CONDITION MONITORING A. R.L Thanmei Sr.E (Telecom), NT

Transcription

1 CONDITION MONITORING A t R.L Thanmei Sr.E (Telecom), NT

2 Analogy

3 What is condition monitoring? The non-invasive monitoring of systems to obtain knowledge of their condition; to distinguish wear, impending failure or other deterioration without disrupting the normal operation of those systems.

4 CAUSES OF MACHINE FAILURE Failures can be subdivided into only two categories Catastrophic failures are sudden and complete. Incipient failures are partial and usually gradual. The goal of machine condition monitoring and fault diagnostics is to detect this onset, diagnose the condition, and trend its progression over time. The time until ultimate failure can then hopefully be better estimated, and this will allow plans to be made to avoid undue catastrophic repercussions.

5 Frequency of failures can be summarized in what is called a bathtub curve. The beginning of a machine s useful life is usually characterized by a relatively high rate of failure. These failures are referred to as wear-in failures. They are typically due to such things as design errors, manufacturing defects, assembly mistakes, installation problems and commissioning errors. The machines then passes into a relatively long period of operation where failures occurrence is relatively low. The failures that do occur mainly happen on a random basis. This period of a machine s life is called the normal wear period and usually makes up most of the life of a machine. The frequency of failures again increases as machine life progresses. These failures are called wear out failures. This gradually increasing failure rate at the expected end of a machine s useful life is primarily due to metal fatigue, wear mechanisms between moving parts, corrosion, and obsolescence

6 Basic Maintenance Strategies Maintenance strategies can be divided into three main types: Run-to-failure Scheduled Condition-based maintenance.

7 Condition-Based (Predictive, Proactive, Reliability Centered, On-Condition) Maintenance Actual assessment of condition of the machinery is used in order to optimally schedule maintenance. To achieve maximum production, and still avoid unexpected catastrophic failures. Advantages of Condition Monitoring Avoid dismantling for survey at fixed intervals Improved reliability Optimized maintenance intervals Less maintenance induced failures Reduced breakdowns Identification and removal of the root cause of failures Improved safety Early identification of potential failures

8 Condition based Maintenance should be employed when the following conditions apply: Expensive or critical machinery is under consideration. There is a long lead-time for replacement parts (no spares are readily available). The process is uninterruptible (both scheduled and unexpected interruptions are excessively costly). Equipment overhaul is expensive and requires highly trained people. Reduced numbers of highly skilled maintenance people are available. The costs of the monitoring program are acceptable. Failures may be dangerous. The equipment is remote or mobile. Failures are not indicated by degeneration of normal operating response. Secondary damage may be costly.

9 Types of Condition Monitoring Periodic Monitoring Periodic monitoring involves intermittent data gathering and analysis with portable, removable monitoring equipment. This type of monitoring is usually applied to noncritical equipment where failure modes are well known. Continuous Monitoring Permanently installed monitoring systems are typically used, with samples and analysis of data done automatically. This type of monitoring is carried out on critical equipment.

10 Machine parameters Velocity Acceleration Displacement Temperature

11 Amplitudes Peak-Peak / 2 Peak x RMS x = Peak = RMS = Peak

12 Selection of Transducer Relationship between the different transducer types in terms of response amplitude and frequency. For constant velocity vibration amplitude across all frequencies, a displacement transducer is more sensitive in the lower frequency range. An accelerometer is more sensitive at higher frequencies. While it may appear as if the velocity transducer is the best compromise, transducers are selected to optimize sensitivity over the frequency range that is expected to be recorded.

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14 Velometer The piezoelectric effect produces an opposed accumulation of charged particles on the crystal. This charge is proportional to applied force or stress. A force applied to a quartz crystal lattice structure alters alignment of positive and negative ions, which results in an accumulation of these charged ions on opposed surfaces. These charged ions accumulate on an electrode that is ultimately conditioned by transistor microelectronics.

15 Proximitor The core applications for this transducer is monitoring shaft expansion, relative vibration and speed on a range of rotating machinery from turbines to pumps and compressors.

