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Asset Performance Management through Life

On By Author of #PowerofSeeIn Complexity, Engineering, Maintenance, Management, Rapidinnovation, reliabilityLeave a comment

Abstract: 

The use of the terms Reliability (R) and Maintainability (M) are now in vogue. Does improvement in Reliability and Maintainability (R&M) relate to Maintenance Optimisation or Asset Optimisation? In this paper we would examine whether such a relationship exists. We would also explore whether the DOM (Design Out Maintenance) strategy can be effectively employed in improving Reliability and Maintainability (R&M) of an industrial facility or engineered systems in order to achieve the twin objectives of profitability and sustainability. 

Introduction:

First let us state the definitions of Reliability and Maintainability. Then let us expand on what is actually meant by Maintenance or Asset Optimisation. 

Reliability — “The probability that an item will perform a required function, under a stated condition for a stated period of time.” 

Reliability is therefore the extension of quality into the time domain and may be paraphrased as the ‘probability of a non-failure in a given period of time. 

Maintainability — “The probability of repair in a given time. 
Expanding on that, Maintainability means the probability that a failed item will be restored to operational effectiveness within a given period of time when a repair action is performed in accordance to prescribed procedures. 

Maintenance Optimisation or Asset Optimisation: 

The idea of an optimised maintenance program suggests that an adequate mix of maintenance strategies and actions needs to be formulated and fine tuned in order to improve uptime and extend the total life cycle of the physical asset and assure safe working conditions while bearing in mind limiting maintenance budgets and environmental legislations. This does not seem to be straightforward and may require a holistic view. Therefore, a maintenance concept for each installation or factory it is necessary to plan, control and improve the various maintenance strategies, actions and policies as applied to that installation within the given constraints of time, manpower, skills, kowledge, budgets and legislations. 

A maintenance concept or strategy may in the long term even become a guiding philosophy for a facility to performing maintenance/engineering. In some case, advanced maintenance strategies are almost considered policies on their own. What is certain is that maintenance strategies determine the business philosophy concerning maintenance and engineering and they are needed to manage the complexity of maintenance per se. In practice, it is clear that more and more companies are spending time and effort determining the right maintenance concept and strategies applicable in their context. 

Maintenance Strategies

The usual mix of maintenance strategies that are used for Maintenance/Asset Optimisation are RTF(Run to Failure), TBM (Time Based Maintenance), UBM (User Based Maintenance; also known as Opportunity Maintenance), CBM (Condition Based Maintenance), E-Maintenance and DOM (Design Out Maintenance). 

At present, RTF, TBM, UBM, CBM and E-Maintenance accept the inherent reliability of the physical asset, which they intend to maintain as a given fact. The governing concept is that once a machine is designed, manufactured and installed the upper limits of reliability and maintainability are fixed and can not be improved upon during the operational stage. This is true to a great extent. However, such implicit acceptance effectively limits the upper limits of productivity, performance and profitability of a manufacturing facility. Hence, maintenance, as usually practiced, will fail to sync with the constant market pressure of improving productivity, performance, profitability and sustainability. Failure to do so can often force a company out of business or settle for lower profits till new or additional equipment are purchased to meet desired business goals. Clearly, this is a costly proposition even for cash rich companies. 

The alternative lies in innovating or making greater use of DOM (Design Out Maintenance) strategy on a given set of physical assets considering the operating context of a facility. DOM — instead of considering a system as given, looks at the possible changes (usually small innovations) or possible measures needed to avoid or minimise maintenance in the first place. Adopting a DOM policy implies that maintenance is proactively involved at different stages of an equipment life cycle to solve problems of failures or solve problems that prevents an organisation to achieve its business goals. This may be either done at the procurement stage or after the installation stage, when a machine is in operation. Therefore, it is prudent to apply the DOM strategy both at the procurement stage and at the operating stage to get the best benefits. 

Ideally DOM strategy intends to completely avoid or minimise maintenance throughout the operating life of equipment. Though it may appear on the surface to be unrealistic it is completely possible to do so. One approach will be to consider a diverse set of maintenance requirements at the early stages of equipment design during the procurement process based on available knowledge of potential failure patterns and problems studied against business requirements. The other approach will be to consider the behaviour of the equipment during the operating stage and eliminate, avoid or minimise possibilities of failures through simple modifications/innovations on existing equipment. 

