The Analysis of Condition Monitoring and Fault Diagnosis - Essay Example

Condition Monitoring and Fault Analysis Name: Reg No. Course: Date: A key part of fault finding techniques is the documentation of equipment. In order to help support fault diagnosis and fault location, the documentation useful include, but not limited to the ones described herein. Drawings help determine possible fault points. General arrangement drawings is one such a document. From the drawings of the arrangement, the surface nature, joints, weight bearers and force balances can be determined easily, rotators and possible places of stress concentration can be easily located and analysed. Electrical drawings is the other important drawings in fault diagnosis. From the drawings, it can be determined points of circuit convergence and divergence. The circuit breakers can also be useful in fault analysis. Convergence and/or divergence joints are possible points of failure and require monitoring (Anon, 2016). Maintenance documents are too a useful resource for fault location. Parts list is one of the maintenance documents. From the parts lists, parts that are more exposed to fault can be determined. This follows deductions on the tribology and physics of the material used for the parts for example some parts on an equipment may constitute fragile material (Anon, 2016). Manufacturer’s manuals are another important maintenance documents. From the documents, it can be determined the environment within which a said part of the equipment will be used. It can also be used to locate the possible constraints (force, exposure, and general usability) and thus possible fault locations (Ltda., 2016). Commissioning documents provide vital information that can be useful in fault location. Factory acceptance testing (FAT), for example can be used to determine how the level of trust by the inspectors where a list of fault areas need redress can be concluded. From it the equipment being used are determined and proved if excellently functional or otherwise. A bad report may imply increased sources of failure that need monitoring. Equipment commissioning documents can as well be used in determining whether or not the equipment meet the required standards or not. Qualification documents are a good measure of standard acceptability. Documents that show low qualification may imply a highly faulty system or installation. Design qualification (DQ) for example is useful in determining whether a given system meets standard design rules. A DQ report implying compromised design locates faults more easily (McCall and French, 1978). Cooling water system is one of the systems that require close monitoring. Several operational issues have been identified with the cooling water system. Herein are discussed some of the problems particularly the type of inspection and test equipment that would be appropriate as well as how they would be used to detect and locate the faults. Increase in current flow to the motor is one such a problem. This problem can be checked by the electric multimeter which is a combined multirange voltmeter, multirange ohmmeter and multirange current meter. An increase in the current flow to the motor results to increase in the current meter reading. As such, if beyond tolerable amounts, it can be concluded that there’s a fault. One other test equipment is the current tong meter. It is mainly used to measure the AC. It measures the magnitude of a sinusoidal current (mainly high AC which are easily read). It is clamped around a conductor in order to measure the current. They are used if large increments result to failure since they are less sensitive to low currents (thus cant accurately measure small changes). An oscilloscope is the other equipment that is useful. It is mainly used when low current increments cause a significant impact on the motor (Power Plant Engineering, 2013). Reduction in the pump’s output flow and pressure is another common problem. Pump pressure is determined by the pressure gauge. A reduction in pressure is read/detected by a reduction in the pressure gauge below a certain threshold. Pressure sensors are used to measure high speed changes in pressure. As such they may be needed in this circumstance if high speed changes in pressure are a significant fault in the system. For dirty/ wastewater, an ultrasonic flow meter is appropriate. They are appropriate where low pressure drop, chemical compatibility and low maintenance are required. Low flow is detected when the meter reading falls below certain threshold. Misalignment between the pump and motor shafts causes excessive noise, vibration, coupling-and bearing-temperature increases hence premature failure of bearings, couplings and/or shafts. The misalignment can be detected using a straightedge tool. In the case of misalignment, the tool fails to indicate flatness. True straightness is checked using a laser line level as an optical straightedge where it illuminates accurately a straight line on a flat surface. Misalignment is detected when there’s deviation from the straight line on the flat plane of the laser light (Bloch and Geitner, 2012). In order to determine the faults in the pumping system, a fault finding table was constructed as shown below. The faults in this case are simply the failed equipment. Problem Equipment Reasons Loss of water flow from TA102 to TA101 Failed pump PU102 Loss of power Failed impeller Failed valve SV102-1 Loss of power Seized valve Failed level switch LS-101-1 Loss of power Seized switch Failed level switch LS 102-2 Loss of power Seized switch Failed valve CV101 Loss of power Seized valve Failed valve SV 102-2 Loss of power Seized valve Failed flow transmitter FT101 Loss of power Seized transmitter Failed valve SV102-2 Loss of power Seized valve Loss of water flow from TA101 to TA102 Failed valve SV101 Loss of power Seized valve Failed level detector LS101-2 Loss of power Seized detector Failed detector LS102-1 Loss of power Seized detector Overflow of water from TA102 to TA101 Failed pump PU102 Failed power cut Failed FS102 Seized switch Failed power Failed SV102-1 Seized valve Failed power Failed LS101-1 Failed power Seized detector Failed LS102-2 Failed power Seized detector Uncontrolled overflow from TA101 to TA102 Failed LS101-2 Failed power Seized