Reliability Centered Maintenance (RCM) for the cement industry

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The Cement Institute

Reliability Centered Maintenance (RCM) for the cement industry

Reliability Centered Maintenance (RCM) is the process for determining a more effective maintenance approach. RCM’s philosophy employs preventive maintenance (PM), predictive maintenance (PdM), real-time monitoring (RTM1), fault execution (RTF, also called reactive maintenance), and proactive maintenance techniques in an integrated manner to increase the likelihood that a machine or component will function as required during its design lifecycle with minimal maintenance. The goal of the philosophy is to provide the indicated function of the installation, with the reliability required and availability at the lowest cost. RCM requires maintenance decisions to be based on maintenance requirements backed by a strong technical and economic justification.

 

A brief history of RCM

Reliability-centered maintenance originated in the airline industry in the 1960s. By the late 1950s, the cost of maintenance activities in this industry had become high enough to warrant special research into the effectiveness of these activities. As a result, in 1960, a working group composed of representatives of both airlines and the FAA (Federal Aviation Administration) was formed to investigate preventive maintenance capabilities. The establishment of this working group subsequently led to the development of a series of guidelines for airlines and aircraft manufacturers to use when establishing their aircraft maintenance programs.

This led to Msg-1 of Maintenance Steering Group 747 (MSG); evaluation of maintenance and development of the Air Transport Association (ATA) program in 1968. MSG-1 was used to develop the maintenance program for the Boeing 747 aircraft, the first maintenance program to use RCM concepts. MSG-2, the subsequent review, was used to develop maintenance programs for the Lockheed L-1011 and Douglas DC-10. The success of this program is demonstrated by comparing the maintenance requirements of a DC-8 aircraft, maintained using standard maintenance techniques, and the DC-10 aircraft, maintained using MSG-2 guidelines. The DC-8 aircraft has 339 points requiring an overhaul, just seven points on a DC-10. Using another example, the original Boeing 747 required 66,000 hours of work on major structural inspections before a significant heavy inspection in 20,000 hours of operation. By comparison, the DC-8, a smaller, less sophisticated aircraft that uses the day’s standard maintenance programs required more than 4 million hours of work before reaching 20,000 hours of operation.

In 1974, the U.S. Department of Defense commissioned United Airlines to write a report on the processes used in the civil aviation industry for the development of aircraft maintenance programs. This report, written by Stan Nowlan and Howard Heap and published in 1978, was titled Reliability Focused Maintenance, and has become the report that based all subsequent Reliability-Centered Maintenance approaches. What Nowlan and Heap found was that many types of failures could not be prevented no matter how intensive maintenance activities were. In addition, it was discovered that for many points the probability of failure did not increase with age. As a result, an age-based maintenance program will have little or no effect on the failure rate.

 

RCM in the cement industry and utility arena

As with any philosophy, there are many paths or processes that lead to a final goal. This is especially true for RCM and the cement industry where the consequences of the failure can vary considerably.

 

Aerial view of cement manufacturing plant. Concept of buildings at the factory, steel pipes, giants

RCM’s rigorous analysis has been extensively employed by the aircraft, space, defense and power plant industries where functional failures have the potential to cause major loss of life, national security implications and/or a serious environmental impact. The cement industry in recent years has understood the importance and benefits of an implementation of the RCM and little by little more companies and plants towards this maintenance philosophy and culture are observed.

A rigorous RCM analysis is based on Effects of Analysis and Failure Modes (FMEA) and includes failure probabilities and system reliability calculations. The analysis is used to determine the appropriate maintenance tasks to address each of the identified failure modes and their consequences.

For the cement industry, a simplified or intuitive RCM analysis process may be more appropriate. This is due to the high cost of analyzing the rigorous approach, the relatively moderate impact of a failure on most facility systems, the type of systems and components maintained, and the number of redundant systems implemented. The simplified approach follows the same principles as rigorous ones but recognizes that not all failure modes will be analyzed. For most systems in the cement plant, the most economical and efficient approach is to use a combination of rigorous (formal) and intuitive analysis that depends on system criticality and the impact of failure. Failure modes that result in high costs or injuries to personnel, or where the resulting reliability is still unacceptable in terms of safety, environment or operational impact, still take the rigorous approach, but all other failure modes will use intuitive analysis.