As a consequence, equipment modifications along with process modifications and modification of maintenance processes are geared either at increasing reliability by raising the MTBF (Mean Time Between Failures) or improving maintainability by lowering MTTR (Mean Time To Repair). This may be done in various ways. In some situations, both MTBF and MTTR are to be addressed simultaneously. Per se DOM aims to improve the following:  
1. Equipment Availability by extending the MFOL (Mean Free Operating Life), 

2. Production Capacity by minimising unplanned downtime, 

3. Safety (by eliminating the consequences of failures and reducing failure rates), 

4. Extend the total life cycle of an equipment (by using an equipment for the maximum possible years)

5. Life Cycle Costs (LCC) by minimising maintenance costs 

6. Sustainability through optimised use of resources to run the system at the best operating condition. 

In all the above cases it is imperative to lower or effectively contain the failure rate, potential hazards of an equipment and minimise loss or excess use of resources. 

Modifications (usually small innovations), which lie at the heart of DOM may include the following (not an exclusive list): 

  1. change of dimensions and material flows
  2. change of material 
  3. change of condition of surfaces, structures and interfaces
  4. change of ergonomics 
  5. change of maintenance process, planning and procedures
  6. change of designs, controls and knowledge
  7. change of items and parts, lubricants and redundancy 
  8. change through effective scaling 
  9. change in use of resources 
  10. change in set ups, speeds, and operational processes
  11. change of environment, reactions and interactions
  12. change of thermal and energy flows

However, adoption of DOM strategy does not exclude application of other available strategies in the whole process of improvement. Judicious application of all available strategies is often necessary to achieve the business goals of a manufacturing facility for which a completely new process has been developed, which critically focuses on improving Reliability and Maintainability of a facility. Finally, it depends on the how the DOM projects are formulated, implemented and managed across a manufacturing facility. Here agility and constancy of purpose are two critical management factors that would determine the quality of the results — profitability and sustainability, which effectively translates to lowering the Total Cost of Ownership of facility, which is the essence of Asset or Maintenance Optimisation. 

Design DOM Innovation maintainability reliability

Respect the minds of people by going to where the action is – a fundamental rule of change management

On By Author of #PowerofSeeIn #powerofsee, Advising, Complexity, Consciousness, Design Kata, Education, Engineering, Failure Analysis, Maintenance, Management, Rapidinnovation, rcm, reliability, vibration analysisLeave a comment

All through my professional life, I have been connected to improving something on the shop floor — be it a machine, process or a quality problem.

And I have seen that it is very difficult to improve anything on the shop floor by just passing down verbal instructions or by commanding someone to do something or by conducting a training program in a classroom or handing over a well-documented piece of paper complete with all instructions and a to-do list.

In most cases, people don’t get the idea. As a result, workers on the shop floor soon lose interest in the improvement process and don’t like engineers and managers who just pass down orders sitting at their desks. Respect for engineers and engineering is soon lost. And improvements don’t take place. The company suffers as a result.

Respect for engineers and engineering comes from respecting the minds of workers and supervisors.

This is best done by engineers going down to the area of the shop floor where the improvement is to be made and then explain what they want the workers and supervisors to do and what exactly is to be done. It can be explained verbally by physically touching the parts or equipment where the improvements are to be made or through rough sketches quickly drawn on scraps of paper to instantly clarify the points.

This is an important point in making a change, which is often forgotten by engineers. I call this rule — ‘Respect the minds of people by going to where the action is.”

Attention — the Essential Energy to Achieve & Improve Anything.

On By Author of #PowerofSeeIn Complexity, Critical Thinking, Dibyendu De, Education, Engineering, Failure Analysis, Industry 4.0, IOT, Maintenance, Management, Rapidinnovation, rcm, reliabilityLeave a comment

Information enters our consciousness either because we intend to focus attention on it or as a result of attentional habits based on biological or social instructions.

For example, driving down the extremely busy and often chaotic streets of Kolkata, we pass by hundreds of cars without actually being aware of them. Their shape, size and colours might register for a fraction of a second, and then they are immediately forgotten the next moment.

But our primary objective is to reach from one place to another without an accident or suffering a scratch. But how do we achieve that goal?

So while driving, we occasionally notice a particular vehicle, perhaps because it is moving unsteadily between lanes or because it is moving too slowly or because it looks strange in some way.

The image of the unusual vehicle enters our focus of consciousness and we become intensely aware of it unusual behaviour.

In our minds, such visual information about the car (the abnormal behaviour) gets related to information about other errant cars stored in our memory, which helps us determine into which category the present instance fits. Is this an inexperienced driver, a rash driver, a drunken driver, a momentarily distracted (talking on a mobile phone) but competent driver?

