Condition Based Diagnostic Techniques for Predictive Maintenance- A key of Success to Paper Industry by Sanjay Tyagi, B. P. Thapliyal, R. M. Mathur and A. K. Ray Central Pulp and Paper Research Institute, Saharanpur Purpose of Maintenance of Industry • Fundamental purpose of maintenance in any process industry is to provide the required capacity for production at the lowest cost. • Should be regarded as a RELIABILITY function , not as a REPAIR function Objective of the Maintenance To achieve the correct level of operational reliability and best possible personal safety at minimum cost Cost of Maintenance in Few Industries S. No. Industries Maintenance cost (% of total sales) 1. Pharmaceuticals Industry 16 % 2. Car manufacturing 4% 3. Chemical Industry 6% 4. Engine manufacturing 7% 5. Casting/Forging 8% 6. Paper Manufacturing 10% 7. Steel Industry 15% 8. Electronics 2% Classification of Maintenance Time based Maintenance (TBM) Preventive Maintenance Condition bases Maintenance Maintenance Breakdown Maintenance or corrective breakdown Corrective or Break Down Maintenance (Run to breakdown) • It covers the measures carried out in order to correct or repair faults after they have occurred. • Referred as “repair work” in everyday language. • If industry running too many in expensive machines where process duplicates , less of production is not significant as spares machines can take care off production. • In case of process industries like paper if large unduplicated process machine run to breakdown it severely affected production. Time Based Preventive Maintenance Plant management decides to take some actions with the aim of preventing failure occurring or at least reducing the chance of failure. • Maintenance on fixed or duty basis • Opportunity Maintenance • Design out maintenance • Management Policy • Experience has shown that in a vast majority of cases, above time based maintenance is UNECONOMICAL. • Instead of the reducing failure rate of the machine by replacing wear parts regularly, the opposite often happens. • Reliability of newly serviced machine is reduced temporarily by the interference. • As the actual failure pattern for each individual machine cannot be predicted, an individual approach is therefore needed. • Here role of ON-CONDITION maintenance comes On - Condition Maintenance • Each machine is considered individually by making fixed interval condition measurement to obtain a quantitative value of the ‘health’ of the machine. • In this way servicing is only allowed when measurements show it is necessary. • Basis is that most mechanical components give some warning of their impending failure. Predictive Maintenance • Predictive maintenance technique use sensing instruments to determine health in much the same way a doctor uses medical instruments to determine human health • Instead of stethoscope, blood pressure , X-rays , ECG etc, Predictive maintenance use technologies like Thermography , vibration analysis , oil analysis , ultrasonic measurements to gain early warning in order to plan corrective action. Why condition based diagnostic techniques for predictive maintenance preferred ? • Only 11-17% of failure are time or age related. • On average 83 – 89 % of failure are random. Today’s Maintenance is too Costly • 65% of maintenance performed is corrective • 30 % of maintenance is preventive of which 60% is unnecessary • 5% is predictive Use of condition based Predictive maintenance has dramatically reduces non- value added maintenance by eliminating the need of unnecessarily shutdown of the equipment for maintenance checks Principle of Condition Monitoring Some techniques of Condition based Predictive Maintenance •Thermography: infrared imaging to detect abnormal temperature or hot spots. •Vibration monitoring: accelerometer instruments can be used to detect abnormal or high vibration particularly in bearings. •Oil Analysis: Analysis of oil can detect the deterioration or breaking down of an internal equipment part. •Ultrasonic measurement: Use of ultrasonic technologies to detect leaks or blockages on utility system. Vibration Monitoring • Best known technique for rotating machines such as pumps, air compressor steam turbine etc. • All machines to have some level of small vibration • Increase in the level of vibration is the indication of some mechanical fault in machine. • Vibration analysis uses accelerometer instruments to detect these vibration movements . • Results can be plotted (magnitude v/s frequency) using a mathematical representation called Fast Fourier's Transform (FFT). Which highlight the level of vibration and identifies which frequencies they are present in. Relation Between Vibration and Mechanical Component Typical vibration analysis FFT plot (magnitude vs. frequency) 21 • Vibration analysis plot contain multiple fault frequencies • Analyst needs a detailed knowledge of the operating characteristics of the equipment (such as number of fan blades , RPMs, pulley ratios, bearing types etc) Following type of problems can be determined using vibration analysis • Unbalance of rotary