By Christo Roux
In today’s increasingly complex and demanding maintenance world, where equipment is becoming more technically complex, operational targets are higher than ever and skilled resources are becoming a scarce commodity, equipment reliability has become essential for the success of an operation.
Although not a new discipline, the role of reliability engineering as a core principle is often overlooked in equipment availability. This article will explore some of the topics relating to what constitutes a reliability strategy, how to adopt it and the associated cost benefits.
The Evolution of Maintenance
In his book Reliability-Centered Maintenance, John Moubray1 refers to the three generations of maintenance practices to date. These are:
First Generation—The first generation is the period up to WWII. Industry was mostly unmechanized, therefore equipment failure was not a concern and downtime did not matter much. Equipment was simple and generally overdesigned. As a result, basic maintenance requirements involved simple cleaning, service and lubrication routines.
Second Generation—During and after WWII, things changed dramatically; there was a huge increase in the demand for goods, and at the same time a decrease in available resources. The level of mechanization rose steadily and equipment became more complex. By the mid-1960s, there was a clear focus on reducing downtime and the concept of preventative maintenance came into being. This consisted mainly of overhauls conducted at fixed intervals. Maintenance costs started to rise steeply relative to operating costs. This, in turn, led to growth in planning and control systems.
Third Generation—By the mid-1970s, the rate of change had accelerated, as had expectations placed on industry. These included higher safety standards, understanding and controlling environmental impact, inventory management, reduction in overall expenditures, higher levels of automation, etc. At the same time, the cost of maintenance was still rising, in absolute terms and as a portion of total expenditure. It is easy to see how equipment availability and reliability became a key focus.
In the mining world, a similar change or evolution has taken place. We have seen extensive changes and advances in mining practice, as well as a trend toward increased mechanization and higher production targets. With many of the new technologies and mining methods being applied, it has become essential to remove the human factor from dangerous and potentially hazardous environments or situations. With the growth in complex equipment such as autonomous or teleremote mining operations, the demands on the maintenance practitioner also have grown. Maintenance has become a essential part of operations.
It is quite clear our maintenance world is still changing, and like natural evolution it will continue to change and we will need to adapt our maintenance practices and principles accordingly.
Reliability vs. Maintainability
For many years the focus in maintenance, and one of the most reviewed Key Performance Indicators (KPI) has been equipment availability, or at least the target availability. This is especially true in the mining industry, where mining cycles and lost blasts have a compound affect on the production of the mine.
Availability, in its simplest form, is measured as: A = Uptime/(Uptime + Downtime).
There are traditionally two approaches to the calculation of equipment availability; the first being Engineering Availability, which calculates availability based on downtime related only to engineering failures. The second measure is commonly referred to as Operational Availability, based on all failures that cause downtime, including those that might be deemed operations-related.
Reliability by design is the starting point in the reliability potential of a piece of equipment. It is the role of the OEM (Original Equipment Manufacturer) to understand how the design of the unit, in terms of reliability, will perform in certain standard conditions, and how this will affect the installed components, subsystems, systems and ultimately overall unit reliability. The design should always be based on the standard operating context as a benchmark, and an overall equipment reliability target.
These will naturally not be the only criteria, as safety, environmental impact, ease of maintainability and specific operational functionality will play an important role in the overall design.
Equipment Specification and Selection
The correct specification and selection of the required equipment is a critical phase in the on-site reliability of a piece of equipment. It is essential the correct equipment is selected for the required application. The engineering and purchasing departments of the mining house must actively pursue reliability as part of the acquisition process.
Key factors to be considered are life cycle costs, maintainability, parts availability and employee skills. The initial purchase cost should not be the sole issue; the selected unit should be chosen on the basis that it is correct for the application and that it will be able to deliver the required output within its design capability, without overburdening or abusing the equipment by performing functions it was not designed for.
Reliability of Replacement Components—OEM-recommended spares should always be the first choice, as these have been selected and designed to support the overall designed reliability. All too often, component price is the only factor considered in the component purchasing process, ignoring reliability or overall life cycle cost of the unit. Purchasing must assume an active role in equipment reliability; without this support and involvement, acceptable levels of reliability will not be achieved.
Operating Practices and Procedures—Without proper operating procedures, equipment damage and subsequent downtime will always be a major cause of poor reliability. It is essential the operations team take ownership of the unit and this includes the reliability of the equipment.
Maintainer and Operator Skills—Maintainers and operators must be given adequate knowledge, skills and established procedures to perform their assigned tasks. Training is very important; without it, acceptable skill levels will not be achieved.
Standard Procedures—All too often it is the procedures that are not comprehensive enough, and do not provide sufficient data to correctly and effectively operate or maintain a unit. This will lead to sub-standard execution of their tasks, which is often seen as employee shortcomings, when in reality they are not.
It is important that maintenance strategies are applied to suit the local conditions and operating context of the equipment. Maintenance workers must shift their focus from reacting quickly to breakdowns, to preventing the failure in the first place.
Maintenance planning and scheduling are an essential part of any maintenance program. Planners need to ensure that all planned preventative and predictive tasks are scheduled and that the correct resources are assigned and available for the tasks. A good planning system is mandatory to achieve an acceptable level of reliability.
Defining Optimal Reliability
There are many views as to what should constitute optimum reliability for a piece of equipment. However, it can be objectively identified, and the following factors should be considered in the assessment:
• Total cost of ownership
• Life Cycle Cost
• Environmental considerations
As shown in Figure 1, it is widely accepted that as one increases the inherent reliability of a product, there will be an associated increase in acquisition costs related to the technology or redundancy that must be built into the unit to achieve higher reliability. A good example of this is the high cost associated with aircraft acquisition and maintenance—it is essential the inherent reliability of an aircraft is as close to 100% as possible because people’s lives depend on it.
Naturally, as reliability increases, operational costs decrease. There is, however, a point at which higher acquisition costs to improve reliability are no longer cost-effective. This point is generally defined as “optimal reliability” from a cost point of view.
From a design point of view, optimal reliability is achieved when the unit is able to perform at the desired level of output without engineering failures (breakdowns) occurring between the maintenance intervals. The component and part lives also must support the predicted life cycle costs.
From an owner or maintainer’s point of view, optimal reliability means achieving the above, while taking local operating conditions and context into account. That is, once any required adjustments are made to either the operation cycle or maintenance strategy, the equipment is able to achieve the desired level of reliability. This may involve changing the service interval, or ensuring that more inspections are done, or that production targets are adjusted to reflect what is realistically achievable within the local operating context. The above may affect the overall Life Cycle Cost, but when this ensures that the required reliability is achieved then one would consider that a level of optimal reliability has been achieved.
Considering that evolution, by definition, is a continuous process, and that maintenance has evolved so much since its first appearances prior to WWII, it is clear it will continue changing as the demands from industry change. Safety, environmental, cost and reliability considerations will be core to these new industry demands for many years to come.
How we react to these changes will determine how successful we are in our operations. The solution to successful maintenance development and sustainable equipment reliability is clear; it requires a holistic approach in which each role player in the organization accepts responsibility in supporting the reliability of the equipment. If you improve the reliability of your equipment, production quality, increased capacity and profitability will follow.
1. Moubray, John, Reliability-Centered Maintenance, Second Edition, Industrial Press, 1997.
Christo Roux is maintenance director for Sandvik Mining and Construction’s underground mining business segment.