As soon as the event is matched to an already known class of events, it is identified. Now it has to be evaluated: Is this something to worry about? If the answer is yes, then we must immediately decide on an appropriate course of action: Should we speed up, overtake, slow down, change lanes, stop?

All these complex mental operations must be completed quickly and in real time. But it doesn’t happen automatically. There seems to be a distinct process that makes such reactions possible. This process is called attention. It is attention that selects the relevant bits of information from a potential of thousands of bits available.

It takes attention to retrieve the appropriate references from memory, to evaluate the real-life event and then choose the right thing to do.

Despite its great powers, attention can’t step beyond the limits as already described. It can’t notice or hold in focus more information that can be processed simultaneously. Retrieving information from memory and bringing it into the focus of awareness, comparing information, evaluating, deciding — all make demands on the mind’s limited processing capacity. For instance, the driver who notices an errant car will have to stop talking on his cell phone if he wants to avoid an accident, which is, in fact, his goal.

Some people learn to use this priceless resource very efficiently while others simply waste it. The mark of a person who is in control of his/her consciousness is the ability to focus attention at will, to stay away from distractions, to concentrate as long as it takes to achieve a goal and not longer. The person who can do this effortlessly usually enjoys the normal course of everyday life and can effectively meet the challenges of everyday life.

Improving reliability of industrial equipment needs such keen attentional energy which Reliability Centred Maintenance helps one to achieve. It, of course, depends on how well a Reliability Centred Maintenance System is designed, developed and implemented.

But what is essential is the development of memory bank, which can be only developed through comprehensively designed training and education system run over a long period of time.

Computerised Maintenance systems, Condition Based Maintenance technology, rigorously developed Maintenance Planning, Internet of Things, Artificial Intelligence can all help but without a broad-based deep memory bank of different types of failures, failure modes, interactions and mechanisms that create failures, methods to detect failures, interpretation and evaluation of relevant information and deciding the right course of action –improving reliability of industrial systems would remain as a desire only,

Attention is the key to achieving desired outcomes and improving any system. It can’t be ignored.

 

By Dibyendu De

Corolisis Effect & Negative Damping – a Report

On By Author of #PowerofSeeIn Complexity, Creativity, Critical Thinking, Dibyendu De, Education, Engineering, Failure Analysis, Maintenance, Rapidinnovation, rcm, reliability, vibration analysisLeave a comment

Report on Thaisen Fan (Scrubber)

img_0182

Brief description of the phenomenon:

After cleaning of the fan blades, vibration of the fan gradually increases during operation and in a span of 10 to 14 days vibration level reaches an unacceptable level, which necessitates the next cleaning cycle. However, for so long, this matched the scheduled production window provided by operation. However, after the recent changing of the rotor and the bearings, the fan now reaches unacceptable level of vibration within a short span of time that does not coincide with the scheduled “production window” of the operation, which causes “unplanned downtime.”

Goal of the investigation: To correct the imperfection in the system so that the fan cleaning cycle coincides with.the scheduled production window.

Result of the investigation:

 

1. The problem of rising vibration within a short period of time is an inherent problem (a birth defect) of the fan. The main reason is the Coriolis effect on the fan. Coriolis force is a force exerted by a moving fluid on the disc or impeller rotating in the fluid. If the rotation is CCW (counter clockwise) then the fluid moves to the right of the impeller and away from the centre. Similarly, when the impeller moves in the CW (clockwise direction) the fluid moves towards the left of the impeller and away from the centre.

In this case, with the fan moving in the CCW direction the Coriolis force moves toward the right of the impeller in the same direction as the damping force. This effect (the fan moves in the CCW direction) produces negative damping (since the two forces are in the same line of action).

Negative damping is a phenomenon, when damping force, which usually opposes the driving force, acts in the same direction as the driving force. In such a case the vibration of the system is amplified.

Combination of negative damping and Coriolis effect produces this phenomenon of gradually rising vibration of the fan in a short period of time, which goes away upon regular cleaning. In the present context nothing can be done to eliminate the phenomena of Coriolis Effect and Negative damping. However, if a similar system is to be installed in the future, we would be pleased to provide necessary suggestions and recommendations so that such phenomena are eliminated right from the start.

2. Present signatures indicate misalignment and dynamic imbalance

3. Weak foundations

Actions to be taken to increase the cleaning cycle to match scheduled “production window.”

