Papers by Keyword: Life Assessment

Abstract: A large number of inclusion defects were found during the metal supervision process of 15Cr1Mo1V steel main steam pipeline of the Russian-made thermal power unit. In this paper, the tracking supervision research of 15Cr1Mo1V steel pipe elbow with inclusion defects is carried out. The variation law of strength, toughness, metallographic structure and creep rupture strength with inclusion defects at different operating time is studied. Type and composition of inclusions are analysed and creep fatigue crack evaluation of the most serious inclusion defects discovered is performed. The results show that with the increase of service time, the room temperature and high temperature strength of the material gradually decreased, the impact toughness deteriorated, the ductile-brittle transition temperature increased and greater than room temperature, the metallurgical organization aging grade rose from 3 to 4, creep rupture strength decreased, creep aging was increasingly serious, and creep residual life reduced. The main inclusions are plastic MnS、SiO₂ and severe inclusion levels up to 3. Longitudinal inclusions are mostly long-chain features, and the ends are sharp but no sharp cracks are found at the sharp ends; the transverse inclusions are granular. Creep fatigue crack evaluation show that there was no obvious growth of material inclusion defects with the increase of service time, it is necessary to strengthen the supervision and inspection of brittle inclusions in the follow-up operation.

Abstract: In order to improve the economy of operation of transformer, this study presents a strategy to ensure the safety of power transformer for the situation of overload operation of parallel transformer. According to the variation of actual transformer operation, the authors divide the daily load curve into two typical time periods. In the high load operation period, except the constraint of minimum power loss for the economic operation, the factor for hot-spot temperature rise of the transformer should also be considered, so that an economic operation mode and parallel switching time could be obtained. This strategy estimates the hot spot temperature by the finite difference method, and obtains the optimal switching time through binary searching, according to the environment temperature and load curve. The analysis of the example of the operation of two sets of three winding transformers in parallel with different capacity shows that the method of optimization of the operation could reduce the loss. In the meantime, it could ensure the operation safety of the transformer, and prolong the service life of transformer.

Abstract: A third-class model based on condition monitoring is built in this paper. And an assessment system with operating information, the hottest temperature, and electric filed strength as indicators is realized. Then the equation of health level index for electric power equipment in this model is given. In the end, the health level index and life assessment of transformer are analyzed and calculated by example.

Abstract: Pattern of number of PD events ("NE" for short) variation detected by UHF online monitoring was found through experiments, demonstrating that in the first half life of oil-paper insulation the NE value declined at the beginning and then kept stable, while it increased sharply in the later half. Least square linear regression was applied to calculate the changing rate ("CR" for short) of the latest 168 measurements of NE, which turned out to be an appropriate indicator of life stage for its monotonicity over time from the initiation of PD till final breakdown. The Grubbs method was also applied to exclude erroneous data and to determine the credible variation of CRs.

Abstract: The effective methods of the ageing and life assessment for large and medium-sized power transformers used in nuclear power plants are analyzed and described, including the thermal ageing life assessment method for transformer solid insulation, the gas analysis method of CO and CO2 in the transformer oil, the average degree of polymerization method, furfural content analysis method, and the analysis method based on the insulation ageing-related electrical parameters. The analysis results show that the methods used can reasonably assess the remaining life of the transformers. These methods have important reference value to the ageing and life management for the large and medium-sized power transformers in nuclear power plants.

Abstract: Most of the steel structures used in industrial and non-industrial applications are exposed to outdoors weathering conditions. Organic coating typically protects them from corrosion. The maintenance actions can be done efficiently only if there is sufficient information of the condition. Therefore, the deterioration of the coating system and its lifetime has to be assessed accurately. This paper focuses on the development of parameters based on adhesion strength useful for that purpose. Three parameters are proposed, namely stress intensity factor, strain energy density, and J-integral.

