Sulzer (United States)

Abstract The year 2024 marks one hundred years since Wilfred Campbell published his landmark work on vibrational analysis of rotating disk following a series of disk failures in steam turbines. Despite the absence of advanced engineering analytical tools, Campbell came up with an elegant method to visually demonstrate and capture the mode shapes in rotating disks. The first part of this paper reviews Campbell's life and analytical and experimental work in this area. Regardless of the current advanced engineering capabilities to predict nodal shapes in turbine disks, turbine disks still experience failures related to vibration. The second part of the paper discusses a recent case study where a turbine disk failure occurred as a result of vibration. The discussion includes metallurgical root cause failure analysis and engineering analysis to predict the vibrational characteristics. Metallurgical failure analysis confirmed that the primary mode of failure was fatigue and did not have any issues with the disk material or its mechanical properties. Finite element modeling and analysis were used for the engineering analysis to predict the natural frequencies of the bladed-disk. The engineering analysis showed the evidence of potential resonance, and the failure was related to nodal vibration issues.

Abstract Gas turbine blades made from nickel-based superalloys, valued for their high temperature stability and creep resistance, undergo various forms of microstructural degradation during extended service at elevated temperatures that can ultimately lead to blade failure. To extend blade and turbine rotor life, Sulzer has developed evaluation and rejuvenation processes that include microstructural assessment and stress rupture testing of specimens from service-exposed blades. While stress rupture testing presents certain limitations and challenges in evaluating material condition, Sulzer has successfully rejuvenated hundreds of gas turbine blade sets across multiple superalloy types, including GTD 111, IN 738 LC, and U 500, demonstrating the effectiveness of heat treatment rejuvenation in improving microstructure and mechanical properties of service-degraded components.

Abstract A gas turbine failed catastrophically at a process plant during operation. The failure resulted in the torque tube and air separator breaking into multiple pieces. The bolts connecting the torque tube to the air separator, the bolts connecting the torque tube to the turbine discs and the bolts connecting the torque tube to the compressor section also failed. A detailed metallurgical root cause failure analysis was performed to understand what happened. The analysis included reconstruction of the torque tube and air separator from the broken pieces, and evaluation of all fracture surfaces. Based on the patterns seen on the fracture surfaces, the fracture mechanisms and crack propagation paths were determined for the torque tube and the air separator. Mechanical properties were tested using specimens extracted from the broken pieces. Microstructural evaluation was also performed. Similar analyses were performed on the broken bolts. Based on the fracture surface evaluation of the bolts, the bolt fractures were believed to be collateral damage. Multiple preexisting cracks and a material defect were found in the torque tube. Fracture had propagated from one of these preexisting cracks in the torque tube. The question was if the torque tube fractured first, or the air separator fractured first.

Abstract An extensive de-risking program was conducted to qualify the subsea dense gas pump project design. As part of this program, a subsea pump prototype, a back-to-back centrifugal pump, was designed, constructed, and evaluated using a dense CO2/N2 mixture, referred to as dense gas. This dense fluid has a gas-like viscosity, but a density closer to that of a liquid. The pump prototype was evaluated at varying suction pressures ranging from 150 to 200 bar, up to a maximum discharge pressure of 350 bar. The machine was operated at a maximum speed of 6,000 rpm, delivering a flow rate of up to 700 m3/h of gas mixture. The composition and pressure of the working fluid was selected to simulate Brazilian Pre-salt field conditions at the seabed. A vertical integrated pump-motor unit with environmentally friendly barrier fluid (BF) was configured using radial centrifugal impellers in a similar fashion as a multiphase subsea booster, to pump the homogeneous dense mixture. The main objectives of the test campaign were to validate the hydraulic performance prediction and assess the rotordynamic behavior of the pump when operated with a dense fluid. Additionally, a series of slug tests were performed to prove the robustness of the pump in case of the transient high-load scenarios. The pump passed all the required tests and demonstrated anticipated robustness, which is crucial for subsea operation. The measured hydraulic performance exceeded predictions at high-load, high-speed conditions, which may be partly attributed to the conservatism in the selection process. The successful combination of hydraulic performance, robust rotordynamic behavior, and an efficient control strategy provides strong evidence for the viability and effectiveness of the current subsea pump design for dense gas application.

forma descritiva.A pesquisa teve aprovao tica n 4.526.452.Resultados: Participaram da pesquisa, 121 estudantes, prevalecendo pessoas do sexo feminino (74%), com idade entre 18 e 23 anos (69%).Entre os fatores acadmicos, prevaleceram estudantes dos cursos de Enfermagem (25%), Direito (17%) e Biomedicina (8%), que cursam de forma integral (75%).Os universitrios consideravam a carga horria (terico e prtico) exaustiva (47%), relataram lidar com presso no meio acadmico (42%) e passaram a ter privao do tempo de convvio com a famlia (40%).Aps o ingresso na universidade, os estudantes autodeclararam desgaste emocional (50%), alterao (piora) da memria (45%) e da concentrao (43%), aumento do cansao fsico (64%) e mental (71%).Concluso: A sade mental dos estudantes apresentaram alteraes aps ingresso

