RU2164344C2 - Method for inspecting and predicting condition of gas- turbine engines primarily those with intershaft bearings - Google Patents

Abstract

FIELD: aviation; power engineering; gas-transfer stations in gas and oil industries. SUBSTANCE: method involves periodic measurements of iron particles in lubricating oil while engine is running. In the process threshold concentration of iron particles for normal wear C_g≠ 1,8÷2,0 g/t is determined and if further growth of C_g is detected, operating time of engine to pre-failure condition (300-400 h) is evaluated. EFFECT: improved safety and in-service maintenance of engine. 8 dwg

Description

 The invention relates to the field of aviation, electric power, gas and oil industry, in particular to drives of gas pumping units at gas compressor stations, and in particular to methods for diagnosing the condition of engines of gas turbine engines with shaft bearings in operation.

 The invention serves to increase the safety of the system, determine the moment of occurrence of special control over the operation of the system. The development of the gas industry [1] is inextricably linked with the construction and commissioning of powerful gas pipelines connecting gas fields with industrial regions of the country.

 A gas turbine engine designed to drive centrifugal superchargers is widely used as the main energy equipment of compressor stations. However, the use of gas turbine units is associated with the need to diagnose the state of gas turbine engines.

 Known methods for monitoring the status of drives - methods for recording the state of contacting media [2], when the important diagnostic information is oil, which is used to lubricate and cool friction surfaces (bearings, gears, etc.). Diagnostic control is carried out by the presence of chips and the iron content in the oil. Chip signaling devices are used, which give a signal in the presence of metal particles in the oil.

So on the American engine GF-6, the amount and T ^{o of} oil are recorded, the readings of the chip detectors and the pumping line, the pressure drop across the oil filter, the parameters of the minimum oil pressure warning device. However, the method does not determine threshold values for the concentration of metal particles for normal, increased wear.

 A known method of monitoring the state of engine drives using [3] a device for determining impurities in the oils of automobile engines. If the oil contains water or impurities, its properties as a lubricant and insulator deteriorate. The device is an electric probe for measuring the electrical conductivity of oil without sampling. The probe is equipped with a printed circuit and is connected to an electrical measuring circuit configured so that when the permissible level of pollution is exceeded, a light signal is issued. The probe is connected to an ohmmeter having a measuring device and then to a signaling device and a warning lamp.

 However, with this method, metallic impurities are not detected in the oil, only qualitative indicators of engine reliability are determined.

 Known methods for monitoring the state of gas turbine drives when chip detectors are used. The particle conductivity detector [4] is designed to determine the presence of metal particles in a lubricating oil. The detector has a contact type sensor with a number of contacts. The output signal is proportional to the number of contacts that are simultaneously closed by metal particles. Has a sump where the screen filter is placed; indicator chains are used to signal the appearance of metal particles in the oil.

 Known failure indicator of metal bearings [5], installed in the oil line. The alarm sensor communicates with the pump and is located after the pump, in front of the filter. Oil enters the sensor and exits through the valve. The conductive elements are sensitive to the presence of metal particles that are contained in the lubricant. The conductors are connected to the relay; a fuse and a switch are connected to the winding of the signal step-down transformer. The signaling device has red and green lamps (associated with the transformer winding).

 However, in these methods of monitoring the condition of the drives using these signaling devices there are no parameters for indicating impurities in the oil. To determine the malfunction of a specific unit. There is a known method [6] for monitoring the state of a gas turbine drive using X-ray spectral analysis — a method for determining very small compounds (thousandths of a percent) of most chemical elements in a test substance. X-ray spectral analysis is based on the use of the dependence of the radiation frequency of the lines of the characteristic X-ray spectrum of elements on their atomic number and the relationship between the intensity of these lines and the number of atoms participating in their formation.

 An X-ray pattern records the spatial distribution of X-ray diffraction scattering by a sample. This is a shadow image of an object in x-rays, revealing the macroscopic structure of foreign inclusions.

 Analysis by absorption spectra is used to determine heavy elements in the lungs (oil, oils). A continuous X-ray spectrum is used and the dependence of the magnitude of the absorption jump on the concentration of the element being determined in the sample is determined. If the analyzed sample is characterized by a constant composition of impurities, then the attenuation of the continuous reactive spectrum that has passed through the analyzed and standard samples is compared with an X-ray photometer.

 Quantitative x-ray analysis is based on the assumption that the line intensity of the characteristic spectrum is directly proportional to the number of atoms of the elements in the sample - emitters, placed under the exciting x-ray beam in the fluorescence method.