detector Failed LS102-1 Failed power Seized detector Failed valve SC101 Seized valve Failed power From the table, the possible parts that can fail include the pump, the valves and the sensors. The faults that can be easily drawn from the table are as tabulated below Pump no flow high flow low flow Valves Fail closed Fail open Fail mid range (half open) Level sensors Fail on Fail off Fail to switch The failure of a pumping system arises due to component parts failure. Investigating the potential causes of failure and how the components could fail is very important in averting the failure. Some of the component parts of the pumping system that could easily fail include pump drive end bearing, the impellor and the mechanical seal. Drive end would be described as the end that is connected to the driven device. In this case therefore the drive end bearing is the bearing at the shaft end of the motor. With this regard of position, the bearing experiences additional stress arising from torque. This arises from the excessive loads that cause premature failure. Tight fits, brinelling and improper preloading also bring about early fatigue failure. Load reduction can avert this problem (Bloch and Geitner, 2012). Overheating of the root causes of drive end bearing failure. Temperatures exceeding 400oF anneals the ball and ring material. The loss in hardness results in reduced bearing capacity thereby causing early failure. Extreme heating may result in bearing deformation. High temperatures also destroy the lubricants. Heavy electrical heat loads, inadequate heat paths and insufficient cooling when loads and speeds are excessive are the main culprits causing high temperatures. Lubricant failure is another cause of the bearing failure. Excessive wear of the balls follow the lubricant failure (which arises from restricted lubricant flow or excessive temperatures), causing overheating and associated problems/catastrophic failures (Bloch and Geitner, 2012; Bloch and Geitner, 1997). The failure of the impeller arises from cavitation, dirt or solids in the water. Cavitation simply means formation of bubbles in the fluid which later collapse. The collapsing results in shockwaves which easily damage the blades. Sanction cavitation occurs when the pump is under high vacuum condition/low pressure. It may result in large chunks of material being removed from the impeller. Discharge cavitation arises when the pump discharge pressure is extremely high. It is expected that premature wear affects the impeller vane tips and pump housing as illustrated below. Some of the causes of cavitation include Having the pump at too high of a distance above the fluid source, Having too small of a diameter of suction pipe, Having too long of, a distance of suction pipe, Having too many fittings on the suction pipe, Handling a liquid with a low vapor pressure and Running the pump too fast. The loss or damage of the impeller vanes results degraded pump performance. It leads to fluctuating flow rate ad discharge pressure. It can cause excessive pump vibration which could then damage pump bearings, wearing rings and seals. The solids and dirt damage the vanes of the impeller causing similar damages. The mechanical seal is another very important component. Mechanical seals consist of mating and seal rings and the shaft sleeves and retainers. Mechanical seal failure can be caused by dry running, high temperatures or when it starts to leak. High temperatures result in seal embrittlement and compression set and low pressure leakage. Proper functioning of the of the mechanical shaft seals with hard/hard seal face material pairings depends on lubrication by pumped material. Poor lubrication and dry running produces the results below. First, dry running results from absence of pumped medium in the pump. It results in friction between the seal faces to increase with a consequence of rise in temperatures which can be high enough to burn the elastrometers where the O-ring is in contact with the hot seal ring. Associated with friction is the vibration of some parts of the seal. This reduces the life of the seal as well as fatigue on account of vibrations. For the purpose of a generalized understanding, a seal damage by component is as shown described herein. The complete seal could be clogged or vibrated to damage. Seal rings could be fractured, deposits outside seal faces or thermal cracks arising from high temperatures. The elastrometer could be burnt and decomposed by high temperatures which in turn leads to lost flexibility or even ruptured/fractured. Metal parts could be cracked, deformed by high temperatures, pitted or worn just like the shaft/sleeve (). A failure modes and effect analysis (FMEA) is used to determine the most appropriate maintenance strategy that should be applied to equipment associated with the pumping system. Using the figure below as an example of the cooling water system, the process of carrying out FMEA can be as described below. First, a system FMEA is carried out by breaking down the system into constituent systems/equipment. In this case, the cooling water system is broken down into pumps, valves, heat exchanger, flow meters, pressure sensors and temperature sensors. FMEA, as a process, simply involves determining risk number associated with failure of the equipment hence the due priority that should be given to the equipment relative to others. This risk analysis, therefore depends on the outcome effect associated with the failure. The outcome depends on the nature of failure. For example, a failure process may lead to health and environmental problems, failure of the whole production associated with equipment failure or equipment downtime associated with the failure. For each component/equipment these factors are given an index depending on their strength. Strongest likely effect is attributed a value of five and one with least impact is attributed a value of one in that order between 1 and 5 depending on strength of effect. For FMEA, the index of associated risk is computed by multiplying all the factors. The equipment with the highest risk factor is given the highest priority of monitoring. For the example of the cooling water system, the components were broken down and analysed in accordance with the above described criterion. The