Condition-Based Maintenance Will Not Stop Your Machines From Failing
By John Lambert
March 31, 2020
By John Lambert
By John Lambert
The ultimate goal for anyone in industrial maintenance should be to gain the optimum full life of machine assets. To do this, plants need to make changes to the current maintenance processes or at least the way many of them are doing things. A lot of companies have some variation of a condition-based maintenance (CBM) program but are scratching their heads as to why they still get machine failures. They are not wrong in performing CBM, but that alone will not stop their machines from failing.
Let me explain why condition monitoring works. The premise behind CBM is that most failures give some warning that they are about to occur.
The P to F Interval
This warning is called a potential failure and is defined as an identifiable physical condition, which indicates that a functional failure is either about to occur or in the process of occurring.
Functional failure is defined as the inability of an item to meet a specified performance standard. The P to F interval is a well-known illustration (see Figure 1). There are many different techniques to measure and detect potential failures. For instance, if you had a slow-turning gearbox, you may use oil analysis. The most popular instruments to measure potential failures are for vibration, ultrasound, oil analysis, and temperature.
The sooner a potential failure can be detected, the longer the P-F interval can be. Longer P-F intervals mean that inspections need to be done less often, and more time is required to take whatever action is needed to avoid the consequences of the failure. The bottom line is, we take measurements and monitor them over time. If they change, then we react to the change.
Does Performing This Type of CBM or Condition Monitoring Work?
Yes, since you can avoid downtime and save money. Failure comes in many forms and there are many ways to combat it. If you detect the potential failure early enough (and it can be months before the actual failure), it means the breakdown can be avoided. You can schedule an outage to do a repair or maintenance. It’s not a breakdown because the machine hasn’t stopped, and it’s not downtime. This is cost avoidance and the plant can save on the interrupted loss of production because of downtime costs. Avoid the downtime, control the outage, and schedule the maintenance work. It’s a win.
Think about secondary damage. The seal might go in a gearbox and costs (costs are estimates) $1,000 to replace. If you don’t catch it and the bearing becomes contaminated, it becomes an overhaul of the gearbox for $5,000. But if the bearing seizes onto a shaft, now you have to replace the shaft and more.
The cost of secondary damage can be huge; therefore, condition monitoring does work and, if done right, saves time and money. However, there’s a problem with condition monitoring, and it’s the same with predictive maintenance: machine failure.
Root Cause Analysis and Defect Elimination are a Must
The definition of insanity is “to do the same thing over and over and expect a different result.” If we just keep replacing bearings and don’t figure out what’s causing the failure, are we crazy? Are we guilty of only repairing the effect and not finding the cause? To only fix the fault/effect is reactive maintenance. A CBM program or any program needs a defect elimination process. This is usually done through a root cause analysis, which is the process of defining, understanding, and solving a problem.
This fishbone diagram (below) is a basic tool used in root cause analysis. We know that the “effect” is that the machine is down, but what is the true “cause” of the failure.
The process was to set up a cross-functional team to brainstorm the cause of the failure. You must make sure that you have people who have direct knowledge of the process being examined. A step by step process is then needed to drill down in order to find the true cause of the failure.
This was just one tool used. We can also use the “Five Why.” Simply to ask the question why enough times until you get down to the root cause of the issue. Of course, don’t limit yourself to asking only five questions; ask as many as necessary.
These are only two of the tools that are available; others include failure modes and effects analysis (FMEA). Whatever you use, ensure you do defect elimination as part of your maintenance processes. Defect elimination is the removal of that cause, which will give you a longer life of your machine assets. The idea is making sure “you fix forever, rather than forever fixing.” Therefore, when something fails, you make sure it does not reoccur, over time you reduce the number of failures and increase your uptime.
After defect elimination, whether you’re overhauling, repairing, or redesigning, you are reinstalling the machine. For this you need to implement precision maintenance skills and techniques.
Precision maintenance is simple; it means to work to a recognized standard. A set of tolerances that you and your team agree on. The tighter the tolerance, the better the result. However, you cannot have a tolerance that cannot be measured.
Precision maintenance means “upskilling” your people. Getting the right tools and the right training. It’s machinery acceptance standards, precision balancing, alignment, base flatness standards, and the removal of machine stress.
More importantly, it’s commissioning to a standard and documenting the process.
The answer to the question why that was asked in root cause analysis above is usually found in precision maintenance.
Controlling Factors in the Life of a Machine
A machine’s design can have an effect on the machine’s life. However, in maintenance, very often we have to live with the design we have been given. If it’s a pump that was underdesigned for the application, the pump would begin life in a functional failure state because it does not meet requirements. Therefore, the design has to be done right; otherwise, the inevitable redesign is done. A review of the machine’s design should be a must in any breakdown analysis.
A machines is overhauled many times throughout its life. It’s extremely important that it be done correctly. Many companies will contract this work out, because they do not have the facilities to do the work correctly, as one of the biggest issues during overhaul is contamination. When a machine is overhauled, the most important aspect is that the OEM specification for machine fits is maintained. The goal is to make the machine new again.
Installation is the key. It’s the most critical thing for all machines. A well-designed machine or a well overhauled machine can be ruined with poor installation practices. The installation must be done to a standard such as the ANSI/ASA S2.75-2017/Part 1 or the OEM specification.
Commissioning is actually a continuation of the installation. In fact, it should start with the review of the installation documentation. It should be done by another group, other than the group that did the installation, such as the reliability group.
Each machine is different, so we cannot publish a list of what to do, but all of the OEM operation procedures should be followed. When the button is pushed to start the machine, this is where you should be taking measurements for thermal expansion (offline to running) so we know if a correction is necessary before putting the machine into service.
When the machine is online, different parameters should be measured, such as temperature, sound, and vibration, as part of your CBM program. These measurements are the benchmarks used to compare the new measurements taken throughout the life of the machine. Changes from these results mean the machine is deteriorating. However, if you have done a good job at understanding the root causes and using the precision maintenance techniques in the areas that you can control, this should be because the machine is worn out and has had a good long life. MRO
John Lambert is the President of BENCHMARK PDM. He can be reached at firstname.lastname@example.org or by visiting the BENCHMARK PDM web site at www.benchmarkpdm.com.