In recent years I’ve visited several plants that lacked a formal maintenance program. Some had computerized maintenance systems available — but they weren’t being used. The reason seems to be that management purchased the system and thus it was applied “from the top.” Unfortunately, this often is done without knowledge about the system or the work that is required to make it a useful tool.
Often, the computer program had been delivered as an “empty shell” with little or no information included. The plant personnel already had more than enough work to do, and thus the software wasn’t used at all. The plant personnel simply didn’t have time to enter the required information. This situation represents a waste of money and worse, it’s a waste of a potentially useful maintenance tool.
I also found that the people on the plant floor didn’t know how to collect and analyze maintenance information, even if it was available. Operators and maintenance personnel would be well served by learning some of the basic methods used when planning for maintenance.
It’s important to stress that plant people can do this, perhaps aided by some suitable external resource that can provide guidance, advice and assistance when required. Involving plant personnel with the techniques not only teaches them about appropriate planning maintenance procedures, it motivates them to take part in, and perform, the maintenance required.
Rules and regulations
Plants that have pressurized vessels, or other equipment that can be considered dangerous, must abide by specific rules and regulations regarding their use and maintenance. The applicable rules and regulations often require periodic inspections that must be performed by independent and certified third parties. Whether or not there’s a formal maintenance system in operation, the plant must comply with these requirements. It’s of utmost importance that pressure vessels be clearly identified, and each inspection must be planned and executed according to the regulations.
A good way to start a maintenance planning program is to investigate how the plant and its equipment are intended to be used. It’s knowledge about how the equipment is going to be used that forms the basis for the maintenance planning. This information, the operating profile, is the key tool for the maintenance planners. Update the information continuously to ensure that the planner can optimize the work schedule.
Resources and limitations
Before evaluating the required maintenance tasks, evaluate the resources available for maintenance objectively and realistically. You want to know about limitations to the level and complexity of the maintenance work that can be performed in-house. If the limitations are too severe, either change the system deficiencies so the work can be done in-house or outsource the work.
Analyze the following factors and their effect on the maintenance work:
- Maintenance resources available (personnel, shop facilities, instruments, tools, etc.)
- The competence of the personnel (verifiable skills and training)
- Access to spare parts and spare parts information
- Access to information (maintenance instructions)
If you don’t have the personnel, the tools, the spare parts and the information, you simply can’t perform the maintenance. Establishing a realistic view of a technician’s competence might be more difficult, as it’s harder to assess a priori. Nevertheless, note any limitations, expressed or inferred.
Keep resource limitations in mind when evaluating maintenance tasks to be performed. If any are lacking, arrange to have them available before the work starts.
Levels of maintenance
When drafting your standardized maintenance procedures, it’s useful to assign each task a “level” that corresponds to the skills required to perform the work. It’s important to do this in advance, as it makes it easier to “sort” the procedures that need to be prepared. A system of four levels is usually sufficient, though this number can be increased or decreased if desired. An example might be:
Level 1 — Autonomous (maintenance performed by the machine operator)
Level 2 — Simple (maintenance requiring a technician)
Level 3 — Qualified (maintenance requiring a skilled/certified technician)
Level 4 — Outsourced (maintenance subcontracted to specialists)
Level 1 — Autonomous maintenance
The maintenance activities included here can be performed by the machine operator, with the equipment in operation and using readily available resources. The task shouldn’t take longer than about 20 minutes to 30 minutes to perform. It should be possible to perform these tasks as part of a normal daily routine, without the need for work orders. It’s enough to verify that the task has been performed by noting it the operator’s or machine’s daily log book.
The necessary instructions should be available through the maintenance system software, though the operators would normally get them through training and then simple check lists to confirm via a signature that the task has been performed. Some maintenance routines placed on this “level” aren’t performed daily. These might be simpler maintenance tasks performed weekly, monthly or after a specific number of operating hours or machine cycles. Such irregularly scheduled tasks should have written instructions or check lists to ensure the work will be performed and not simply forgotten. Take staffing into consideration to ensure that not too many tasks are scheduled simultaneously.
