Objectives of maintenance
The fundamental objective of a suitably managed department is not the pressing solution of failures that occur. Unfortunately, this seems to be the objective of many installations. In fact, the objectives are wider and more varied.
Maintenance department of an installation has six objectives which must mark and run its work:
- Assure the security of the installation for people, meaning that the normal or abnormal functioning does not endanger people. Of course, this objective is not sole for maintenance, but for the whole organization.
- Assure that the installation is secure for environment, so that a situation where the environment is damaged cannot happen. Of course, this objective is also not sole for maintenance, but for the whole organization.
- Achieve a certain value of availability.
- Achieve a certain value of reliability.
- Guarantee a long shelf life, at least according with the plant’s repayment term.
- Achieve all of that, trimming the budget given. Often, the optimal budget for the maintenance of that installation.
Many of the accidents that occur in the installations happen because these suffer from functioning failures that turns them insecure. The vast majority of the installations are do manged according to manufacturer's instructions and the engineering that designed them, and safety standards established with the help of risk analysis are fulfil. These are installations with a probability of accident almost negligible. Only a failure in a component, equipment or system, changes the controlled conditions and makes the probability of an accident unacceptable. Thus, the first maintenance objective must assure that degradation that usage and time make on equipment outweigh enough to not risk people’s security.
Likewise, many of the environmental accidents and incidents that cause a negative impact in environment happen due to an unexpected functioning of these, occurring from a failure in a component, equipment or system. The majority of the installations are do manged according to manufacturer's instructions and the engineering that designed them, and standards established with the help of environment risk analysis are fulfil. These are installations with a probability of environmental accident or incident almost negligible. In the majority of the installations, only a failure in a component, equipment or system, changes the controlled conditions and makes the probability of an environmental accident unacceptable. Therefore, the second objective of maintenance must assure that degradation that usage and time make on an equipment outweigh enough without risk of the environment suffering a negative impact.
The availability of an installation is defined as the proportion of time when that installation has been in willingness of production or been used, regardless of whether it has or has not been used, for reasons beyond its technical condition.
The most important maintenance objective is to guarantee that the installation is in disposition of produce or be used a certain minimum number of hours per year. It is an error to think that the objective of maintenance is to achieve the maximum availability possible (100%) as this can become very expensive. Thus, achieving the marked availability objective with a certain cost is generally enough.
As will be seen further on, availability is an indicator that offers great possibilities of reckoning. Therefore, only for certain installations that operate intermittently (plants which produce in campaign, plants or installations that only function in certain periods) the objective of availability focuses on the hours reckon to produce, and the availability or not of the plant when it is not require to produce is relatively trivial. The definition of availability calculation estimation plays a crucial role in judging if the department of maintenance of any industrial installation is doing its job accurately or an improvement is needed.
The principal factors to bear in mind in the estimation of availability are the following:
- Total number of production hours.
- Total number of unavailability hours, that might be caused due to different types of performance of maintenance:
- Programmed maintenance interventions that require plant stoppage.
- Programmed corrective maintenance interventions that require plant stoppage or load reduction.
- Non-programmed corrective maintenance interventions that unexpectedly stop production and thus, they had an incident in the planning already made in energy production.
- Partial unavailability number of hours, meaning, the number of hours when the plant is able to produce but with an availability lower than nominal due to the poor condition of one section of the installation, that hinder it to work under full load.
Regarding to the acceptable values of availability in several types of industrial installations, achieving the availability objectives higher than 92% in a sustainable way (one or various years may be achieved, but not a continuous way) is quite an ambitious objective. Usually, industrial installations seek out for their goals between 99% (for the most demanding installations) and 50% in the less demanding cases when providing a much higher production than the market is able to assimilate.
There are several calculation estimations for this indicator that will be seen further on, on the chapter dedicated to maintenance indicators. It is crucial to highlight that the IEEE develop an specific rule for the reckoning of the installation that can be extrapolated to other type of installations, trying to avoid partial interpretations that may benefit some part at the expense of another (contractor owner, and so).
Reliability is an indicator that measures the capacity of a plant to achieve the production plan intended. In an industrial installation, it usually refers to fulfilment of the production intended, and, in general, understood by both internal and external clients. The achieving of this load program may have consequences like financial penalties, and hence the importance of measuring these value, and bearing it in mind when designing the maintenance management of an installation.
Factors to keep in mind for the reckoning of this indicator are two:
- Annual hours, as shown in the previous section.
- Annual hours of stoppage and load reduction exclusively due to the non-programmed corrective maintenance.
As can be seen, in order to reckon this objective, it is not consider neither the hours dedicated to programmed preventive maintenance that imply plant stoppage, nor the hours dedicated to programmed corrective maintenance. For the coherent and correct reckon of this factor, the definition of which is the dissimilarity between programmed and non-programmed corrective maintenance has to be provided always. Therefore, in several industrial installations is common to consider a failure detected, but whose repair could be delayed 48 hours or more, it is considered to be programmed corrective maintenance, and thus it does not count to the reckoning of the reliability.
The objective of maintenance seeks this parameter to always be above an intended value established in the design techno-economical design of the plant, and its value is frequently quite high (same or higher than 99,0%). A well-managed installation ought not to have any problem to reach this value.
The shelf life of a plant.
The fifth great maintenance objective is to guarantee a long shelf life for the installation. In other words, the industrial plants must present a condition of deterioration consonant with what intended, in a way that neither the availability nor the reliability nor the maintenance cost could be out of the objectives settled for a long period of time, usually in accordance with the repayment term of the plant. The lifespan of a typical industrial installation is placed between 20 and 30 years, when the benefits of the plant and its maintenance objectives must always be inside the values intended.
A bad-managed maintenance, with a low proportion of hours intended to preventive tasks, with poor budget, lack of means and personnel, and based in provisional repairs, provokes the rapid degradation of any industrial installation. It is remarkable of bad-managed plants that although little time has passed since its initial start, the visual aspect does not correspond to its youth (in terms of lifespan).
The achieving of the budget.
The objectives of availability, reliability and shelf life cannot be obtain at any cost. The department of maintenance has to achieve the objectives intended adjusting its expenses to what was settled in the annual budget of the plant. As said in the previous section, this budget has to be reckon with extreme care, since a lower budget than the plant needs worsen irretrievably the results of production and limit the shelf life of the installation; on the other hand, an upper budget than the installation needs worsen the operating account results.