 The source of information on the internal conditions existing in the oil system of the drive and transmission is the concentration of metals as wear products in lubricating oil. The concentration of metal in oil is very undesirable down to its traces, which requires the use of X-ray spectrometric analysis, which determines the concentration of metals up to 1 / million parts of oil (1 ppm), 3 - 5 μ.

 The occurrence and development of a defect in friction units is accompanied by a sharp increase in the concentration of metals in the lubricating oil in comparison with the concentration of metals in the absence of a defect. In the latter case, the concentration of metals in the oil will remain almost constant.

 When determining the amount of metal (or a combination thereof) and identifying it using X-ray spectral analysis, it is possible to detect incipient damage to a particular component of the lubricant system by increasing the metal concentration above normal, corresponding to the absence of a defect. The analysis must be performed continuously during the entire time the engine is running, which is impossible for many reasons. Therefore, the frequency of analyzes should be a compromise between the frequency of analysis for normal wear conditions and the frequency reflecting the history of damage to a particular mechanism, for example, for gas turbine engines and gearboxes, the frequency of analysis of oil samples is 10 ± 2 hours.

 The compositional value of various structural alloys used for components and parts of the oil system (bearings, pumps, drives, etc.) allows you to obtain the necessary information about the type of damaged parts. A comparison of the metals found in the analysis of lubricating oil samples taken during excessive wear and tear with the combination of metals contained in the parts of the components and other elements of the oil system gives an idea of where the damage occurred.

 In the method [7], which contains a periodic measurement of the amount of metal in the lubricating oil of the oil system during engine operation, the threshold concentrations of metal particles are determined with the maximum permissible concentration characterizing the state, increased wear of the friction elements of the drive, and the state of the engine is evaluated.

 However, the existing method for assessing the metal content in oil, allowing confirming the destruction of the engine, does not predict the onset of destruction, the precautionary state.

The purpose of the invention is to increase the reliability of the drives of gas pumping units by predicting the beginning of the destruction of engines. To solve this problem, in a method for monitoring and predicting the state of gas turbine engines, mainly engines with inter-shaft bearings, and on the basis of these engines drives gas pumping units, which includes periodically measuring the level of iron particles in samples of lubricating oil of the oil system exposed to contacting media and rubbing surfaces in the process of engine operation, determining threshold values for the concentration of iron in the engine oil for normal and high shennogo wear particles in the measurement of iron concentration C _w in the oil is determined thresholds iron concentration within With _x = 1.8 - 2.0 g / m, and further growth in the presence of C _x in normal wear and increasing vibration predict predotkaznoe state and set the operating time of the GPA drive engine to the pre-failure state equal to 300–400 h. In this case, the pre-failure state region is characterized by a sharp increase in the average value (4–8 times) and the scatter of the measured values of the iron concentration above 1.8 g / t, depending on the change in m Asla, the operating mode of the drive, previously practically not affecting.

The invention is illustrated in FIG. 1, which shows the law of change in the concentration of metals (C _g , g / t) in oil during engine running hours (τ, hour), where I is the running-in period of engine components, II is linear (within acceptable values) is normal surface wear , III - an intensive increase in the average value; С _Ж - prediction of the pre-failure condition (destruction, breakdown), while taking into account the occurrence of vibration of the drives, turning on the chip alarm in place and concluding that it is possible to further use the engine.

 In FIG. 2 is a block diagram of an X-ray analysis of metals. The circuit includes 1 - an x-ray tube, 2 - a filter with a sample of oil to be studied; 3 - a control panel with a digital display indicator; in FIG. 3 - 8 are graphs of changes in the iron content in the working oil of aircraft engines depending on the operating time.

Assessment of changes in the content of wear products in the working oil MS-8P is carried out by analyzing these changes in the operation of engines installed on aircraft with different operating times, i.e. the nature of the change in this indicator is estimated. A typical dependence (Fig. 1) of a change in the metal content in oil on the operating time [7] is known, including:
- the period of running-in engine components,
- normal wear,
- intensive wear preceding the destruction of any engine assembly.

 The change in the metal content in the working oil is determined depending on the engine operating time at the stages of normal and increased wear of friction units, including when the engines are placed under special control when deviations from normal operation indicators appear.

 Oil samples are taken from engines that, during operation, have failed due to the destruction of their components.