equipment were then analysed as shown in the table below. Equipment Description Equipment Number Score A. Consequences of failure with respect to Safety Score B. Consequences of failure with respect to the polluting the environment Score C. Consequences of failure with respect to loss of manufacturing output Score D. Consequences of failure with respect to equipment downtime Risk factor Pump PU101 3 3 2 2 36 Pump PU102 5 4 3 3 180 Pump PU103 2 3 3 2 36 Pump PU104 3 1 2 1 6 Valve HV101-1 2 2 2 4 32 Valve HV101-2 3 2 3 3 54 Valve HV102-1 4 3 4 1 48 Valve HV102-2 5 2 5 1 50 Valve HV103-1 3 3 1 1 9 Valve HV103-2 1 2 5 1 10 Valve HV104-1 1 1 4 1 4 Valve HV104-2 4 4 2 2 64 Heat Exchanger HE101 1 5 3 3 45 Heat Exchanger HE102 2 5 5 1 50 Flow Meter FI101 5 5 1 2 50 Flow Meter FI102 1 5 4 3 60 Flow Meter FI103 4 3 5 5 300 Flow Meter FI104 4 2 5 2 80 Pressure Sensor PI101 2 4 4 4 128 Pressure Sensor PI102 1 2 5 1 10 Pressure Sensor PI103 1 3 3 4 36 Pressure Sensor PI104 4 5 1 1 20 Temperature Sensor TI101 4 2 1 5 40 Temperature Sensor TI102 5 2 5 4 200 Temperature Sensor TI103 5 3 5 2 150 Temperature Sensor TI104 5 4 1 2 40 From the risk factor analysis, it can be concluded that the flow meter number FI103 has the highest risk factor of 300 and should therefore be accorded the highest attention followed by temperature sensor TI102 with a factor of 200. The valve HV104-1 has the lowest risk factor of 4 and thus should be accorded the least attention. Higher priority is given in the order of increasing risk factor. With regards to this analysis, an equipment can be categorised as either being Vital, essential, supporting or non-critical. Equipment with the highest factor is said to be the most vital equipment. 10% of the FMEA score fall under vital equipment. This includes equipment with a score 200-300. Equipment between 70% to 90% score are said to be essential. In this case, an equipment with a score above 100 can be said to be essential. 40% - 70% of the equipment can be said to be supporting equipment with a factor above 50. The equipment with less than 50 FMEA score can be said to be non-critical equipment. They constitute less than 40% of the total equipment. The vital equipment require continuous monitoring and immediate replacement in the event of anticipated failure. In that order, non-critical equipment calls for reduced monitoring and in the event of failure, replacement can be weighed against such factors as cost of replacement. On the basis of FMEA results, it is important to apply equal importance in monitoring all the equipment since failure of one equipment easily leads to failure of the others sometimes within a short time. Failure of temperature sensors for example can lead to undetected failure of the motor. FMEA forms a continuous improvement programme. This is because in helps identify the components that need be improved first relative to others. After the improvement, those that were given less priority become the first in need for attention and eventually, the series of improvements hence FMEA forming part of a continuous improvement programme. To address this point clearly, a change in FMEA process can help in improved equipment. Extension from the basic process as done earlier can help improve the equipment to near perfect status. Some of the criteria used as an extension, i.e after the first FMEA process 1, include loss of business profit, the time taken to repair the equipment, the cost of repair, availability of parts and the mean time between failure. Equipment whose failure causes big loses can be attributed a factor 5 while those with small loses can be attributed factor 1. Equipment whose failure calls for long time to repair the equipment can be attributed 5 as opposed to those with a short time which are attributed 1. Expensive costs of failure in case of equipment is attributed 5 whereas cheap ones are attributed an FMEA factor 1. Long lead times associated with availability of parts are attributed a factor 5 and 1 for those with short lead times. If the mean time to repair is long, the FMEA score attribute is 1 in the order of reducing effect up to short mean time to repair which is attributed 5. In the event of a system failure, some analytical tools are used in determining the potential root cause. One such example that can be used to illustrate some of the analytical tools is the cooling water system. The tools used include a fault tree which is used to identify probable causes and the cause and effect diagram. For the fault tree diagram, a fault is identified then pathways leading to the fault are identified. Some of the potential faults in this system include motor overheats, reduced impeller effect, impaired pimp drive end and mechanical seal failure. Using the faults in the previous table of faults, the several other trees can be as shown below. Pump no flow high flow low flow Valves Fail closed Fail open Fail mid range (half open) temperature sensors Fail on Fail off Fail to switch The cause-effect analysis involves grouping the causes. The causes associated with this kind of problem are either human causes/problems (which range from untrained, unsupervised or just basic human error) or machine initiated problems, methodology problems or material related problems. The figure below is an illustration of the same. References Anon, (2016). [online] Available at: http://machining.grundfos.com/media/16611/shaftseal_chapter5.pdf [Accessed 16 Apr. 2016]. Anon, (2016). [online] Available at: http://www.schaeffler.com/remotemedien/media/_shared_media/08_media_library/01_publications/barden/brochure_2/downloads_24/barden_bearing_failures_us_en.pdf [Accessed 16 Apr. 2016]. Bloch, H. and Geitner, F. (1997). Major process equipment maintenance and repair. Houston, Tex.: Gulf Pub. Co. Bloch, H. and Geitner, F. (2012). Machinery failure analysis and troubleshooting. Oxford: Butterworth-Heinemann. Ltda., C. (2016). Cost and Importance of Documentation in Engineering. [online] Cim-team.com.br. Available at: http://www.cim-team.com.br/modern-electrical-engineering-blog/cost-and-importance-of-documentation-in-engineering [Accessed 16 Apr. 2016]. McCall, J. and French, P. (1978). Metallography in failure analysis. New York: Plenum Press. Power Plant Engineering. (2013). Springer Verlag. Read More

