAINING LIFE ASSESSMENT AND PERFORMANCE CHARACTERIZATION OF CENTRIFUGAL COMPRESSORS IN LNG TRAINS

LectureRasGas LNG Trains-1 and 2, comprising of three refrigeration centrifugal compressors each, were commissioned in 1999 and 2000, respectively. Three compressors have achieved 15 years of trouble free operation through risk based Predictive and Preventive Maintenance Strategies and surveillance program. None of these compressors’ major components such as the rotor, dry gas seals or bearings have been replaced so far except three cases due to design upgrades (Rotor Re-rate, Thrust Disk fretting issue). Industry and technical literature survey indicates that several hundred compressors have achieved service life of over 20 years. However, the frequencies of maintenance interventions are not common/standardized due to site specific variations, shutdown 3rd Middle East Turbomachinery Symposium (METS III) 15-18 February 2015 | Doha, Qatar | mets.tamu.edu Copyright© 2015 by RasGas Co. Ltd, Qatar, and Turbomachinery Laboratory, Texas A and M Engineering Experiment Station 2 windows and differences in applications. In the LNG business, major maintenance activities of these compressors are required to be aligned with Gas Turbine Driver’s 8 yearly Major-Inspection Cycles to avoid extended outages and very high adverse economic consequences. Train-1/2 compressors’ running life would exceed 23 years, well beyond API recommended service life of 20 years, when the next Gas Turbine Major-Inspection (MI) is scheduled. This Paper presents Engineering Studies on these six Compressors for the assessment of all potential failure modes, estimating remaining operational life and identifying requisite life-extension recommendations for meeting the challenge of achieving failure free operation for the extended period of 8 years. The compressor components are susceptible to low and high cycle fatigue, erosion, corrosion, creep, wear, and accumulated damages resulting in performance degradation and may eventually lead to failures. Review of rotor-dynamic design and performance, head/end wall O-ring life estimation, balancing drum condition review, and acoustic mapping were performed to evaluate the compressor train reliability and to benchmark the current system performance. To predict the static and dynamic stress distribution on compressor impellers (14 in total), detailed finite element (FE) models of the impellers are developed and validated using results from modal testing of spare impellers. The stress predictions using conservative estimates of alternating fluid pressure loads and rotor spin motion as forcing functions allow computing the impeller endurance limit, i.e., the stress limit corresponding to its infinite life. A stress based life prediction method, using Goodman diagram, was used to determine the impeller margin of safety. Aerodynamic excitations and structural resonant vibrations mostly contribute to the acoustic emissions. Non-intrusive acoustic and vibration measurements were performed near the compressors and piping to benchmark the current operating condition of the system, which will serve for future Condition monitoring and periodic system evaluation. Rotordynamic response measurements from bode plot, waterfall plots, and orbit plots was reviewed to identify the rotor critical speeds, sub-synchronous whirl, rotor misalignment, and rubbing. The compressor efficiency and pressure ratios are characterized and trends developed to evaluate historic performance. This study for the assessment of the remaining life of centrifugal compressors provides a reference for development of long term maintenance philosophy for all RasGas LNG trains and gas processing plants