 

The Primary Principles of RCM are:

  1. RCM is function-oriented: it seeks to preserve the function of the system or equipment, not just operability for the sake of efficiency. Function redundancy, across multiple teams, improves functional reliability, but increases the life cycle cost in terms of acquisition and operation costs.
  2. RCM is system focused: it is more concerned with maintaining system function than individual component function.
  3. RCM focuses on reliability: it treats failure statistics actuarially. The relationship between the age of operation and the failures experienced is important. RCM is not overly concerned with the simple failure rate; seeks to know the conditional probability of failure at specific ages (the probability of failure occurring in each given operating age range).
  4. RCM recognizes design limitations: its goal is to maintain the inherent reliability of equipment design, recognizing that changes in inherent reliability are a matter of design rather than maintenance. At best, maintenance can only achieve and maintain the level of equipment reliability that is provided by design. However, RCM recognizes that maintenance comments can improve the original design. Additionally, RCM recognizes that there is often a difference between perceived design life and intrinsic or actual design life, and addresses this through the Age Exploration (EE) process.
  5. RCM is driven by security and the economy: security must be guaranteed at any cost; thereafter, profitability becomes the criterion.
  6. RCM defines the failure as any unsatisfactory condition: therefore, the failure may be a loss of function (operation ceases) or an acceptable loss of quality (operation continues).
  7. RCM uses a logical tree to monitor maintenance tasks: it provides a consistent approach to maintaining all types of equipment.
  8. RCM Tasks Must Be Applicable: Tasks Must Address Failure Mode and Consider Failure Mode Characteristics.
  9. RCM tasks must be effective: tasks must reduce the probability of failure and be profitable.
  10. RCM recognizes three types of maintenance tasks:
    • Timed (PM): scheduled when appropriate.
    • Directed condition (PdM and real-time monitoring): it is carried out when the conditions indicate that they are necessary.
    • Troubleshooting (one of several aspects of proactive maintenance) – The computer runs in the event of a failure. This is acceptable for some situations and some types of equipment.
  11. RCM is a living system: it collects data from the results obtained and returns them to improve future design and maintenance. This information is an important part of the proactive maintenance element of the RCM program.

 

RCM logical tree

The RCM analysis carefully considers the following questions:

A functional failure is essentially the inability of a equipment/system to meet its specified performance standard. A complete loss of function is a functional failure; however, in the hydraulic unit example above, if the system output is less than specified, a functional failure has occurred, even if the system is still operating.

1. What does the system or equipment do? What is your function?
2. What functional failures can occur?
3. What are the possible consequences of these functional failures?
4. What can be done to reduce the probability of the failure, identify the onset of the failure, or reduce the consequences of the failure?

The answers to these four questions determine the necessary actions required to maintain the systems or equipment. The RCM logical tree used to answer these questions.

 

Failure

Failure can be defined in many ways. In a broad sense, failure is simply an unsatisfactory condition. However, RCM forces us to consider the failure not only from the point of view of the team, but also from the point of view of the system. A team may be operating (a hydraulic unit in a clean room, for example), but if its output is less than required, it would be considered an error. On the other hand, a protection relay in a power system may have failed, but if you have not disconnected the circuit (the circuit is still energized), the function of the system does not change. Essentially, the definition of failure depends on the function of a computer or system and the operating context in which the computer/system is used.

 

Functional failure

A functional failure is essentially the inability of a equipment/system to meet its specified performance standard. A complete loss of function is a functional failure; however, in the hydraulic unit example above, if the system output is less than specified, a functional failure has occurred, even if the system is still operating.

 

Consequences of failure

The consequences of the failure determine the priority of maintenance activities or the design improvement required to prevent them from occurring. If equipment failure results in little or no consequence, minimal maintenance activities are generally required. However, if equipment failure results in great financial hardship, personal injury, or environmental damage, maintenance activities or a new design may be required.

The figure in the annex shows six different failure patterns. Although there is a pattern titled “Best New” in both the “Bathtub Curve” and “Worst New” failure patterns, there are higher incidents of initial failure. These are caused by design flaws or built into a product.

