Self-Inflicted Reliability Problems of Rotating Machinery
The root cause of poor reliability can come from many sources. You may experience reliability issues due to the age of your plant. Or perhaps poor design decisions were made. Or the original construction crew cared nothing for reliability. And there may be other reasons, outside of your control, that resulted in the reliability problems you experience today.
In any reliability improvement initiative, you will need to address these issues, but first, you need to address the self-inflicted reliability issues.
“But we don't have self-inflicted reliability problems."
It is a bitter pill to swallow, but yes, you do. But that is good news because it is much easier to deal with the self-inflicted root causes than the inherent reliability problems you adopted.
What are self-inflicted reliability problems?
In order to determine why equipment fails prematurely (or why you experience slowdowns, safety incidences, or quality problems), you could go through a detailed failure modes, effects, and criticality (FMECA) analysis process, or you could perform root cause failure analysis (RCFA) after each failure occurs. Or you could learn from the experience gained at thousands of plants around the world and consider some of the most common root causes of equipment failure - we will focus on rotating machinery.
The number three cause of reliability problems
Let’s start with the most obvious problems and then we will work backward to their root causes. Most equipment, like motors, pumps, fans, compressors, and turbines, are designed to run for many, many years without unplanned downtime. Yes, they may have some components that wear out, but many of the components, such as the bearings and gears, are designed to give years of trouble-free operation. But that assumes that all of the parts were installed correctly, the components are precision-aligned, the bearings and gears are correctly lubricated, all fasteners are tightened to the correct tension, there is no resonance, belts are tightened to the correct tension, and the rotors are precision-balanced.
And it assumes that the equipment is operated as per design. Pumps, for example, should be operated at their “best efficiency point.” What happens at your plant? Do these root causes exist? If you are not sure, then they almost certainly do. We will now take a quick look at just a few of those areas so that you can see why seemingly minor issues cause such serious problems.
When two shafts are “collinear” (no angle or offset between their centerlines), it reduces the stress on the bearings, couplings, shafts, and the rest of the machine components. Research was performed that revealed that just 5/60th
of a degree of angular misalignment can halve the life of your bearings. If you use laser alignment with appropriate tolerances, and you remove soft foot in all its forms (base issues, pipestrain, etc.), then you will have eliminated a common root cause of failure.
When you balance to ISO 21940-11 grade G 1.0, the cyclical forces on the bearings, shaft, and structure are minimized, and thus you gain greater reliability. If you do not have a balancing standard, then unbalance will be a root cause of failure.
And if you wait until the unbalance generates “high” vibration, “forcing” you to perform corrective maintenance, then you will have reduced the life of the equipment and supporting structure.
Why is that? The life of a bearing is inversely proportional to the cube of the load. That sounds very complicated, but an easier way to say it is that if you double the load, the life will be reduced to one-eighth (23). Therefore, while the rotor is out-ofbalance, the bearings are being stressed, and their life expectancy will be reduced.
Misalignment also generates these forces, and that is why it must be minimized.
The unbalance is also generating forces that stress the structure, potentially resulting in fatigue failure of the structure itself or its foundations. The unbalance forces are also amplified by resonance. The structure will “naturally” vibrate back-and-forth, or side-to-side, or in other ways at certain frequencies. If the vibration generated by unbalance (or misalignment, or pump-vane vibration, or other avoidable “forcing frequencies”) is close to one of these natural resonant frequencies, the motion will be amplified. That is not good for the machine or structure.
When you correctly lubricate bearings and gears, whether you use grease or oil, and that lubricant is free of contaminants, you will achieve maximum life. But if bearings are not adequately greased, their life will be reduced. If the
oil is contaminated, or the viscosity is incorrect, or the additives are depleted, then the life of gears and bearings will be greatly reduced.
