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ОглавлениеThe term process describes the flow of materials and information. In order to achieve our business objectives, we use energy and knowledge to carry out the process.
The purpose of running a business is to produce or distribute goods (or services) efficiently. A business uses its mission statement to explain its objectives to its customers and staff. This is a top-down approach and enables us to see how to fulfill the mission, and what may cause mission-failure. We call this a functional approach, because it explains the purpose, or function, of the business. We can judge the success or failure of the business by seeing if it has fulfilled its function, as described in the mission statement. A high-level function can be broken down into sub-functions. These, in turn, can be dissected further, all the while retaining their relationship to the high-level function.
After reading this chapter, readers who are unfamiliar with this approach should have acquired an understanding of the method—this is the mission or function of this chapter. The main elements of the method are as follows:
•The functional approach, methodology, and communication;
•Identification of functional failure, use of Failure Modes and Effects Analysis, and consequences of failures;
•Reduction of frequency and mitigation of the consequences of failures;
•Cost of reducing risks;
•Damage limitation and its value.
The U.S. Air Force initiated a program called Integrated Computer Aided Manufacturing (ICAM) in the 1970s. They developed a simple tool to communicate this program to technical and non-technical staff, named ICAM-DEFinition or IDEF methodology1,2. With IDEF, we use a graphical representation of a system using activity boxes to show what is expected of the system. Lines leading to and from these boxes show the inputs, outputs, controls, and equipment.
As an illustration, consider a simple pencil. What do we expect from it?
Let us use a few sentences to describe our expectations.
A.To be able to draw lines on plain paper.
B.To be able to renew the writing tip when it gets worn.
C.To be able to hold it in your hand comfortably while writing.
D.To be able to erase its markings with a suitable device (eraser).
E.To be light and portable, and to fit in your shirt pocket.
The item must fulfill these functional requirements or you, the customer, will not be satisfied. If any of the requirements are not met, it has failed. Figure 2.1 illustrates a functional block diagram (FBD) of how we represent the second function in a block diagram.
Figure 2.1 FBD of pencil system.
Note that we state our requirements in the most general way possible. Thus, pencil does not have to be a graphite core held in a wooden stock. Pencil can easily be a metal holder, and still meet our requirements. The second function is met whether we have a retractable core or if we have to shave the wood around the core.It could have a hexagonal or circular section, but must be comfortable to hold. The writing medium cannot be ink, as it has to be erasable. Finally, its dimensions and weight are limited by the need for comfort and size of your shirt pocket!
Every production or distribution process has several systems, each with its own function, as illustrated by the following examples.
•A steam power-generation plant has a steam-raising system, a power generation system, a water treatment system, a cooling system, a control and monitoring system, and a fire protection system.
•A courier service has a collection and delivery system, a storage and handling system, a transport system, a recording and tracking system, and an invoicing system.
•An offshore oil and gas production platform has a hydrocarbon production system, an export system, a power generation system, a communication system, a fire and gas protection system, a relief and blow-down system, an emergency shutdown system, and a personnel evacuation system.
•A pizza business with a home delivery service has a purchasing system, a food preparation system, a communication system, and a delivery system. Sometimes, all these systems may involve just one person, who is the owner-cook-buyer-delivery agent!
We can use functional descriptions at any level in an organization. For example, we can define the function of a single item of equipment. Jones3 illustrates how this works, using the example of a bicycle, which has the following sub-systems:
•Support structure, e.g., the seat and frame;
•Power transmission, e.g., pedals, sprockets, and drive chain;
•Traction, e.g., wheels and tires;
•Steering, e.g., handles and steering column;
•Braking, e.g., brakes, brake levers, and cables;
•Lighting, e.g., dynamo, front and back lights, and cables.
We can define the function of each sub-system. For example, the power transmission system has the following functions:
•Transfer forces applied by rider to drive-sprocket;
•Apply forces on chain;
•Transmit the force to driven-sprocket to produce torque on rear wheel.
