In our last blog, we discussed operating standards which focused more on issues related to the operation of the equipment. In this blog, we will discuss deterioration prevention which focuses on the equipment related maintenance issues. Deterioration prevention covers areas such as establishing equipment base lines, standardizing repair policies and procedures, and standardization of spare parts.
Equipment restoration
Equipment restoration implies that equipment is to be maintained at a certain baseline level. The equipment does always have to be in an as-new condition, but the baseline must be acceptable for achieving design capacity, quality, and reliability. If the equipment is worn out, then predictive techniques such as vibration analysis cannot be used effectively. Vibration analysis would try to read all sources of vibration, and if the equipment is in a worn out or substandard condition, there would be too many transient vibration signals for vibration analysis tools to be effective. The same would hold true for other predictive techniques if the equipment is not kept at an acceptable baseline. Once the equipment is at the specified baseline, then predictive monitoring techniques can be effective in finding and trending deterioration. With this information actions can be taken and out of tolerance conditions corrected to keep the equipment at acceptable baseline.
Predictive and reliability tools
Once the equipment is at an acceptable baseline, then MTBF (Mean Time Between Failure) and MTTR (Mean Time To Repair) calculations can be used to track the equipment condition to insure that excessive breakdowns or long duration breakdowns are not occurring. In addition, technologies such as vibration analysis, oil analysis, thermography, and ultrasound can be used to detect wear or deterioration and alert the maintenance workforce that a restoration process is required for the equipment.
Standardization of repair policies and procedures
Just as in the previous blog, operator variability will impact the reliability of the equipment, so too maintenance variability will impact equipment reliability. Just as the operators may operate the equipment differently, two maintenance technicians may perform the same repair differently, with different results, and with perhaps mistakes being made. The solution to this problem is similar to the operations situation. It is the proper training and development of standardized job plans for each of the major maintenance tasks. This will insure that the equipment is rebuilt or repaired exactly the same way so that the proper reliability and utilization of the equipment can be achieved.
Standardized spare parts
In it is important that the inventory and purchasing personnel purchase OEM equivalent spare parts. In many cases when maintenance specifies a spare part, the purchasing department, in an attempt to save money, will purchase a spare part that is not exactly as specified. This creates problems with equipment reliability and may actually increase downtime. If the component must be changed two or three times to save just a few dollars on the initial price of an item, this is a poor decision. The related downtime and lost capacity will more than offset the small savings purchasing lowest cost spare parts generated.
A second area under spare parts is to look at how to insure that spare parts are purchased when needed and are not over purchased, so that the spare parts actually deteriorate while on the shelf. Some companies will purchase MRO components in bulk and the shelf life expires before the stock can be used. In an attempt to prevent this occurring many companies develop good supplier relationships so that the parts can be delivered utilizing just in time processes.
Storage of spare parts
In many instances spare parts are stored incorrectly in maintenance storage areas. For example, many bearings are unwrapped and left open on the shelf in storage. Unwrapping a bearing actually begins its deterioration. Bearings are extremely sensitive components and need to be protected while in storage.
Simply unwrapping a bearing and handling it with dry hands creates deterioration. The PH balance in the human body is so acidic, it will actually begin to corrode a bearing if the steel is touched with dry hands during acquisition, storage or installation. This corrosion leads to pitting, and interferes with proper shaft and housing fits and in some cases can actually deteriorate the raceway of the bearing.
Also V- belts are components that can be deteriorated quickly. In many companies, V- belts tend to be stored at high elevations on pegs in the storage areas. While this in itself is not incorrect, if the temperature reaches towards the higher level in the stores area, 120°F or above during the summer, this re-initializes the vulcanization process that was used to create the belts in the first place. This temperature will over cure the compound of the V- belts rendering them white and brittle. The belts must be stored at room temperature if they are to be protected in storage.
In some plants, major components of rotating equipment are setting motionless in storage. While this is not bad itself, two of three ingredients required to destroy the equipment are present. These are (1) a bearing not rotating, (2) mounted under load. The third item that is needed to complete the destruction of the component is some form of external vibration. If there is a punch press, overhead crane, forklift, or even sonic vibration, this will create microscopic motion in the bearing. This rocking action in the bearing eventually will rupture the stationary fluid film barrier. This results in metal to metal contact that destroys the bearing. This is a condition known as a false brinnelling and is widely known about in the bearing industry. Unfortunately, many companies do not understand this problem and henceforth some components are allowed to deteriorate and then when installed experience a very short life before failing. The individual rebuilding the component is usually the one blamed, when actually the component was destroyed in storage.
Some companies also have “bone yards” where they store major spare parts and assemblies outside in the weather. Then when the component is needed, they will go outside and dig it out of the field and install it and then wonder why it fails after a short time. If components are stored outdoors, they must be protected. This means they must be protected from condensation and moisture, heat, cold and etc. Some companies will lose hundreds of thousands of dollars annually in component cost and unnecessary equipment downtime due to major spare parts deteriorating and as they sit out in the “Boneyard”.
Accessibility of equipment
In some cases, it may take longer to disassemble a piece of equipment to get at a worn component, that it does to actually change the component itself. This has an impact on the meantime to repair calculation (MTTR), or simply put, the time it takes to repair a component when it fails. Equipment should be designed or redesigned so that it is easily accessible for inspections, services, and minor adjustments. If this is not done, it will result in unnecessary downtime, with the resulting lost capacity and the equipment may also provide substandard performance.
In this blog, we have discussed the third step to Zero Breakdowns – deterioration prevention. This step has focused on the equipment related maintenance issues. In the next blog, we will discuss design deficiencies. Unfortunately, a lack of understanding of the basics of component design is misunderstood, which leads to excessive costs for redesign. Our next blog will highlight this problem.