A Comprehensive Guide to Industrial Maintenance Techniques

Posted on Aug 22, 2024 in Other subjects

Corrective Maintenance

Corrective maintenance, the original maintenance technique, remains widely used today. This approach involves repairing a machine after it fails. Corrective maintenance can be categorized into five main types:

1. Fail Repair: Restoring a failed component to its operational state.
2. Salvage: Disposing of non-repairable material and utilizing salvaged parts from irreparable items in repair, overhaul, or rebuild programs.
3. Rebuild: Returning a component to its original specifications by disassembling it, replacing worn or unserviceable parts, and ensuring initial tolerances.
4. Overhaul: Restoring a component to good condition using an “inspect and repair only as appropriate” approach.
5. Servicing: Maintenance required as a result of corrective action.

Effective corrective maintenance involves the following steps:

1. Fault recognition
2. Localization
3. Diagnosis
4. Repair
5. Checkouts

Advantages:

• Full utilization of the component’s lifespan.
• Reduced inspection and repair costs and time.

Disadvantages:

• Unpredictable failures can disrupt production.
• The need to stock spares for every part for immediate repairs.
• Addressing only the broken part without identifying the root cause can lead to recurring failures.
• Limited applicability when component failure poses safety risks to employees.

Preventive Maintenance

Gaining traction in the 1940s and 1950s, preventive maintenance is currently the most prevalent technique. It centers around periodic component inspections and scheduled maintenance based on time cycles or usage. Understanding the machine’s statistical failure patterns is crucial for effective preventive maintenance, as the goal is to perform maintenance before failure occurs. Task selection criteria, which vary by industry and machine type, are essential for accurate scheduling.

Advantages:

• Predictable maintenance schedules reduce the need for extensive spare part inventory.
• Minimal production disruptions as maintenance can be scheduled during breaks or downtime.
• Enhanced control and fewer unexpected issues.

Disadvantages:

• Underutilization of the machine’s lifespan.
• Increased maintenance costs.
• Ineffectiveness against random machine failures, leading to unnecessary replacements.
• Persistent risk of failure despite maintenance efforts.

Predictive Maintenance

Predictive maintenance employs various techniques, including visual inspections, vibration analysis, thermography, temperature monitoring, ultrasonic testing, lubricant analysis, electrical condition monitoring, and nondestructive testing. This approach aims to reduce maintenance costs compared to traditional methods like preventive and corrective maintenance by ensuring component availability and performance. It involves tracking equipment status through monitoring functions, enabling timely substitutions and repairs to minimize unexpected failures. A well-defined maintenance plan is crucial, allowing for proactive problem identification and resolution. Maintaining a detailed history of task duration and workforce requirements enhances program effectiveness.

Advantages:

• Significant maintenance cost reduction.
• Early failure detection facilitates timely spare part procurement, minimizing inventory needs.
• Parameter analysis helps identify failure root causes.

Disadvantages:

• Requires equipment with measurable indicators related to their condition.
• Challenges in establishing clear and reliable parameters for perfect equipment status.
• Continuous monitoring may not be feasible, necessitating periodic checks for critical components.

Total Productive Maintenance (TPM)

TPM is a methodology focused on maximizing machine availability by optimizing maintenance and production resources. Unlike traditional approaches, TPM integrates operators into the maintenance process. Operators receive training in basic maintenance and fault-finding, collaborating with technical experts in dedicated teams. This empowers operators to understand machinery, identify potential problems, and proactively address them, reducing downtime and production costs. TPM strives for”zero errors, zero work-related accidents, and zero losse” through close collaboration between production and maintenance units.

Pillars of TPM:

1. Initial phase management
2. Health and safety
3. Education and training
4. Autonomous maintenance
5. Planned maintenance
6. Quality maintenance
7. Focused improvement
8. Support system

Advantages:

• Cost reduction
• Enhanced customer satisfaction
• Reduced accidents
• Improved environmental control
• Increased staff confidence
• Cleaner work zones
• Enhanced teamwork
• Stronger worker-machine relationships

Disadvantages:

• Difficulty in implementing an effective TPM system
• Requirement for motivated and responsible employees

Tools for TPM Implementation:

5S:

A workplace organization method encompassing:

1. Sorting: Eliminating unnecessary items, prioritizing essentials, and ensuring easy accessibility.
2. Straightening or Setting in Order: Arranging work, workers, equipment, parts, and instructions for optimal workflow and division of labor.
3. Systematic Cleaning
4. Standardization
5. Sustaining: Enforcing adherence to rules and procedures to prevent backsliding.

Poka-Yoke:

Techniques that prevent mistakes, minimizing defects in products and processes, and enhancing quality and reliability.

Reliability-Centered Maintenance (RCM)

RCM aims to increase availability and reduce maintenance costs in industrial plants. Analyzing a plant using RCM yields several benefits:

• Improved understanding of equipment and system operation.
• Comprehensive failure analysis and development of preventive mechanisms.
• Definition of actions to ensure high plant availability.