Similarly, we can examine the other sub-systems and define their functions. The functional failure is then easy to define, being the opposite of the function description; in this case, fails to transfer force.
2.2 FUNCTIONAL BLOCK DIAGRAMS (FBD)
These systems and sub-systems below them are aligned to meet the overall objectives. An FBD provides an effective way to demonstrate how this works. It illustrates the relationship between the main function and those of the supporting systems or sub-systems.
We describe the functions in each of the rectangular blocks. On the left side are the inputs—raw materials, energy and utilities,or services. On the top we have the systems, mechanisms, or regulations that control the process. The outputs, such as intermediate (or finished) products or signals, are on the right of the block. Below each block, we can see the means used to achieve the function; for example, the hardware or facilities used to do the work. As a result of this approach, we move away from the traditional focus on equipment and how they work, to their role or what they have to achieve.
In the example of the pencil that we discussed earlier, let us examine failure of the third function, that is,
•It is too thin or fat to hold, or
•It has a cross-section that is irregular or difficult to grip,
•It is too short.
We then break down the main function into sub-functions. In the case of the pizza business, the sub-functions would be as follows:
•A purchasing system that will ensure that raw materials are fresh (for example, by arranging that meat and produce are purchased daily);
•A food preparation system suitable for making consistently high quality pizzas within 10 minutes of order;
•A communication system that will ensure voice contact with key staff, customers, and suppliers during working hours;
•A delivery system that will enable customers within a range of 10 km to receive their hot pizzas from pleasant agents within 30 minutes of placing the orders.
Each of the sub-functions can now be broken down, and we take the delivery system as an example:
•To deliver up to 60 hot (50–55°C) pizzas per hour during non-peak hours, and up to 120 hot pizzas per hour from 5:30 p.m. to 8:00 p.m.;
•To arrange deliveries such that agents do not backtrack,and that every customer is served within 30 minutes of order;
•To ensure that agents greet customers, smile, deliver the pizzas, and collect payments courteously.
These clear definitions of requirements enable the analyst to determine the success or failure of the system quite easily. The IDEF methodology promotes such clarity, and Figure 2.2 shows the Level 0 FBD of the pizza delivery system. Note that we have not thus far talked about equipment used, only what they have to do to satisfy their functional requirements.
For example, the agents could be using bicycles, scooters, motorcycles,or cars to do their rounds. Similarly, they may use an insulated box to carry the pizzas, or they may use some other equipment. The only requirement is that the pizzas are delivered while they are still hot. We can break this down to show the sub-functions, as shown in Figure 2.3. Note that the inputs, outputs, controls, and facilities/equipment retain their original alignment, though they may now be connected to some of the sub-function boxes.
Figure 2.2 Level 0 FBD of pizza delivery system
Figure 2.3 Level 1 FBD—Relationship of intermediate functions pizza delivery system.
We are now ready to address more complex industrial systems, and use a gas compressor in a process plant as an example (see Figure 2.4). We have broken down the main function A0 into sub-functions A1, A2, A3, and A4 in Figure 2.5. Thereafter, we have expanded one of these sub-functions A2 further, as illustrated in Figure 2.6.
Figure 2.4 Level 0 FBD of a gas compression system.
The method is applicable to any business process. We can use an FBD to describe an industrial organization, a supermarket chain,the police force, or a pizza franchise. The diagram itself may appear complex at first sight, but after some familiarization it becomes easier. The clarity and definition it brings makes it a good communication tool.
Figure 2.5 Level 1 identification of sub-system.
Figure 2.6 Level 2 FBD of a gas compression sub-system.
2.3 FAILURE MODES AND EFFECTS ANALYSIS (FMEA)
The performance standards embedded in the definition of the function allows identification of the success or failure of each of the systems or sub-systems. If there is a failure to achieve the objective, it is possible to identify how exactly this happens. In doing so, we identify the mode of failure. Each failure may have several failure modes.
