scholarly journals Risk-Based Planning of Diagnostic Testing of Turbines Operating with Increased Flexibility

Energies ◽  
2020 ◽  
Vol 13 (13) ◽  
pp. 3464
Author(s):  
Martyna Tomala ◽  
Andrzej Rusin ◽  
Adam Wojaczek
Keyword(s):  
Power Unit ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
Diagnostic Testing ◽  
Turbine Rotor ◽  
Testing Time ◽  
Rotor Steel ◽  
Term Operation ◽  
Life Consumption ◽  
Start Ups

An increase in the share of renewable sources in the energy mix makes coal-fired power plants operate in new conditions that require more dynamic operation and adequate flexibility. The frequency of the power unit start-ups increases and so does the frequency of changes in loads. This intensifies some life consumption processes, such as low-cycle fatigue and crack propagation in the turbine components. Further operation of power unit elements that have already been in service for a long time has to be supplemented with new diagnostic and repair procedures that take into account the intensification of life consumption processes. This article gives predictions about the propagation rate of potential cracks in the turbine rotor for different scenarios of the power unit’s long-term operation. A method is presented of rational selection of the diagnostic testing time based on risk analysis. The method is used to estimate the optimal interval after which diagnostic testing of a 200 MW turbine rotor should be carried out. Changes in the rotor steel crack toughness are evaluated based on the results of testing of microspecimens cut out of the rotor. Turbines with more frequent start-ups and shorter start-up times necessitate performance of diagnostic testing of the rotor central bore after about 12 years of turbine operation.

scholarly journals Analysis and management of operating risk created by turbine operation under flexible regimes

2019 ◽  
Vol 137 ◽  
pp. 01026 ◽  
Author(s):  
Andrzej Rusin ◽  
Adam Wojaczek ◽  
Martyna Tomala
Keyword(s):  
Power Unit ◽  
Power Plants ◽  
Considerable Increase ◽  
Low Cycle Fatigue ◽  
Diagnostic Testing ◽  
Propagation Rate ◽  
Rotor Steel ◽  
Start Up ◽  
Long Time ◽  
Non Destructive

The new conditions in which coal-fired power plants, especially 200 MW units, have to operate require a considerable increase in the dynamics of their operation. The power unit start-up frequency increases and so does the frequency of changes in loads. This intensifies some wear processes, such as low- cycle fatigue and crack propagation in particular. Therefore, further operation of power units which have already been in service for a long time has to be supplemented with results of analyses and tests taking account of the intensification of wear processes. The paper presents a proposal for an extension of standard diagnostic testing of turbines by adding small punch tests (SPT) of the rotor material micro specimens. The SPT method enables a fast quasi non-destructive assessment of changes in mechanical properties, especially rotor steel embrittlement due to the turbine previous operation. The other element of the proposed testing is the analysis of the propagation rate of potential cracks in the rotor and assessment of the rotor failure probability for different scenarios of the power unit further operation.

scholarly journals Low cycle fatigue modelling of a steam turbine rotor steel

2019 ◽  
Vol 23 ◽  
pp. 149-154
Author(s):  
Ahmed Azeez ◽  
Robert Eriksson ◽  
Mattias Calmunger ◽  
Stefan B. Lindström ◽  
Kjell Simonsson
Keyword(s):  
Steam Turbine ◽  
Low Cycle Fatigue ◽  
Turbine Rotor ◽  
Rotor Steel ◽  
Cycle Fatigue ◽  
Steam Turbine Rotor

Life-Refurbishment of Service-Degraded Gas Turbine Buckets

2004 ◽  
Author(s):  
Yomei Yoshioka ◽  
Daizo Saito ◽  
Kazutoshi Ishibashi ◽  
Junji Ishii ◽  
Atsuhiko Izumi ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Low Cycle Fatigue ◽  
Hot Isostatic Pressing ◽  
Development Program ◽  
Charpy Impact ◽  
Turbine Rotor ◽  
Fatigue Properties ◽  
Maintenance Cost ◽  
Life Consumption ◽  
Non Destructive

Various methods have been developed, and used in practice, to reduce the maintenance cost of gas turbine hot parts by extending the replacement life. The life-refurbishment process by Hot Isostatic Pressing (HIP) is one of our accomplishments for the buckets retired due to the scheduled life and was confirmed to rejuvenate the microstructures and the tensile, Charpy impact, creep and low cycle fatigue properties to a condition equivalent to or even better than the new ones under the development program. According to above mentioned accomplishments, a number of HIP refurbished buckets were reinstalled in a Chubu Electric Power Co. Inc. (CEPCO) 1100°C-class gas turbine rotor on December 1999 and operated successfully for 2 years under the joint program. Those buckets also served for destructive and non-destructive evaluations after operation. From those tests, we reconfirmed the reliability of the HIP refurbished buckets and also validated that the life-consumption rate was the same as new ones.

