Journal of Engineering for Gas Turbines and Power, 1995
A model of the forced vibrations of a flexible, asymmetric, and unbalanced shaft, supported by tw... more A model of the forced vibrations of a flexible, asymmetric, and unbalanced shaft, supported by two magnetic bearings, is derived to simulate the effect of different schemes of active control on shaft dynamic behavior. Simulation results were compared for several cases of single and multi-access bearing controls, rigid-body mode only and rigid with flexible mode control, and linear and nonlinear bearing responses. It is shown that the multi-access bearing response, calculated from the known equation of the stable ROCL (Reduced Order Closed Loop) and based on the direct velocity-displacement feedback, provided the most precise shift in critical frequencies and also reasonable suppression of shaft vibration amplitudes. The nonlinear bearing design was also briefly discussed. The stability analysis showed that stability limits were influenced by more parameters in this case, but no particular advantages were observed in suppression of the vibration amplitudes as compared to the linear c...
Acoustic resonances in internal flows can cause noise, vibration, and even equipment damage. One ... more Acoustic resonances in internal flows can cause noise, vibration, and even equipment damage. One geometry prone to acoustic resonance is a deadleg at the point where the main flow turns into a side branch. Here, we report experimental and computational fluid dynamics (CFD) studies of flow-generated pulsation in such a geometry over a wide range of mean flow velocities. Experimental results of the normalized pulsation pressure amplitudes (P*) versus Strouhal number characterized the flow–acoustic field for acoustically tuned and detuned systems and for branch to main pipe diameter ratio of 1.0. The unsteady CFD simulations revealed the characteristic volume integral of the cross-product of the vorticity field and the velocity field (ω×U) in the vicinity of the T-junction which helped in quantifying the acoustic source power for different conditions. In addition, the cross-product (ω×U) in the direction along the main line is almost exactly out of phase with the acoustic velocity at t...
In-ditch/in-service characterization of pipelines using nondestructive evaluation (NDE) can provi... more In-ditch/in-service characterization of pipelines using nondestructive evaluation (NDE) can provide valuable data for confirming operating pressure and qualifying pipelines for transporting natural gas of different quality or gas mixture, as well as for determining repair criteria for integrity management programs. This is especially relevant for vintage pipelines that may not have material test reports (MTR) available, and for aging infrastructure that have been subjected to suspected or unknown integrity threats. However, measurement of material fracture toughness currently requires the removal of large samples for laboratory testing, such as compact tension (CT) fracture testing or Charpy impact testing. The present work introduces a new concept, the Nondestructive Toughness Tester (NDTT), that provides a NDE solution for measuring the fracture toughness of pipeline steel in a superficial layer of material (∼0.005 inches). The NDTT uses a specially designed wedge-shaped stylus to...
Volume 3: Operations, Monitoring, and Maintenance; Materials and Joining
Effective purging of air out of a pipeline section before commissioning by direct displacement wi... more Effective purging of air out of a pipeline section before commissioning by direct displacement with natural gas has been safely practiced for decades with the recognition that flammable interfacial mixing zone between the driving gas (behind) and the air (ahead) is inevitable. In cases when the purge velocity is below a threshold dictated by the gravity current velocity (defined in AGA Purging Principles and Practices, 2001), natural gas being lighter than air can in fact ride over air being the heavier gas and short circuit the flow path to the vent at the other end of the pipe section, thus trapping behind pockets of air that could potentially introduce risk of internal explosion with subsequent damage to the pipe section and pose a safety issue to field personnel. Therefore, maintaining the purge velocity above this threshold by a good margin has been a common practice in the purging procedure to-date. In fact, maintaining the purge velocity above the threshold can be controlled ...
Current trends in greenfield natural gas compression facilities and high-pressure gas transmissio... more Current trends in greenfield natural gas compression facilities and high-pressure gas transmission pipelines are designs for high pressure operation, e.g. PN150. At such high pressures, sound pressure level (SPL) of the noise generated during a planned blowdown can be as high as 165–175 dBA at 1 m distance away from the blowdown stack tip. Even double hearing protection would not be sufficient for an operator opening the blowdown valve at the blowdown assembly even for a short period of time. Blowdown silencers mounted on top of the blowdown stack are limited to the degree of noise suppression they offer (typically of the order of 30 to 40 dB), let alone the requirement for extensive support structures to hold the massive weight on the stack top. One innovation to alleviate this issue, is to place a silencer on a skid on a ground-level pad/support system, at a sufficient distance away from the blowdown stack. In this way, the blowdown valve operator would be exposed to a much lower ...