Abstract The rotating blades of a steam turbine perform the important task of converting the thermal energy of the steam into rotating mechanical work or torque. Hence, these blades have to be very robust and they need to be installed properly in the discs of the turbine. Damping mechanisms are used to improve the stiffness of the blades and to minimize the vibrations of the blades. Different types of blade damping mechanisms are used in steam turbines. Shroud bands, lashing or damping wires, pins, tie-bolts and lashing stubs/ snubbers are the most common types of damping mechanisms used in steam turbines. Several factors such as stress distribution, additional centrifugal stresses due to the added weight of the damping mechanisms, aerodynamic effects, resulting harmful mode shapes and critical vibration frequencies etc., need to be considered in the selection and the design of the damping mechanisms. Due to the various types of operating conditions and stresses, the damping mechanisms can experience failure in service. Metallurgical evaluations of some of the recent failures of damping mechanisms are discussed here. Failures of shroud bands, blade tenons, tie-bolts and damping wires are the particular examples presented. SCC (stress corrosion cracking), fatigue and overload were found to be the main modes of failures in these examples. The purpose of discussing these examples is to make the designers, the manufacturers and the users aware of these potential issues so that corrective actions can be taken.

Abstract Fretting occurs when there is cyclic relative motion of extremely small amplitude between two tightly fit mating surfaces. In this process, the tight fitting load may lead to adhesion of mating surface. The subsequent relative movement breaks the adhesion and lead to local grooves and pits. The localized damage in conjunction with the stresses associated with the cyclic relative motion may lead to surface cracking. This crack subsequently may propagate by fatigue provided there is high enough cyclic stress at that location. The paper discusses a blade failure induced by such fretting related fatigue. The metallurgical evaluation of the fracture surfaces of the blades showed evidence of classical fatigue failure. However, the crack initiation location did not coincide with high stress location identified by the finite element analysis. This discrepancy along with the evidence of fretting at the crack initiation sites confirms that failures were induced by fretting. Finally, some methods to eliminate or minimize fretting damage are discussed.

Static and dynamic load tests were performed on a three-pad, rocker-pivot, tilting-pad journal bearing (TPJB) with three interchangeable pad configurations, each with measurably different pad flexibilities. Measured dynamic-stiffness data for the bearing were readily fitted by a frequency-independent, constant-coefficient [K][C][M] model. The test-bearing had a 101.74 mm diameter with L/D = 0.6. Tests were conducted over the speed range of 6–12 krpm, with unit loads varying from 0.172 to 1.724 MPa. An ISO VG 46 lubricant was used as the test fluid. Pad flexibility was characterized as the change in the pad's bending stiffness or the change in pad thickness. A finite-element model (FEM) was created to predict the structural bending stiffness of each pad configuration, showing a significant pad flexibility increase as pad thickness decreased. To examine the effect of pad flexibility on the rotordynamic coefficients, the measured results were compared across pad configurations and showed that the pad flexibility increase reduced the direct damping coefficients by 12–20%. As pad flexibility increased, the direct-stiffness coefficients could increase or decrease, depending on the unit load. They varied from an increase of 12% at low unit loads to a decrease of 3% at high unit loads. Results show that the pad's structural bending stiffness or flexibility is important when predicting the bearing’s dynamic performance. Damping is consistently overpredicted when neglecting pad flexibility. A nondimensional pad flexibility parameter αflex was developed. It related the average deflection across the pad surface to the pad's arc length and was to relate the pad flexibility of multiple bearings of different sizes. A bearing code was used to predict the percent change in direct damping coefficients for rigid-pad/flexible-pivot and flexible-pad/flexible-pivot models for a surface speed of 54 m/s and a unit load of 783 kPa for the three-pad configuration tested here plus five additional tested bearings from the literature. For the minimum pad thickness configuration tested here, the code predicted a 20% drop in predicted Cxx (off-load axis direct damping) when comparing a model that included pad flexibility with a model that neglected pad flexibility. In terms of αflex, the two thinnest pad configurations tested here are quite flexible compared to both TPJB's pads used in industry and previously tested TPJB pads.

Apparatus (1) for injecting a liquid in an area of a thermal spray gun (100). The apparatus (1) includes an injector cleaning device (10) having an inlet connectable (19) to at least one feedstock supply line (18), an inlet connectable (17) to at least one gas supply line (16), and an inlet connectable (21) to at least one liquid medium supply line (20). An injector (30) orifice is coupled to the injector cleaning device (10) and is adapted to at least one of inject a liquid jet into a hot stream created in the area of the thermal spray gun (100) and receive feedstock, gas and liquid passing into the inlets.

A resistência à corrosão por pite tem sido correlacionada com as condições morfológicas da superfície: um acabamento superficial liso contribui para diminuir o potencial de iniciação de pites. Esse estudo teve por objetivo investigar a relação entre a resistência à corrosão por pite e a rugosidade em superfícies usinadas do aço inoxidável superaustenítico ASTM A744 grau CN3MN. As amostras fundidas sofreram um torneamento cilíndrico com diferentes combinações das condições de corte, resultando, assim, em diferentes padrões de rugosidade superficial. As superfícies das amostras, então usinadas, foram caracterizadas quanto à rugosidade e ao endurecimento. Após submetidas a um teste por imersão, que acelerava a corrosão, essas superfícies foram examinadas num esteroscópio, tendo sido, também, determinada a perda de peso devido à corrosão. Observou-se que as amostras exibiram diferentes comportamentos com relação à resistência à corrosão, de acordo com as condições de usinagem aplicadas. Uma correlação entre a resistência à corrosão e a rugosidade superficial ficou evidente, assim como à perda de peso devido à formação de pites. Esse estudo identificou que a corrosão pode ser controlada através da seleção dos parâmetros de usinagem apropriados.