Level 2 — Simple maintenance
The maintenance tasks included here can be performed by the operator who has received some maintenance training or with assistance of a maintenance technician. The tasks might require an equipment shutdown lasting no more than one hour. These maintenance activities require a short written procedure prepared by the maintenance planner.
Level 3 — Qualified maintenance
These maintenance tasks require a longer equipment shutdown and fully-trained maintenance personnel to perform the work. The work orders should provide detailed instructions (or reference to where such information can be found) regarding the procedures required. Lock-out/tag-out procedures and other safety information must be included on the work order.
Maintenance at this level requires detailed procedures and a thorough evaluation of the type of maintenance (condition-based, preventive or run to failure) best suited to each task and each unit. Be sure to code each maintenance procedure or work order in a way that links them to the position number or component code provided on the equipment drawings specific to the plant.
Level 4 — Outsourced maintenance
These maintenance activities should be performed only by the OEM’s authorized service personnel or by specially–trained maintenance technicians. Maintenance required at this level might require that equipment be sent to outside service centers. Technicians performing the work normally issue detailed service reports, which must be kept on file at the plant for future reference. If the production line the equipment supports must be kept in continuous operation and no standby unit is in place, the contractor must provide a new or replacement unit to keep the line operating.
The plant’s maintenance department normally doesn’t prepare work orders for maintenance at this level. Determine the number of operating hours, condition variables or other factor that triggers the need for outsourced services. Identify how long it takes before the equipment can be returned to service, especially if the unit must be sent to a service center.
Any preparatory work plant personnel must perform in anticipation of such service requires a work order that includes safety information (shut-down procedures, lock-out/tag-out, hazard information, etc.) as well as information about steps to take when reactivating the units (safe start, operational check, etc.).
Identification of units
Identify and locate every physical unit to be included in the maintenance system by means of component lists derived from system drawings. Each unit must have a unique identification number that corresponds to the numbering system used in the plant. Verify that the installed equipment matches the equipment on the component list. It’s not unusual to find that equipment has been replaced with another type.[pullquote]
Segregate out the equipment that doesn’t require detailed maintenance procedures. Examples include replaceable instruments, simple valves and pipe runs. These might only require simple visual inspections (check lists) and spare part information. Include and clearly identify any equipment subject to examination by outside authorities (pressure vessels, safety valves, etc.).
Normally, motor-driven equipment must have written maintenance procedures. However, anything that can be subjected to wear, such as expansion bellows, should be identified, even though maintenance might consist of only an inspection. The main task is to generate a list of equipment that requires maintenance at the established levels, a list to be used for further development.
The purpose of this basic list is to segregate units that require no maintenance. The main criterion that removes a unit from the list is the ability to replace it as a single unit with no need to dismantle it or change wear parts. The remaining units should be graded according to how vital they are for plant operation. The following grades form a good starting point:
- Units without redundancy that, if shut down, would seriously affect plant operations
- Redundant units (stand-by units) that, if shut down, would seriously affect plant operations
- Non-vital equipment, with or without redundancy
It’s important to analyze each unit’s maintenance requirements. Prioritize the vital units and analyze their maintenance requirements first. This ensures that necessary maintenance tasks are identified for each unit and that appropriate maintenance procedures get written. Initially, this information might need to be based on OEM specifications concerning lubrication, inspection intervals, spare parts, test operation, maintenance intervals and the different maintenance tasks to be performed. Make the procedure descriptions “traceable” by giving correct and detailed references to the OEM instructions or other information sources.
MTTR and MTTF
The mean time to repair (MTTR) and mean time to failure (MTTF) are essential elements of a plan for reliable maintenance activities. Establish the maintenance activities for a unit using the manufacturer’s maintenance recommendations and either specify the time intervals between maintenance or specify condition monitoring. Sometimes you can obtain the necessary information from the staff’s experiences or from other reliable sources.
