Application of the hottest vibration analysis tech

2022-08-05
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Application of vibration analysis technology in equipment fault diagnosis

motors, pumps, fans and other equipment are important equipment in petrochemical production. Once these equipment fail, it will have an adverse impact on safety production. Therefore, it is of great significance to strengthen the maintenance and monitoring of such equipment to ensure its safe production. My comrades and I have gained some experience in the research of rotating machinery fault self diagnosis technology through the research on vibration analysis technology and the application and practice of rotating equipment self diagnosis technology. Now I will introduce it to you in the hope of getting criticism and correction from experts and comrades

I. Development and practical application of vibration analysis technology

in the past, we mainly relied on traditional simple means such as listening, touching and watching to judge the running state of rotating equipment in the process of equipment operation and maintenance. This kind of perceptual judgment is far from the actual operation state of the equipment. The change of the frequency spectrum of the equipment vibration waveform cannot be detected by human listening, touching and seeing. Therefore, some sudden faults often occur, such as the most common bearing faults, gear faults, blade falling off and dynamic balance faults; We are often in a passive maintenance state, so that small problems can lead to major accidents. In particular, the continuity of chemical production often leads to a chain reaction of damage to other equipment due to the untimely handling of damage to one equipment. It brings heavy burden to safety production and maintenance. Therefore, mechanical experts and equipment managers at home and abroad are looking for a better solution, so that the cause of the accident can be accurately judged in the initial state of the fault, so that the equipment can be pre maintained, while the electro-hydraulic servo universal experimental machine takes the servo valve or proportional valve as the control element to control, changing passive into active. After extensive exploration and continuous practice, we have adopted the vibration analysis system to detect the faults of rotating machinery. Condition monitoring and fault diagnosis of equipment is to quantitatively measure the technical state of the machinery when the machinery is running or the mechanical structure is basically not disassembled. Through the processing and analysis of the measured signals and in combination with the historical status of the diagnostic object, it can quantitatively identify the real-time technical state of the mechanical equipment and its parts and components, predict the abnormal and future technical state of the machinery, and analyze and judge the fault location and cause, Timely determine necessary countermeasures and the most appropriate repair time. Equipment condition monitoring and fault diagnosis technology is conducive to modern equipment management; Overcome the phenomena of "excessive maintenance" and "insufficient maintenance" in the maintenance work, so as to achieve the goal of the most economical cost and the highest comprehensive efficiency of the equipment within the life cycle of the equipment. The accident analysis of many large-scale machinery at home and abroad shows that the performance and complexity of modern mechanical equipment are continuously improving and the correlation of each part is becoming larger and larger due to the development of modern mechanical equipment in the direction of large-scale, automation, high precision, high efficiency and electromechanical integration; Mechanical equipment has a series of characteristics such as high sudden failure rate, large shutdown loss, high maintenance cost and long maintenance cycle; In order to ensure the normal operation of large machinery and make it play the best technical performance, it is necessary to carry out regular condition monitoring and fault diagnosis. Through a period of practical application, we have not only mastered the operation of the instrument, but also explored some diagnostic rules and practical skills, and achieved good results in practical application. At present, the vibration analysis technology is becoming more and more mature in the fault diagnosis of rotating machinery

II. Introduction to the working principle of equipment vibration analysis

generally speaking, equipment vibration signals are very complex, but from the perspective of data processing classification, they are divided into deterministic signals and non deterministic signals. Through the practical application of fault diagnosis, it is concluded that in rotating machinery, the connection and rotor of the unit are misaligned and unbalanced, the gear teeth in the gearbox are pitted, peeled and broken, the parts in the rolling bearing are damaged, and there is oil film whirl in the sliding bearing. These common faults are all deterministic signals, which can be described by functional relationship, That is, their characteristic frequencies can be determined through theoretical calculation and spectrum analysis technology, so as to determine the type and location of the fault. The vibration analysis instrument uses the voltage acceleration sensor to convert the vibration signal into electrical signal, process and analyze the vibration signal, and obtain the accurate values of various vibration quantities of the equipment, so as to judge whether the equipment is in good operation, the fault location and cause, and the maintenance method. In order to better study the fault diagnosis technology of vibration analysis equipment, it is necessary to have a certain understanding of waveform theory, mechanical theory and computer application. There are many parameter indexes of vibration. After long-term practice and learning, we believe that time domain spectrogram, frequency domain spectrogram, axis trajectory diagram, pulse index and kurtosis index are very effective for equipment fault analysis. The following describes the equipment fault analysis based on the data collected by lm8900 system produced by Beijing limeng Tengfei Development Co., Ltd. and the rotating machinery self diagnosis system software developed by the company