 To assess normal or increased wear, oil samples are taken according to the recommended methods [8]. On engines, MS-8P oil sampling is carried out every (50 ± 10) h of plaque, not more than 15 minutes after the engine is stopped, with the first portion spilled (in the amount of 10-15 ml). When sampling oil, the sampling date, engine hours, oil grade, facts of a possible oil change are recorded, increased vibrations or the “Shavings in oil” signal are noted.

 Samples within 15 hours from the moment of sampling are analyzed on a Bars-3 X-ray spectral instrument. In the selected samples, the iron content in copper is determined.

 It was revealed that the most informative metal for gas turbine engines of all the Bars-3 detected on the device is iron, therefore, the change in its content in oil is evaluated.

The results of the analysis are plotted on graphs to assess the dependence of the iron content in oil on engine life, i.e. C _w = f (τ)
As a criterion for the state of the engine in terms of oil, an increase in the iron content over the time of operation of the engine is taken. In this case, the excess of the normalized values obtained in the analysis of iron concentration is considered (4 g / t - for setting the engine under special control, 6 g / t - for taking the engine out of operation).

In addition, the nature of the change in the dependence C _f = f (τ) is estimated taking into account the oil change and the appearance of signs of improper engine operation (vibration, the “Chip in oil” signal firing, etc.). When detecting a noticeable increase in the iron content in oil, in some cases in combination with other indicators, it is concluded that the engine components are likely to fail.

The change in the concentration of metal in oil C _W , depending on the operating time of the engine, preceding the destruction, is observed in the form of two types:
- a sharp increase in C _g to C _MPC values
- a slight increase in the level of concentration of metals within C _w <4.0 g / t, which with a sufficiently large operating time (over 2500 h) increases sharply.

Regardless of the operating time and the concentration of iron in the normal operation area, the breakdown of the nodes is preceded by a noticeable increase in the average value of the metal (iron) content, but not reaching the limit values of C ₁ = 4 g / t and C ₂ = 6 g / t. Over a period of time, the metal content changes, the amount of dispersion increases, depending in particular on the change in oil and the operating modes of the drives (the results of the changes do not go beyond the permissible limits), which indicates increased wear of the parts. Subsequently, immediately before the breakdown, during the period of about 100-150 hours, an intensive (4-8 times) sharp increase in the concentration of iron ( _Cg ) is observed to a value that exceeds the permissible concentration or less, but is accompanied by increased vibrations or the Chip in Oil signal .

The results of analyzes of the iron content in the oil of the 1st engine, presented in the graph of FIG. 3, showed how a constant and small iron content (≈ 1.0 g / t) in oil during the period of production up to 2250 h sharply increased during the next selection (i.e. after 50 h) and exceeded 10 g / t. In addition, the “Shavings in oil” signal was triggered. The engine was removed and when it was disassembled, the destruction of the shaft bearing was recorded. In this case, there was a sharp increase in the concentration of iron to values far exceeding the maximum permissible concentrations (C _MPC = 6.0 g / t) and the destruction of the engine assembly was observed with an operating time exceeding 2000 hours.

 The change in metal content in the oil of the second engine is shown in FIG. 4. The graph shows that prior to operating hours of 1950 hours, a noticeable change in the metal content in the oil was not observed, and the iron level was 0.7 g / t and almost remained constant. However, in the oil sample taken after the next 50 hours, the iron content increased by 2 times and reached the level of 1.4 g / t. In subsequent oil samples, the iron content at an operating time of 2050 h was 2.3 g / t, at 2100 h - 4.1 g / t, and at an operating time of 2150 h reached 9.4 g / t, which significantly exceeded the maximum normalized value of 6 g / t After that, the engine was decommissioned and when it was disassembled, the destruction of the inter-shaft bearing was revealed, which was the reason for the uniform (2 times after each selection) rapid increase in the concentration of iron in the oil samples.

 Changes in the iron content in the oil of the third and fourth engine from operating hours are shown in the graphs of FIG. 5 and 6, respectively. So, for the 3rd engine (Fig. 5), a constant and small iron content (below 1 g / t) in the oil in the operating zone up to 2750 h periodically increased, approaching 2 g / t. Then, with an operating time of 3750 h, the iron concentration began to increase sharply and after 200 h reached a value of 6.3 g / t, which exceeded the MPC. After that, the engine was decommissioned.

 For the 4th engine, the iron content was almost constant (≈ 1.0 g / t) until the operating time of 3350 hours, then the iron concentration increased to 2 g / t. This value decreased slightly several times, and after 3800 hours of engine operation, the iron content began to increase sharply and in 150 hours increased from 2 g / t to 6.5 g / t.