Influence of Creep on Low-Cycle Fatigue Life Assessment of Ultra-Supercritical Steam Turbine Rotor

2014 ◽  
Author(s):  
W. Z. Wang ◽  
J. H. Zhang ◽  
H. F. Liu ◽  
Y. Z. Liu
Keyword(s):  
High Temperature ◽  
Steam Turbine ◽  
Fatigue Damage ◽  
Low Cycle Fatigue ◽  
Turbine Rotor ◽  
High Temperature Creep ◽  
Cycle Fatigue ◽  
Term Operation ◽  
Start Up

Linear damage method is widely used to calculate low-cycle fatigue damage of turbine rotor in the long-term operation without fully considering the interaction between creep and low cycle fatigue. However, with the increase of steam turbine pressure and temperature, the influence of high-temperature creep on the strain distribution of turbine rotor becomes significant. Accordingly, the strain for each start-up or shut-down process is different. In the present study, the stress and strain during 21 iterations of continuous start-up, running and shut-down processes was numerically investigated by using the finite element analysis. The influence of high-temperature creep on low cycle fatigue was analyzed in terms of equivalent strain, Mises stress and low cycle fatigue damage. The results demonstrated that the life consumption of turbine rotor due to low cycle fatigue in the long-term operation of startup, running and shutdown should be determined from the full-time coverage of the load of turbine rotor.

Optimizing Lifetime Consumption and Increasing Flexibility Using Enhanced Lifetime Assessment Methods With Automated Stress Calculation From Long-Term Operation Data

2013 ◽  
Author(s):  
Jan Vogt ◽  
Thomas Schaaf ◽  
Klaus Helbig
Keyword(s):  
Power Plants ◽  
Low Cycle Fatigue ◽  
Combined Cycle ◽  
Transient Temperature ◽  
Steam Turbines ◽  
Transfer Coefficients ◽  
Term Operation ◽  
Flexible Mode ◽  
Start Up ◽  
Safety Margins

In the past most of the steam turbines were designed as base load machines. Due to new market requirements based on the effect of renewable energies, power plant operators are forced to operate with more frequent start-up events and load changes, resulting in a fundamental higher low cycle fatigue (LCF) lifetime consumption. Traditional methods of lifetime assessment often use representative start-ups, for the calculation of LCF damage, which can provide very conservative results with reasonable safety margins. For a high number of starts these safety margins may result in an overestimation of the LCF damage. At Alstom, an enhanced method for lifetime assessment has been developed, that evaluates the actual lifetime consumption from real operation data in an automated manner and provides much more realistic results. The operation data is used to calculate the transient temperature distribution and heat transfer coefficients along the rotor for each start-stop cycle. The corresponding stress distribution in the rotor is evaluated by means of a Finite-Element-method analysis. Finally the number of remaining cycles is extracted for the most critical locations using material data. In combination with the creep damage the lifetime consumption is evaluated. The entire process is highly automated, but also facilitates easy monitoring through the lifetime engineer by graphic presentation of calculation results. Using this enhanced method of lifetime assessment, the computed lifetime consumption is closer to the actual value, supporting the planning of overhauls and component replacements and minimizing the risk of failure or forced outages. The utilization of remaining lifetime can be optimized in favour of a more flexible mode of operation (e.g. low load operation and fast start-up) or extension of operational lifetime for conventional and combined cycle power plants.