components • Mechanical looseness • Misalignment of drive system , shafts etc. • Belt deflection • Bearing deterioration and gear wear Machine Condition and Vibration Spectrum ILLUSTRATED VIBRATION DIAGNOSTIC CHART(1/3) PROBLEM SOURCE MASS UNBALANCE PHASE RELATONSHIP TYPICAL SPECTRUM 1× RADIAL REMARKS (1)Force Unbalance will be in_phase and steady. (2)Amplitude due to unbalance will increase by square of speed. A.FORCE UMBALANCE 1× RADIAL (1)Coupling Unbalance tends toward 180 degree out_of_phase on same shaft. (2)Amplitude may varies with square of increasing speed. B.COUPLE UNBALANCE (3)And cause high axial vibration as well as radial. (1)Overhung Rotor Unbalance causes high C.OVERHUNG ROTOR UNBALANCE 1× AXIAL & RADIAL 1X RPM in both Axial and Radial. (2)Axial reading tend to be in_phase whereas radial phase reading might be unsteady. Cited from Technical Associate Co. USA Machine Condition and Vibration Spectrum ILLUSTRATED VIBRATION DIAGNOSTIC CHART(2/3) PROBLEM SOURCE MISALIGNMENT A.ANGULAR MISALIGNMENT B.PARALLEL MISALIGNMENT PHASE RELATIONSHIP TYPICAL SPECTRUM REMARKS (1)Angular misaligment is characterized by high axial vibration,180 degree 1× 2× out_of_phase across the coupling. (2)Typically will have high axial AXIAL 1× vibration with both 1X and 2X RPM. 2× (1)Radial misaligment has similar symptoms to Angular,but show high radial vibration which approach 180 RADIAL degree out_of_phase across coupling. (2)2X often larger than 1X,but it depend on coupling type and construction. (3)Misaligment become severe,much higher harmonics(4X-8X) can be generated. C.MISALIGNED BEARING COCKED ON SHAFT 1× (1)Cocked bearing will generate axial 2× vibration and cause the Twisting AXIAL 1 2 3 4 2:00 5:00 8:00 11:00 motion with 180 degree phase shift 1 PHASE 4 top to bottom and/or side to side. 2 3 (2)Atempt to align coupling or balancing will not alleviate vibration,Bearing must be removed and correctly installed Cited from Technical Associate Co. USA Machine Condition and Vibration Spectrum ILLUSTRATED VIBRATION DIAGNOSTIC CHART(3/3) REMARKS (1) Eccentricity occurs when center of rotation offset from a sheave,gear,bearing,motor,etc. 1X MOTOR ECCENTRIC ROTOR PHASE RELATIONSHIP TYPICAL SPECTRUM 1X FAN PROBLEM SOURCE (2)Largest vibration occurs at 1xRPM of eccentric components in a direction thru centers of the two rotors. (3)Horizontal and vertical phase readings usually differ either by 0 or 180 degrees. RADIAL (4)Balancing eccentric rotors result in reducing vibration in one direction but increasing it in other direction. BENT SHAFT 1× (1)Bent shaft cause high axial vibration AXIAL with axial phase difference tending toward 180 degrees. 2× (2)Dominant frequency component normally 1X if bent near shaft center,but at 2X if bent near the coupling. Cited from Technical Associate Co. USA Pressure Fluctuation Analysis of Pump EXAMPLE OF BASIC EXPERIMENTAL DATA Damaged Vane Good Pump Damaged Pump Damaged Pump Pressure Fluctuation Analysis of Pump EXAMPLE Good Pump Pump Pump OF BASIC TEST DATA pump with with cut vane slightly causing damaged cavitation vane Pressure Fluctuation Analysis of Pump EXAMPLE Good v 0.05 OF FILED TEST DATA condition 7 1 3 2 0 5 4 10 20 6 8 30 40 -0.05 Time v 0.05 for one revolution Pump of with 1 3 shaft defected impeller 7 4 5 2 6 9 8 0 -0.05 Time for one revolution Pump v 0.05 with of shaft eccentric 3 4 2 -0.05 Time for one revolution 8 5 1 0 of shaft shaft 6 7 Thermal Imaging or Thermography • Thermography is a temperature profiling of surface or point based on IR Technique • It is based on the principle that every object units certain amount of IR energy and the intensity of this IR radiation is a function of temperature. Thermal imaging is used primarily on electrical panels to identify loose connection but now it is use in other applications . • Checking for blockages in pipes. • Carrying out heat survey in plants. • Mill drive train misalignment • Leakages from steam traps. • Misaligned pumps. What is Thermography? The term "Thermography" refers to the capturing of thermal patterns and data emitted by an object with the use of an infrared imaging and measurement camera. An image is then produced with the camera that can give you data that is otherwise unattainable. Infrared Zoon Wavelength 8 to 14 μm What is Infrared? Infrared light is not visible to the naked eye because infrared wavelengths are too high on the electromagnetic spectrum. The wave lengths are longer than those of visible light and shorter than those of radio waves. This part of the electromagnetic spectrum is what we perceive as heat or “heat radiation”. Infrared is mostly associated with “hot spots”, but did you know that ANYTHING above absolute zero emits infrared heat? 34 INFRARED CAMERA Hot Connector Diagnostics Thermal Image of Compressor Use of Thermography in Maintenance Monitoring of temperature and thermal patterns on • Pumps • Motors • Bearings • Pulleys • Fans • Drives • Conveyors etc while equipment is on line and running under full load. Condition Monitoring Industrial pumps are known to work continuously for many hours. If a pump stops working or starts to wear, this can cost a factory much needed time. Using an IR camera to monitor the temperature of these type pumps, a maintenance worker can spot troubled pumps BEFORE the failure and address with little or no down time - saving you time and money. 