Maintenance Concepts

Defining Maintenance

• The cost components of maintenance include labour and material costs, as well as lost production capacity due to ineffective or absent maintenance.
• Failure is defined as any deviation or change in a product or system from its satisfactory working condition to a condition that is below the acceptable or set operating standards for the system.

Corrective Maintenance (CM)

• Corrective maintenance is a passive maintenance approach that applies repairs after failure has been detected.
• It can lead to unplanned maintenance activities, interruptions to machinery or processes, and potential hazards.
• It may also result in higher costs associated with maintenance, particularly if breakdowns lead to outsourcing maintenance work.

Preventive Maintenance (PM)

• Preventive maintenance involves ongoing routine maintenance activities to avoid failures before they occur.
• Examples of preventive maintenance include:
  • Scheduling routine maintenance tasks, such as oil and filter changes, on a regular basis.
  • Regularly inspecting machinery, such as sheet metal guillotines, to maintain their integrity.
• Preventive maintenance activities may also include design and installation of machinery, maintaining a history of repairs, and implementing regular inspections.

Predictive Maintenance (PDM)

• Predictive maintenance involves collecting data to identify when maintenance is required.
• Examples of predictive maintenance include:
  • Collecting oil samples to analyse viscosity and chemical constituents, and identifying when the next oil change is due.
  • Implementing condition monitoring systems to acquire data from critical gearboxes and plan maintenance during regular shutdowns.

Preventive Maintenance Activities

• Major PM activities include: equipment dismantling, machine overhauls, worn parts replacement, equipment modification/upgrade, equipment installation, equipment recalibration, and test runs.
• These activities may involve equipment makers/suppliers.

Routine PM Activities

• Typical examples of routine PM activity include: inspections, minor repairs/adjustments, lubrication, and cleaning.
• Inspections involve sensing faulty parts or operation using all senses and instruments, such as:
  • Visible observation (e.g., low coolant/oil levels)
  • Tactile/hearing (e.g., loose parts vibrating)
  • Faulty gauges, safety interlocks, faulty lights/indicators, and leak checking (gas, hydraulic)

Importance of Equipment History

• Documented equipment history is essential for establishing routine cycles of PM activities.
• It helps in determining how often PM activities should be applied and what resources are needed.
• Documented equipment history includes:
  • When the machine was last serviced
  • Causes of failure or state of condition
  • Ongoing maintenance costs

Additional Notes

• Cleaning is an important part of maintenance, providing benefits such as aesthetics, friction reduction, and wear prevention.
• Lubrication is a routine maintenance activity that can help reduce mechanical wear when done regularly.
• Minor equipment adjustments include tasks such as bolt tightening.

Predictive Maintenance

• Applies various technologies and analytical tools to measure, monitor, and compare system and component operating characteristics with established standards and specifications to predict system or component failures.

Types of Maintenance

• There are three fundamental approaches to industrial maintenance: Predictive, Preventive, and Corrective.
• Predictive Maintenance is considered the most complex of the three approaches.

Levels of Complexity and Cost

• Different levels of complexity and associated cost lead to varying extents for applying these three fundamental approaches.
• Predictive Maintenance has the highest level of complexity and direct cost.

Predictive Maintenance Methods

• Chemical Analysis: pH Monitoring
  • Establishes acidity or alkalinity levels with a numerical value from 0 to 14.
  • Machine oils and lubricants have OEM specified pH levels, and periodic monitoring can help avert more serious damage.
• Tribological Analyses
  • Helps clarify the effects of surface friction on material degradation (wear).

Predictive Maintenance vs. Other Approaches

• CM (Corrective Maintenance) is remedial, focusing on returning equipment/systems to their original operating state after failure has occurred.
• PM (Preventive Maintenance) is precautionary, attempting to minimize the occurrence of CM through ongoing service.
• PDM (Predictive Maintenance) is forecasting, measuring a condition, and extrapolating data into the future to predict future events.

Characteristics of Predictive Maintenance

• Requires collecting data, analyzing it, and using it to predict future events.
• Associated with high costs, including more time, higher skill levels, dedicated instrumentation, and greater commitment from management.

