An article on Reliabilityweb.com on the benefits of planning and scheduling clearly shows this has great benefits in terms of maintenance efficiency – a planned job always costs less than an emergency where materials have to be expedited and overtime labor is expended. Less delays are incurred if the correct parts are on hand and jobs don’t have to be rescheduled or stopped and started. Impact on production can be reduced if work can be done in a shorter time frame or during an already planned maintenance outage window.
The article also mentions that planning and scheduling improves equipment reliability, reduces the risk of unexpected failures, and enhances overall operation efficiency. This is clearly true, but let’s dive a little deeper into why.
One of the cornerstones of reliability-centered maintenance (RCM) is a risk-based equipment strategy. After you identify failure modes and quantify the risk with probability and consequence of failure, you prescribe tasks that mitigate these risks to an acceptable level and in a cost-effective manner. These take the form of preventive and predictive maintenance tasks, spare parts and other measures. In order for these to be effective, they have to be specific, repeatable and actually mitigate the risk. Vague instructions to the planner, such as “check pump” or “PM compressor” do not meet this criteria.
On the other hand, these are all simplified examples of specific and repeatable tasks that ensure the expected outcome is achieved:
- Check alignment and correct as needed to within +/- 0.002 inches;
- Drain, flush and refill seal pot with ISO VG22 buffer fluid;
- Perform infrared monitoring of motor windings, maximum allowable temperature is 100 degrees F over ambient;
- Collect oil sample from point A and send for water and wear particle analysis;
- Check pulsation dampener charge to ensure pressurization to 80 percent of pump discharge pressure, recharge with dry nitrogen as needed.
Facilities, such as a refinery, may only get one chance every eight to 10 years to perform preventive maintenance tasks (PMs) and inspections, so it is critical that these tasks are completed properly and mitigate risk as intended.
Equally important during your equipment strategy implementation process is reconciling these new recommendations with current, legacy tasks. Most times, these legacy tasks are well-founded and can be tied to failure modes identified in the equipment strategy. Sometimes, they are overreactions to a onetime failure and may be misguided or overly prescriptive. But these could be clues that you missed a failure mode during your equipment strategy development process.
In one experience, a high-speed packaging line was idled eight hours a week to perform PMs. However, the maintenance window was instead used to perform reactive repairs to avoid being penalized by the production loss accounting system. Maintenance technicians assigned to the PMs knew that many of the tasks did not adequately mitigate a risk or the interval was incorrect, so they largely ignored them. For example, a quarterly task is not effective if the P-F interval for that failure mode is two weeks. Another example is if a diaphragm failure on a metering pump occurs once a year due to lack of a pulsation dampener PM, a five-year overhaul of the gearbox and stroke adjustment is not effective.
A planner feedback form, whether it’s a sheet of paper or paperless document integrated into a computerized maintenance management system (CMMS), provides feedback to ensure the right tools, parts, or other resources are included in the job plan. It also provides an opportunity to audit the spare parts bill of material (BOM). Similarly, craft feedback to reliability is important to validate tasks and their frequency. You can refine assumptions about probability of failure (POF) and provide more data for mean time between failures (MTBF) used to calculate it. As mentioned earlier, the equipment strategy can be improved and updated by incorporating failure modes identified by crafts during a PM or reactive repair. The work notification in your CMMS provides a place to document as found/as left conditions and codify them using damage and cause codes for data mining by reliability engineers as part of a bad actor program.
You may do an effective job at prescribing mitigating risks with spare parts recommendations only to be challenged by accounting. Surely, risk mitigation trumps a little inventory holding cost. However, also consider prescribing more cost-effective preventive and condition-based tasks to replace risk mitigation. This may not always be the case, and best-in-class organizations have a periodic review process where maintenance or reliability engineers can override these challenges. This is especially so where the risks are environment, health and safety (EHS) related and not quantified in dollars. They may simply exceed the allowable threshold of the risk matrix. For financial risk, a lifecycle cost analysis may be needed to compare the alternatives.
Lastly, engineering input may be needed in the development of the work scope of a repair and specification of any procedures or methods that need to be followed. This may include additional visual inspections, nondestructive examinations (NDE), or dimensional inspections. Your support for returning equipment to like new or most reliable condition often can be the difference on job planning decisions. A good relationship between the engineer and the operations maintenance coordinator (i.e., work request and scheduling gatekeeper) will help ensure a stopgap repair philosophy does not develop.
In conclusion, RCM equipment strategies are not just a desktop exercise conducted by reliability engineers. There is an essential feedback loop to this in the maintenance work process. Reliability plays a key role in efficient and effective delivery of maintenance services to the plant. Optimized PMs that effectively mitigate risk and job plans that ensure equipment is returned to most reliable condition the first time are two elements of a best-in-class asset management program.