Many facilities employ two or more centrifugal compressors, operated in either series or parallel... more Many facilities employ two or more centrifugal compressors, operated in either series or parallel configurations. An accurately designed surge control system that includes multiple compressors with the associated piping systems is a vital element of a facility’s design and ongoing operational integrity. The design must ensure compressors are not subjected to damaging fast dynamic events leading to large capital costs and significant down time for operators. Examples of such fast dynamic events are those following emergency shutdown (ESD) of fast stop of one or all compressor units in a station. Typical studies are not accurate enough to capture the complex interactions leading to 2 catastrophic events, especially for complicated system arrangements. This paper introduces three methods of surge control analysis that can be conducted to assess the effectiveness of any surge control system design to prevent the compressor from surge. The first method utilizes the perturbation theory to...
ONE OF THE key issues in the design and construction of any gas pipeline is the prevention of mat... more ONE OF THE key issues in the design and construction of any gas pipeline is the prevention of material fracture. Since the gas is generally transported under high operating pressures, it must be ensured that the gas pipeline is sufficiently tough to arrest the propagation of any potential fracture. For several decades, control of gas pipeline fracture propagation has been under scrutiny due to economic considerations and ecological and safety hazards related to pressurised pipe failure. The Battelle Two Curve approach has been widely used to determine the minimum material arrest toughness by comparing the gas decompression wave velocity with the fracture velocity, both as functions of the local gas pressure. Sufficient knowledge of the gas decompression behavior following the rupture is therefore crucial in determining running fracture arrest toughness levels. The decompression behaviour is influenced by the operating conditions, fluid composition and the material properties of the ...
Many facilities employ two or more centrifugal compressors, operated in either series or parallel... more Many facilities employ two or more centrifugal compressors, operated in either series or parallel configurations. An accurately designed surge control system that includes multiple compressors with the associated piping systems is a vital element of a facility’s design and ongoing operational integrity. The design must ensure compressors are not subjected to damaging fast dynamic events leading to large capital costs and significant down time for operators. Examples of such fast dynamic events are those following emergency shutdown (ESD) or fast stop of one or all compressor units in a station. Typical studies are not accurate enough to capture the complex interactions leading to catastrophic events, especially for complicated system arrangements. This paper introduces three methods of surge control analysis that can be conducted to assess the effectiveness of any surge control system design to prevent the compressor from surge. The first method utilizes the perturbation theory to r...
Journal of Engineering for Gas Turbines and Power, 1995
A model of the forced vibrations of a flexible, asymmetric, and unbalanced shaft, supported by tw... more A model of the forced vibrations of a flexible, asymmetric, and unbalanced shaft, supported by two magnetic bearings, is derived to simulate the effect of different schemes of active control on shaft dynamic behavior. Simulation results were compared for several cases of single and multi-access bearing controls, rigid-body mode only and rigid with flexible mode control, and linear and nonlinear bearing responses. It is shown that the multi-access bearing response, calculated from the known equation of the stable ROCL (Reduced Order Closed Loop) and based on the direct velocity-displacement feedback, provided the most precise shift in critical frequencies and also reasonable suppression of shaft vibration amplitudes. The nonlinear bearing design was also briefly discussed. The stability analysis showed that stability limits were influenced by more parameters in this case, but no particular advantages were observed in suppression of the vibration amplitudes as compared to the linear c...
Acoustic resonances in internal flows can cause noise, vibration, and even equipment damage. One ... more Acoustic resonances in internal flows can cause noise, vibration, and even equipment damage. One geometry prone to acoustic resonance is a deadleg at the point where the main flow turns into a side branch. Here, we report experimental and computational fluid dynamics (CFD) studies of flow-generated pulsation in such a geometry over a wide range of mean flow velocities. Experimental results of the normalized pulsation pressure amplitudes (P*) versus Strouhal number characterized the flow–acoustic field for acoustically tuned and detuned systems and for branch to main pipe diameter ratio of 1.0. The unsteady CFD simulations revealed the characteristic volume integral of the cross-product of the vorticity field and the velocity field (ω×U) in the vicinity of the T-junction which helped in quantifying the acoustic source power for different conditions. In addition, the cross-product (ω×U) in the direction along the main line is almost exactly out of phase with the acoustic velocity at t...
In-ditch/in-service characterization of pipelines using nondestructive evaluation (NDE) can provi... more In-ditch/in-service characterization of pipelines using nondestructive evaluation (NDE) can provide valuable data for confirming operating pressure and qualifying pipelines for transporting natural gas of different quality or gas mixture, as well as for determining repair criteria for integrity management programs. This is especially relevant for vintage pipelines that may not have material test reports (MTR) available, and for aging infrastructure that have been subjected to suspected or unknown integrity threats. However, measurement of material fracture toughness currently requires the removal of large samples for laboratory testing, such as compact tension (CT) fracture testing or Charpy impact testing. The present work introduces a new concept, the Nondestructive Toughness Tester (NDTT), that provides a NDE solution for measuring the fracture toughness of pipeline steel in a superficial layer of material (∼0.005 inches). The NDTT uses a specially designed wedge-shaped stylus to...
