Designing Equipment for Maintainability and Reliability
Maintainability is the term used to describe the ease with which any piece of industrial equipment can be inspected, lubricated, tested, adjusted, or repaired. Sound equipment maintainability demands that any new piece of equipment is properly installed, with no shortcuts to complete commissioning and startup procedures.
Other critical considerations are ease of accessibility to system components and of servicing, easy access of condition monitoring devices (such as vibration analyzer transducers and oil analysis sampling valves), ease of carrying out repairs, and constant consideration for continuous improvement of any system component or the equipment itself.
1. How does your plant establish equipment maintainability for a new piece of equipment?
Logic: The first consideration must be based on the lifecycle cost of the machine that is being replaced with a complete review of the maintenance history of that machine. The design criteria of the new machine can then be compared and considered.
Items to be reviewed include operational loads, speeds, operating temperature conditions expected, maintenance levels expected or anticipated, spare parts selection (such as bearings, filters, and seals), and operational tolerances (such as vibration, lubricant cleanliness levels and alignments). The design engineer may not necessarily be correct with initial machine design criteria, so always be prepared to question any standard that may be in doubt. Remember, no amount of maintenance will correct a bad design.
2. Once selected, how does your plant develop pre-delivery, installation, commissioning, and startup procedures?
Logic: These considerations must include a review of the manufacturer’s line card specifications, and maintenance recommendations to comply with warranty provisions, correct mounting and fitting of hardware, machine cleanliness standards, correct lubricant specifications and levels, acceptable filter standards, alignment standards, and the preparation of additional desired plant maintenance requirements with complete detailed written installation, commissioning, and startup procedures.
3. After the machine has been installed and commissioned with startup complete, what condition monitoring program does your plant apply?
Logic: Depending on the machine’s production criticality and of the equipment systems themselves, condition monitoring may include operating temperatures, oil and/or process fluid flow rates and pressures, lubricant contamination levels, vibration standards of rotating components, and alignment standards between drive and driven components.
A sound practice is to employ every suitable condition monitoring technology available initially, establish baseline histories, and discontinue those that do not provide any valuable machine condition information. Above all, begin gathering lifecycle cost information immediately after startup and ensure that operators and maintenance personnel are thoroughly trained in operational and maintenance procedures.
4. After startup, how does your plant determine what is acceptable operation of the new equipment?
Logic: It is normal to ask the equipment manufacturer what constitutes normal operation between routine maintenance activities or procedures. Is it 5,000 or 10,000 hours between routine maintenance? For example, oil drain intervals and a sound, regularly scheduled oil analysis program will often effectively allow the extension of oil drain intervals beyond the manufacturer’s recommended period.
In addition, synthetic lubricants are extremely cost-effective with today’s sophisticated industrial equipment. Approximately 70 per cent of today’s lubrication-related machine failures are caused by contamination of the oil, so lubricant cleanliness and effective filtration are critical. Cleanliness of the equipment itself is also important. Any dirt and dust covering a machine can cause an unacceptable temperature increase by several degrees, creating premature component failures. Any increase in machine loads or speeds can introduce unacceptable operating conditions that will cause premature component failure. Operations and maintenance personnel must be well aware of these considerations as critical training after a new machine is installed is often neglected.
5. Does your plant develop a program to maintain accurate maintenance records for the new equipment?
Logic: Once in operation, operations and maintenance personnel must be aware of changes in operational and maintenance requirements, and how these may affect documentation of all maintenance activities both routine and unusual, because accurate recordkeeping is critical.
During an initial inspection of new equipment systems, operational loads, speeds, and temperatures must be recorded. Relubrication and filter change intervals must be carefully documented, condition monitoring practices established, and results documented with care and accuracy.
Operations and maintenance personnel must be trained to recognize that any change in what is considered normal operation may cause a change in the equipment’s standard behaviour, such as operating temperature, weather conditions, the use of a non-standard replacement filter or component, or the extension of any particular maintenance interval.
6. How does your plant handle modifications to equipment?
Logic: Often after a new piece of equipment is installed, operating conditions may demand modifications. It is of critical importance that any modification be carefully designed, and properly documented after completion. Often a plant will increase loads or speeds in order to increase production. The results can be disastrous if the modification is not carefully planned and implemented. When modifications that increase machine loads or speeds are carried out without consideration of certain components, these may fail prematurely.
For example, doubling the load on a rolling element bearing can reduce the bearing’s life by up to 90 per cent. Doubling the speed can reduce its life by 50 per cent. Many modifications can directly improve the maintainability of the equipment. These include repositioning of oil filters, oil sampling valves, and vibration transducers for easier maintenance access.
7. When a breakdown does occur, how do you research the failure?
Logic: Often, failures occur so frequently that plant personnel consider such failures as normal. They are not. Every failure that causes a serious production loss must be investigated thoroughly in an effort to totally eliminate the cause, or, at the very least, extend the meantime between failures (often referred to as MTBF).
Questions to be answered include which part caused the failure, including why, how and when, and what were the operating conditions at the time? Did lubrication problems contribute to the failure? Could a preventive maintenance activity prevent the failure? Could a condition monitoring technology have predicted the failure? Did human error contribute to the failure? How can a recurrence be prevented?
Finally, it is suggested that with any new piece of equipment unfamiliarity will generate questions, and plant engineering and maintenance personnel are encouraged to establish good working relationships with manufacturers, and exchange information with other plants with similar equipment.
Stay in touch with applicable technical groups and subscribe to reliable maintenance and engineering publications. Equipment design, manufacturing and production standards, and operating conditions continue to evolve, and plant personnel must be willing and prepared to continually review technology, learn new applicable technologies, and be willing to change their approach to equipment reliability, and maintainability improvement possibilities. MRO