Knowing the MTTR and MTTF gives the maintenance planner a tool to estimate when the work must be performed as well as an estimate of the labor content required to perform the task. This also helps to establish the technician’s required skill level. Use the information in the computer-based maintenance system to update and improve the maintenance procedures. The data in the maintenance system can be changed, updated or placed at different skill levels based on experience collected over time. Experience-based information often is better than that from other sources.
Evaluating the maintenance requirement
It’s not sufficient to evaluate only the units needing maintenance. Study the system, the working environment in which the units operate and how the unit or system might affect the operation of the plant itself. Identify bottlenecks that can harm the whole system — or the whole plant. Check bottlenecks with extra care and evaluate their condition to ensure that no unforeseen problems can threaten plant operation.
Keep in mind that the plant’s designers probably didn’t have maintenance foremost in their mind. Instead, they probably had instructions to design and build it as cheaply as possible. Also, the plant probably was erected by workers having little knowledge about maintenance. Most plants can show horrendous examples of the effect of this lack of knowledge. There’s no doubt that plant maintenance often can benefit from a bit of a redesign, an option that shouldn’t be ruled out.
Maintenance requirements typically come in three varieties: condition-based, time-based or run to failure. These classifications are by no means exhaustive and they’re only meant to provide guidance when evaluating the kind of maintenance suitable for each unit evaluated.
Condition-based maintenance (CBM)
This can be the most economical choice, but only if the cost of the monitoring devices isn’t too high and extensive dismantling to check the condition of the equipment isn’t required. CBM works best when simple checks are sufficient to get an indication of the equipment’s condition.
A simple visual inspection can detect leaks or other mechanical faults. You can use touch to detect heat and vibrations. You can listen for damaged bearings and even smell to detect overheating or oil leaks. Also, trending the recorded process variables can be used to detect the need for maintenance. However, for vital or costly equipment, use instruments because they detect faults long before an operator can using only the five senses.
This is the type that manufacturers normally recommended. It’s based solely on the number of operating hours or calendar days a unit has been in operation. This method normally is used when condition monitoring is too difficult or when there’s a clear correlation between operating time and mechanical failure. When using time-based maintenance, consider how the unit is used. The recommended maintenance intervals normally apply to units in fairly constant operation. It’s not useful for units that are mainly in standby mode.
For the latter type of equipment it’s better to multiply the number of starts by an “equivalent” number of operating hours. For example, an emergency generator is tested every week (52 starts per year) and each start can be considered equal to 20 running hours. Multiplying the number of starts by 20 gives a value that should be added to the true running hours to arrive at the maintenance trigger point. This method is recommended because each start causes more wear than an hour in normal operation.
Run to failure
This maintenance approach is used for highly reliable equipment, when it’s difficult to perform condition monitoring or when instrumentation is costly in comparison to the equipment value.
Although not normally recommended, run to failure can be used if the unit in question won’t interfere with plant operation should it cease to function, assuming it can be replaced easily and rapidly. If not, it might be possible to alter the installation to enable a rapid replacement. This maintenance type can be tied to the unit — if the unit needs to be included in the maintenance system at all.
The design of any vital system should be reconfigured if some run-to-failure component can fail often and without warning.
Writing the procedures
After the relevant data for each applicable unit has been captured and its maintenance requirement analyzed, it’s time write procedures. Enter them directly into the computerized maintenance system or write them by hand on a note pad — the important thing is to have the procedures written.
Although it’s essential to involve plant personnel in the equipment analysis, it’s probably unfair to force them to enter data into the computer system. As one operator put it, “If I wanted to sit and write all day, I would have gotten me an office job.” Management should consider outsourcing the initial maintenance procedure drafting and development using a competent technical writer with knowledge about maintenance and producing suitable procedures.
If plant personnel follow the advice given above, the result will be a valuable information resource that forms the basis of the comprehensive set of maintenance procedures. It would reduce the labor required to write the procedures, thus saving a substantial amount of money.
Gunnar Gustafsson is educated as a Marine Engineer with a long experience from operating and maintaining ships, oil rigs and power plants of various types, He now puts his education and experience to good use as a technical writer. Contact him at [email protected].