Mean Down Time (MDT)

• Total time needed to bring failed equipment back into an acceptable operational state
• Comprised of:
  • Time needed to issue the maintenance work order
  • Time for arrival of maintenance crew at the failed equipment
  • Time for completing all maintenance tasks and checks needed to ensure the equipment is operational

Availability

• Proportion of time over which equipment is available for use
• Calculated as: Availabili ty = MTBF / (MTBF + MDT)

Component Life Time

• Failure rate largely changes during lifetime and follows a "bath-tub" trend
• Failure rate can be calculated using the formula: λ = Number of Failures / Length of Operating Hours
• Example: λ = 3 / (15 + 35 + 60 + (4 x 80)) hr ≈ 0.007, MTBF ≈ 142.85 hrs

Mean Time To Failure (MTTF)

• Applicable to components that cannot be brought back into an acceptable operational condition (i.e., disposable items)
• Different from MTBF

Mean Time Between Failures (MTBF)

• Caution: MTBF calculation can be inaccurate if done during wear-out failures (i.e., changing failure rate)
• MTBF can vary with time if calculated during wear-out failures
• Example: MTBF calculation during wear-out failures can be an oversimplification of use

Total Productive Maintenance (TPM)

• Implementing TPM involves performing a Service FMEA (Failure Mode and Effect Analysis)

Service FMEA

• Occurrence (OCC): provides numerical ranking about the expected frequency of each failure
• Severity (SEV): provides numerical ranking about the effects and criticality of each failure
• Detection (DET): provides numerical ranking about the likelihood of determining a failure
• Risk Priority Number (RPN): calculated by multiplying OCC, SEV, and DET to prioritize potential failures

Performing Service FMEA

• Provides recommendation(s)/action(s) to reduce or completely eliminate potential failures and consequences
• Action taken: provides follow-up information to ensure recommended actions were taken to eliminate/reduce potential failures

Benefits of Implementing TPM

• Reduces breakdowns

Failure Mode and Effect Analysis (FMEA)

• Purpose: identify potential failures, determine their effects on the overall operation, and propose solutions to eliminate them

FMEA Classification

• Not in good condition: Limited capability, Average OEE, Average scrap rate
• Good: Reliable machine, Nice appearance, Very little scrap, All PM done, Some improvements done, Good (low) OEE, Meet all standards
• Excellent: Perfect condition, Looks brand new, Excellent capabilities, No scrap, Equipment improved, No breakdowns, Perfect PM done, Excellent (very low) OEE

Assessing Current Equipment Conditions

• Overall equipment effectiveness (OEE) is a reliable approach to evaluate the current equipment conditions

Maintenance Costing

• Corrective Maintenance (CM) costs can be reduced through effective Preventive Maintenance (PM) activity
• PM activities require cost justification, and there are simplified methods to help justify the costs associated with a PM programme

Calculating PM Program Cost

• The number of PM activities (annual) can be calculated by dividing the available work hours (annual) by the frequency of PM activities
• Example: with 2400 available work hours and a frequency of 8 hours (for 95% reliability), there are 300 PM activities per year
• The PM Program Cost (annual) is calculated by multiplying the number of PM activities (annual) by the Cost per single PM activity
• Example: 300 PM activities/year * 120/PMactivity=120/PM activity = 120/PMactivity=36,000/year

Reliability and Maintenance Costs

• The cost of running a PM program (at 95% reliability) occurs on top of the CM activity costs (for the expected 5% failure rate)
• The total cost of an ongoing PM program includes the costs of the PM program and the occasional CM remedial activity

Preventive Maintenance Costs

• The costs associated with a new PM program can be established, including the costs of the PM program and the occasional CM activity
• Example: the costs of the new PM program were found to be $900/month
• The feasibility of continuing the PM program depends on the reduction in breakdowns and the associated CM costs

Health and Safety Considerations

• Minimise skin contact with lubricants and machining/cutting oils through appropriate work methods and equipment.
• Dispose of wipes after application to prevent skin contact.
• Soluble oils and synthetic fluids should only be applied as per recommended dilutions.
• Avoid skin contact with concentrates.
• Considerations may also need to be taken where oil mists, vapours or sprays exist.

Lubricant Application and Environmental Considerations

• Lubricants will eventually need to be replaced and disposed of.
• Disposal should be governed by relevant industry practice and local regulations and standards.
• Lubricants should never be discharged into streams or sewage systems.

