Predictive maintenance: Analyze data properly

Smart maintenance keeps that ‘new machine feeling’ intact.

10/02/2015



Anyone who has owned a new car or bike will remember the thrill and excitement of those first few years with their vehicles: shining parts, flawless performance, and maintenance-free running. As is the natural course of things, a few years later the shining parts begin to rust and the roaring engine starts to sputter while the suspension creaks and squeaks.

Though some may be motivated to discard their vehicles and get a new one, most people either cannot afford that luxury or see prudence in doing so, particularly when all that's needed is good maintenance to keep things running smoothly for many years ahead.

The same dilemma is faced by plant owners; neatly cabled control panels, dust-free HMI screens, and smoothly operating mechanical parts don't last forever. And unlike a vehicle, replacing everything in a plant instead of maintaining it is an absurd idea. While new equipment can make a good first impression, what builds long-term charm is smart maintenance of all that equipment.

Reactive vs. preventive

The term "maintenance" broadly covers any continuous activity undertaken to improve the faltering health of equipment and assets, ensuring that both short-term and long-term performance are not adversely affected. There are two main types of maintenance activities, defined by the state of assets being maintained: reactive maintenance and preventive maintenance.

Reactive maintenance is, as the name suggests, maintenance carried out to remedy a failure or incident. Replacing broken tool parts on a machine, restarting a conveyor that stopped due to overloading, repairing damaged pipelines, and run time debugging of a software error all fall under reactive maintenance.

Preventive maintenance, by comparison, focuses on preventing failures or incidents by promptly replacing or repairing equipment during routine shutdowns/inspections before they fail and cause trouble during operation. Replacing filters every two months, changing generator oil every 50 hr, and adjusting low inlet pressure on compressors are typical examples of preventive maintenance. Choosing between which method to use depends a lot on the process, application, and budget in question. Reactive maintenance is relatively low-cost in itself, but depending on the criticality of processes in question, the shutdown/failure cost could be very significant. Similarly, preventive maintenance incurs much higher costs, but the potential shutdown and damage averted can save a significant amount of operating expense (OPEX).

The key here is for end users to evaluate which processes are critical and which processes don't affect productivity as much. A water-filtration system failure for residents of a plant facility with clean tap water is hardly the type of failure that requires monitoring. A similar system providing treated water to an ammonia plant for production becomes very critical, by comparison, and requires frequent monitoring.

Since the ultimate goal of any plant owner is to maximize productivity and minimize expenditures, a very general approach to choosing a maintenance strategy is to evaluate average failure cost against average maintenance cost and choose the lower cost.

Preventive maintenance: going deeper

Preventive maintenance is further divided into three categories with varying degrees of system uptime/reliability and operating costs:

Periodic maintenance: Perhaps the most typical form of maintenance, periodic maintenance is based on following original equipment manufacturer (OEM) and learned-from-experience timelines for expected failures. These potential issues are addressed by replacing components as scheduled to ensure smooth operation. This maintenance incurs medium to high costs and marginally high uptime.

Preventive maintenance: Going a step over periodic maintenance, preventive maintenance also includes reliability tests and health checks to ensure asset availability. Results are compared with past data to predict when failures may occur. Issues are addressed before expected failures happen. This maintenance incurs high costs and high uptime.

Condition-based maintenance/monitoring (CBM): This advanced form of preventive maintenance relies on sophisticated software algorithms and continuous monitoring of data from field sensors and instruments to accurately predict the state of each component. CBM presents a holistic view of plant reliability and can help maintain a plant with practically no downtime at all. This maintenance incurs very high costs and very high uptime.


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