Tools vs. sensors: Get a grip!
Unscheduled downtime in any industry can cost millions of dollars. Unexpected shutdowns also may result in wasted product, equipment damage, and significant safety issues. Plant facility managers know that maintaining stable, continuous operations depends on regular maintenance and quick detection of potential problems. Fortunately, the last decade has produced new categories of monitoring tools to help process industries achieve those goals.
Today, rapid advances in wireless condition monitoring (CdM) technologies provide a more practical and cost-effective way for process plant managers to continuously monitor voltage, amps, temperature, power, and vibration on less critical equipment. Most wireless sensors can be installed quickly and removed just as quickly. The question is: when do you apply CdM, and when do you rely on traditional preventive maintenance (PM) with handheld tools like digital multimeters, temperature probes, thermal imagers, or vibration meters?
As you might expect, there is more than one good answer. The best answer for your facility depends on where you are on your reliability and maintenance journey and how much benefit sensors will deliver for your applications.
Identify your strategies
Defining where you are on the reliability journey includes determining what percentage of assets are operated on a run-to-fail basis, how much is covered by PM strategies, and how much is predictive. Reliability strategies can be defined as a systematic approach for developing new maintenance requirements where they do not exist for optimizing an existing maintenance program.
Linking each maintenance action to a failure mode is key to the successful application of any reliability strategy. This is achieved through the proven foundations and techniques of: reliability-centered maintenance, PM optimization, and failure mode and effects analysis. They are focused on creating time-directed, condition-directed or failure-finding tasks that make up a maintenance program, which is designed to minimize system and component degradation ensuring that equipment continues to perform optimally in its current operational context.
Sometimes confusion between what is “preventive” and what is “predictive” exists. PM is a strategy that occurs during fixed intervals, regardless of an asset’s condition at the time. Further, there are two types of PM actions: scheduled restoration and scheduled discard. Both actions are carried out by the PM task(s) prescribed to address the precise failure mode. In other words, the purpose of the PM strategy applied is to address the causes of failure that are more akin to age-related failures. Granted, developing PM strategies to mitigate equipment failures that are deemed as infant mortality, normal wear out, and random failures (also known as non-age-related) is difficult.
Predictive maintenance (PdM) is a maintenance strategy that employs the evaluation of the condition and performance of equipment during normal operation to identify the probability of failures. CdM is also a subset of PdM, in which asset health is directly monitored and evaluated in real time against performance parameters so that actionable data can drive the same proactive maintenance activities as that of PMs: scheduled restoration and/or scheduled discard. Both activities are purposed to restore the equipment’s performance capacity back to full. The formal term for these actions is condition-directed tasks.
CdM over time with wireless, remote sensors can be beneficial, especially if they send data to a computerized maintenance management software (CMMS) system. The CMMS system stores the data and can alert maintenance managers and planners if the equipment exceeds acceptable operation parameters. It can even automatically generate work orders based on the alarms.
CdM may not be the best choice for all assets. The challenge is to determine which assets should be monitored with sensors to minimize downtime and waste and deliver the best return on investment.
The first step is to rank assets by criticality to the operation. Consider factors such as the impact that losing each asset would have on the overall process. Would the entire plant have to shut down or just a section? Can the plant continue to operate while that asset is being repaired or replaced? What is the cost to repair or replace that asset? How does that asset affect safety, worker comfort, and environmental conditions? What is the cost of losing that asset in both downtime and potential wasted product and lost production?
After you have established the relative criticality of each asset, you can rank them accordingly. Some inexpensive or easy to replace assets, such as light bulbs are probably best suited to a run to failure approach. Similarly, you don’t need continuous monitoring data on every asset. You don’t really need continuous data on assets that are functioning correctly. You need data on equipment that is acting up, which may indicate that your operations are about to be disrupted. When you’ve decided on the data you need, it can be helpful to talk to a technology provider to decide the best way to measure that data and the optimal measurement intervals.
Keep your options open
Deciding between continuous monitoring and routine-based maintenance is something of an art as well as a science. Often, the most critical (and expensive) assets have their own built-in monitoring system. However, less expensive but still critical equipment (Tier 2 and 3 assets), may benefit from continuous monitoring with sensors. For those assets, route-based maintenance with handheld tools may not be frequent enough to catch a problem in time to prevent a failure or the worsening of an issue.