16 How it works? The tip of the probe generates an EMF into the surrounding area as a magnetic field. If a conductive target intercept the magnetic field, eddy currents are generated on the surface of the target and power is drained from the EMF. As the power varies with the target movement in the field, the output voltage of the driver also varies. A small dc voltage indicates the target is close to the probe tip and large dc voltage indicates that the target is far away from the probe tip. The variation of dc voltage is the dynamic signal indicating the vibration or displacement.

17 Thermal Imaging Each body above the absolute zero ( C = 0 Kelvin) emits an electromagnetic radiation from proportional to its intrinsic temperature. A part is infrared radiation, which can be used to measure a body s temperature. With the help of a lens (input optics) the beams are focused on a detector element, which generates an electrical signal proportional to the radiation. The signal is amplified and, using successive digital signal processing, is transformed into an output signal proportional to the object temperature. The measuring value may be shown in a display or released as analog output signal, which supports an easy connection to control systems of the process management.

18 Displacement is a good measure at lower frequencies especially less than 5 Hz. The failure mode is generally the stress causing due to the displacement. Velocity measures how often the displacement is being applied in a given time period. It is related to the fatigue mode of failure. Velocity amplitude unit is a good measure in the range of Hz frequency. Even at small displacement amplitude the repeated motion can cause fatigue failure. Above the 2000 Hz the failure is normally force related. Acceleration is measure of the likelihood of force being the mode of failure.

19 Standards API 670 Machine Protection System ISO ( Mechanical Vibration- Evaluation of machine by measurement of non rotating parts) Part 3 Industrial Machines with nominal power above 15 kw and nominal speeds between rpm.

20 API 670 CASING VIBRATION Velomitor measurements are recommended for Casing Vibration and to be monitored in a frequency range between 10 hertz and 1,000 hertz; amplitude from 0 to 20 millimeters per second rms. SHOCK Accelerometers shall be capable of surviving a mechanical shock of 5,000 g, peak, without affecting the accuracy requirements specified. CHEMICAL RESISTANCE Probes, probe extension cables, and oscillator demodulators shall be suitable for environments containing hydrogen sulfide and ammonia. The standard temperature sensor shall be a 100-ohm, platinum, three-lead resistance temperature detector with a temperature coefficient of resistance equal to ohm/ohm/ C from 0 C to 100 C (32 F to 212 F).

21 Accuracy as per API 670

22 Online Monitoring System A monitor system shall include the following alarm and integrity comparison functions: a. For each channel, alarm (alert) and shutdown (danger) setpoints that are individually adjustable b. An alarm (alert) output from each channel to the corresponding alarm (alert) relay. Nonvoting (OR) logic is required. c. A shutdown (danger) output from each channel or voted channels to the corresponding shutdown (danger) relay. Delays for shutdown (danger) relay activation that are field changeable (via controlled access) from 1 to 3 seconds. The display shall be updated at a minimum rate of once per second. Unless otherwise specified, the system shall continuously indicate: 1. The higher radial shaft vibration at each bearing. 2. All axial position measurements. 3. The highest temperature for each machine case. 4. The highest casing vibration for each machine case. 5. All standard speed indication and overspeed detection channels.

23 Parameters Radial Shaft Vibration Monitoring :The fullscale range for monitoring radial shaft vibration shall be from 0 to 125 micrometers (0 to 5 mils) true peak-to-peak displacement. Axial Position Monitoring : The full scale range for axial position monitoring shall be from 1.0 to +1.0 millimeters ( 40 to +40 mils) axial movement. Velocity shall be monitored in a frequency range from 10 hertz to 1,000 hertz: amplitude from 0 to 25 millimeters per second rms. Acceleration shall be monitored in a frequency range between 1,000 hertz and 10 kilohertz from 0 to 500 meters per second squared true peak (0 to 50 g s true peak). Temperature Monitoring :The full-scale range for temperature monitoring shall be available in either SI (0 C to 150 C) or U.S. Customary Units (0 F to 300 F)

24 Mounting Radial Shaft Vibration Probes For monitored radial bearings, two radially oriented probes shall be provided. These two probes shall be: a. Coplanar, 90 degrees (±5 degrees) apart, and perpendicular to the shaft axis (±5 degrees). b. Located 45 degrees (±5 degrees) from each side of the vertical center. Two axially oriented probes shall be supplied for the thrust bearing end of each casing. Both probes shall sense the shaft itself or an integral axial surface installed within an axial distance of 300 millimeters (12 in.) from the thrust bearing or bearings

25 Velometer This mounting configuration uses tapered pipe threads. The accelerometer is already built onto the stud and sealed in its case. However, this type of accelerometer mount is not appropriate for applications where frequencies above 2 khz must be monitored. This design is often used for solid-state velocity transducers (accelerometers with a built-in acceleration to velocity integrator).