As an example, consider engine-driven emergency generators. An important function is that they must start if the main power supply fails. They have other functions, but let us focus on this one for the moment. What are the causes of its failure to start and how can it happen? We have to establish fuel supply and combustion air, and crank the engine up in order to start it. Several things may prevent the success of the cranking operation. These include weak batteries or problems with the starter motor or the starting-clutch mechanism. If any of these failures occurs, the engine will not be able to start. These are called failure modes.
We can take this type of analysis down to a lower level. For example, the clutch itself may have failed due to a broken spring. At what level should we stop the analysis? This depends on our maintenance policy. We have the following options:
•Replace the clutch assembly, or
•Open the clutch assembly at site and replace the main element damaged, for example, the broken spring.
We can carry out the FMEA at a sub-system functional level, for example, fails to start or stopped while running, as discussed above. It is also feasible to do an FMEA at a level of the smallest replaceable element, such as that of the clutch spring. When designing process plants, a functional approach is generally used. When designing individual equipment, the manufacturers usually carry out FMEAs at the level of the non-repairable component parts. This enables the manufacturer to identify potential component reliability problems and eliminate them at the design stage. Davidson4 gives examples of both types of FMEA applications.
In a functional analysis, we identify maintenance significant items, failures of which can cause loss of system or sub-system function. In this case, we stop the analysis at assembly level because we will replace it as a unit, and not by replacing, for example, its broken spring. Unlike the manufacturers, we cannot usually justify analysis at the lower level, because the cost of analysis will exceed the benefit. The volume of work in a component level FMEA is much higher than in a functional FMEA.
For each failure mode, there will be some identifiable local effect. For example, an alarm light may come on, or the vibration or noise level may rise. In addition there can be some effect at the overall system level. If the batteries are weak, the cranking speed will be slow, and there will be a whining noise; this is the local effect. The engine will not start, and emergency power will not be available. This may impair safety in the installation, leading to asset damage, injury or loss of life; this is the system effect.
We can identify how significant each failure mode is by examining the system effects. In this case, failure to start can eventually cause loss of life. However, if we have another power source, say a bank of batteries, the failure to start of the engine will not really matter. There may be some inconvenience, but there is no safety implication. The failure is the same; that is, the engine does not start, but the consequences are different.
The purpose of maintenance is to ensure that the system continues to function. How we maintain each sub-system will depend on the consequences, as described by the system effects. For example, if the failure of an item does not cause immediate loss of function, we can limit the maintenance to repairing it after failure. In each situation, the outcome is dependent on the configuration of the facility. The operating context may differ in seemingly identical facilities. The FBD and FMEA will help identify these differences and take the guesswork out of decision making.
The elegance of the functional approach will now be clear. For every business, we can define its objectives at the top level, or its overall functions. We can break these down to identify the related systems and sub-systems. Next, we identify the functions of each system and sub-system, and carry out an FMEA. The analysis is applicable to an operating plant or to one that is still on the drawing board. As a result of this top-down approach, we can concentrate the planning effort on what really matters to the organization.
Individuals and organizations can fall into the trap of rewarding activity instead of the results achieved. Movement and activity are often associated with hard work. Sometimes this is of no avail, so activity by itself has no merit. We have to plan the work properly so as to achieve meaningful results.
The functional analysis concentrates on the results obtained, and the quality standards required. We have discussed its use in the context of maintenance work, but we can apply the method in any situation where we can specify the results clearly. For example, Knotts1 discusses their use in the context of business process re-engineering.
2.5 PREVENTION OF FAILURES OR MITIGATION OF CONSEQUENCES?
Once we identify the functional failures, the question arises as to how best to minimize their impact. Two solutions are possible:
1.We can try to eliminate or minimize the frequency of failures or
2.Take action to mitigate the consequences.