III. basic Atlas

1. Time domain Atlas

time domain waveform is the most common engineering signal. The time domain waveform is intuitive and easy to understand, but it contains a large amount of information. It is not easy to see the time domain atlas contained, which can evaluate the overall performance of the equipment. Through the time domain waveform atlas, we can see whether the equipment exceeds the standard and the problems of parts and components. In the time domain waveform collected by lm8900 system, five parameters of "peak value, mean value, effective value, kurtosis index and pulse index" are given. During collection, three different data types of "acceleration, velocity and displacement" can be selected according to the running speed of rotating equipment

the so-called 3-loop control speed with displacement control is used for the diagnosis of high-speed rotating equipment, and the speed is above 10000rpm. Judging the equipment operation status by the effective value of acceleration, the Japanese standard is that it is in good condition if it is less than 0.5mm/s, but domestic equipment generally can not meet this requirement. After practice, the value is enlarged to 1mm/s, which basically meets the requirements. In petrochemical production, there are few equipment whose rotational speed exceeds the past 10000rpm, so the acceleration value can generally be used as auxiliary data for equipment fault diagnosis

speed, for diagnosis of medium speed rotating equipment, the speed is between 600rpm and 10000rpm; The effective value of speed is less than 4.5mm/s; It can be judged that the equipment operates normally. If it exceeds 11.8mm/s, it is a dangerous value and must be stopped for maintenance. The speed value is the most commonly used value for fault diagnosis of rotating machinery

displacement is used for the diagnosis of low-speed equipment. If the speed is below 600rpm, the displacement is the judgment basis for the fault diagnosis of low-speed equipment. 0.06mm is the dangerous value, and if it is greater than 0.1mm, it must be stopped for maintenance. Since the fault of low-speed equipment can be easily diagnosed by other methods, the displacement value is generally only used as auxiliary data for equipment fault diagnosis

kurtosis index is an abstract concept with the meaning of "fourth order origin moment of random process x (T); it reflects whether there is impact in the waveform and the kurtosis and flatness of small groups." In recent years, diagnostic engineers have conducted in-depth research on this index and found that the kurtosis index is an important basis for diagnosing the faults of rolling bearings, gears and rotating parts on rotors, and put forward a relatively complete theory, that is, the "double bathtub" curve. In the development process of the faults of rotating machinery bearings or gears, the kurtosis index rises suddenly after the first smooth transition, and then goes through the smooth transition again and rises suddenly again, This sudden rise will cause serious damage to the equipment, so timely finding the second bathtub bottom plane is the best and last time to solve the equipment failure. The kurtosis index is dimensionless. Theoretically, when the kurtosis index exceeds 3, it means that the equipment needs to be overhauled. However, practice has proved that under different circumstances, setting the kurtosis index as 4, 5 and 6 as dangerous values can meet the use requirements

pulse index is a common dimensionless index, which is easy to understand. It is an auxiliary value for fault diagnosis of rotating mechanical equipment

2. Frequency domain diagram

frequency domain diagram can analyze the specific problems of rotating machinery equipment faults in detail. It is an important tool for equipment diagnosis. Frequency domain atlas and time domain atlas can be converted to each other by fast Fourier transform

IV. monitoring object and method for judging fault type

a, object

1 rotor

2 rotor parts

3 foundation and accessories

b. judge the fault sequence:

first the unit vibration, then the foundation vibration,

first find the rotor system, then the auxiliary parts

c. diagnosis of fault types of rotating machinery

1 rotor system:

(1) unbalance

(2) misalignment

(3) loose rotor components

(4) rotor deformation (bending, cracks)

2 rotor parts: (1) rolling bearing

(2) sliding bearing

(3) gear Crank connecting rod mechanism

3 rotor system (unit) and auxiliary parts:

rigid instability

whether the lubricating oil pressure is appropriate (oil film whirl)

ventilation system (cooling system)

d, common rotor faults and characteristics

v. actual collection and analysis

in the process of practical application, we tested the semi lean liquid potassium carbonate solution pump 1107-ja of Liaotong company and the torch gas compressor gb701a of ethylene company, Coincidentally, the gb701a compressor of ethylene company is in the early stage of maintenance, so the fault map of the equipment is successfully collected, and the reference opinions for the maintenance of the equipment are put forward

1. The flare gas compressor gb701a is a twin-screw positive displacement pump with relatively complex structure. At the time of detection, the equipment was in the early stage of maintenance. Through detection, the characteristic spectrum of the equipment fault was successfully checked, and a reference basis was provided for maintenance. The following is the inspection of the equipment

equipment name: flare gas compressor gb701a

equipment No.: gb701a

name of measuring point: main screw bearing A2

measuring point No.: main screw bearing A2

equipment power: 25kW

installation location: ethylene battery limit

sampling time: 2005513 09:19:17

data type: speed

measuring point name: auxiliary screw shaft extension end A1

measuring point No.: A2 at the shaft extension end of the auxiliary screw

equipment power: 25kW

installation location: ethylene battery limit

sampling time: 2005513 09:19:17

data type: speed

diagnosis conclusion:

according to the comprehensive monitoring vibration map of the screw compressor, we found that the vertical and horizontal vibration of part a of the compressor are both large, and the horizontal vibration is larger. We believe that the main cause of the vibration may be at screw A1, where there may be bearing problems and rotor balance problems. It is recommended to focus on inspection and troubleshooting, and it is recommended to replace it as soon as possible, To avoid major failures. We believe that the faults of the screw compressor may be:

I. there is a large wear fault of the bearing at the screw compressor shaft a, and it is recommended to disassemble, check and replace it in time

II. The bearing of screw compressor a is loose, that is, the bearing runs out of sleeve. It is suggested that the screw compressor should focus on checking the bearing at this measuring point. It is also necessary to check whether the screw compressor rotor assembly is loose and whether the dynamic balance is out of tolerance. The reason may be the screw pressure of the whole machine

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