 In the 5th engine, the change in iron content was similar. Since the operating time of 2400 hours, its value from 1 g / t began to constantly increase, reaching in some cases values exceeding 4 g / t. When the engine was running for 3450 hours, the iron concentration became equal to 11.5 g / t, which caused the engine to be removed.

 It can be concluded that the values of the concentration of metals preceding the destruction of the engine exceeded the MPC values and were recorded during operating hours of more than 2000 hours.

 In addition, in these studies, 2 more characteristic changes in the content of metals in the working oil were noted when the engine collapsed during 1000 hours or less. These data are shown in the graphs of FIG. 7 and 8.

 In FIG. Figure 7 shows that the iron content in the MS-8P oil reached a significant value of 3 g / t with an engine running time of 850 hours. During its further operation, the iron concentration in the oil continued to increase and in some cases exceeded the normalized values of 4 g / t and 6 g / t . The exception was samples taken immediately after changing the oil in the oil system.

When the engine was running for 1100 hours, the iron concentration in the oil reached 8.2 g / t, while increased vibrations were recorded. The iron content in this case did not decrease even after a complete oil change. Then, there was a gradual increase in the concentration of _Cf to values exceeding the _{maximum permissible concentration} , at which increased vibrations were recorded when the engine was running for 1100 hours. This case of a change in the iron concentration from the running time can be attributed to case II, which is typical for the 2nd engine. The engine was removed, and as a result of its development, the destruction of one of its components was recorded.

 There was a destruction of the motor shaft bearing without reaching standard values (4 g / t and 6 g / t) - FIG. 8. In this case, a one-time increase in the concentration of iron (5.4 g / t) occurred already at 300 hours. However, after changing the oil, this value decreased to 3 g / t.

 After this, a monotonic increase in the concentration of iron occurred, although its absolute value did not exceed the normalized value of 4 g / t. The described change in the iron content in the oil is more intense than during normal engine operation and coincided with the appearance of increased vibrations. After 800 hours of operation, the engine was disassembled, and the destruction of the inter-shaft bearing was discovered.

 As can be seen from the above data, the first and second group of engines in which the destruction of individual nodes occurred is united, in that the iron concentration in all cases, after its constant and small value, began to increase, and over a short period (150 ... 350 h) reached values exceeding the MAC.

 Therefore, if the iron content in the oil taken from the engine oil system begins to increase, and this process continues after reaching 2 g / t, then such an engine must be taken under control, since this indicates engine operation with increased wear. If after several selections of the oil the level of iron in it stabilizes at a value below 2 g / t, then it is possible to return to its normal operation. In addition to sampling at a time strictly specified by the regulations, it is necessary to monitor other indicators, such as the frequency of oil change in the oil system, the level of vibration, and the cases of triggering of the "Shavings in oil" alarm. This will make it possible to more correctly assess the state of the engine by changing the metal content in the working oil during its operation, to evaluate the time the engine is running to a pre-failure state and to determine the moment of special control over the operation of the engine.

Used Books
1. Belokon N.N., Porshakov B.P. Gas turbine installations at compressor stations of gas mains. M .: Nedra, 1969.

 2. Birger I.A. Technical diagnostics. M .: Nauka, 1978. p. 189, 192.

 3. French patent N 2164975, F 16 N 29/00.

 4. England patent N 1314458, G 01 N 15/06.

 5. Patent of England N 1256291, F 16 N 29/00, G 01 P 13/00.

 6. Blokhin M.A. Methods of x-ray spectral studies. M., 1959.

 7. Bulletin N 205.0515.2 (512-BD-V). Assessment of the technical condition of engines by the concentration of metallic impurities in oil, 1989. Prototype.

 8. Instructions for sampling oil to determine the concentration of wear products from the lubrication systems of gas turbine engines and gearboxes of civilian aircraft. State Research Institute of Civil Aviation, 1976.

Claims (1)

 A method for monitoring the state of a gas turbine engine, including periodic measurement of iron particles in lubricating oil of the oil system during engine operation, determination of threshold values of iron concentration for normal and increased wear, characterized in that when measuring the concentration of iron in oil, a threshold value of iron concentration is determined within = 1.8-2.0 g / t, and if there is a further increase in iron concentration with normal wear and vibration, a precautionary state is predicted and The engine operating time to this state is 300–400 h.

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