Maintenance Approaches

Many organizations have many different approaches (or some may call practices) when it comes to their maintenance programs. All

approaches have at their basis the requirement to keep their facility’s assets at whatever capacity level is necessary for their current operational needs. Some of these maintenance programs are more structured than oth-ers—some maintenance programs are based on an RCM analysis, and some organizations even develop an annual or even multi-year mainte-nance program plan to guide their maintemainte-nance decisions strategically and tactically. The truth is that an organization will have a maintenance pro-gram whether they admit it or not; their propro-gram will simply be more cost-ly than it has to be since they will live in a reactive maintenance state.

All assets requires some form of care—maintenance, for example.

Belts and chains require adjustment, alignment of shafts such as pump-motor or blower-pump-motor shafts need to be properly maintained, filters need to be changed at regular intervals, proper lubrication on rotating machin-ery is required, and so on. In some cases, certain components need replacement after a specified number of hours of operations, e.g., a pump bearing on a hydraulic system to ensure that the system lasts through its design life. Anytime we fail to perform maintenance activities, we may be shortening the operating life of the asset. Over the past few decades, many cost-effective approaches have been developed to insure an asset reaches or exceeds its design life. Instead of waiting for assets to fail and then fix them, maintenance actions are performed to keep assets in good working condition to provide continuous service.

Why Have a Structured Maintenance Program

The most important reason to have a maintenance program with a structured approach is to ensure that assets don’t fail prematurely, that they keep producing or providing service as intended. Maintenance pro-grams should improve production capacity and reduce overall facility costs by:

• Reducing production downtime — the result of fewer asset failures.

• Increasing life expectancy of assets, thereby eliminating prema-ture replacement of machinery and asset.

• Reducing overtime costs and providing more economical use of maintenance personnel due to working on a scheduled basis, instead of an unscheduled basis, to repair failures.

• Reducing cost of repairs by reducing secondary failures. When parts fail in service, they usually damage other parts.

• Reducing product rejects, rework, and scrap due to better overall asset condition.

• Identifying assets with excessive maintenance costs, indicating the need for corrective maintenance, operator training, or replacement of obsolete assets.

• Improving safety and quality conditions.

A structured maintenance program can have different philosophies, approaches, and practices embedded within the program. The basic phi-losophy is really only two-fold: do some form of maintenance to an asset to prevent failure or allow the asset to be run-to-failure. The basic approaches to maintenance can be grouped into four major categories:

Condition Based Maintenance (also known as Predictive Maintenance), Preventive Maintenance, Proactive Maintenance, and Corrective Maintenance. A brief description of each of these approaches is discussed on the following pages with more details on each covered within chapters 4 and 8.

Condition Based Maintenance (CBM)

Condition Based Maintenance (CBM), also known as Predictive Maintenance (PdM), attempts to evaluate the condition of an asset by per-forming periodic or continuous asset monitoring. The ultimate goal of CBM is to identify proactive maintenance actions to be performed at a scheduled point in time when the maintenance activity is most cost effec-tive and before the asset fails in service. The “prediceffec-tive” component stems from the goal of predicting the future trend of the asset’s condition.

This approach uses principles of statistical process control, trend analysis, and preselected thresholds to determine at what point in the future main-tenance activities should be scheduled.

CBM inspections typically are performed while the asset is operating, thereby minimizing disruption of normal system operations. Adoption of CBM/PdM in the maintenance of an asset can result in substantial cost savings and higher system reliability.

There are a number of different CBM / PdM technologies that can be used to evaluate assets condition. A few of the more common technolo-gies (or data) are:

• Vibration analysis

• Infrared (IR) thermography

• Acoustic / Ultrasonic — sound level measurements

• Oil analysis

• Electrical — amperage plus other data

• Shock Pulse Method (SPM)

• Partial discharge & Corona detection

• Operational performance data — pressure, temperature, flow rates, etc.

Basically, in the CBM approach, the maintenance need is based on the actual condition of the machine rather than on some preset schedule.

Activities such as changing oil are based on a predetermined schedule (time), like calendar time or asset runtime. For example, most of us change the oil in our cars every 3,000–5,000 miles driven. This is effec-tively basing the oil change needs on asset runtime. No concern is given to the actual condition and performance capability of the oil. It is changed because it is time to change it. This methodology would be analogous to a preventive maintenance task.

On the other hand, if we ignore the vehicle runtime and have the oil analyzed at some regular period to determine its actual condition and lubrication properties, then we may be able to extend the oil change until the car has been driven 10,000 miles, or maybe even more.

This is the advantage of utilizing condition based maintenance. CBM is used to define needed maintenance tasks based on quantified asset con-ditions or performance data. The advantages of CBM are many. A well-established CBM program will eliminate or reduce asset failures cost-effectively. It will also help to schedule maintenance activities to mini-mize overtime cost. In addition, we will be able to minimini-mize inventory and order parts, as required, well ahead of time to support the downstream maintenance needs.

Past studies have shown that a well-implemented CBM program can provide an average savings of 10% (7–15%) over a program utilizing pre-ventive maintenance (PM) alone. These savings could easily exceed 30–40% if there is not a good PM program in place. In fact, independent surveys and technical papers presented at the International Maintenance Conferences 1999–2002 combined with the author’s own experience indi-cate the following industrial average savings resulting from a good estab-lished condition based maintenance program:

• Reduction in maintenance costs: 15–30%

• Reduction in downtime: 20–40%

• Increase in production: 15–25%

On the down side, starting a full-blown CBM program utilizing all of the previously mentioned technologies can be quite expensive. Some technology’s test equipment may cost in excess of $40,000. In addition, training plant personnel to utilize PdM technologies effectively will require considerable funding as well. This is one reason to have an RCM-basis for choosing where to apply which CBM technology; it helps to determine the test equipment purchase that can provide the most “bang for your buck.” Program development will require an understanding of pre-dictive maintenance and a firm commitment to make the program work by all facility organizations and management.

