Determination of Crack Initiation on L-1 LP Steam Turbine Blades: Part 1—Measurements on Rotor Train, Material Specimens and Blades

2011 ◽  
Author(s):  
Zdenek Kubin ◽  
Vaclav Cerny ◽  
Pavel Panek ◽  
Tomas Misek ◽  
Jan Hlous ◽  
...  
Keyword(s):  
Steam Turbine ◽  
Turbine Blades ◽  
Rotating Blade ◽  
New Material ◽  
Blade Tip ◽  
Manufacturing Accuracy ◽  
Torsional Excitation ◽  
Run Up ◽  
One Year

After 10 years of operation of a steam turbine with large output power there was an accident during the turbine run-up. One of rotating blade fell off. All 6 LP rotors (two machines) were checked and many cracks on the L-1 blades were found. Due to economic reasons, blades with an identical geometry were manufactured quickly and a new material was used. A better material was chosen in terms of yield limit. The egalization of rotor grooves was performed because of manufacturing accuracy. Tip-timing measurement was installed on two L-1 stages to monitor and protect the blades. After one year of smooth operation new inspections were made. Surprisingly, it was found that the blades made of the new material had comparatively more cracks than the original blades. A new investigation has been started. This article describes measurements including rotor torsional excitation, blade tip-timing measurements, modal analysis and material tests. A computational analysis is presented in Part 2. Application of both approaches revealed what hypotheses should be rejected and, on the other hand, which of them should be analyzed in a deeper way. Consequently, the unstalled flutter has been identified as the most probable cause of blade cracks.

Determination of Crack Initiation on Blade L-1 LP Steam Turbine Blades: Part 2—Computational Analyses

2011 ◽  
Author(s):  
Josef Kellner ◽  
Zdenek Kubin ◽  
Jan Hlous ◽  
Lubos Prchlik
Keyword(s):  
Modal Analysis ◽  
Steam Turbine ◽  
Turbine Blades ◽  
Original Material ◽  
Economic Reason ◽  
Bladed Disk ◽  
New Material ◽  
One Year ◽  
Computational Analyses

After ten years operation, one L-1 blade of steam turbine with large output power suddenly fell down. All 6 LP rotors (two machines) were checked and many cracks on L-1 blades were found. Due to economic reason, new blades were made with same geometry, but with better material in term of yield limit. Some L-1 stages were made from blades of original material, the rest was made from new material blades. Also the tip-timing measurement was installed on two L-1 stages to monitor blades. The investigation of blade cracks reason started. After one year of smooth operation there was an inspection. Surprisingly, the cracks were indicated again. The blades from new material had relatively more cracks than the original blades. This part describes some computational analyses which were done. For example, the modal analysis and forced vibration of mistuned bladed disk and of whole rotor train with attached L-1 blades, CFX and CFD calculations were done. The measurement of rotor torque, damping, Tip-Timing, experimental modal analysis of blades and rotor train and material test are presented in Part 1 – [7]. Application of both approaches (experimental and computational) rejected some hypotheses and revealed which hypotheses should be analyzed in a deeper way. The unstalled flutter has been identified as the most probable blade failures.

Studies on Determination of Natural Frequencies of Industrial Turbine Blades

1995 ◽  
Author(s):  
Mahesh M. Bhat ◽  
V. Ramamurti ◽  
C. Sujatha
Keyword(s):  
Steam Turbine ◽  
Dynamic Behavior ◽  
Turbine Blade ◽  
Natural Frequencies ◽  
Complex Structure ◽  
Turbine Blades ◽  
Blade Root ◽  
Steam Turbine Blade ◽  
Manufacturing Tolerances

Abstract Steam turbine blade is a very complex structure. It has geometric complexities like variation of twist, taper, width and thickness along its length. Most of the time these variations are not uniform. Apart from these geometric complexities, the blades are coupled by means of lacing wire, lacing rod or shroud. Blades are attached to a flexible disc which contributes to the dynamic behavior of the blade. Root fixity also plays an important role in this behavior. There is a considerable variation in the frequencies of blades of newly assembled turbine and frequencies after some hours of running. Again because of manufacturing tolerances there can be some variation in the blade to blade frequencies. Determination of natural frequencies of the blade is therefore a very critical job. Problems associated with typical industrial turbine bladed discs of a 235 MW steam turbine are highlighted in this paper.