Preventive Actions in RCM:

• Grouped maintenance tasks in a maintenance plan.
• Defined operating procedures for production and maintenance.
• Identified modifications and improvements.
• Developed training plans.
• Determined stock part requirements.

RCM Methodology:

RCM involves a series of steps for each plant system:

1. Phase 0: Coding and Listing
2. Detailed study of system operation.
3. Identification of functional and technical failures.
4. Determination of failure modes and causes.
5. Study of failure mode effects and classification (critical, major, tolerable).
6. Determination of preventive measures.
7. Grouping preventive measures into categories (maintenance plans, improvements, training, procedures).
8. Implementation of preventive measures.

Advantages:

• Increased efficiency

Disadvantages:

• High implementation cost and complexity

Single Minute Exchange of Die (SMED)

SMED aims to reduce machine changeover or initialization time to a single-digit minute timeframe (ideally under 10 minutes). It distinguishes between:

• Internal Adjustments: Performed while the machine is stopped, outside of production hours.
• External Adjustments: Performed while the machine is running or during production.

SMED Implementation Stages:

1. Identify internal and external adjustments.
2. Separate internal and external adjustments.
3. Convert internal adjustments to external adjustments.
4. Rationalize all aspects of adjustment operations.

Benefits of SMED:

• Reduced downtime during changeovers.
• Minimized waste during startup.

Reliability, Maintainability, and Availability Parameters & Failure Curves

Reliability:

The probability of a component performing its intended function under specified conditions for a given period. It is an inherent characteristic and is expressed as a probability.

Reliability Function:

Maintainability:

The ease and speed with which a system or equipment can be restored to operational status after a failure. It depends on factors like equipment design, installation, personnel availability and skill levels, maintenance procedures, test equipment, and physical constraints.

Availability:

The probability of a system operating satisfactorily at any given time.

Availability Formula:

Reliability and Maintainability Models (Probability Distributions)

Several probability distributions are used in reliability and maintainability analysis, including:

• Weibull Distribution: Commonly used for modeling lifetimes in industrial reliability, particularly for failures related to wear-out, fatigue, or aging.
• Lognormal Distribution: Frequently used in maintainability analysis as it represents the distribution of most repair times, especially for tasks with multiple sub-tasks of varying durations.
• Normal Distribution: Applicable to straightforward maintenance tasks with consistent completion times, such as simple replacements.
• Exponential Distribution: Used for tasks where completion times are independent of previous maintenance, like substitution methods for failure isolation.

Weibull Distribution:

This distribution models failure where the failure rate is proportional to a power of time.

K Values:

• K < 1: Failure rate decreases over time (early failures).
• K = 1: Constant failure rate (random failures).
• K > 1: Failure rate increases over time (wear-out failures).

Maintainability Programs: Elements

• Design for Maintainability: Incorporating design changes to improve working conditions and the work environment.
• Management Approach: Defining management elements, communication channels, responsibilities, inspection procedures, supervision, and operator training.
• Analysis and Testing: Continuous review and testing to assess the effectiveness of implemented solutions.
• Cost Analysis: Evaluating the financial viability of solutions by comparing costs and improvements.
• Data Collection and Failure Analysis: Gathering and analyzing data on failures to identify trends and areas for improvement.
• Design for Maintainability (Tools): Developing new tools and technologies to enhance productivity and address maintenance challenges.

Benefits of Maintainability Programs:

• Improved maintainability and reduced maintenance time.
• Enhanced system reliability and availability.
• Reduced maintenance costs.
• Improved safety for maintenance personnel.
• Simplified maintenance procedures.

Reliability Block Diagrams (RBD)

RBDs visually represent the reliability of a complex system by illustrating how component reliability contributes to overall system success or failure. Components are depicted as blocks connected in series or parallel configurations.

• Series Configuration: All components in a series path must function for the system to operate. Failure of any component in the series leads to system failure.
• Parallel Configuration: Redundant components are arranged in parallel. The system functions as long as at least one component in the parallel path is operational.

Series Configuration:

Parallel Configuration:

Unscheduled Failure Analysis: Root Cause Analysis (RCA)

RCA is a structured process for identifying the underlying cause of an event or failure. It involves a systematic investigation to determine the root cause and prevent recurrence.

Key Questions in RCA:

• What happened?
• Where did it happen?
• What changed?
• Who was involved?
• Why did it happen?
• What is the impact?
• Will it happen again?
• How can recurrence be prevented?

Disadvantage of RCA:

• Reactive approach; analysis occurs after a failure.

Quantitative Analysis: Fault Tree Analysis (FTA)

FTA is a deductive, top-down approach to failure analysis using Boolean logic to determine the probability of a specific system failure or undesired event. It visually represents the logical relationships between events leading to a failure.

Applications of FTA:

• Understanding failure logic.
• Resource optimization.
• Safety performance monitoring.
• Diagnostic manual creation.