As such, if beyond tolerable amounts, it can be concluded that there’s a fault. One other test equipment is the current tong meter. It is mainly used to measure the AC. It measures the magnitude of a sinusoidal current (mainly high AC which are easily read). It is clamped around a conductor in order to measure the current. They are used if large increments result to failure since they are less sensitive to low currents (thus cant accurately measure small changes). An oscilloscope is the other equipment that is useful.

It is mainly used when low current increments cause a significant impact on the motor (Power Plant Engineering, 2013). Reduction in the pump’s output flow and pressure is another common problem. Pump pressure is determined by the pressure gauge. A reduction in pressure is read/detected by a reduction in the pressure gauge below a certain threshold. Pressure sensors are used to measure high speed changes in pressure. As such they may be needed in this circumstance if high speed changes in pressure are a significant fault in the system.

For dirty/ wastewater, an ultrasonic flow meter is appropriate. They are appropriate where low pressure drop, chemical compatibility and low maintenance are required. Low flow is detected when the meter reading falls below certain threshold. Misalignment between the pump and motor shafts causes excessive noise, vibration, coupling-and bearing-temperature increases hence premature failure of bearings, couplings and/or shafts. The misalignment can be detected using a straightedge tool. In the case of misalignment, the tool fails to indicate flatness.

True straightness is checked using a laser line level as an optical straightedge where it illuminates accurately a straight line on a flat surface. Misalignment is detected when there’s deviation from the straight line on the flat plane of the laser light (Bloch and Geitner, 2012). In order to determine the faults in the pumping system, a fault finding table was constructed as shown below. The faults in this case are simply the failed equipment. Problem Equipment Reasons Loss of water flow from TA102 to TA101 Failed pump PU102 Loss of power Failed impeller Failed valve SV102-1 Loss of power Seized valve Failed level switch LS-101-1 Loss of power Seized switch Failed level switch LS 102-2 Loss of power Seized switch Failed valve CV101 Loss of power Seized valve Failed valve SV 102-2 Loss of power Seized valve Failed flow transmitter FT101 Loss of power Seized transmitter Failed valve SV102-2 Loss of power Seized valve Loss of water flow from TA101 to TA102 Failed valve SV101 Loss of power Seized valve Failed level detector LS101-2 Loss of power Seized detector Failed detector LS102-1 Loss of power Seized detector Overflow of water from TA102 to TA101 Failed pump PU102 Failed power cut Failed FS102 Seized switch Failed power Failed SV102-1 Seized valve Failed power Failed LS101-1 Failed power Seized detector Failed LS102-2 Failed power Seized detector Uncontrolled overflow from TA101 to TA102 Failed LS101-2 Failed power Seized detector Failed LS102-1 Failed power Seized detector Failed valve SC101 Seized valve Failed power From the table, the possible parts that can fail include the pump, the valves and the sensors.

The faults that can be easily drawn from the table are as tabulated below Pump no flow high flow low flow Valves Fail closed Fail open Fail mid range (half open) Level sensors Fail on Fail off Fail to switch The failure of a pumping system arises due to component parts failure. Investigating the potential causes of failure and how the components could fail is very important in averting the failure. Some of the component parts of the pumping system that could easily fail include pump drive end bearing, the impellor and the mechanical seal.

Drive end would be described as the end that is connected to the driven device. In this case therefore the drive end bearing is the bearing at the shaft end of the motor.

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