Lubrication and Reaction with Oxygen

• When exposed to oxygen, lubricants can undergo chemical degradation.
• Accumulated air and moisture in lubricating systems can be detrimental to ferrous surfaces.
• The presence of air and moisture can cause additives to react with oils.
• This reaction can lead to combustion products and sludge formation.

Importance of Temperature in Lubrication

• Temperature is a key factor in lubrication, particularly in high-temperature conditions.
• Additives help reduce the degradation of lubricants at high temperatures.

Adhesive Wear and Lubrication

• Adhesive wear arises from localised bonding across small surface features.
• Effective lubrication reduces wear by preventing localised welding at points.
• Lack of lubrication or overheating can lead to joint seizure and cessation of motion.

Functions and Properties of Lubricants

• A lubricant can serve multiple functions, including removal of heat, attaining correct alignment and joint separation, providing corrosion resistance, and reducing friction.
• A lubricant needs to have certain qualities, such as the correct viscosity, containing additives for special functions, being physically and chemically stable, and being non-toxic.

The Maintenance Organisation

• Maintenance planners provide logistical support for supervisors, enabling efficient task execution and effective maintenance processes.

Roles and Responsibilities

• Maintenance planners' tasks include:

  • Planning, scheduling, and coordinating corrective and preventive maintenance activities
  • Developing weekly schedules and assisting supervisors in determining job priorities
  • Ensuring CMMS software data files are complete and current
  • Assisting with stores and purchasing functions
  • Identifying, analysing, and reviewing equipment maintenance problems with maintenance engineering

• Maintenance supervisors', foremen, or coaches' tasks include:

  • Directing the maintenance workforce and providing on-site expertise
  • Ensuring work is accomplished safely and efficiently
  • Reviewing work planning and scheduling with planners
  • Ensuring quality of work
  • Ensuring equipment availability meets the profit plan
  • Working with plant or production supervision to ensure first-line maintenance is performed by operators
  • Verifying hourly personnel qualifications and recommending training as needed
  • Enforcing environmental regulations
  • Focusing on proactive maintenance vs. reactive maintenance
  • Administering union collective bargaining agreements
  • Monitoring CMMS

Goals and Objectives

• Goals and objectives of a maintenance organisation include:
  • Obtaining accurate records for equipment maintenance
  • Tracking equipment failure data (e.g., Mean Time Between Failure, Mean Time To Repair)
  • Collecting information such as repair durations and time between successive maintenance operations

Maintenance Organisation Structure

• Maintenance engineers identify, analyse, and review equipment maintenance problems with maintenance planners.

Maintenance Management

• Maintenance managers oversee maintenance planners and supervisors.

Computerised Maintenance Management Systems (CMMS)

• CMMS becomes necessary in larger organisations to facilitate maintenance operations and data collection.

Occupational Hazards during Industrial Maintenance

• Exposure to toxic chemicals was the main focus of the inquiry, and it was possible due to the reliance on personal protective equipment (PPE) to protect workers from hazards in confined spaces.

Failures in Safety Protocols

• Problems arose with the appropriateness of protective equipment, availability and control of equipment through the supply network, and failure of some workers to wear the equipment.
• Inadequate compliance system and failure of the chain of command to operate optimally were also identified as significant failures.

Case Study: Occupational Hazards during On-Site Industrial Maintenance

• 90 persons were severely injured and 37 persons were fatally injured in Finland between 1994 and 2004 due to maintenance incidents.
• Risk assessment surveys were conducted in companies to identify hazards, estimate their likelihood of occurrence, and evaluate the expected consequences.

Case Study: Aircraft Maintenance Errors and Contributing Factors

• Aircraft maintenance errors were attributed to maintenance personnel errors, including:
  • Systems operated unsafely during maintenance (13%)
  • Incomplete installations (8%)
  • Contact between maintenance workers and hazards (7%)
  • Incorrect assembly processes or locations (7%)
  • Towing events (7%)
• Contributing factors to occurrences included:
  • Memory lapses (20.1%)
  • Violations (17.2%)
  • Pressure (23.5%)
• Recommendations for promoting safety include:
  • Providing relevant safety-related information to maintenance crew personnel
  • Instructing workers on safe work methods before working independently
  • Appropriately planning work and conducting independent identifications of potential hazards
  • Considering work conditions to promote safe working practices