If we can determine the root cause of the failure, we may be able to address the issue of frequency of events. Usually, this will mean elimination of the root cause. Historically, human failures have accounted for nearly three quarters of the total. Hence, merely designing stronger widgets will not always do the trick. Not doing the correct maintenance on time to the right quality standards can be the root cause, and this is best rectified by re-training or addressing a drop in employee motivation. Similarly, changes in work practices and procedures may eliminate the root cause. All of these steps, including physical design changes, are considered a form of redesign. In using these methods,we are attempting to improve the intrinsic or operational reliability of the equipment, sub-system, or system. As a result,we expect to see a reduction in the failure rate or frequency of occurrence.
An alternative approach is to accept the failure rates as they are, and devise a method to reduce their consequences. The aim is to do the applicable and effective maintenance tasks at the right time, so that the consequences are minimal. We will discuss both of these risk reduction methods, and the tools we can use, in Chapter 10.
Once we identify the tasks, we schedule the tasks, arranging the required resources, materials, and support services. Thereafter, we execute the work to the correct quality standards. Last, we record and analyze the performance data, to learn how to plan and execute the work more effectively and efficiently in the future.
When there are safety consequences, the first effort must be to reduce the exposure, by limiting the number of people at risk. Only those people who need to be there to carry out the work safely and to the right quality standards should be present. Maintaining protective devices so that they operate when required is also important. Should a major incident take place in spite of all efforts, we must have damage limitation procedures,equipment designed to cope with such incidents, and people trained in emergency response.
At the time of this writing, the details of the Fukushima Dai-ichi power station disaster in Japan in March 2011, following the severe earthquake and tsunami, are not very clear. However, the management of damage limitation seems very poor. Apart from the physical damage occurring to the soil around the plant with conflicting radiation levels being reported in the produce, seawater, and sea life, the release of information seems very poorly managed. As we will see in Chapter 7, people feel a great sense of dread and uncertainty when there is a lack of full and timely disclosure of information.
Some years ago, we saw an example showing the usefulness of such damage limitation preparedness. In September 1997, an express train traveling from Swansea to London crashed into a freight train, at Southall, just a few miles before reaching London-Paddington station. The freight train was crossing the path of the passenger train, which was traveling at full speed, so one can visualize the seriousness of the accident. The response of the rescue and emergency services was excellent. The prompt and efficient rescue services should be given full credit as the death toll could have been considerably worse than the seven fatalities that occurred.
The functional approach is aligned closely with the objectives of a business. The IDEF methodology is an effective way to understand and communicate this approach. We used this tool to understand the functions of a range of applications, from pencils and pizza business to gas compression systems in process plants. A clear definition of the functions enables us to identify and understand functional failure. Thereafter, we use the FMEA to analyze functional failures. We make a distinction between the use of the functional and equipment level FMEAs. Using a top-down approach, we identify functional failures and establish their importance.
In managing risks, we can try to reduce the frequency of failures or mitigate their consequences. Both methods are applicable,and the applicability, effectiveness, and cost of doing one or the other will determine the selection. Lastly, we touched on the importance of damage limitation measures.
REFERENCES
1.Knotts, Rob. 1997. “Asset Maintenance Business Management:A Need and An Approach.” Exeter: Proceedings, 7th International M.I.R.C.E. Symposium on System Operational Effectiveness, pp. 129-133.
2.Mayer, R.J. 1994. “IDEFO Functional Modeling: A Reconstruction of the Original.” Air Force Wright Aeronautical Laboratory Technical Report. Knowledge Based Systems Inc. AFWAL-TR-81-4023.
3.Jones, R.B. 1995. Risk-Based Management: A Reliability-Centered Approach. Gulf Professional Publishing Company. ISBN: 0884157857.
4.Davidson J. 1994. The Reliability of Mechanical Systems. Mechanical Engineering Publications, Ltd. ISBN: 0852988818. pp. 78-82.
Further Reading
1.Anderson R.T., and L.Neri. 1990. Reliability Centered Maintenance:Management and Engineering. Springer. ISBN: 9781851664702.
2.Moubray J. 2001. Reliability-Centred Maintenance. Industrial Press, Inc. ISBN: 978-0831131463
3.Smith A.M. 1992. Reliability Centered Maintenance. McGraw-Hill. ISBN: 978-0070590465
