Effective Maintenance Management. V. Narayan
vessel. The level is held constant, within a tolerance band, using this controller. Referring to Figure 1.2, the valve will open more if the level reaches the upper control setting, allowing a larger outward flow. It will close to reduce flow, when the liquid reaches the lower control setting. As in the earlier example, here the level-controller helps keep the process in control by adjusting the valve position.
Consider now a supermarket that has a policy of ensuring that customers do not have to wait for more than 5 minutes to reach the check-out counter. Only a few check-out counters will be open during slack periods. Whenever the queues get too long, the manager will open additional check-out counters. This is similar to the control action in the earlier examples.
Companies use internal audits to check that the staff observes the controls set out in their policies and procedures. Let us say that invoice processing periods are being audited. The auditor will look for deviations from norms set for this purpose. If the majority of the invoices take longer to process than expected, the process is not in control. A root cause analysis of the problem will help identify reasons for the delays.
Figure 1.1 Process control chart.
Though these examples are from different fields of activity, they are similar when seen from the systems point of view. In each of these examples, we can define the work flow by a process, which is subject to drift or deviation. If such a drift takes place, we can see it when the measured value falls outside the tolerance band. The process control mechanism then takes over to correct it. Such a model allows us to draw generalized conclusions that we can apply in a variety of situations.
1.5 IMPACT OF EFFICIENCY ON RESOURCES
1.5.1 Efficiency of utilization
Earlier,we looked at some of the factors influencing the efficiency in the manufacturing phase. For this purpose, we define efficiency as the ratio of the outputs to the inputs. We can also examine the way the consumer uses the item. We define efficiency of utilization as the ratio of the age at which we replace an item to its design life under the prevailing operating conditions.
Figure 1.2 Level controller operation.
First, we examine whether we use the item to the end of its economic life. Second, is it able to reach the end of its economic life? In other words, do we operate and maintain it correctly? If not, this can be due to premature replacement of parts. When we carry out maintenance on a fixed time basis, useful life may be left in some of the parts replaced. Alternatively, we may replace parts prematurely because of poor installation, operation, or maintenance. In this case, the part does not have any useful life left at the time of replacement, but this shortening of its life was avoidable.
Manufacturers are concerned with production efficiency because it affects their income and profitability. From their point of view, if the consumer is inefficient in using the products, this is fine, as it improves the demand rate for their products. Poor operation and maintenance increases the consumers’ costs. If these consumers are themselves manufacturers of other products, high operating costs will make their own products less profitable. This book helps the consumer develop strategies to improve the efficiency of utilization.
1.5.2 Efficiency and non-renewable resources
An increase in efficiency, whether it is at the production or at the consumption end, reduces the total inputs and hence the demand for resources. We can ease the pressure on non-renewable resources greatly by doing things efficiently. In this context,the efficiency of both producer and consumer are important.
The first step in improving efficiency is to measure current performance. Qualitative or subjective measurements are perfectly acceptable and appropriate in cases where quantitative methods are impractical.
1.6 MAINTENANCE—THE QUESTIONS TO ADDRESS
We have looked at the holistic aspects of maintenance so far. What do we actually achieve when we carry out maintenance? Capital investments create production capacity. This capacity will decrease with use and time, unless we take the right actions—which we call maintenance.Equipment degrades with use, due to a variety of reasons. It can get internally fouled by particulates or residues from the process or materials of construction.It may deteriorate due to wear, corrosion, erosion, fatigue,or creep. These mechanisms lead to component and equipment failure, resulting in equipment unavailability, and maintenance costs. Unavailability can affect safety or production,so we want to keep that as low as economically possible. Planned downtime has lower consequences than unplanned downtime, so we try to minimize the latter.
What do we mean by the term maintenance? The British Standard BS 4778-3.1:1991 defines it as “...actions intended to retain an item in, or restore it to, a state in which it can perform its intended functions.” In simple terms, we need equipment to do something for us, i.e., to have a function. To retain that function over its life, we have to do maintenance.
Loss of process safety can lead to serious accidents, such as that in the Texas City Refinery in March 2005. An Independent Safety Panel Review headed by (former Secretary of State) James Baker investigated and concluded that “When people lose an appreciation of how their safety systems were intended to work, safety systems and controls can deteriorate, lessons can be forgotten, and hazards and deviations from safe operating procedures can be accepted. Workers and supervisors can increasingly rely on how things were done before, rather than rely on sound engineering principles and other controls. People can forget to be afraid.”1,2.
Maintenance is central to process plant performance, as it affects both profitability and safety. How well we do it depends on our ability to answer the questions, what work to do, when to do it, and the process steps to use. Doing so efficiently means we will do the minimum volume of work at the right time in the right way.
When an item of equipment fails prematurely, we incur additional maintenance costs and a loss of production and/or safety. As a result we cannot utilize the full capability of the equipment. Timely and effective maintenance helps avoid this situation. Good maintenance results in increased production and reduced costs. Correct maintenance increases the life of the plant by preventing premature failures. Such failures lead to inefficiency of utilization and waste of resources. The need to minimize these losses is why we need to maintain equipment. We will examine the purpose and mechanics of maintenance further in Chapter 9. There, we will see that the role of maintenance is to ensure the viability and profitability of the plant. In Chapter 10, we offer guidance on the strategies available to you to find the most applicable and effective tasks and to select from these the ones with the lowest cost. At the end of Chapter 10, you should have a clear idea of what tasks are required and when they should be done in order to manage the risks to viability and profitability of the plant. In Chapter 12, we will discuss how a plant performing poorly can take systematic steps to become a top performer.
We began this chapter by defining the production and distribution processes and then looked at some of the factors that influence efficiency. We use costs to measure performance; low costs imply high efficiency. When measuring costs, we make simplifications,as a result