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Ideas on maintenance

Before the industrial revolution, hardly any maintenance was carried out. Objects of use were usually produced as single pieces and were mostly designed on ‘run to fail’.

Later, maintenance consisted of a series of operations dictated to the user based on the manufacturer’s experience. Not all parts were designed with the same robustness. Some parts were more subject to wear and tear than others. The underlying idea behind that maintenance policy is that failure can be prevented or delayed. Especially for mass-produced goods it was and is possible to formulate generic maintenance rules. These rules are drawn up on the basis of average conditions of use. However, follwing these maintenance rules were no guarantee against failure. Often this failure was due to non or poorly maintained parts due to incorrect or incorrect material choices. Before the period of mass-produced consumer goods product were overdesigned, oversized and overdimensioned.

In the 1980s, the focus was on increasing the reliability of the various components of a composition. The sum of the reliability of a system was the result of the reliability of the individual components. Much effort was put into discovering and eliminating the weakest link in systems. If this was not possible, parts were redundantly designed. Maintenance activities focused in that days on increasing reliability. Later, attention was paid to the quality of the produced goods as indicators for maintenance efforts.

Today, perceptions about expected performance and presentation seem to shift slowly. In the case of maintenance, a balance has to be find between higher revenues due to better utilization of the assets on the one hand and maintenance costs on the other. The design, the materials used also affect the maintainability of an asset. In addition, the ‘licence to operate’ has to be taken into account, and regulations on the environment, safety and health are also increasing. The level of maintenance and its effectiveness depends on a lot of other factors: e. g. the availability of a sufficient number of trained staff, the availability of tools and spare parts and consumables. In addition, the operating conditions play an important role in the correct choice of a maintenance policy. Evaluation of choices of maintenance policy is difficult, sometimes before the end of the technical service life, a device needs to be replaced in favor for more advanced technologies. In short, there are (and were) different and shifting ideas about maintenance. Many of these are based on assumptions and short-sightness. Ideally, owners of capital-intensive assets should have a longer-term focus. Conscious choices in maintenance are often the result of a carefully chosen strategy. Maintenance must not longer regarded as a cost item.

ISO 55000 and maintenance

The different maintenance activities during each stage of the life cycle and their possible contribution to performance are in most organizations not proper identified. The effective management of physical assets consequently will go further and be more difficult to achieve than in the past. Effective management of assets implies activities to maintain, and often increase, operational effectiveness, revenue and customer satisfaction, while simultaneously reducing capital, operating and support costs (John Steward Mitchell & Amadi-Echendu, 2007).

The concept of integration or so-called terotechnology (Husband, 1976)and later the TUE model (Geraerds, 1988) where the first attempts to address the issue above. The methodology to achieve this integration is described in the PAS55 and later in the ISO 55000. Initially the PAS 55 was a British Standards Institution’s (BSI) Publicly Available Specification for the management of physical assets. PAS 55 was originally produced in 2004 and underwent a substantial revision. PAS 55:2008 was released in 2008. It provides definitions and requirements and specification for establishing a management system for all types of physical assets. Although the structure is different, most of these elements above are now incorporated into the ISO 55001:2014.

The focus of the ISO 55000 is on managing the performance of the assets for the long term. Asset management aims at improving the overall performance by making and executing systematic decisions about the design, use and maintenance of assets. The methodology includes strategic, tactic (maintenance) and operational (technical risks, reliability, performance) decisions. Asset management, as with a quality system such as ISO 9001, requires an environment in which all knowledge, instructions, processes and experience reports are secured. This assumes an intensive collaboration between professionals with a diversity of backgrounds and fields within an organization.

In recent years, asset management concepts as PAS 55 and ISO 55000 in management literature drew more attention of asset managers, asset owners, politicians, regulators and though more limited, of scholars. Asset management has been defined as: “a strategic, integrated set of comprehensive processes (financial, management, engineering, operating and maintenance) to gain greatest lifetime effectiveness, utilization and return from physical assets (production and operating equipment and structures)” (Mitchell & Carlson, 2001). While performance measurement in general has been discussed extensively in the literature, few of these discussions focus specifically on the maintenance function and even though ISO 55000 is presented as a generic management framework in practice it is in practice mostly seen as a way to minimize maintenance cost. The ISO 55000 still lacks the adequate consideration of the maintenance during the entire asset life cycle (Amadi-Echendu, 2004).