Volume 3: Operations, Monitoring, and Maintenance; Materials and Joining
Effective purging of air out of a pipeline section before commissioning by direct displacement wi... more Effective purging of air out of a pipeline section before commissioning by direct displacement with natural gas has been safely practiced for decades with the recognition that flammable interfacial mixing zone between the driving gas (behind) and the air (ahead) is inevitable. In cases when the purge velocity is below a threshold dictated by the gravity current velocity (defined in AGA Purging Principles and Practices, 2001), natural gas being lighter than air can in fact ride over air being the heavier gas and short circuit the flow path to the vent at the other end of the pipe section, thus trapping behind pockets of air that could potentially introduce risk of internal explosion with subsequent damage to the pipe section and pose a safety issue to field personnel. Therefore, maintaining the purge velocity above this threshold by a good margin has been a common practice in the purging procedure to-date. In fact, maintaining the purge velocity above the threshold can be controlled ...
Current trends in greenfield natural gas compression facilities and high-pressure gas transmissio... more Current trends in greenfield natural gas compression facilities and high-pressure gas transmission pipelines are designs for high pressure operation, e.g. PN150. At such high pressures, sound pressure level (SPL) of the noise generated during a planned blowdown can be as high as 165–175 dBA at 1 m distance away from the blowdown stack tip. Even double hearing protection would not be sufficient for an operator opening the blowdown valve at the blowdown assembly even for a short period of time. Blowdown silencers mounted on top of the blowdown stack are limited to the degree of noise suppression they offer (typically of the order of 30 to 40 dB), let alone the requirement for extensive support structures to hold the massive weight on the stack top. One innovation to alleviate this issue, is to place a silencer on a skid on a ground-level pad/support system, at a sufficient distance away from the blowdown stack. In this way, the blowdown valve operator would be exposed to a much lower ...
Many facilities employ two or more centrifugal compressors, operated in either series or parallel... more Many facilities employ two or more centrifugal compressors, operated in either series or parallel configurations. An accurately designed surge control system that includes multiple compressors with the associated piping systems is a vital element of a facility’s design and ongoing operational integrity. The design must ensure compressors are not subjected to damaging fast dynamic events leading to large capital costs and significant down time for operators. Examples of such fast dynamic events are those following emergency shutdown (ESD) of fast stop of one or all compressor units in a station. Typical studies are not accurate enough to capture the complex interactions leading to 2 catastrophic events, especially for complicated system arrangements. This paper introduces three methods of surge control analysis that can be conducted to assess the effectiveness of any surge control system design to prevent the compressor from surge. The first method utilizes the perturbation theory to...
ONE OF THE key issues in the design and construction of any gas pipeline is the prevention of mat... more ONE OF THE key issues in the design and construction of any gas pipeline is the prevention of material fracture. Since the gas is generally transported under high operating pressures, it must be ensured that the gas pipeline is sufficiently tough to arrest the propagation of any potential fracture. For several decades, control of gas pipeline fracture propagation has been under scrutiny due to economic considerations and ecological and safety hazards related to pressurised pipe failure. The Battelle Two Curve approach has been widely used to determine the minimum material arrest toughness by comparing the gas decompression wave velocity with the fracture velocity, both as functions of the local gas pressure. Sufficient knowledge of the gas decompression behavior following the rupture is therefore crucial in determining running fracture arrest toughness levels. The decompression behaviour is influenced by the operating conditions, fluid composition and the material properties of the ...
Many facilities employ two or more centrifugal compressors, operated in either series or parallel... more Many facilities employ two or more centrifugal compressors, operated in either series or parallel configurations. An accurately designed surge control system that includes multiple compressors with the associated piping systems is a vital element of a facility’s design and ongoing operational integrity. The design must ensure compressors are not subjected to damaging fast dynamic events leading to large capital costs and significant down time for operators. Examples of such fast dynamic events are those following emergency shutdown (ESD) or fast stop of one or all compressor units in a station. Typical studies are not accurate enough to capture the complex interactions leading to catastrophic events, especially for complicated system arrangements. This paper introduces three methods of surge control analysis that can be conducted to assess the effectiveness of any surge control system design to prevent the compressor from surge. The first method utilizes the perturbation theory to r...
Uploads
Papers by Kamal Botros