Study of wear mechanism of contact surfaces of steam turbine blades made of titanium VT6 alloy

2021 ◽  
pp. 81-89
Author(s):  
A.M. Zolotov ◽  
M.O. Smirnov ◽  
T.A. Chizhik
Keyword(s):  
Mechanical Properties ◽  
Steam Turbine ◽  
Wear Mechanism ◽  
Turbine Blades ◽  
Microstructural Analysis ◽  
X Ray ◽  
Different Types ◽  
Steam Turbine Blades ◽  
Contact Surfaces

The contact surfaces of the banding shelves of adjacent steam turbine blades made of titanium VT6 alloy after operation are studied by fractography, micro-X-ray and microstructural analysis and determination of mechanical properties. The different types of destruction of the contact surfaces are analyzed and explained. It is shown that the reason for intensive abrasion of the turbine blades' binding meshes is violation of the welding mode in the station conditions.

scholarly journals Theoretical and Experimental Investigation of a 34 Watt Radial-Inflow Steam Turbine With Partial-Admission

2020 ◽  
Author(s):  
Patrick H. Wagner ◽  
Jan Van herle ◽  
Jürg Schiffmann
Keyword(s):  
Steam Turbine ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Pressure Ratio ◽  
Turbine Blades ◽  
Tip Clearance ◽  
Experimental Results ◽  
Partial Admission ◽  
Blade Tip

Abstract A micro steam turbine with a tip diameter of 15 mm was designed and experimentally characterized. At the nominal mass flow rate and total-to-total pressure ratio of 2.3 kg h−1 and 2, respectively, the turbine yields a power of 34 W and a total-to-static isentropic efficiency of 37%. The steam turbine is conceived as a radial-inflow, low-reaction (15%), and partial admission (21%) machine. Since the steam mass flow rate is limited by the heat provided of the system (solid oxide fuel cell), a low-reaction and high-power-density design is preferred. The partial-admission design allows for reduced losses: The turbine rotor and stator blades are prismatic, have a radial chord length of 1 mm and a height of 0.59 mm. Since the relative rotor blade tip clearance (0.24) is high, the blade tip leakage losses are significant. Considering a fixed steam supply, this design allows to increase the blade height, and thus reducing the losses. The steam turbine drives a fan, which operates at low Mach numbers. The rotor is supported on dynamic steam-lubricated bearings; the nominal rotational speed is 175 krpm. A numerical simulation of the steam turbine is in good agreement with the experimental results. Furthermore, a novel test rig setup, featuring extremely-thin thermocouples (ϕ0.15 mm) is investigated for an operation with ambient and hot air at 220 °C. Conventional zero and one-dimensional pre-design models correlate well to the experimental results, despite the small size of the turbine blades.

A Correlation Between Vibration Stresses and Flow Features of Steam Turbine Long Blades in Low Load Conditions

2011 ◽  
Author(s):  
Naoki Shibukawa ◽  
Tomohiro Tejima ◽  
Yoshifumi Iwasaki ◽  
Itaru Murakami ◽  
Ikuo Saito
Keyword(s):  
Steam Turbine ◽  
Pressure Fluctuation ◽  
Cfd Simulation ◽  
Aerodynamic Force ◽  
Turbine Blades ◽  
Operating Conditions ◽  
Unsteady Pressure ◽  
Low Load ◽  
Vibration Stress ◽  
Blade Tip

The vibration stress of long steam turbine blades during low load operating conditions is examined in this paper. A series of experiments has been carried out to investigate the vibration stress behavior, and the steady and unsteady pressure fluctuation. It is found that a steady pressure distribution over the blade tip is much to do with the unsteady pressure and fluctuation of the vibration stress. A precise investigation of unsteady wall pressure near blade tip explains the relationship between pressure fluctuation and the vibration stress, and reveals the existence of particular frequency which affects blade axial modes. Blade to blade flow mechanisms and aerodynamic force and properties during low load operating condition were investigated by a steady CFD simulation. FFT of aerodynamic force by another steady full arc CFD simulation provides various pattern of harmonic excitation which account for the behavior of vibration stresses well. The mechanism of the rapid stress increase and a step drop were examined by considering CFD results and measured unsteady pressure data together.

scholarly journals BTT & RFLB - THE OPTIMUM SET FOR STEAM TURBINE BLADES MONITORING

2018 ◽  
Vol 20 ◽  
pp. 5-9
Author(s):  
Miroslav Balda
Keyword(s):  
Fatigue Life ◽  
Steam Turbine ◽  
Turbine Blades ◽  
Residual Fatigue Life ◽  
Timing System ◽  
Blade Tip ◽  
Steam Turbine Blades ◽  
Residual Fatigue ◽  
Blade Tips

BTT, Blade Tip Timing system, is a commercially available system generating files of precise times of blade tips when passing sensors attached in a machine stator. RFLB, Residual Fatigue Life of Blades, is a postprocessor of those files evaluating estimates of fatigue lives of all blades fitted to the wheel. The set reduces a danger of unexpected blade failures.