Failure Mode and Effects Analysis (FMEA)

FMEA is a systematic method for identifying potential failures in a design, manufacturing process, or assembly process. It analyzes the consequences of these failures and prioritizes them based on severity and likelihood.

When to Use FMEA:

• During design or redesign of a process, product, or service.
• When applying an existing process in a new way.
• Before developing control plans.
• When planning improvements.
• When analyzing existing failures.
• Periodically throughout the lifecycle.

How to Conduct an FMEA:

1. List process steps.
2. Identify potential failure modes for each step.
3. List the effects of each failure mode.
4. Rate the severity of each effect (1-10).
5. Identify the causes of each failure mode and rank their likelihood of occurrence (1-10).
6. Identify existing controls and rank their effectiveness (1-10).
7. Calculate the Risk Priority Number (RPN) for each failure mode (Severity x Occurrence x Detection).
8. Prioritize failure modes based on RPN.
9. Develop actions to address high-priority failure modes.
10. Re-evaluate Occurrence and Detection rankings after implementing actions.

Work Prioritization and Work Orders

Work Prioritization:

Prioritizing maintenance tasks based on their criticality and potential impact on operations. This ensures that resources are allocated effectively to address the most important issues first.

Work Orders:

Documented instructions for completing specific maintenance tasks. They provide technicians with the information needed to perform the work safely and effectively.

Components of a Work Order:

• Reference and Description: Location, machine details, and assigned personnel.
• Planning Section: Description of work, required spare parts, tools, estimated time (MTTR), and required skill level.
• Craft Feedback: Technician’s notes on work completed, any issues encountered, and confirmation of task completion.

Storeroom Management, Homogeneous Poisson Process, and the 5 Myths

Storeroom Management:

Efficient management of spare parts and materials to ensure their availability when needed while minimizing inventory costs.

Objectives of Storeroom Management:

• High service level to users.
• Low inventory investment.
• Cost-effective purchasing.
• Adequate safety stock.
• Complete inventory identification (quantity, location).
• Item availability and accessibility.
• Prompt purchase orders and efficient goods receipt.

Inventory Systems:

• Non-Reparables: Items that cannot be repaired to their original state.
• Reparables: Items that can be repaired to a functional condition.

Homogeneous Poisson Process (HPP):

A statistical model used to predict the probability of failures occurring over time, assuming that failures are independent and uniformly distributed.

Using HPP for Spare Part Estimation:

1. Determine the failure rate (λ) based on historical data.
2. Use the Poisson distribution table to determine the required stock level for a desired probability of success (e.g., 90%, 95%, 99%).

5 Myths of Storeroom Management:

1. More inventory is always better.
2. Inventory management is a clerical task.
3. Inventory is a necessary evil.
4. Technology alone can solve inventory problems.
5. Inventory management is a one-time project.

Economic Considerations and KPIs

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ECONOMIC CONSIDERATIONS

Our target should be optimize maintenance cost finding the optimal point, where the

curve – which represent the cost & maintenance frequency – reaches the minimum.

Talking about money, there are 3 main mistakes on maintenance:

1. Minimum Cost: it is very dangerous to reduce maintenance cost without sense (to

do nothing is the cheapest); we have to do only the necessary that use to be around

5% of the acquisition cost.

2. Continuous Maintenance: is a mistake because you have extra cost on

unnecessary task and probably you won’t have resources for other very important

tasks.

3. Total Availability: despite TPM plan try to reach 100% of OEE, in RCM plan they

look for a compromise or good ratio between Availability & Maintenance Cost (90-

99%)

It is a good idea to compare the equipment cost with an Iceberg; the small part of the cost

above the water line (1/8) is Acquisition Cost, the rest costs are:

• Operating (10%)

Maintenance & Spares (5%)

Training (usually included on Acquisition)

• Risk (MTBF): which increases with time (age-related)

Once the years are passing the cumulative cost gets higher and our opportunity to

influence on those cost gets reduced, so we have to find the ideal moment to change the

equipment.

A good exercise is to use Excel to calculate for different number of years the total

equipment cost/year (considering all the parameters) and looking at the results we can

decide the optimal one, which is the Minimum.

KPI’s (Key Performance Indicator)

Any Maintenance Plan have to be evaluated, so we could use some indicators (KPI’s) to do

the job.

We have to choose the correct number of KPI’s, as too many could make very difficult the

operator to collect the data and few could be no significant to us.

The main are:

• MTBF (Mean Time Between Failure)

MTTF (Mean Time To Failure)

MTTR (Mean Time To Repair)

Worst actors – List of frequently failed equipment

Maintenance cost / Unit output (%)

Maintenance cost / Total Sales (%)

Total Maintenance Cost (per plant, section, …) (€)

Reparation Cost per Workorder

Unscheduled Maintenance Downtime (in hours) ¡Take care of minor Breakdowns!

Scheduled Maintenance Downtime (in hours)

% of Workorders assigned as “Rework Status” over the last month (the ones

• we have to repeat)