41 42 Thermal imge of Plastic moulding showing uneven cooling 43 Thermal Image of Ball Bearing 44 Advantage of Thermography • It is non destructive and non contact type technique • It gives fast, reliable and accurate measurements. • Capable of catching moving targets in real time • Large surface area can be scanned • Measurement in areas inaccessible for hazardous for other methods Disadvantages • Duality cameras are expensive having + 2 or worsen accuracy • Ability to only measure surface areas. Unable to detect the inside temperature Application of Thermography to Paper Industry Steam Traps Leakage from a steam trap 46 Liquid Storage Tank Determination of liquid level 47 Pulley System Hot drive belts 48 Web Process In this web process, you can easily see the non-uniformity of the sheet along the right side 49 50 Motor Coupling Thermal image showing high temperature rise in motor bearing due to misaligned pump Paper Roll Thermal image of paper roll showing moisture variation Tribology based Diagnosis Technology or Lubricant Analysis Tribology:- Branch of science dealing with lubricants and friction in rolling system. • Tribology based diagnosis technology (Lubricant analysis) is now becoming one of the major methods for maintenance engineering. Lubrication Program Followed in Industry - Time based - Oil Lubricant analysis Lubricant Analysis - Lubricant analysis indicates when an lubricant change out is required. - Allows condition based approach to lubricant change would super cede the change frequency based on running hours. - High Iron content indicating wear and tear ( may require further investigation of equipment) - Breakdown in oil additives - High water content - Change in viscosity levels. Tribology based diagnosis technique give prediction regarding machine wear out much earlier as compared to other predictive maintenance techniques. Damage process of machine and lubrication system diagnosis Ultrasonic Measurement What is ultrasonic detection? • Sounds above 20 kHz are ultrasonic • Ultrasonic detectors convert ultrasound to audible sounds. • Ultra sonic inspection can measure efficiency and overall health of your production equipments. • Most versatile maintenance technology available. • Ultrasonic measurement instruments translate high frequency sounds produce by steam or air leaks into the audible range which can be heard through headphones and can be visualized on meter on display. Use of Ultrasonic Testing for Steam Traps • Steam traps are temperature and condensate sensitive devices that open or closes automatically to allow condensate passes to drain. • Steam traps can fail open (in this case both steam and condensate passes to drain) • Steam traps fail closed (this result in internal build up of condensate in steam line) • The fail open steam trap can be detected by the ultrasonic frequencies present from the steam and condensate continuously leaking through the trap. • Failed closed trap can be detected by the absence of ultrasonic frequencies at the trap. Acoustic Emission • This is relatively new technique for the detecting the initiation of cracks in machine structures. •As crack is initiated propagated through material, a stress pulse is generated and transmitted through a material, a stress pulse is generated and transmitted through the material as stress wave. •A transducer mounted on the surface, will detect the disturbance and produce on electric out put. •The source of the wave or location of the crack can be found by using three or more transducers. • The transducers detect high frequencies of 200 kHZ or more. Counters with a threshold limit register a count each time the signal level exceed the threshold values. Several other parameters like rise time, event duration etc. are also used for analysis • Acoustic emission has been successfully used in a number of applications testing of pressure vessels, detection of leaks, cavitations detection, corrosion fatigue crack detection, seal failure detection , detection of damage in rolling . Conclusions • A diagnostic condition – based model can be used for predictive maintenance of equipments and plants in paper industry • Condition monitoring based maintenance may be component of total maintenance system,, involving use of other maintenance strategies as well. It is also to be a part of manufacturing system for machine and production control. • Predictive maintenance is widely accepted approach to the maintenance strategy for paper mills. The benefits of PdM can be extended to promotes a proactive approach to maintenance. Not only in maintenance, this approach also useful as energy conservation measure for plants. • The above strategy would lead to economic benefits and avoidance of unscheduled breakdowns and safety especially for large capacity high speed machines.