How the CBM team should be organized is another issue. We have found that a centralized dedicated team is a good way to start a program.

This approach helps in standardizing testing methods and practices.

The CBM approach consists of scheduling maintenance activities only when equipment or operational conditions warrant — by periodical-ly or continuousperiodical-ly monitoring the machinery for excessive vibration, tem-perature, noise, etc. When the condition gets to a level that has been pre-determined to be unacceptable, the asset is shut down. The asset is then repaired or has damaged components replaced in order to prevent more costly failures from occurring. This approach works very well if person-nel have adequate knowledge, skills, and time to perform the CBM work.

In addition, the company must allow asset repairs to be scheduled in an orderly manner. The approach provides some lead-time to purchase mate-rials for the necessary repairs, reducing the need for a high parts invento-ry. Because maintenance work is only performed when it is needed, there is likely to be an increase in production capacity.

Preventive Maintenance (PM)

As stated previously, a CBM approach is the preferred approach if your organization can handle the expense of implementing this approach.

However, a PM approach is the next best thing and maybe the only approach with certain types of assets. Additionally, regulatory require-ments may force some level of PM to be performed (e.g., crane inspec-tions).

Preventive Maintenance requires that maintenance or pro-duction/operation personnel pay regular visits to monitor the condition of an asset in a facility. The basic objective of PM visits is to take a look at the asset to determine if there are any telltale signs of failure or imminent failure. Also, depending on the type of the asset, a checklist or a procedure with task details indicating what to check or what data to take may be

used, e.g., change filter, adjust drive belts, and take bearing clearance data. The observers also document the abnormalities and other findings.

These abnormalities should be corrected before they turn into failures for a PM program to add any value.

These PM inspections can be based on either calendar time or asset runtime. If CBM is not being performed on a particular piece of equip-ment, or if CBM cannot detect a particular failure, then the next best approach is a runtime-based PM program, but only for equipment and failure modes that have a time basis. If a calendar time-based PM program is all that really adds value, then that approach is still better than a run-to-failure strategy. The exception to this is when an analysis has been per-formed that indicates the most cost-effective strategy is run-to-failure because the total cost of maintenance is less than the corrective mainte-nance necessary for this run-to-failure strategy (assuming that there is no safety impact to this run-to-failure strategy).

The objective of preventive maintenance can be summarized as fol-lows:

• Maintain assets and facilities in satisfactory operating condition by providing for systematic inspection, detection, and correction of incipient failures before they develop into major failure.

• Maintenance, including tests, measurements, adjustments, and parts replacement, performed specifically to prevent failure from occurring.

• Record asset health condition for analysis which leads to the development of corrective tasks.

Proactive Maintenance

Proactive Maintenance is one of those terms used to mean different things to different people. The term can be a controversial one. Some con-sider CBM and PM approaches to be proactive —these approaches do take a proactive approach as opposed to simply reacting to equipment fail-ure. In some cases, tasks that are generated based on what is found during CBM and PM tasks (including work identified as a result of root cause and failure analysis) are considered proactive. In some organizations, proactive maintenance is calculated as a ratio of all maintenance work minus unscheduled corrective maintenance, divided by all maintenance work. Another definition is that anything on the maintenance schedule is proactive — that is, any maintenance work that has been identified in advance and is planned and scheduled. These last definitions make better

sense. Therefore, proactive maintenance can be defined as all work tasks completed to avoid failures or to identify defects that could lead to fail-ures.

Corrective Maintenance (CM)

Corrective Maintenance is another term used in different ways. CM is an action initiated as a result of an asset’s observed or measured condition before or after functional failure. CM work can be further classified into Scheduled, Major Repairs/Projects, and Reactive.

When an asset breaks down, it fails to perform its intended function and disrupts scheduled operation. This functional loss, partial or total, may result in defective parts, speed reduction, reduced output, and unsafe conditions. For example, a wear or slight damage on a pump impeller, which reduces output, is a function reduction failure. Full functional fail-ure that shuts down the asset is called function-disruption failfail-ure.

Function-disruption or reduction failures that are not given due attention will soon develop into asset stoppage if not acted on.

Many abnormalities such as cracks, deformations, slacks, leakages, corrosions, erosions, scratches, excessive heats, noises, and vibrations are the indicators of imminent troubles. Sometimes these abnormalities are neglected because of the insignificance or the perception that such abnor-malities will not contribute to any major breakdowns. The tendency to overlook such minor abnormalities soon may grow and contribute to seri-ous catastrophic failures. It is not uncommon to receive queries from pro-duction staff in response to a “high temperature or vibration condition”

about how long we can continue running.

It has been observed that a high percentage of the failures occur dur-ing startups and shutdowns. However, asset failure could also be due to poor maintenance. Causes that go unnoticed are called “hidden abnormal-ities.” The key to achieving zero failures is to uncover and rectify these hidden abnormalities before failure actually occurs.

In many organizations, CM is called repair maintenance; it is conduct-ed to correct deficiencies and to make the asset work again after it has failed or stopped working.