Abstract: The aim of this collaborative study was to measure mechanical properties of 14MoV67-3 steel taken from small sections of material machined in-situ from an operating high pressure collector pipe after different operating lifetimes (from 0h to 186 000h) at elevated temperatures (540°C). Conventional methods of measuring mechanical properties of materials, such as the uniaxial tensile test require relatively large test samples. This can create difficulties when the amount of material available for testing is limited. One way of measuring mechanical properties from small quantities of material is using micro tensile test samples. In this work, micro-samples with a total length of 7.22mm were used. Digital Image Correlation method (DIC) was employed for the strain measurements in a uniaxial tensile test. This paper shows that there is measurable difference in the yield, ultimate tensile strength and elongation to failure as a function of the plant operating conditions. This work demonstrates, therefore, a ‘semi-invasive’ method of determining uniaxial stress-strain behaviour from plant components.

Abstract: An important characteristic of a steam power plant is its ability to maintain reliability and safety of the plant against frequent start-ups and load changes. Transient regimes arising during start-ups, shut-downs and load changes give rise to unsteady temperature distribution with time in steam turbine rotor(HP/IP), which results in non-uniform strain and stress distribution. The rapid increase of temperature and rotational speed during starts-ups, especially, makes conditions more severe and causes main components’ damage and reduction of life span for steam turbine. Thus accurate knowledge of thermal and centrifugal stresses are required for the integrity and lifetime assessment for the turbine rotor. So far, only elastic calculations are currently performed for simplicity. However, it is well known that the materials of steam turbine rotor deform inelastically at high temperature. Existing models proposed to describe the viscoplastic(rate-dependent) behavior are rather elaborate and difficult to incorporate with computer simulations in the case of complex structures. In this paper, the life assessment for steam turbine rotor was established by combining the inelastic behavior and the finite element method. The inelastic analysis was particularly focused on viscoplastic behavior that is simple enough to be used effectively in computer simulation and matches the essential features of the time-dependent inelastic behavior of materials reasonably well for cyclic loading under non-isothermal conditions. Using this study, life consumption of steam turbine rotor can be obtained.

Abstract: As a number of aged fossil power plants recently increased, the precise life assessment of critical equipments gets to be important more than ever. Despite of infrequent likelihood of failure, the equipments in high pressure and temperature operation condition have traditionally been considered as critical because of huge consequence of the equipments and hence life assessment of fossil power plant has been focused on all of the severe operated equipments for past decades. Nowadays, with Risk-Based Inspection technology being developed rapidly, most of the power plant utilities get a chance to reduce the scope of the inspection and test and to extend the interval for the life assessment. This paper provides methodology based on Risk-Based Inspection technology to optimize the life assessment work scope and interval and also demonstrates the enhanced life assessment procedure including risk assessment of equipments.

Abstract: The operation mode of thermal power plants has been changed from the base load to duty cycle. From the changeover, fossil power plants cannot avoid frequent thermal transient state, for example, start up and stop, which results in thermal fatigue damage at the heavy section components. The rotor is the highest capital cost component in steam turbine and requires long outage for replacing the new one. For optimized power plant operation life and inspection management of rotor is necessary. It is known as general that start-up and shutdown operation greatly affect on steam turbine life. The start-up operation condition is especially severe because of the rapid temperature and rotational speed increase, which causes damage and reduction of main components life of steam turbine. The start-up stress of rotor which is directly related life is composed of thermal and rotational stresses. The thermal stress is due to the variation of steam flow temperature and rotational stress is due to the rotation speed of itself. In this paper, the analysis method of start-up stress of rotor which considers simultaneously temperature and rotation speed transition is proposed, which includes a case study regarding 500MW fossil power plant steam turbine rotor. Also, the method of damage quantitative estimation of fatigue damage to operation condition is described. The method can be applied to find weak points to the fatigue damage. Using the method, total life consumption can be obtained, and can be also used for determining future operation mode and the life extension of old fossil power units.