Research was performed to determine which particles caused the greatest damage. It was not the 40 μm particles, or the 10 μm particles - it was the tiny “3-5 μm” particles. And you may think that if you can’t see the water in oil, then the oil must be fine. Sadly, that is not correct. By the time you can see the water, the life of the bearing has been reduced by 70 percent.
We could continue the discussion, but suffice to say that there is a great deal we can do to avoid problems that arise due to imperfect maintenance and operating practices. The number two cause of reliability problems It is one thing to understand all of the root causes we have just discussed – and there are many others – but it is another thing to be able to get approval to establish standards and purchase all of the tools, such as laser alignment systems, that enable the technicians and operators to do the job correctly.
But owning the tools and having standard operating procedures will not solve the problem.
The problem will only be solved when the maintenance technicians and operators want to use them properly, and they are given the time and encouragement to use them. So we will need to address the desire, i.e., the culture. Culture is the key to success. The number one cause of reliability problems A strong case could be made that the root cause of all failures ultimately derives from the lack of senior management support for a culture that values reliability. Without their support, it will be impossible to change the culture and thus change behaviour.
Just think of the initiative to improve safety at your plant. If senior management did not support it, do you think your plant would have made the gains that it has made? Senior management enabled people to be employed in safety roles, it invested in the training and tools, it agreed to signage that provided warning and feedback on progress, it stood strong when there were opportunities to cut corners that would risk safety, and it made it quite clear how important safety is to the future of the organization. (Well, I hope that is the case at your plant.)
You need the same thing to happen with reliability improvement. Everyone within the organization needs to understand that reliability is critically important to the organization and that senior management will stand strong when shortcuts that compromise reliability are proposed.
Therefore, you need to gain senior management support so you can change the culture and thus successfully implement a reliability improvement initiative that eliminates the self-inflicted root causes.
But wait, is there more?
Since we are discussing root causes, let’s consider the root cause of the lack of senior management support. Is it their fault for not appreciating the opportunity to improve reliability, or is it your fault because you have not presented the business case for reliability improvement? It is common for people to talk about the “commonsense” benefits of reliability improvement. It is also common for reliability and condition monitoring teams to assume that senior management appreciates the benefits of what they have achieved, without ever communicating the financial benefits of their actions.
Therefore, perhaps the true root cause of poor reliability is the inability (or unwillingness) of reliability and condition monitoring team leaders to establish a business case, sell the business case, and continually communicate the value of the reliability improvement initiative.
Where does condition monitoring fit into this?
Many people will believe that if they have a condition monitoring program, the reliability will be optimized. Sadly, that is not true. Most faults detected are avoidable, and while it is important to get an early warning, it is much more important
to avoid the problem in the first place. Condition monitoring can help by detecting the root causes of failure: misalignment, unbalance, lubrication issues, looseness, and so on. If those problems are cost-effectively nipped in the bud, then we
will avoid future failures. Another way that condition monitoring can play an important role is by performing acceptance testing. As part of the purchase agreement, the condition monitoring specialists can perform tests to ensure the new or overhauled equipment is “defect-free.” You may be surprised at how many problems you bring into the plant.
As you can imagine, there is a great deal more that could be said about all of these topics. In an attempt to clarify the process we are discussing in this article, we developed a process called Asset Reliability Transformation, or ART. You can learn more, without charge, at www.reliabilityconnect.com .
The condition monitoring group has an important role to play. Providing an early warning minimizes the impact of premature failure, and detecting and eliminating the root causes ensures that we achieve the greatest life and value from our precious assets. The reliability improvement team has an even more important role to play. Proactively eliminating the root causes of failure ensures there will be fewer failures. But trying to improve reliability without aligning every activity to the goals of the organization, and thus gaining support from senior management, which then drives the necessary cultural changes, will never achieve the true potential of the initiative.
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Once you understand how grease actually works to lubricate a bearing, it becomes obvious why over-greasing causes so much trauma to both bearings and the grease itself. Remember, all we want from our lubricant is to provide a little separation in the war zone. Nothing more… nothing less.