Complexity of maintenance

Capital-intensive infrastructural assets consist of various, complex systems and components manufactured by different Original Equipments Manufacturers (OEMs) and vendors. Since the operating conditions of each piece of equipments are diverse, and change overtime, deterioration due to usage and operating will be different. As a result, maintenance intervals of each system may differ. On top of that, when there are strict regulations on safety, the respective maintenance requirements are even tighter. How often and what type of activities must be performed is determined during the design stage. It is undesirable to stop normal operation for maintenance. Adding on to the complexity, the maintenance function requires support of other resources such as facilities, equipment, human resources and spare parts. Not performing or postponing maintenance jeopardizes the overall asset’s safety, reliability and operational risk. The maintenance of infrastructural assets is a complex problem and a meaningful approach to optimize maintenance decisions aligning with enterprise objectives is needed. Another important issue is the growth in cost of maintenance. Like many other countries the Netherlands experiences severe infrastructure needs, owing to ageing assets. Managing the maintenance function till now has primarily focused on costs related to technical and operational issues (Amadi-Echendu, 2004; Hoskins et al, 1999). Maintenance is a labor-intensive and therefore cost-intensive and relies heavily on human interaction or activities; there is little or no growth in productivity over time. Since the Baumol effect, a phenomenon described by (Baumol & Bowen, 1965), there is a rise of salaries in maintenance jobs without an increase of productivity, in response to rising salaries in other technical jobs.

Maintenance schedules and policies

In the past several decades, maintenance and replacement problems of deteriorating systems have been extensively studied. Thousands of maintenance and replacement models have been created. These models can be categorised in maintenance policies: age replacement policy, random age replacement policy, block replacement policy, periodic preventive maintenance policy, failure limit policy, sequential preventive maintenance policy, repair cost limit policy, repair time limit policy, repair number counting policy, reference time policy, mixed age policy, preparedness maintenance policy, group maintenance policy, opportunistic maintenance policy, etc. Each policy has, depending on the situation, different characteristics, advantages and disadvantages. A maintenance model within the same policy sometimes has different cost structures and/or different maintenance restoration degrees (minimal, imperfect, perfect).

Maintenance aims to improve system availability and reduce failure and downtime. Cost reduction is also necessary. Generally, an optimal system maintenance policy may be the one which either:

  • minimizes system maintenance cost rate,
  • maximizes the system reliability measures,
  • minimizes system maintenance cost rate while the system reliability requirements are satisfied, or maximizes the system reliability measures when the requirements for the system maintenance cost are satisfied.

An optimal maintenance schedule should therefore consider/incorporate various maintenance policies, system configurations, shut-off rules, maintenance restoration degrees, correlated failures and repairs, failure dependence, economic dependence, non-negligible maintenance time, etc

Instant Yardstick

Instant Yardstick


In the book “Systematic Maintenance Organization” from V.Z. Priel (1974),  I found an interesting Multi-variable chart for the assessment of maintenance performance. This chart provides an opportunity for qualitative assessment, inasmuch as the squares can be entered to the appropriate spot representing the condition of the variable. Although the answer does not purpose to be ‘scientifically’ derived, it has advantage in expediency. So if certain conditions are satisfied the final assessment will be favorable, but one unfavorable answer may spoil the overall picture. This chart shows visually what cannot be grasp with figures presented in spreadsheets. The interdependencies becomes obvious.

Dynamic Maintenance Strategy

For many complex capital goods, the cost of maintenance represent a large fraction of the Total Cost of Ownership (TCO).  These maintenance costs are often much larger than the procurement cost (AberdeenGroup 2003). Therefore, it is essential that asset owners develop strategies that minimize these cost whilst maximizing the uptime and safety. Another issue of maintenance is that the most one-off build assets are designed according to specific needs. As a result, there is not much failure data available at the OEM’s. This also explains why maintenance plans are often developed and performed by the company itself or by contractors, instead of the OEM’s. These characteristics ask for a dynamic maintenance strategy. That strategy needs to adapt to the increasing availability of data during the life-time. Whereas preventive maintenance may be appropriate at the start, other types of maintenance may later become preferable as more information becomes available. Later (when decisions could be based on available data) that dynamic policy should lead to reduced downtime.

Importance of Maintenance

During the past decades widespread mechanization and automation has reduced the number of production personnel while capital employed in production equipment has increased. Therefore, the importance of the maintenance function and of maintenance management has grown. The widespread mechanization and automation has reduced the number of production personnel and increased the capital employed in the production assets. As a result, the fraction of employees working in the area of maintenance as well as the fraction of maintenance spending on the total operational costs has grown over the years. It is not uncommon that the maintenance and operations departments the same size. The maintenance costs can be the largest part of any operational budget. The main issue faced by the maintenance management, whether its output is produced more effectively, in terms of contribution to company profits and efficiently, in terms of manpower and materials employed.