Preventive maintenance and repair optimization is a valuable process. It can be used to improve the efficient use of resources, balance program demand and increase equipment reliability. Preventive maintenance and repair programs are often under- or overdeveloped, resulting in additional management time, missed inspections and inadequate maintenance practices. Regardless of the age of your program, the main ingredients needed to perform preventive maintenance and repair optimization successfully include defining inspection validity, effective frequencies, durations, task lists and standardized inputs. When thoughtfully performed, preventive maintenance and repair optimization can increase the effectiveness and sustainability of your program.
Where to Begin with Preventive Maintenance and Repair
Collect baseline data by reviewing program performance, including completion and effectiveness history. Once the baseline has been established, begin checking your inspections for validity. This is defined as an inspection that is performed consistently within the designed frequency and manpower duration. If the track record of an inspection is consistently good, it should be considered valid and allowed to be further reviewed later. For inspections where the identified equipment has not incurred any unplanned stops and has one or more of the following characteristics, it should be considered invalid and marked for deletion:
· Low completion rate (>50 percent)
· Redundant to another inspection
· Obsolete or decommissioned equipment
Once validation is completed, the frequency, duration and task list of the valid inspections should then be further analyzed.
Defining Effective Frequencies
Defining effective frequencies (inspection intervals) when first developing a preventive maintenance and repair program depends on the failure mode, technique, equipment criticality, etc. For mature programs, additional consideration can be made. In some cases, failures may have happened in between inspections even though the defined task list is adequate for its detection. Here, the inspection interval would be reduced in order to perform the inspection to detect and prevent future failures. In other situations when inspections have been performed multiple times without generating any corrective work, consider increasing the inspection interval.
Defining Effective Durations
Inspection durations, including manpower requirements during the program’s development stage, are generally estimated. By analyzing completion patterns (history) and attaining verbal feedback from those doing the inspection (improvement ideas), durations can be adjusted as the program matures. This would also hold true for manpower requirements. In some cases, you may be able to utilize a different inspection technique and reduce the number of inspectors. Some may choose to use a stopwatch and time the inspection to define the duration.
Defining Effective Task Lists
Task lists vary greatly depending on the established inspection template, type of inspection, equipment or reliability technique. What makes a task list effective or ineffective? A few examples are listed in Table 1.
Ineffective task lists are overpopulated, unclear, inaccurate and not specific. Conversely, effective task lists are simple to understand and well-organized. Be as clear and specific as possible in a checklist form, using verbs such as measure, grease, sample and tighten. Avoid run-on sentences. Arrange the task list so the equipment to be inspected is in the same order as it will be walked. Avoid inaccuracies by removing decommissioned equipment or invalid tasks. Utilize reliable detection techniques and replace old-school invasive inspections. Finally, provide acceptance criteria (limits) whenever possible, e.g., 50 mm thickness, target cleanliness of 16/14/12, more than 65 degrees C, etc. This will avoid opinion-oriented questions that are subjective, inconsistent and ineffective.
Using Standardized Inputs
When developing a preventive maintenance and repair program, it is important to consider valid inputs to be used. Otherwise, a program will become cluttered with pet peeves. When reviewing, these same inputs should be considered to identify gaps or determine the additional validity of existing inspections. The following are suggested preventive maintenance and repair program inputs:
Key preventive maintenance and repairs: My company has generated key preventive maintenance and repairs for similar assets around the world. These are things that the company has learned to monitor, including frequency and best detection technique(s) regarding potential failures.
OEM Recommendations: Inspections recommended by the equipment supplier should be followed. However, your management team may decide to modify the inspection intervals as equipment history is developed.
Regulatory and Compliance: This includes inspections the facility is required to complete to fulfill program or legal commitments. Some examples are operational permitting, safety regulations, ISO obligations, etc.
Equipment History: Equipment history is the review of the equipment’s performance and maintenance needs in order to identify any gaps and/or adjustments that may be needed, carefully considering equipment failures, corrective work and root cause analysis findings.
Balancing Program Demand
Once all of the inspection modifications have been made, performing a workload balancing exercise is highly recommended. This can be done using Excel to perform all calculations. The idea of the workload balancing is to establish even, stable and consistent program demand by optimizing plan start dates (weeks). This process considers the work center, technique/type, frequency and duration of each inspection, as shown in Figure 1. The tool should also simulate a two-year plan, as seen in Figure 2.
Figures 1 and 2 show program demand fluctuated 3-37 hours per week. The same inspections with modified start weeks (Figures 3 and 4) now have a reduced fluctuation in program demand of 3-27 hours per week. Although this is a simple example, it can be used to stabilize your program and maximize its sustainability.
Preventive Maintenance and Repair Results
In 2015, one of our manufacturing sites performed a preventive maintenance and repair optimization project in one portion of the plant. As a result, it was able to improve the preventive maintenance and repair completion by 45 percent and effectiveness by 80 percent. The project was also able to reduce system stops by 37 percent, system stop duration by 68 percent and program demand by 43 percent, as shown in Figure 5.
In addition, workload balancing was performed during the project. The baseline was taken before any changes were implemented and showed a very large variance. After all project modifications were completed and final workload balancing was performed, the project was able to stabilize the program demand and fluctuation (Figure 6).
Preventive maintenance and repairoptimization is highly recommended if:
· Annual program hours are greater than 50 percent of the available hours.
· Completion of program hours is less than 70 percent.
· Mean time between failures is below target.
· Availability is below target.
· Optimization has not been previously performed (program more than 5 years old).
· The current preventive maintenance and repair program does not consider all existing reliability techniques.
· The current program doesn’t consider condition-based maintenance as the main strategy.
We previously published this article in the Reliable Plant 2016 Conference Proceedings.
By David L. Hull, LafargeHolcim