Countermeasures

1. Take care to align the rotor properly. Care to be taken while putting shims.

2. Dynamically balance the fan in two planes to eliminate the imbalance

3. Cleaning cycle can be initiated when vibration of the fan on the bearings reaches 7 mm/sec (rms). It is safe to run the fan upto this point.

4. Monitor the condition of the foundation by taking vibration measurements in displacement and acceleration modes. Displacement should be taken in the horizontal direction on the topmost accessible point of the columns and at the base.  Acceleration should be taken in both vertical and horizontal directions. Displacement should not cross 50 microns in the horizontal direction or at the base of the columns. Similarly acceleration both in the vertical and horizontal directions must not cross 1.5 g. This would ensure safety of the equipment. In case it crosses corrective actions are to be taken to rectify the foundation.

Result:

After alignment and dynamic balancing in two planes vibrations came down to below 1 mm/sec and maintained its reliability till the next cleaning cycle (10 to 14 days) which matched the scheduled production window of operation — thus avoiding unplanned downtime.
Dibyendu De
dde@rgbwaves.com
9836466678

Eccentric Stator

On By Author of #PowerofSeeIn Complexity, Dibyendu De, Education, Engineering, Failure Analysis, Maintenance, Management, Rapidinnovation, rcm, reliability, vibration analysisLeave a comment

General Symptom: 2Lf (Lf = Line frequency)

Stator problems would create high vibration at 2Lf. Stator eccentricity produces uneven stationary air gap between the rotor and stator that produces a very directional source of vibration.

Soft foot is often the cause of eccentric stator.

Other key indicators:

  1. 2Lf peak would be comparably high
  2. For a 2 pole motor this peak would be close to 2N (N= running speed). Would need sufficient resolution to separate them
  3. A spectrum may reveal beating — 2Lf and 2N peaks may appear to rise and fall if we don’t have sufficient resolution to separate them.
  4. Time waveform  — a combination of 2N and 2Lf would reveal a beat type pattern if the time period covers more than a few seconds. If the time period isn’t long enough, then we would see a wobble or take on the classic M or W shapes due to combination of 1N, 2N and 2Lf.
  5. Thermal images would reveal heat bands in the direction perpendicular to the direction of high vibration
  6. Vibration would be highest at the point where the stator is closest to the rotor. Move the accelerometer around the motor housing to see if the peak is high in one or two locations.

Dibyendu De

Eccentricity in general

On By Author of #PowerofSeeIn Complexity, Dibyendu De, Education, Engineering, Failure Analysis, Maintenance, Rapidinnovation, rcm, reliability, Uncategorized, vibration analysisLeave a comment

Symptoms are generally 1x radial (Vertical and Horizontal for a horizontally mounted machine).

Eccentricity occurs when the centre of rotation is offset (like offset misalignment) from the geometric centreline of a gear, motor rotor or a pulley.

It would generate strong 1x radial peak — in the direction parallel to the rotor/gear/pulley. This condition is common and mimics unbalance.

For gear eccentricity we would see 1x sidebands

For motor rotor eccentricity we would see pole pass sidebands.

Time waveform would be sinusoidal when viewed in velocity. Vibration from gear will also have gear mesh vibration and modulation of the turning shaft of the offending gear.

Phase: If belt driven, phase readings taken parallel and perpendicular to belts will either be in phase or 180 degrees out of phase. For a direct driven component, vertical and horizontal readings will be 90 degrees out of phase.

Rotor Bow

On By Author of #PowerofSeeIn Complexity, Dibyendu De, Education, Engineering, Failure Analysis, Maintenance, Management, Rapidinnovation, rcm, reliability, vibration analysis1 Comment

General symptom: 1x radial (Vertical and Horizontal direction of horizontal machines)

Usually a rotor bow in a motor looks like a static imbalance. Broken bars and loose connections (at motor terminals and at MCC) cause motors to heat up (localized) owing to uneven current flow through the phases causing rotor bow — uneven weight distribution around the rotor’s centreline. Hence we see high amplitude peak at 1x running speed in the radial and horizontal directions.

Localized overheating can be seen on the motor body through infrared thermal imaging.

The effect of can also be seen on the rotating air gap — a high peak at 2xLf with pole pass sidebands around 1x and 2x peaks. The 2x peak often comes up when the effect is more severe.

The time waveform would be sinusoidal when viewed in velocity.