If you have wireless connectivity in your plant, monitoring AC/DC voltage, current, power, temperature, and vibration with wireless sensors can help identify adverse conditions that could lead to a costly breakdown ahead of time. Wireless sensors are also safer for your staff and processes because they often don’t require shutdown, and data from the sensors can be viewed from virtually anywhere on a mobile device or PC.
Some of the most common assets that lend them-selves to wireless sensors include:
- Motors and drives
- Centrifugal pumps and compressors
- Shell-and-tube heat exchangers and reactors
- Process instrumentation
- Small transformers
- Pre-commissioning activities
Match technology, equipment
Deciding when to rely on handheld test tools and when to apply wireless sensors is specific to each plant. Factors to consider include:
- Age of equipment and the point in its lifecycle. Monitoring older equipment with wireless sensors allows you to keep constant tabs on it and to be alerted immediately if it starts to exceed established limits.
- Problem assets. Applying sensors to assets that chronically act up can save your maintenance crew a lot of return visits, while allowing you to continuously track asset performance in real-time.
- Available resources. If, like most plants, your maintenance team is stretched thin and many of your most experienced technicians are retiring, you can extend the reach of those remaining by moving some of the assets on the route to CdM sensors.
Handheld test tools will always be part of the maintenance and reliability picture. For example, a piece of equipment that requires only monthly vibration testing because it is in a low-wear, non-aggressive application, can be maintained efficiently through route-based monitoring with a handheld vibration meter unless problems arise. Similar cases can be made for routine electrical, temperature, and thermal readings on many assets. On the other hand, if you need to monitor assets that are hard to reach, in an extremely hazardous environment or showing intermittent hard-to-diagnose symptoms, wireless sensors can save time and help reduce personnel risk.
Motors and pumps on an even keel
Motors are critical to multiple functions in nearly all processing plants. Loose or misaligned motor shafts can accelerate bearing wear and cause early failure. An increase in temperature may indicate that bearings need lubrication or insulation is breaking down. These problems can be detected earlier with vibration testing and thermal monitoring.
You can install a remote, wireless vibration sensor to identify misalignment or bearing wear and then use a handheld thermal imager to pinpoint the exact location of the problem. If the motor in question is obstructed by other equipment, you can mount a remote thermal imaging sensor to capture images of the motor at regular intervals from the exact same distance at the exact same angle and monitor the results from a mobile device to identify issues as they develop.
Pumps are equally critical to many processes. If a pump fails, it can halt any number of critical operations and have both financial and safety implications. Again, vibration screening with a remote sensor may help notify personnel of potential problems early. You can use either a handheld vibration meter or vibration sensor to screen for loose or imbalanced pump shafts that can cause bearing wear. In addition, monitoring current and voltage with wireless sensors over time can make the detection of problems, such as inrush current during startup and intermittent voltage spikes or drops that can trip circuits and cause unexpected shutdowns, easier.
Analyzing power quality
Sometimes, the problem is not with your equipment. Instead, it may be an issue with the power entering your plant. Here too, you have the option of using handheld power quality or wireless power monitoring devices to collect critical data on three-phase systems. Both types allow you to see trends and fluctuations-such as unbalance, voltage dips, and spikes.
Power quality analyzers also can indicate harmonics, power factor, and other variables that can be costly and damaging to equipment. Three-phase power monitoring devices can feed data to a CMMS system so you can receive alarms if the equipment operates outside pre-specified conditions. The main difference is that power quality and energy analyzers provide the full range of power quality health as well as energy savings, while power monitors are tools that allow you to evaluate and confirm the performance of the equipment based on its nameplate to ensure that it is operating to the power specifications for which it was designed.
Multiply available resources
Wireless sensors especially are effective for finding intermittent problems, which are the most difficult and time-consuming to diagnose. After installing the sensors, the technician can move to other tasks and let the sensors log data for hours, days, or even weeks if necessary. If those sensors are connected to a CMMS system, they can easily be reviewed from a dashboard on a mobile device or PC. You can set up the CMMS system so that if a particular asset exceeds its parameters, the system will send an alarm, and immediate remedial steps can be taken. The key to making this work is having good baseline measurements for your assets.
Data from both wireless sensors and wirelessly-equipped handheld tools can be sent to the same database to provide a comprehensive asset history for analysis and documentation for internal and regula-tory requirements. By wirelessly syncing measurements taken with handheld tools and comparing them to CdM data, organizations have a more comprehensive picture of their equipment health.
Frederic Baudart, CMRP, is head product specialist for Fluke Corp. Gregory Perry is senior maintenance reliability consultant with Fluke Accelix.