Development of Higher Temperature Abradable Seals for Gas Turbine Applications

2004 ◽  
Author(s):  
Raymond E. Chupp ◽  
Yuk-Chiu Lau ◽  
Farshad Ghasripoor ◽  
Donald J. Baldwin ◽  
Chek Ng ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Field Tests ◽  
Rotating Blade ◽  
New Material ◽  
Blade Tip ◽  
Higher Temperature ◽  
Sprayed Coating ◽  
Thermally Sprayed ◽  
Unit Performance ◽  
Blade Tips

Improving sealing between rotating and stationary parts in industrial turbines can significantly increase unit performance. Abradable seals are being developed to reduce blade-tip clearances where an abradable material is placed on the stationary shroud or casing opposite the rotating blade tips to reduce clearances with minimum risk to the turbine components during rubs. A newly developed metallic abradable material is a thermally sprayed coating on the first stage of gas turbine shrouds to reduce tip clearances; thereby, improving turbine power and efficiency by about 1/2 percent. This material is an improvement over currently available metallic abradables increasing the maximum operating temperature from 750°C to about 950°C with no special treatments required on the rotating blade tips. Initial engine field tests have shown the new material to be abradable and on target to meet life requirements.

scholarly journals Synchronous Vibration Measurements for Shrouded Blades Based on Fiber Optical Sensors with Lenses in a Steam Turbine

Sensors ◽  
2019 ◽  
Vol 19 (11) ◽  
pp. 2501 ◽  
Author(s):  
Dechao Ye ◽  
Fajie Duan ◽  
Jiajia Jiang ◽  
Zhonghai Cheng ◽  
Guangyue Niu ◽  
...  
Keyword(s):  
Steam Turbine ◽  
Optical Sensors ◽  
Turbine Blades ◽  
Nodal Diameter ◽  
Comparison Results ◽  
Fiber Optical ◽  
Fiber Optical Sensors ◽  
Blade Tip ◽  
Relative Errors ◽  
Working Distance

It is important to obtain accurate dynamic vibrations of steam turbine blades for safe operation. Strain gauge (SG) measurements cannot fully obtain vibrations of all blades and nodal diameter (ND) details. The blade tip timing (BTT) technique could resolve this problem because it has the advantage of measuring all blades’ vibrations. This article proposed an improved BTT technique for measuring synchronous vibrations of shrouded blades in a steam turbine based on fiber optical sensors with lenses. The newly developed sensor was equipped with a Plano-convex lens, and the optical path was specifically designed to collimate the beam within a large working distance from 4 to 19 mm and improve the measuring accuracy. A method to search the spectra of all peak vibration amplitudes of all the blades was proposed to obtain the ND details of synchronous vibration. Experimental results validated the efficiency and accuracy of the proposed methods and sensors. Comparison results of BTT measurements with SG measurements showed that the relative errors of normalized frequency and strain were small and acceptable.

Residual Fatigue Lives of Steam Turbine Blades

2016 ◽  
Vol 827 ◽  
pp. 121-124
Author(s):  
Miroslav Balda ◽  
Olga Červená
Keyword(s):  
Data Processing ◽  
Steam Turbine ◽  
Turbine Blades ◽  
Time Measurement ◽  
Blade Tip ◽  
The Common ◽  
Steam Turbine Blades ◽  
Residual Fatigue ◽  
Precise Time

The paper deals with an assessment of blade tip movements based on precise time measurement known under abbreviation BTT - Blade Tip Timing. In addition to the common way of BTT data processing, a new Residual Fatigue Lives of Blades system (RFLB) proceeds further up to estimation of blade damages by processing output files generated by BTT systems.

scholarly journals Theoretical and Experimental Investigation of a 34 Watt Radial-Inflow Steam Turbine with Partial-Admission

2020 ◽  
Author(s):  
Patrick Wagner ◽  
Jan Van herle ◽  
Jurg Schiffmann
Keyword(s):  
Steam Turbine ◽  
Pressure Ratio ◽  
Turbine Blades ◽  
Turbine Rotor ◽  
Tip Clearance ◽  
Experimental Results ◽  
Tip Leakage ◽  
Hot Air ◽  
Partial Admission ◽  
Blade Tip

Abstract A micro steam turbine with a tip diameter of 15 mm was designed and experimentally characterized. At the nominal mass flow rate and total-to-total pressure ratio of 2.3 kg/h and 2, respectively, the turbine yields a power of 34 W and a total-to-static isentropic efficiency of 37 %. The steam turbine is conceived as a radial-inflow, low-reaction (15 %), and partial admission (21 %) machine. Since the steam is limited in the system (solid oxide fuel cell), a low-reaction and high-power-density design is preferred. The partial-admission design allows for reduced losses: The turbine rotor and stator blades are prismatic, have a radial chord length of 1 mm and a height of 0.59 mm. Since the relative rotor blade tip clearance (0.24) is high, the blade tip leakage losses are significant. Considering a fixed steam supply, this design allows to increase the blade height, and thus reducing the losses. The steam turbine drives a fan, which operates at low Mach numbers. The rotor is supported on dynamic steam-lubricated bearings; the nominal rotational speed is 175 krpm. A numerical simulation of the steam turbine is in good agreement with the experimental results. Furthermore, a novel test rig setup, featuring extremely-thin thermocouples (0.15 mm) is investigated for an operation with ambient and hot air at 220 °C. Conventional zero and one-dimensional pre-design models correlate well to the experimental results, despite the small size of the turbine blades.

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