Phase: expect 90 degree shift between vertical and horizontal axes. The inner race will move in and out once per revolution with a bent shaft

External Noise in Vibration Analysis

On By Author of #PowerofSeeIn Complexity, Critical Thinking, Education, Engineering, Failure Analysis, Maintenance, Rapidinnovation, rcm, reliabilityLeave a comment

Quite often, vibrations external to a machine (emanating from other machines or structures) can be transmitted through the foundation (from other machines) and structural supports (e.g. grinding frequencies generated from grinding of materials). It can also be transmitted through liquids (e.g. water hammer, turbulence) and air (acoustic pressures, electromagnetic radiation).

In most cases, low frequency vibrations are transmitted in this manner. This is because low frequency vibrations travel great distances.

In case such transmitted vibrations match the resonant frequency of the machine or any of its components, vibrations are greatly amplified (resonance).

Such vibrations can damage components like anti-friction bearings through a phenomenon called false brinelling if the affected machine is in the stand-by mode.

It is wise to suspect presence of such external noise if a frequency peak is found in a vibration spectrum (FFT) which can’t be identified or appears strange.

In that case we can check whether any machine near to the machine of interest exhibits that particular frequency. Or we can stop the machine to check whether the unusual or odd frequency still appears on a stationary machine. Alternatively, we can stop other local machines (usually not possible) to see whether the odd frequency disappears from the signature.

In case, the frequency happens to coincide with 2x, 3x, 8x harmonics of 1x (fundamental frequency) then we may use time synchronous averaging to see whether the amplitude contributed by the external noise averages away.

 

Rethinking Maintenance Strategy

On By Author of #PowerofSeeIn Complexity, Creativity, Critical Thinking, Dibyendu De, Education, Engineering, Failure Analysis, Maintenance, Management, Rapidinnovation, reliability, vibration analysis1 Comment

As of now, maintenance strategy looks similar to strategy taken by the medical fraternity in themes, concepts and procedures.

If things go suddenly wrong we just fix the problem as quickly as possible. A person is healthy to the point when the person becomes unhealthy.

That might work fine for simple diseases like harmless flu, infections, wounds and fractures. And it is rather necessary to do so during such infrequent periods of crisis.

But that does not work for more serious diseases or chronic ones.

For such serious and chronic ones either we go for preventive measures like general cleanliness, hygiene, food and restoring normal living conditions or predictive measures through regular check ups that detects problems like high or low blood pressures, diabetes and cancer.

Once detected, we treat the symptoms post haste resorting to either prolonged doses of medication or surgery or both, like in the case of cancer. But unfortunately, the chance of survival or prolonging life of a patient is rather low.

However, it is time we rethink our strategy of maintaining health of a human being or any machine or system.

We may do so by orienting our strategy to understand the dynamics of a disease. By doing so, our approach changes radically. For example. let us take Type 2 diabetes, which is becoming a global epidemic. Acute or chronic stress initiates or triggers the disease (Initiator). Poor or inadequate nutrition or wrong choice of food accelerates the process  (Accelerator) whereas taking regular physical exercise retards or slows down the process (Retarder). Worthwhile to mention that the Initiator(s), Accelerator (s) and Retarder (s) get together to produce changes that trigger of unhealthy or undesirable behavior or failure patterns. Such interactions, which I call ‘imperfections‘ between initiator (s), accelerator (s) and retarder (s) change the gene expression which gives rise to a disease, which often has to be treated over the entire lifecycle of a patient or system with a low probability of success.

The present strategy to fight diabetes is to modulate insulin levels through oral medication or injections to keep blood sugar to an acceptable level. It often proves to be a frustrating process for patients to maintain their blood sugar levels in this manner. But more importantly, the present strategy is not geared to reverse Type 2 diabetes or eliminate the disease.

The difference between the two approaches lies in the fact — “respond to the symptom” (high blood sugar) vs “respond to the “imperfection” — the interaction between Initiators, Accelerators and Retarders”. The response to symptom is done through constant monitoring and action based on the condition of the system, without attempting to take care of the inherent imperfections. On the other hand, the response to imperfections involve appropriate and adequate actions around the I, A, R s and monitoring their presence and levels of severity.

So a successful strategy to reverse diabetes would be to eliminate or avoid the initiator (or keep it as low as possible); weaken or eliminate the Accelerator and strengthen or improve the Retarder. A custom made successful strategy might be formulated by careful observation and analysis of the dynamics of the patient.

As a passing note, by following this simple strategy of addressing the “system imperfections“, I could successfully reverse my Type 2 Diabetes, which even doctors considered impossible. Moreover, the consequences of diabetes were also reversed.