26 Amplitude Amplitude Amplitude Waveform Amplitude Frequency Time Time

27 Amplitude Amplitude Diagnosis Waveform Time FFT Spectrum Data Collector/Analyzer Frequency

28 Amplitude Sub- Harmonic 1X 2X Bearing Bearing Gears Bearing 1x Trend of Balance 2x x Trend of Bearings.5 Alarm in/sec Warning.1 in/sec Warning Time (Days) Time (Days)

29 Alert and Danger alarm levels established for the machine are too low to allow the machine to pass through its resonance and the alarms will trigger. These spurious alarms can be dealt with in three ways 1. Trip Multiply can be used to temporarily elevate the alarm levels while the machine is in the RPM ranges corresponding to its resonance. Note that when the machine is outside these RPM ranges, its normal alarm levels are used. Notice also that Trip Multiply provides appropriate alarm levels at all stages of machine operation, ensuring it is never without shutdown protection. 2. Inhibit functionality can be used to temporarily suppress all alarms. Some, such as Rack Inhibit, essentially disable all functions of the monitoring.thus, this type of inhibit will essentially result in running completely blind. Selective inhibit is also available. 3. Alarm Time Delays can be used to ensure that a channel must continuously be above its alarm setpoint for a pre-established duration before the alarm will trigger. This can be useful on machines that pass very rapidly through a resonance.

30 Other Technique Ultrasound Detector 16 Hz and 16,000 Hz. Below 16 Hz are known as infrasound Above 16,000 Hz as ultrasound. Ultrasonic energy data is collected in the 20 khz khz range produce a high frequency "footprint. Ultrasonic CM can detect even incipient faults in bearings as well as adequacy of lubricant. Deteriorating equipments produce a broad range of sound. The high-frequency ultrasonic components of these sounds are extremely short wave in nature. It is relatively easy to detect its exact location by separating these signals from background plant and operating equipment noises. Ultrasonic detectors are capable of accurately interpreting the sounds created by under-lubrication, over-lubrication and early signs of wear.

31 A laser Doppler vibrometer (LDV) is a scientific instrument that is used to make noncontact vibration measurements of a surface. The laser beam from the LDV is directed at the surface of interest, and the vibration amplitude and frequency are extracted from the Doppler shift of the reflected laser beam frequency due to the motion of the surface. The output of an LDV is generally a continuous analog voltage that is directly proportional to the target velocity component along the direction of the laser beam. Some advantages of an LDV over similar measurement devices such as an accelerometer are that the LDV can be directed at targets that are difficult to access, or that may be too small or too hot to attach a physical transducer. Also, the LDV makes the vibration measurement without mass-loading the target, which is especially important for MEMS devices.

32 Wireless Technology The one best-suited for condition monitoring applications is b/g (often referred to as Wi-Fi). Wireless technology eliminates the need for hardwiring for communications and also dramatically reduces sensor cable lengths. Benefits include reduced installation cost, mobility/portability, untethered operation, convenience and reliability.

33 Cloud Technology Cloud brings together a large number of computers to operate a single application. In the past, network-based data collection and analysis required the use of a computer. This data, and the results, would be available only to computers on the network. Cloud computing leverages the power of the Internet. The cloud consists of layers, primarily the back end and the front end. The front-end layers are the ones you use and interact with. The back-end layers consist of hardware and software architecture that support the interface you see. The cloud applies to a CBM solution by allowing access to data from anywhere in the world by anyone with approved access, including thirdparty analysts. This also makes it easier to monitor remote installations - pipelines, offshore drilling rigs, small facilities with limited resources - via existing Internet connections, 3G cellular technology, or satellite communication.

34 AOS Server HQ Process Plant Emerson Service Professional Process Plant KEY: Submit Data Reliability Engineer Subsidiary Access to Reports via Internet Link

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