Thermal Aging Effect on Environmental Fatigue Life of CF8M Cast Stainless Steel at Strain Rate 0.04%/s Under PWR Operating Condition

2010 ◽  
Author(s):  
Ill-Seok Jeong ◽  
Wan-Jae Kim ◽  
Hyun-Ik Jeon
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Strain Rate ◽  
Thermal Aging ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
Operating Conditions ◽  
Pressurized Water ◽  
Operating Condition ◽  
Term Operation

In order to see the effect of thermal aging on environmental fatigue life of CF8M cast austenitic stainless steel (CASS), low-cycle environmental fatigue tests of thermally aged CF8M CASS at the condition of fatigue strain rate 0.04%/s were conducted at the operating condition, 15MPa, 315°C of pressurized water reactor (PWR) environment. Test results of low cycle fatigue life tests for thermally aged specimens simulating 60 operating years were compared with ones of un-aged CF8M CASS in room temperature air and PWR operating conditions to see the effect of the thermal aging on environmental fatigue life. This kind of experiment would be useful to verify the fatigue integrity of long-lived components and to predict plant safety of long term operation beyond design life because current approach of evaluating environmental fatigue is so conservative to apply it to the long-lived components in pressure boundary of nuclear power plants.

High Power Steam Turbine Lifetime Increase by Means of Front End Seal Arrangement and Start-Up Heating Conditions Improvement

2019 ◽  
Author(s):  
Leonid Moroz ◽  
Roman Kochurov ◽  
Julija Bakhmutska ◽  
Vladimir Goloshchapov
Keyword(s):  
Steam Turbine ◽  
High Power ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
High Stress ◽  
Economic Benefits ◽  
Film Condensation ◽  
Condensation Process ◽  
Front End ◽  
Start Ups

Abstract Use of high power steam turbines in maneuver regimes by power plants became a widely-distributed practice in chase of short-term economic benefits. At the same time, these actions resulted in much higher levels of lifetime consumption for turbines which are not designed for high numbers of start-ups. The purpose of the present study is to improve operational flexibility for 325 MW steam turbine through design modifications. For the accurate simulation of rotor thermo-structural state and lifetime, an improved methodology was developed. The approach allows engineers to account for the steam film condensation process and the steam flow physics for regions with the anticipated high-stress levels at front-end seal zone, and the influence of the inter-casing space steam film condensation on the flow parameters in the front-end seals chambers. Based on the simulation results for the 325 MW supercritical steam turbine HP rotor, the design changes of the front-end seal arrangement and heating conditions modification during the pre-warming phase are proposed. The results show that the proposed changes make it possible to provide a more uniform heating and lower thermo-stress level for the high-pressure cylinder rotor at the front-end seal region during the pre-warming phase, which results in an increased allowable number of turbine start-ups. The influence of heating conditions on thermo-stresses and low cycle fatigue lifetime for the baseline and modified designs as well as modeling details for transient thermo-structural analysis have been discussed.

Effect of Microstructure on Mechanical Behavior of a Combined Steam Turbine Rotor Steel

2015 ◽  
Author(s):  
Ming-Liang Zhu ◽  
Lin-Bo Mei ◽  
Fu-Zhen Xuan
Keyword(s):  
Power Plants ◽  
Rupture Strength ◽  
Plastic Zone Size ◽  
Turbine Rotor ◽  
Combined Cycle ◽  
Load Shedding ◽  
Rotor Steel ◽  
Fracture Appearance Transition Temperature ◽  
Fracture Appearance ◽  
Lower Temperature

High-pressure low-pressure (HLP) combined rotors have been gradually used in advanced power plants. In the present work, tensile, impact, fatigue and creep experiments were conducted to comprehensively investigate mechanical properties of a newly developed combined rotor steel 25Cr2NiMo1V based on microstructure influence. Fatigue crack growth (FCG) rates were obtained by both constant amplitude method and the load-shedding technique. A new method based on cyclic plastic zone size being equalling to grain size was introduced to defferentiate corresponding FCG data in the Paris regime and the near-threshold regime. Results show that 25Cr2NiMo1V steel has sufficient lower temperature strength and toughness in LP zone, and good high temperature creep properties in HP zone. Fracture Appearance Transition Temperature (FATT) at center core of LP is lower than 3°C with a tensile strength of 850 MPa, and creep rupture strength of HP for 105 h is respected to reach 165 MPa at 566°C. By comparison with other combined rotor materials in literature, the properties of 25Cr2NiMo1V steel enable it particularly suitable to HLP rotor material for advanced combined cycle power plants.

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