Based on these failure patterns, a different scenario occurs for predictive maintenance: Predictive maintenance can predict installation defects or OEM (Original Equipment Manufacturer) errors and prevent premature failure.

Maintenance actions in an RCM program for the cement industry

RCM’s objectives are to identify the most cost-effective and applicable maintenance techniques to minimize the risk and impact of failure on facilities and equipment utilities. This allows maintaining the functionality of systems and equipment in the most economical way. The specific objectives of RCM for the cement industry are:

  • Ensure the realization of the inherent levels of security and reliability of the equipment.
  • Restoring equipment to these inherent levels when deterioration occurs.
  • Obtain the necessary information to improve the design of those elements whose inherent reliability turns out to be inadequate.
  • Achieve these goals at minimal total cost, including maintenance costs, support costs, and the financial consequences of operational failure.

 

For this purpose, there are four results of an RCM analysis:

  1. Do not perform maintenance: this is known as reactive maintenance, repair, repair in case of failure or execution in case of failure (ICF). This type of maintenance assumes that a failure is equally likely to occur anywhere, and that a failure is not detrimental to operation. When this is the only type of maintenance practiced, high failure rates, large parts inventories, and excessive amounts of overtime become common. A purely ICF maintenance program ignores many of the opportunities to influence the team’s survivability.
  2. Perform Preventive Maintenance (PM): consists of regularly scheduled inspections, adjustments, cleanings, lubrication, and replacement of components and equipment. PM is also known as time-based or interval-based maintenance. It is done without taking into account the condition of the equipment. PM schedules inspection and maintenance at predefined intervals in an attempt to reduce equipment failure. However, as Nowlan and Heap discovered, a PM program can result in a significant increase in inspections and costs without any increase in reliability.
  3. Performance condition-based maintenance (CBM): CBM consists of predictive maintenance (PdM) and real-time monitoring. PdM primarily uses non-destructive testing techniques to measure and improve equipment performance. Real-time monitoring uses current performance data to assess the condition of the machinery. CBM replaces arbitrarily timed maintenance tasks with maintenance that is scheduled only when warranted by the condition of the equipment. Continuous analysis of equipment condition data allows planning and scheduling of maintenance or repair activities before a functional or catastrophic failure.
  4. New Design: when failure of a system or piece of equipment is an unacceptable risk and none of the above tasks can help mitigate the failure, a redesign of the equipment or system is required. In most cases, adding redundancy eliminates risk and adds very little to overall maintenance costs.

Impact of RCM on a facility lifecycle

A facility life cycle is often divided into two broad stages: acquisition (planning, design, and construction) and operations. RCM affects all phases of the acquisition and operations stages to some extent.
Decisions made early in the acquisition cycle profoundly affect the life cycle cost of an installation. Even though expenses for the plant and equipment may occur later in the procurement process, its cost is committed at an early stage. As conceptually shown in the figure below, planning (including conceptual design) corrects two-thirds of the facility’s resources.

 

RCM Elements

Overall lifecycle costs

The later design phases determine an additional 29% of the life cycle cost, leaving only around 5% of the life cycle cost that can be affected by the later phases.
Therefore, the decision to include a facility in an RCM program, including condition monitoring, which will have a major impact on its life cycle cost, is best made during the planning phase. As RCM decisions are made later in the life cycle, it becomes more difficult to achieve the maximum possible benefit from the RCM program.
Despite the fact that maintenance is a relatively small part of the overall life cycle cost, generally 3% to 5% of the operational cost of an installation, RCM can still introduce significant savings during the operation and maintenance phase of its useful life. of the installation. Savings of 30% to 50% on the annual maintenance budget are often realized through the introduction of a balanced RCM program.

 

Reliability Centered Maintenance is the process of determining the most effective maintenance approach. As the airline industry demonstrated 40 years ago and as demonstrated by different plants that have incurred in implementation, RCM can not only improve the reliability of a system, but can also significantly reduce the maintenance required. In today’s competitive global economy, this translates into money saved, both by reducing failures and by reducing work. And a properly implemented RCM program will continue to save money year after year. To remain competitive, most cement plants can no longer afford to stay on the sidelines doing the tasks as they always have. Let RCM move your maintenance program into the 21st century.

 

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