Fixing diseases as and when they surface or appear is similar to Breakdown Maintenance strategy, which most industries adopt. Clearly, other than cases where the consequences of a failure is really low, adoption of this strategy is not beneficial in terms of maintenance effort, safety, availability and costs.

As a parallel in engineering, tackling a diseases through preventive measures is like Preventive Maintenance and Total Productive Maintenance — a highly evolved form of Preventive Maintenance. Though such a strategy can prove to be very useful to maintain basic operating conditions, the limitation, as in the case of human beings, is that it does not usually ensure successful ‘mission reliability’  (high chance of survival or prolonging healthy life to the maximum) as demonstrated by Waddington Effect. (You may refer to my posts on Waddington Effect here 1 and here 2)

Similarly, predictive strategy along with its follow up actions in medical science, is similar to Predictive Maintenance, Condition Based Maintenance and Reliability Centered Maintenance in engineering discipline. Though we can successfully avoid or eliminate the consequences of failures; improvement in reliability (extending MTBF — Mean Time Between Failures) or performance is limited to the degree of existing “imperfections” in the system (gene expression of the system), which the above strategies hardly address.

For the purpose of illustration of IAR method, you may like to visit my post on — Application of IAR technique

To summarize, a successful maintenance strategy that aims at zero breakdown and zero safety and performance failures and useful extension of MTBF of any system may be as follows:

  1. Observe the dynamics of the machine or system. This might be done by observing  energy flows or materials movement and its dynamics or vibration patterns or analysis of failure patterns or conducting design audits, etc. Such methods can be employed individually or in combination, which depends on the context.
  2. Understand the failures or abnormal behavior  or performance patterns from equipment history or Review of existing equipment maintenance plan
  3. Identify the Initiators, Accelerators and Retarders (IARs)
  4. Formulate a customized comprehensive strategy  and detailed maintenance and improvement plan around the identified IARs keeping in mind the action principles of elimination, weakening and strengthening the IARs appropriately. This ensures Reliability of Equipment Usage over the lifecycle of an equipment at the lowest possible costs and efforts. The advantage lies in the fact that once done, REU gives ongoing benefits to a manufacturing plant over years.
  5. Keep upgrading the maintenance plan, sensors and analysis algorithms based on new evidences and information. This leads to custom built Artificial Intelligence for any system that proves invaluable in the long run.
  6. Improve the system in small steps that give measureable benefits.By Dibyendu De

 

 

The Case of Burning BagHouse Filters

On By Author of #PowerofSeeIn Complexity, Education, Engineering, Failure Analysis, Management, Nemetics, Rapidinnovation, UncategorizedLeave a comment

Recently I was invited to investigate a case of frequent burning of baghouse filter bags.

There were five such baghouses connected to five furnaces of a steel plant.

The client reasoned that the material of the bags was not suitable for the temperature of the gas it handled. However, with change of material the frequency of bag burning did not change. So it needed a different approach to home onto the reasons for the failures.

Hence, this is how I went about solving the case:

First I did a Weibull analysis of the failures. Engineers use Weibull distribution to quickly find out the failure pattern of a system. Once such a pattern is obtained an engineer can then go deeper in studying the probability distribution function (pdf). Such a pdf provides an engineer with many important clues. The most important clue it provides is the reason for such repeated failures, which are broadly classified as follows:

  1. Design related causes
  2. Operation and Maintenance related causes
  3. Age related causes.

In this case it turned out to be a combination of Design and Age related causes.

It was a vital clue that then guided me to look deeper to isolate the design and age related factors affecting the system.

I then did a modified FMEA (Failure Mode and Effect Analysis) for the two causes.

The FMEA revealed many inherent imperfections that were related to either design or aging.

Broadly, the causes were:

  1. Inability of the FD cooler (Forced Draft cooler) to take out excess heat up to the design limit before allowing the hot gas to enter the bag house.
  2. Inappropriate sequence of cleaning of the bag filters. It was out of sync with the operational sequence thus allowing relatively hot dust to build up on the surface of the bags.

Next, the maintenance plan was reviewed. The method used was Review of Equipment Maintenance (REM). The goal of such a review is to find maintenance tasks that are either missing or redundant for which new tasks are either added/deleted or modified. With such modification of the maintenance plan the aim is to achieve a balance between tasks that help find out incipient signals of deterioration and tasks that would help maintain longevity and stability of the system for a desired period of time.

Finally the investigation was wrapped up by formulating the Task Implementation Plan (TIP). It comprised of 13 broad tasks that were then broken up into more than 100 sub-tasks with scheduled dates for completion and accountability.